FIRE ANTS ON SEA TURTLE NESTING BEACHES IN SOUTH FLORIDA, USA,
AND ST. CROIX, USVI
by
Danielle Kioshima Romais
A Thesis Submitted to the Faculty of
The Charles E. Schmidt College of Science
in Partial Fulfillment of the Requirements for the Degree of
Master of Science
Florida Atlantic University
Boca Raton, Florida
December 2013
ACKNOWLEDGMENTS
I would like to thank all who helped me, encouraged me, guided me and
cheered for me throughout the development of this research. Thanks to my family,
friends, co-workers, professors and mentors.
Dr. James K. Wetterer, I would like to thank you for the trust you invested in
me from the very beginning. Thank you for the opportunity to conduct research in
this topic. Thank you for the great ideas and the freedom to develop the work as my
own. Dr. Jon Moore and Dr. Erik Noonburg, I would like to thank you for being
members of this thesis committee. Thank you for the timely and valuable advice on
methodology.
Thanks to Claudia Lombard from the U.S Fish and Wildlife Service in St.
Croix, USVI, for being so helpful during the Sandy Point survey. Thanks to Dr.
Mark Deyrup at Archibold Biological Station for conducting the final identification
of all the ant species surveyed. Your expertise is unmatched. Thanks to Dr. Kirk
Rusenko and the Sea Turtle Research Team at Gumbo Limbo Nature Center for the
logistic and GIS support during the surveys conducted in Boca Raton, FL.
iii
Thanks to the Environmental Science Program staff and faculty for setting the
stage for learning and meaningful research to take place. Thanks to the Geosciences
Department for all the help in getting through this process as well. Thanks to the
Biology Department for the TA opportunity. Thanks to Dr. Gawlik and Dr. Markwith
for allowing me to use their lab space during this research.
Thanks to Kavita Balkaran for conducting the survey in Jack Bay. Thanks to
André C. Kioshima for helping with survey in Pompano Beach. Thanks to Ariel
Shtauber for helping with survey in Boca Raton. Thanks to Dr. Sanford Porter for his
expertise on fire ants and also for the images provided. Thanks to Dr. Julio C. de
Souza for images of our beautiful Brazilian Pantanal.
Thanks to Donna Selch, Mark Rochello for creating the sea turtle/fire ant
interaction map. Thanks also to Hilton Cordoba for helping me design the maps for
the study areas. You all rock!
Last, but certainly not least, I would like to thank my wonderful husband, Jeff
Romais, for the unconditional support and love during all this time. Thanks also to
my beloved son, Kiyo, for being such an awesome trooper when I needed to be
absent while working on this research. This is an accomplishment of our entire
family, and I could not have done without the two of you!
iv
ABSTRACT
Author:
Danielle Kioshima Romais
Title:
Fire Ants on Sea Turtle Nesting Beaches in South Florida, USA,
and St. Croix, USVI.
Institution:
Florida Atlantic University
Thesis Advisor:
Dr. James K. Wetterer
Degree:
Master of Science
Year:
2013
The red imported fire ant, Solenopsis invicta, is a South American native
introduced in Alabama in the early 20th century. This predatory species has rapidly
spread throughout the southeastern US and parts of the West Indies, inflicting great
ecological and economic damage. For example, Solenopsis invicta is known to attack the
eggs and hatchlings of ground nesting birds and reptiles. The ants swarm into the nests
attacking hatchlings and diminishing their chance for survival. My thesis research aimed
to survey the distribution of ants on sea turtle nesting beaches in South Florida and St.
Croix, USVI, and to evaluate the possible threat of Solenopsis invicta and other predatory
ants to sea turtle hatchlings.
v
DEDICATION
I dedicate this work to my son, Kiyo Romais. He is my main source of inspiration,
determination and strength. He is the reason I want to excel and make the world a little
bit better.
Kiyo, I know that - when you grow up and become a man – you will make a difference in
this world. Thank you for inspiring me ever since you were conceived to be a better
mom, a better citizen, a role model to you. Thank you for you unconditional love and
never ending curiosity. I love you, Kiyo, to the moon and back 1000 times!
FIRE ANTS ON SEA TURTLE NESTING BEACHES IN SOUTH FLORIDA, USA,
AND ST. CROIX, USVI
TABLES .............................................................................................................................. i
FIGURES ............................................................................................................................ x
1.
INTRODUCTION ....................................................................................................... 1
2.
LITERATURE REVIEW ............................................................................................ 5
2.1
Solenopsis sp. ....................................................................................................... 5
2.2
Fire Ants ............................................................................................................... 6
2.2.1
Native and introduced ranges ........................................................................... 7
2.2.2
Economic and health related impacts ............................................................... 8
2.3
Fire ants as a threat for sea turtle hatchlings ........................................................ 9
3
OBJECTIVES ............................................................................................................ 13
4
METHODS ................................................................................................................ 15
4.1
Study Areas ........................................................................................................ 15
4.1.1
Sandy Point Wildlife Refuge ...................................................................... 16
4.1.2
Jack Bay ...................................................................................................... 16
4.1.3
Boca Raton .................................................................................................. 17
4.1.4
Pompano Beach .......................................................................................... 19
4.2
Survey, Specimen Preservation and Identification ............................................ 21
4.2.1
Survey and Specimen Preservation ............................................................. 22
4.2.2
Specimen Identification .............................................................................. 23
4.3
Sandy Point Wildlife Refuge Follow-Up Study: Phase I ................................... 24
4.4
Baseline Distribution Survey: Phase II .............................................................. 26
4.4.1
Pompano Beach, FL .................................................................................... 26
4.4.2
Jack Bay, St. Croix, USVI. ......................................................................... 27
vii
5
4.5
The Boca Raton Survey: Phase III ..................................................................... 28
4.6
Statistical Analysis ............................................................................................. 29
RESULTS AND DISCUSSION ................................................................................ 32
5.1
Sandy Point Wildlife Refuge Follow-Up Study: Phase I ................................... 32
5.2
Baseline Distribution Survey: Phase II .............................................................. 35
5.2.1
Pompano Beach Survey .............................................................................. 35
5.2.2
Jack Bay, St Croix Survey .......................................................................... 39
5.3
5.3.1
Baseline Survey Results .............................................................................. 41
5.3.2
Methodology Consistency Analysis ........................................................... 44
5.3.3
Possible Threats to Sea Turtle Hatchlings .................................................. 53
5.4
6
The Boca Raton Survey: Phase III ..................................................................... 41
Statistical Analysis ............................................................................................. 56
FINAL REMARKS ................................................................................................... 71
viii
TABLES
Table 1: Ant species surveyed in 2006 (Wetterer and Lombardo, 2010) ......................... 25
Table 2: List of ant species present at Sandy Point, St. Croix, USVI ............................... 33
Table 3: List of ant species in Pompano Beach, FL. ........................................................ 36
Table 4: List of ant species found in Jack Bay, St. Croix, USVI...................................... 39
Table 5: List of ant species present in the Boca Raton study site – Initial Survey ........... 43
Table 6: List of species found in Boca Raton - Survey II ................................................. 46
Table 7: List of species found in Boca Raton - Survey III ............................................... 48
Table 8: List of species found in Boca Raton - Survey IV ............................................... 50
Table 9: Comparison per site between the four sampling efforts in Boca Raton, FL Species observed based on abundance of individuals ...................................... 52
Table 10: Observed (O) versus Expected (E) sites with native and exotic species in
2006 and 2010 - Sandy Point, St. Croix, USVI (P>0.05)................................. 57
Table 11: Observed (O) and Expected (E) number os sites containing Solenopsis
invicta and Solenopsis geminata in 2006 and 2010 - Sandy Point, St. Croix,
USVI(P>0.05)................................................................................................... 59
Table 12: Observed (O) and Expected (E) number of sites with native and exotic
species in Sandy Point and Jack Bay (P<0.05) ................................................ 61
Table 13: Observed (O) and Expected (E) number of sites with native and exotic
species in Pompano Beach and Boca Raton (P>0.05)...................................... 63
Table 14: Observed (O) and Expected (E) number of sites with Solenopsis invicta in
Pompano Beach and Boca Raton survey areas (P>0.05) ................................. 65
Table 15: Observed (O) and Expected (E) number of sites with Solenopsis invicta in.... 67
Table 16: Observed (O) and Expected (E) number of sites with Solenopsis invicta in
the Boca Raton survey area – four replicates (P>0.05) .................................... 69
ix
FIGURES
Figure 1: Solenopsis invicta (Image by S. Porter - USDA) ................................................ 7
Figure 2: Green turtle hatchling in Sandy Point, St. Croix, USVI.................................... 10
Figure 3: Sandy Point, St. Croix Survey Area .................................................................. 16
Figure 4: Jack Bay Survey Area ....................................................................................... 17
Figure 5: Boca Raton Survey Area ................................................................................... 19
Figure 6: Pompano Beach Survey Area ............................................................................ 20
Figure 7: Bait-card placed along dune vegetation (Image by Kavita Balkaran)............... 22
Figure 8: Point-Mount Method ......................................................................................... 23
Figure 9: Identified Ant Species ....................................................................................... 24
Figure 10: Ant Distribution in Sandy Point, St. Croix, USVI - Follow-up Survey.
Green bars and (N) denotes native species, red bars are exotic species. ........ 34
Figure 11: Ant Distribution in Pompano Beach - Baseline Survey. Green bars and (N)
denotes native species, red bars are exotic species. ........................................ 38
Figure 12: Ant Distribution in Jack Bay, St. Croix - Baseline Survey. Green bars and
(N) denotes native species, red bars are exotic species. ................................. 40
Figure 13: Ant Distribution in Boca Raton - Initial Survey. Green bars and (N)
denotes native species, red bars are exotic species. ........................................ 44
Figure 14: Ant Distribution in Boca Raton - Survey II. Green bars and (N) denotes
native species, red bars are exotic species. ..................................................... 47
Figure 15: Ant Distribution in Boca Raton - Survey III. Green bars and (N) denotes
native species, red bars are exotic species. ..................................................... 49
Figure 16: Ant Distribution in Boca Raton - Survey IV. Green bars and (N) denotes
native species, red bars are exotic species. ..................................................... 51
Figure 17: Sea Turtle Nests and Fire Ant Presence in Boca Raton, Fl - 2012.................. 55
Figure 18: Graph of frequency of native versus exotic species – the Sandy Point ant
survey in 2006 against the Sandy Point ant survey in 2010 ........................... 58
Figure 19: Graph of frequency of Solenopsis invicta and Solenopsis geminata per
number of sites – the Sandy Point survey in 2006 against the Sandy Point
survey in 2010 ................................................................................................. 60
Figure 20: Graph of frequency of native and exotic species in Sandy Point and Jack
Bay, St. Croix .................................................................................................. 62
x
Figure 21: Graph of frequency of native and exotic species in Pompano Beach and
Boca Raton ...................................................................................................... 64
Figure 22: Graph of frequency of Solenopsis invicta in Pompano Beach and Boca
Raton, FL ........................................................................................................ 66
Figure 23: Graph of frequency of native and exotic species in Boca Raton..................... 68
Figure 24: Graph of frequency of Solenopsis invicta in Boca Raton - four replicates .... 70
xi
1. INTRODUCTION
The world currently faces a biodiversity crisis where introduced species have
population explosions while native species move toward extinction (Elton, 1958), which
causes a significant shift in the dynamics of populations worldwide. With the
advancement of technology and transportation, humans were able to colonize areas that
would otherwise be uninhabitable. Anthropogenic changes to the environment seem to be
a facilitating factor for exotic species establishment. Along with human settlements, a
variety of species were introduced intentionally or accidentally. This does not imply that
species were not able to move around prior to human intervention, but it correlates the
speed at which these changes occur. As the movement of people increased both in
intensity and in speed, the spread of introduced alien species have also increased
(Simberloff, 1997).
Biological invasion is a process in which a species introduced to a new and
suitable habitat has a population explosion due to the lack of natural enemies and
predators that could keep the population in check. This unbalanced advantage of the
introduced species over the native ones can cause the latter to decline towards extinction.
Invasion by exotic species is the second greatest cause biodiversity loss in the world
1
(CBD, 1992). The first is the loss of habitat due to the conversion of natural areas
for human use.
The impacts caused by invasive species may not be initially felt. Some species
may not become a problem soon after introduction, and they may take years to establish a
viable population. The time it takes for an invasion to occur does not make it a problem
less than other environmental ailments because – if left unchecked and given the
appropriate conditions – the problem can easily go from a manageable eradication effort
to something that no longer can be controlled.
Natural habitats in South Florida are suitable for invasive species, including many
exotic ant species that have been inadvertently introduced. These species are represented
by a wide range of organisms from snails to reptiles, plants, mammals and insects. A
comprehensive assessment conducted by Ferriter et al. (2008), listed 83 species of
invertebrate organisms that is considered invasive in South Florida, six of which were ant
species. Four species out of five invertebrates that were found in all the eight geographic
regions studied were ants(Ferriter et al., 2008). Some of them – like the Burmese python
- have made headlines due to the negative impacts it is causing to the environment and
the economy, as well as the possible threat to humans.
Biological invasions are directly or indirectly related to human sprawl and the
environmental impacts caused by this phenomenon. In other words, sometimes the
invasion takes place as a result of anthropogenic impacts, and the exotic species occupies
an area after human disturbance has occurred. There are other times when the invasion
2
itself is the driving force to disturbance, causing massive impacts to the ecosystem
(Buczkowski, 2010).
Size does not matter when it comes to biological invasion. An example of this is
the red imported fire ant (RIFA), Solenopsis invicta, considered to be an agricultural and
urban pest in many introduced areas (Frank et al., 1997). This species is known for its
powerful sting that can cause death to an adult human being in the most severe cases of
allergic reaction. This species also presents economic impacts due to the costly attempts
to eradicate the species in introduced areas. In ecological terms, the species exerts
dominance over native ant populations and can successfully prey on vertebrates such as
young bird and reptile hatchlings (Krahe, 2005). The increase or decrease of ant
populations can also play a crucial role on the survival of species such as the sea turtles
that nest on the South Florida beaches. Based on previous studies and field observations,
the presence of predaceous exotic ants such as the RIFA along nesting beaches can
impact the survival rate of sea turtle hatchlings nesting in South Florida and St. Croix
(Allen et al., 2001; Forys et al., 2005; Wetterer et al., 2007; J. K. Wetterer & Lombard,
2010).
One main goal with invasive species studies is to understand the invasion process
and to devise efficient strategies to mitigate the impacts (Simberloff et al., 1997).
Determining whether or not an area has the potential to become invaded by an ant species
requires a prior documentation of which ant species are present. Ant distribution surveys
are regarded as fundamental in the development of a baseline understanding of which
species are present in key areas for species conservation, diversity analysis and invasion.
3
In regards to the impacts caused by RIFA to sea turtles along the beaches in South
Florida and St. Croix, it is relevant to understand what species of ants are present in order
to assess possible impacts caused by these species.
4
2. LITERATURE REVIEW
2.1 Solenopsis sp.
There are approximately 185 species worldwide that comprise the cosmopolitan
genus Solenopsis (Hymenoptera: Formicidae) (Pitts et al., 2005). This genus belongs to
the largest and most diverse subfamily of ants, Myrmicinae. Classification of the
Solenopsis genus is considered a difficult task by many taxonomists mainly because
worker ants in most species are small and have few distinct characteristics useful in
identification (Tschinkel, 2013).
Generally speaking, species belonging to this genus can be classified in two
distinct groups: thief ants and fire ants. The first group is comprised of the majority of the
species in the Solenopsis genus, characterized by the small and monomorphic workers.
Thief ants nest around other ants nests and “steal” the brood from the neighboring
colonies, which is how they got their common name. The second group, the fire ants, is
comprised of approximately twenty (20) species native to the New World, characterized
by polymorphic workers and a powerful and painful sting (Pitts et al., 2005; Tschinkel,
2013).
5
The genus Solenopsis is usually associated with fire ants despite the fact that the
majority of species in the genus are considered thief ants. This is because thief ants are
generally smaller in size and more difficult to detect than the fire ants. Since they rarely
come above ground, the thief ants are not collected as often as fire ants (Pacheco et al.,
2007). One example of thief ant is Solenopsis globularia, a species native in the
Caribbean.
The morphological characteristics of Solenopsis ant species are similar whether it
is a thief ant or a fire ant. The difference lies primarily in the size of the workers, but
even that can be sometimes misleading. Some fire ant specialists suggest that the one
characteristic that distinguishes a fire ant from a thief ant within the Solenopsis genus is
the individual’s ability to bite and sting, triggering the burning sensation associated with
fire ants (S.Porter, personal communication, March 11, 2013).
2.2
Fire Ants
Only four of the twenty species of fire ants were identified as native to North
America. The other species are classified as part of a Neotropical assemblage known as
the Solenopsis saevissima species-group (Pitts et al., 2005). Two of the sixteen species of
Neotropical fire ants (Solenopsis richterii and Solenopsis invicta) were inadvertently
introduced to North America in the early 1900s.
6
Figure 1: Solenopsis invicta (Image by S. Porter - USDA)
Solenopsis invicta (Figure 1) is among the five species of ants listed as the worst
biological invaders in the world (Sanders, 2011). Aside from health threats to human
beings, S. invicta can also generate immense costs associated with efforts to control its
spread (Lofgren, 1986). Although economic and health impacts are usually the primary
reasons for controlling these invasive species, they can become major threats to the native
wildlife and ant communities. In fact, invaders such as the red imported fire ant disrupt
ecosystems to the point where native species communities are replaced by the exotic ones
(Mack et.al, 2000).
2.2.1
Native and introduced ranges
Fire ants were recognized to have come originally from South America by
Creighton and Löding in the late 1920s and early 1930s. The range of the two species of
fire ants that invaded the United States (Solenopsis richterii and Solenopsis invicta) was
further determined by Buren. Solenopsis invicta (RIFA) is native to the grasslands of
7
Southern Brazil and Northern Argentina, with its range centered along the Paraguay
River (Tschinkel, 2013). The species seems to have an ecological dominance over other
ant species populations in its native range due to four main factors: number of
individuals, recruitment system, aggressive and continuous foraging behaviors
(Calcaterra et al., 2008). The RIFAs are omnivorous and unicolonial (Parris et al., 2002;
Sanders, 2011). These characteristics along with a set of environmental factors such as
habitat suitability, propagule pressure and lack of natural enemies in the introduced area
increase their chance at becoming invasive.
The first introduction of the exotic fire ant, the black imported fire ant (Solenopsis
richteri) happened in Mobile, Alabama around 1918. The introduction of the red
imported fire ant (Solenopsis invicta) took place around the 1930s in Southern United
States (Pitts et al., 2005). The red imported fire ant spread throughout the southern
portion of the country, out-competing its black exotic counterpart. Nowadays, the RIFA
is found in approximately 1/3 of the United States, comprising most of the southern states
and islands in the Caribbean. Its introduced range is considered by some experts as 4 to 5
times larger than the distribution in the native range.
2.2.2
Economic and health related impacts
Federal, state and municipal government agencies have spent millions of dollars
to control the spread of S. invicta in the United States from the late 1950s to the early
1980s (Lofgren, 1986). It is estimated that if the spread of S. invicta is not monitored and
controlled, the economic impact can range from $3 to $9 billion dollars for California
alone in the next decade or so. These costs are associated with the application of
8
pesticides, property replacement or restoration, medical and veterinary treatments for
sting reactions in humans, pets and livestock (Sanders, 2011).
The presence of S. invicta in urban areas is considered a nuisance to humans. The
attacks can be by one worker’s multiple stings or by several individuals coordinating to
sting simultaneously (Krahe, 2005). This results in an allergic response characterized by a
burning sensation, excessive itching, the formation of a wheal and a blister-like pustule
that can easily turn into a secondary infection (Lofgren, 1986). In some cases, the allergic
reaction can be fatal due to the development of hypersensitivity reactions to the sting
(Lofgren, 1986; Sanders, 2011).
2.3 Fire ants as a threat for sea turtle hatchlings
There are seven identified species of sea turtle worldwide. Four of those seven
species (Loggerhead, Leatherback, Green and Hawksbill) nest in South Florida and St.
Croix regularly (Figure 2). According to the International Union for Conservation of
Nature (IUCN) Red List, their status ranges from vulnerable to critically endangered.
This brings a sense of urgency to conservation efforts (2012).
9
Figure 2: Green turtle hatchling in Sandy Point, St. Croix, USVI
Sea turtles return to the beach in the vicinity of where they hatched to nest.
Nesting specificity makes them even more vulnerable to environmental changes.
Anthropogenic activities are considered a main driver for such changes, disturbing
natural habitats and allowing the establishment of invasive species such as Solenopsis
invicta. Sea turtle nests are often predated by a variety of organisms, both vertebrates and
invertebrates.
Populations of S. invicta have been reported along the beaches of South Florida
and many Caribbean islands, being found as far south as Key West (Davis et al., 2001;
Krahe, 2005; J. K. Wetterer & O'Hara, 2002; J. K. Wetterer & Lombard, 2010). These are
commonly found along the area ranging from the dune into the wrack line (Allen et al.,
2001). Sea turtles nesting success depends on the area where the eggs are laid. Choosing
to nest closer to the water line increases the risk of nest failure. The eggs might be
washed away due to beach erosion processes during a storm surge. In order to guarantee a
better chance at nest success, the sea turtles tend to nest closer to the dune line.
10
Therefore, the nests and hatchlings are more vulnerable to ant predations, particularly by
exotic fire ants (Wetterer et al., 2007).
Fire ants can swarm a sea turtle nest soon after pipping and before emergence,
which can take from several hours to several days (Wetterer et al., 2007). Some studies
indicate that fire ant workers monitor the egg-chamber of freshwater turtles via
underground foraging tunnels (Buhlmann & Coffman, 2001; Krahe, 2005). They can also
act as scavengers feasting on the remains of hatchlings that have been attacked by other
predators (Buhlmann & Coffman, 2001; Krahe, 2005). In either case, the chances for
survival of the hatchlings attacked by the fire ants are greatly reduced. Even if the
hatchling survives the initial attack, the exposure to a few fire ant stings can reduce its
survival rate by 15% (Moulis, 1997). In her research Krahe (2005) indicated that for
loggerhead turtles, the survival of hatchlings stung by RIFA decreased by over 50% ten
days after hatching. There was no significant difference between green turtle hatchlings
that have been stung versus those that were not stung by RIFA. Hatchlings that have been
stung by fire ants show a more lethargic and paralyzed behavior. If they have been stung
in the eye region, they display a “clouded-over eye” that may cause disorientation during
crawling (Krahe, 2005).
11
12
3
OBJECTIVES
In order to mitigate the many problems caused by the spread of invasive alien
species, it is important to determine their distribution and impact to native species. The
dominance of invasive ants, in particular the red imported fire ants, can be first
determined by ant population surveys that provide a baseline of data that can be used in
future comparative analysis.
Seeing the impacts of invasive ants to endangered species such as sea turtles
along shores worldwide, this study aimed to investigate the presence of exotic species of
ants, mainly Solenopsis invicta, on four sea-turtle nesting beaches – two in South Florida
and two in St. Croix, USVI. More specifically, our questions were:
1. Were there any significant changes in the overall ant distribution at Sandy Point,
St. Croix from 2006 (Wetterer & Lombard, 2010) to 2010 (present study)?
2. What species of ants are found in sea turtle nesting beaches in the surveyed areas
in South Florida and St. Croix, USVI?
3. What is the ratio between native and exotic ant species in these areas?
4. What is the percentage of sites with fire ants from genus Solenopsis found in these
areas?
5. Is the presence of surveyed species consistent if collected during multiple days?
13
As a way to answer these questions, this study aimed to document the current ant
species distribution and predict ant dominance on sea turtle nesting beaches.
Documenting the distribution of ants is the first step to determine ant species dominance
and invasion. Further studies can be developed based on baseline data provided in such
distribution analysis.
The overall ratio between native and exotic ant species may infer the level of
disturbance for the area. Generally, we expected to observe a higher number of invasive
and/or exotic species in areas with more anthropogenic influence. The focus was on the
distribution of fire ants from genus Solenopsis, mainly the red imported fire ants
(Solenopsis invicta) due to reported continuous attacks to sea turtle hatchlings and nests.
14
4
METHODS
In order to answer these questions, the present study was conducted in three
different phases: Phase I – follow-up study in Sandy Point, St. Croix to observe any
changes in species distribution for the area; Phase II – baseline surveys to document the
current ant species distribution (exotic and native) on sea turtle nesting beaches in Jack’s
Bay, St. Croix and Pompano Beach, Florida; and Phase III – baseline ant distribution
survey in Boca Raton, Florida aimed at investigating species present and analysis of
consistency of the surveying methods conducted in multiple days.
4.1 Study Areas
The present study selected four areas, based on the high likelihood of being a sea
turtle nesting beach. Two of the areas were located in St. Croix, USVI: Sandy Point
Wildlife Refuge and Jack’s Bay. The two other areas were located in South Florida: Boca
Raton and Pompano Beach. These areas have historically been selected by sea turtles as
primary nesting grounds. Therefore, these areas are important for determining possible
impacts of Solenopsis invicta on sea turtle hatchlings if in fact the invasive ant species is
present in these sites.
15
4.1.1
Sandy Point Wildlife Refuge
Sandy Point Wildlife Refuge is a natural area monitored by the U.S. Fish and
Wildlife Service in St. Croix, USVI. The area is considered one of the most important sea
turtle nesting areas in the island (Figure 3). It hosts the largest population of leatherback
sea-turtles (Dermochelys coriacea) in the United States jurisdiction. Sandy Point is
located at the southwest end of the island, south of Frederiksted. The area has a high
touristic appeal, having an average of 11,000 visitors per year (USFWS, 2008).
Figure 3: Sandy Point, St. Croix Survey Area
4.1.2
Jack Bay
Jack Bay is part of two bays (Jack and Isaac Bays) located at the eastern end of St.
Croix. Comprised of white sandy beaches and upland forest, it is considered one of the
16
few pristine natural areas in St. Croix (Figure 4). The bays host the largest population of
hawksbill and green sea-turtles in the island, and – due to their endangered status – these
nesting areas are constantly monitored. The area is monitored by conservation efforts
from The Nature Conservancy (TNC, 2013).
Figure 4: Jack Bay Survey Area
4.1.3
Boca Raton
Boca Raton is the southernmost town in Palm Beach County. The Boca Raton
study area extends from the lookout Pavilion at the South Beach Park to the end of Red
Reef Park, along the beach. The beach in Boca Raton hosts sea-turtles of various species,
but mainly loggerheads and green turtles nest in the area. The area is monitored by
17
Gumbo Limbo Nature Center in association with the Sea Turtle research conducted by
Florida Atlantic University. The starting point for the survey in this area was at life-guard
tower 1 (26.34979 N and -80.06961 W) and extended to life-guard tower 12 (26.36684 N
and -80.0682W) (Figure 5). The area is characterized by relatively dense dune vegetation
with frequent foot trails for beach access. The beach is heavily used year-round by
tourists and residents to the area.
18
Figure 5: Boca Raton Survey Area
4.1.4
Pompano Beach
Pompano Beach is located in central-east Broward County. The area is highly
urbanized, and the beaches are usually busy with tourists and residents. The study area
chosen in Pompano Beach is highly developed with little or no dune vegetation.
Buildings and other anthropogenic structures make up most of the shoreline in this area.
The area is also highly sought for tourism, fishing and recreational activities. There are
numerous garbage cans and picnic areas that provide abundant food source for
predator/scavenger ants such as Solenopsis invicta.
19
Figure 6: Pompano Beach Survey Area
Despite the disturbed conditions, sea turtles still come to this beach to nest.
Although efforts are made to protect nests, the heavy use of the beach and lack of dune
vegetation to protect hatchlings from getting disoriented by street lights may be key at
20
impacting the survival of these already endangered species in the area. Adding to these
factors, the presence of RIFAs in the area poses an even greater threat.
4.2 Survey, Specimen Preservation and Identification
Previous studies have indicated the expansion of Solenopsis invicta through South
Florida. This spread extends the species distribution as far south as the Florida Keys in
the United States and in many of the Caribbean islands such as St. Croix (Davis et al.,
2001; Krahe, 2005; J. K. Wetterer & O'Hara, 2002; J. K. Wetterer & Lombard, 2010).
They are found along the coast as well as inland, being commonly associated with
disturbed and urbanized areas. The red imported fire ants are considered a major threat to
native ant communities as well as other organismal groups such as the sea turtles and
shore birds nesting along the beach. The main question in this study is if there is any
correlation between the presence of fire ants along the nesting beaches in South Florida
and St. Croix and impacts on sea turtle hatchling survival.
The survey was conducted following the same format as described in Wetterer &
Lombard (2010). In general, surveys were conducted in the morning. A total of 12 – 15
baits were used per study area, with the exception of the survey conducted at Sandy Point
Wildlife Refuge – which was a more extensive area used as a follow-up for the study
conducted in 2006 by Wetterer & Lombard. The surveys conducted in St. Croix used
beach mile markers as guide to place the bait cards. In Boca Raton, cards were places on
each life-guard tower that were located approximately 500 – 600 feet apart. In Pompano
Beach, the bait cards were placed in intervals of 50 – 100 meters since no permanent
markers were observed at the surveyed site.
21
4.2.1
Survey and Specimen Preservation
Following the procedure described in similar studies (Wetterer et al., 2007;
Wetterer & O'Hara, 2002; Wetterer & Lombard, 2010), approximately 1 gram of water
packed tuna bait was placed in a folded and properly marked index card. The cards were
left in the sites for 2 hours, after which they were collected and individually placed into
zip-lock bags (Figure 7). The bags were placed in a home freezer for approximately 2
hours in order to kill the ant specimens. The ants contained in each bag were visually
inspected, described based on characteristics that were visible through analysis under a
dissecting microscope and placed in vials of 95% ethanol for future analysis and
preservation.
Figure 7: Bait-card placed along dune vegetation (Image by Kavita Balkaran)
22
4.2.2
Specimen Identification
A minimum of two individuals per site were mounted using the point-mount
method (Figure 8), commonly used in preparing insects for long-term storage and later
analysis. The individuals were selected based on their size (one larger and one smaller
individual) and how complete was the specimen (Figure 9). For species that were
represented by less than 10 individuals per bait, only one specimen was mounted. We
used clear Elmer’s glue to mount the specimens as opposed to Hide glue which is
commonly used. This product was chosen because it is easier to remove and it does not
dry as fast as Hide glue.
Figure 8: Point-Mount Method
The mounted ants underwent three levels of identification. First, they were
preliminarily identified by Danielle Romais, narrowing their identification based on
genera. The second identification was done by Dr. James Wetterer, who identified most
specimens by species. The third identification was conducted in order to either confirm or
reject the two previous ones. It was done by Dr. Mark Deyrup, senior research biologist
and ant specialist at the Archbold Biological Station in Venus, Central Florida. The
23
specimens were labeled according to standard methods of identification. The final storage
of the specimens is yet to be determined.
Figure 9: Identified Ant Species
4.3 Sandy Point Wildlife Refuge Follow-Up Study: Phase I
In 2006, Wetterer and Lombardo (2010) conducted a survey at Sandy Point
Wildlife Refuge to investigate the prevalence of two species of fire ants (Solenopsis
invicta and Solenopsis geminata) in this area. In this study, Wetterer and Lombardo
(2010) placed 33 baits along 1.7km stretch of beach at Sandy Point Wildlife Refuge in St.
Croix, USVI. In the survey conducted by Wetterer and Lombardo (2010), nine species of
ants were identified. Five species were considered exotic and four were native. Fire ants
(Solenopsis invicta and Solenopsis geminata) occurred in 16 of the 33 baits, 48% of the
sites. Solenopsis geminata was the most common fire ant found at Sandy Point during the
2006 survey, present in 33% of the baits. Solenopsis invicta was found in 15% of the
sites. The native Dorymyrmex antillana was found in 14 of the 33 baits, comprising 42%
of the baits (Table 1) (Wetterer and Lombardo, 2010).
24
Table 1: Ant species surveyed in 2006 (Wetterer and Lombardo, 2010)
Exotic Species
Sites
Native Species
Sites
Solenopsis geminata
11
Dorymyrmex antillana
14
Solenopsis invicta
5
Brachymyrmex heeri
2
Paratrechina
4
Crematogaster steinheili
1
Monomorium floricola
2
Monomorium ebenium
1
Paratrechina
1
longicornis
bourbonica
In September of 2010, a follow-up distribution survey to the study conducted in
2006 (Wetterer and Lombardo, 2010) was conducted along the same stretch of beach at
Sandy Point Wildlife Refuge, St. Croix, USVI, as specified above. The starting point for
the survey in this area was at marker 45 (17°41'3.50"N and 64°53'12.09"W), and it
extended to marker 197 (17°41'0.83"N and 64°54'2.13"W). This survey took place in
September of 2010. The area was surveyed over a period of 3 days (09/18-09/20) due to
storm weather conditions at the time. During the first two days, the survey was conducted
in the morning, starting at 800 hours. In the last day, the survey was conducted in the
afternoon, starting at 1630 hours.
25
The distribution of ants in the study areas was compared to the results obtained in
the 2006 study conducted in the Virgin Islands. The analysis conducted was based on the
different ant species found per bait-card. The species were divided into two categories:
native and exotic. We expected to find at least the same number of exotic species as
found by Wetterer and Lombardo during their study. Due to the high accessibility to this
area, anthropogenic influence is evident, and it facilitates the spread and establishment of
many exotic species such as Solenopsis invicta and Solenopsis geminata.
4.4 Baseline Distribution Survey: Phase II
Two baseline distribution surveys were conducted as part of this study in order to
provide information about ant species present in these areas for future and more detailed
studies. The areas in this initial survey were chosen because they are well documented
sea turtle nesting sites. The two areas were: a stretch of beach in Pompano Beach, FL and
in Jack Bay, St. Croix, USVI.
4.4.1
Pompano Beach, FL
There are no current records of ant surveys conducted in this area, so this study
would provide a baseline data of ant species present along the Pompano Beach coast. Sea
turtles nest on this beach, being more vulnerable to ant predation. This survey was
conducted as a baseline analysis of the ant species present in the beach, so that future
studies can be conducted as for possible impacts on sea turtle hatchlings. This baseline
analysis aimed to investigate which ant species were found, and how their presence may
impact the survival of endangered sea turtles.
26
The starting point for the survey in this area was located in alignment with 5th
Avenue and extended south to the beach access at Atlantic Boulevard (26°13'53.80"N
and 80° 5'20.15"W). The survey area was divided by the Pompano Beach Fishing Pier.
The Pompano Beach survey was conducted in the morning of March 25th, 2012. A total
of 15 baits were placed along the dune vegetation at an interval of 50-100 meters. The
baits were placed at 800 hours in the morning and collected at 1000 hours, as specified
above. The ant specimens were preserved, mounted and identified according to the
methods explained above.
The area surveyed is highly influenced by anthropogenic activities. There are
many picnic areas, playgrounds, garbage cans spread throughout the surveyed area. This
area is also divided by the Pompano Beach Fishing Pier. Due to the high traffic of people
and the use of the beach, it was expected a larger ratio of exotic versus native ants to be
found in the survey.
4.4.2
Jack Bay, St. Croix, USVI.
The Jack Bay survey was conducted on December 18th, 2011 over a period of one
day. A total of 15 bait cards were placed along the edge of the dune vegetation in the
morning. The starting point for the survey in this area was at marker 6 (17°44'46.26"N
and 64°34'41.60"W) and extended to marker 25 (17°44'49.18"N and 64°34'53.43"W).
The baits were placed at 800 hours in the morning at an interval of approximately 50-100
meters, including some sea turtle nests found in the area. The baits with specimens were
collected at 1000 hours. The ant specimens were preserved, mounted and identified
according to the methods explained above.
27
The Nature Conservancy did not report any sea-turtle nest in Jack Bay or Isaac
Bay being predated by fire ants – or other exotic ants. There are no records of ant
distribution surveys conducted in this area of the island. Therefore, this survey serves as
baseline data for any future ant distribution analysis conducted in Jack Bay, St. Croix.
Due to more pristine environmental conditions found in Jack Bay, St. Croix, a higher
number of native ant species was expected.
4.5
The Boca Raton Survey: Phase III
The survey in Boca Raton was conducted to answer two questions in this
research: first, we wanted to investigate which species were present in the area; and
secondly, we wanted to repeat the survey in order to determine consistency in the
methods used. The area was surveyed during 4 different times (06/12/2012; 06/16/2012;
06/29/2012; 07/06/2012) using the same methods described in Wetterer & Lombard
(2006) and other ant distribution studies (Wetterer et al., 2007; Wetterer & O’Hara,
2002).
Each bait card was placed by the lifeguard towers (1-12), starting at the South
Beach Park Pavilion and ending at the Red Reef Park. The GPS coordinates for each
lifeguard tower was obtained, and a PVC stake marked the location where the bait card
was first placed. This was to ensure that subsequent bait cards would be placed in the
same location.
Each of the replicates was conducted in intervals ranging from 5 days to 15 days,
depending on weather conditions. Ants are able to recall sites where they originally found
28
a food source due to chemical trails they leave as well as other cues they are able to
gather from the environment (Collett et al., 2003). By spreading the collecting periods in
longer intervals, we aimed to avoid dependence in the discovery and dominance of the
bait cards which could skew our results. The shortest interval was 5 days between two
survey efforts and the longest interval was 15 days.
The study area chosen in Boca Raton is the site where Gumbo Limbo Nature
Center conducts studies on sea turtle conservation, nesting and hatchling release. The
dune and dune vegetation along the area is more protected and apparently less disturbed.
The area is highly sought for tourism, but local regulations seem to mitigate the impact.
Therefore, we expect to find a more diverse community of ant species. Exotic species of
ants are also expected to be found in this area because of disturbance and other
anthropogenic impacts that facilitate their establishment.
4.6 Statistical Analysis
The surveyed data was analyzed using the Chi-Squared Test in order to determine
if the ratios between native species and exotic species found in a study area were
significantly different from the each other. The critical alpha value to determine
significance for this study was α = 0.05. The Chi-Squared Test (χ2) formula is given
below. It computes the sum of the squared difference between the observed and expected
values divided by the expected value.
29
∑
Equation 1: Chi-Square Formula
First, the native and exotic data collected at Sandy Point, St. Croix in 2006
(Wetterer & Lombard, 2010) was compared against the native and exotic data collected
in 2010 – for this study. The ratio between Solenopsis invicta and Solenopsis geminata
observed in the 2006 survey at Sandy Point was compared to the ratio of the same species
observed in the 2010 survey of the same area. The ratio of native and exotic collected at
Sandy Point in the 2010 survey was compared against the ratio of native and exotic ant
species collected in Jack Bay, St. Croix. Lastly, the ratio between native species versus
exotic species observed in Pompano Beach was compared to the ratio between native and
exotic species observed in Boca Raton – first survey replicate.
These analyses aimed to determine differences between surveying efforts in two
distinct time periods as well as the difference in ratio among areas. The compared areas
were paired based on geographic location. The areas in Florida, Pompano Beach and
Boca Raton, were compared to each other. The two areas in St. Croix, Sandy Point and
Jack Bay, were also compared to each other. The data obtained at Sandy Point in 2006
was compared to the same type of data obtained in 2010, determining temporal
differences in the type of species found.
30
The survey replicates conducted in Boca Raton, FL were compared against each
other to determine if the ratio between native and exotic species was significantly
different. They were also analyzed in terms of the number of sites with RIFAs.
31
5
RESULTS AND DISCUSSION
5.1 Sandy Point Wildlife Refuge Follow-Up Study: Phase I
In a follow-up survey conducted in September of 2010, eleven different species of
ants were found at Sandy Point Wildlife Refuge. Seven species were exotic, and four
were native. Fire ants (Solenopsis invicta and Solenopsis geminata) were found in 38%
of the baits. The native Dorymyrmex antillana was found in 25 of the 60 baits (41%), but
the number of native species found was smaller than the number of exotic species.
Compared to the earlier survey, there was no significant difference on the number of sites
with fire ants. Solenopsis geminata was found in more baits than Solenopsis invicta.
(Table 2).
32
Table 2: List of ant species present at Sandy Point, St. Croix, USVI
Exotic Species
Sites
Native Species
Sites
Solenopsis geminata
13
Dorymyrmex antillana
25
Solenopsis invicta
5
Solenopsis globularia
6
Nylanderia bourbonica
2
Monomorium ebenium
4
2
Brachymyrmex heeri
1
Tapinoma
melanocephalum
Monomorium floricola
1
Paratrechina longicornis
1
Tetramorium simillimum
1
One native species (Crematogaster steinheili) found during the 2006 survey was
not found during the follow-up survey in 2010. The scientific name of one of the exotic
species observed in 2006 changed from Paratrechina bourbonica to Nylanderia
bourbonica (Lapolla et al., 2011). However, three different exotic species that had not
been observed in 2006 were found in the 2010 survey. The overall number of native
species was also lower than the number of exotic species. The number of native species
found in both surveys was not different (4), but the species varied.
The native Dorymyrmex antillana showed dominance over the native species,
being present in 25 of 60 baits. This may be an indicator that either the species is the
native dominant in this area or that the presence of exotic ants has driven the number of
33
native ant species down. Although Dorymyrmex antillana was observed in the majority
of baits, the number of individuals per bait was not high when compared to the two
species of fire ants (Solenopsis invicta and Solenopsis geminata) (Figure 10).
Ant Distribution at Sandy Point, St. Croix, USVI
Species Found
Solenopsis globularia (N)
Monomorium ebenium (N)
Monomorium floricola
Brachymyrmex heeri (N)
Nylanderia bourbonica
Dorymyrmex antillana(N)
Paratrechina longicornis
Tetramorium simillimum
Solenopsis geminata
Tapinoma melanocephalum
Solenopsis invicta
Solenopsis invicta
Tapinoma melanocephalum
Solenopsis geminata
Tetramorium simillimum
Paratrechina longicornis
Dorymyrmex antillana(N)
Nylanderia bourbonica
Brachymyrmex heeri (N)
Monomorium floricola
Monomorium ebenium (N)
0
5
10
15
20
25
30
Solenopsis globularia (N)
Number of Sites
Figure 10: Ant Distribution in Sandy Point, St. Croix, USVI - Follow-up Survey. Green
bars and (N) denotes native species, red bars are exotic species.
In baits where Solenopsis invicta was found (10 of the 60 baits), no other species
were present. The other species of fire ants (Solenopsis geminata) was found in baits
containing other ant species, but the density was visually greater for the fire ant species.
It is not possible to accurately infer that any impact is being caused by the
presence of exotic ants, mainly the fire ant species, on sea turtle hatchlings and nests in
34
Sandy Point, St. Croix. Further studies analyzing the interaction between ants and sea
turtles would have to be conducted in order to statistically make such affirmations.
However, there have been reports of ants swarming sea turtle nests and attacking
hatchlings as they emerge (C. Lombard, personal communication, 2010). These reports
along with the consistent presence of these exotic predaceous ants may be indicators of
threat that the ants may impact the sea turtles.
5.2 Baseline Distribution Survey: Phase II
In order to understand which are the impacts caused by predator ants on
endangered sea turtles, it is important to first know what species of ants are present in the
area of interest. This information is obtained through a baseline study of the area. The
presence of predatory ants, such as the RIFA, may pose an eminent threat to sea turtle
hatchlings. Therefore, it is important to know if they are present in sea turtle nesting areas
to be able to infer possible current or future threats. Baseline studies also serve as a
predictor of future establishments, based on current range expansion trends.
5.2.1
Pompano Beach Survey
Humans have re-designed the shores at the city of Pompano Beach. Although the
beach is still considered a desirable place for recreation, its function as a sea turtle nesting
area is being constantly impacted by this new condition. Exotic ants such as the RIFA
find this type of disturbed habitat suitable for their colonies because of the abundance in
food sources available as a result of the increased number of trash and food residue left
on the beach.
35
Since no previous ant distribution survey has been conducted in Pompano Beach,
this survey aimed to serve as baseline for future studies. Due to the highly anthropogenic
beach - with little or no dune vegetation and high recreational use - the number of exotic
ant species was expected to be higher than the number of native species. The survey was
conducted well within the sea turtle nesting/hatching season in order to provide us with
the most accurate account of possible threat.
A total of three (3) species were identified in Pompano Beach, FL. One of the
three was classified as native species. Two of the three were classified as exotic species
(Table 3).
Table 3: List of ant species in Pompano Beach, FL.
Exotic Species
Sites
Solenopsis invicta
5
Pheidole megacephala
1
Native Species
Dorymyrmex bureni
Sites
6
Twelve (12) of the fifteen baits placed at the Pompano Beach Survey Area
contained ants after the two-hour period. These twelve baits were classified as “active”.
Three baits had no ant specimens. These were classified “inactive”. One was removed by
a beach goer and placed in a trash can nearby. The other two had no ants present.
Dorymyrmex bureni, a native species commonly known as “pyramid ant”, was
found in six (6) of the twelve active baits, representing 50% of the total number of active
36
baits. The baits where these native species were present – and more predominant – were
mainly located north of the Pompano Beach Fishing Pier. One bait at the end of the
surveyed area had Dorymyrmex bureni present. Dorymyrmex bureni was the only native
species found in this area during this baseline distribution survey (Figure 11). This
species seems to be the only native that can be found in the same bait as the RIFA’s,
suggesting that they may be sharing foraging territory (J.A.Moore, personal
communication, November, 2013).
Pheidole megacephala, an exotic species commonly known as “big-headed ant”,
was found in one (1) of the twelve active baits, representing 8% of the total number of
active baits. This bait was located north of the Pompano Beach Fishing Pier, close to a
picnic/recreational area. This exotic species is also considered invasive in many areas of
the world, including Southern Florida. Pest control operators have reported that the bigheaded ant is becoming more pervasive as an invader because it displaces other ant
species in the area (Warner & Scheffrahn, 2010).
Solenopsis invicta, the infamous red imported fire ant (RIFA), was present in five
(5) of the twelve active baits, representing 42% of the total number of active baits. These
baits were predominantly located around and south of the Pompano Beach Fishing Pier.
As expected, the presence of RIFA was mostly in the portion of the surveyed area that
suffered the biggest anthropogenic influence. The area is heavily used by tourists and
local residents using the beach, picnic areas and playground adjacent to the beach. People
also use the pier, and trash that is left lying around usually attracts these ants to the area
(Figure 11).
37
Ant Distribution in Pompano Beach
Species Found
Solenopsis invicta
Dorymyrmex bureni (N)
Pheidole megacephala
Pheidole megacephala
Solenopsis invicta
Dorymyrmex bureni (N)
0
1
2
3
4
5
6
7
Number of Sites
Figure 11: Ant Distribution in Pompano Beach - Baseline Survey. Green bars and (N)
denotes native species, red bars are exotic species.
Sea turtle nests in this area were not found very close to the vegetation line –
where ants are usually found. RIFAs forage through tunnels that radiate from the mound.
Depending on the size of the territory, these foraging mounds can reach close to 100
meters from the main entrance to the mound. The presence of trash cans along the beach
facilitate foraging in the areas of the beach closest to the sea turtle nests. Therefore, the
presence of RIFAs in areas such as Pompano Beach may pose a significant threat to the
survival of the hatchlings, considering that ants can attack them before or after they have
emerged.
38
5.2.2
Jack Bay, St Croix Survey
Contrasting with Sandy Point, on the opposite side of St. Croix, Jack Bay is an
area that is not heavily used by visitors. The area is monitored by The Nature
Conservancy because it is a nesting site for sea turtles. In conversation with the sea turtle
specialist for TNC in St. Croix, she reported no knowledge of fire ant presence in Jack
Bay. Due to the overall pristine condition of the area, a higher number of sites with native
species were expected.
Since there are no previous ant distribution survey for this area, this survey will
serve as baseline data for future studies analyzing the possible threats of predaceous
exotic ants on sea turtle hatchlings in the area. Twelve baits were placed along the
vegetation at Jack Bay. All twelve sites were classified as active because ants were
present in all baits.
A total of three (3) species of ants were identified in Jack Bay. Two of the three
were classified as native species to Caribbean Islands. One species was classified as
exotic (Table 4 ).
Table 4: List of ant species found in Jack Bay, St. Croix, USVI.
Exotic Species
Sites
Native Species
Sites
1
Dorymyrmex antillana
10
Solenopsis globularia
1
Monomorium
floricola
39
As expected, the number of sites with native species was higher than those with
exotic species of ants. In fact, eleven of the twelve baits contained native species of ants.
Only one bait contained exotic ant species. Dorymyrmex antillana, a native species of
pyramid ant, was present in ten of the twelve baits. The species was present in 83% of the
baits used for this study. Solenopsis globularia, a thief ant native to the Caribbean
islands, was observed in one of the twelve baits – present in 8% of the total number of
active baits (Figure 12).
Considering that Jack Bay is a more secluded area, with little and limited access
to its shores, the presence of exotic species was expected to be very low. There was only
one exotic ant species present in the baits used for this study in Jack Bay. Monomorium
floricola, the exotic bicolored trailing ant, was present in one of the twelve baits. It
represented 8% of the total number of active baits (Figure 12).
Species Found
Ant Distribution in Jack Bay, St. Croix, USVI
Dorymyrmex antillana
(N)
Monomorium floricola
Solenopsis globularia (N)
Solenopsis globularia (N)
Dorymyrmex antillana (N)
Monomorium floricola
0
5
10
15
Number of Sites
Figure 12: Ant Distribution in Jack Bay, St. Croix - Baseline Survey. Green bars and (N)
denotes native species, red bars are exotic species.
40
5.3 The Boca Raton Survey: Phase III
The shores of Boca Raton, as it is true in much of the Florida coast, are
considered a prime habitat for sea turtles to nest. As part of an effort to protect these
already endangered species, Gumbo Limbo Nature Center houses a sea turtle hospital and
research facilities that monitor the beach daily during nesting season. The presence of
exotic predaceous ants was observed by the Sea Turtle Research Group that conducts nest
surveys at the beach. However, no official ant distribution survey has been previously
done in the Boca Raton beach area.
In order to provide sea turtle researchers with information about possible
predators to hatchlings, this study carried out a preliminary ant distribution survey. The
primary goal with this survey was to determine which ant species were present at the
beach in Boca Raton, and – from the data obtained – help predict possible threats to sea
turtles hatchlings. Secondly, the study analyzed whether the species collected would be
consistent if surveys were repeated multiple times, and if it was possible to infer
dominance of ant species based on distribution surveys. Four different surveys were
conducted in the same sites. The intervals between each repeated survey ranged from 5 to
15 days.
5.3.1
Baseline Survey Results
Although Boca Raton is an area highly sought for tourism, the dune vegetation
seems to be in healthy condition when compared to the study site in Pompano Beach.
41
Therefore, it was expected that the number of exotic species per site found would be
lower or – at most – equal to the number of native species per site. Twelve bait cards
used in this study were each placed by the lifeguard towers (1-12) located from South
Beach Park to Red Reef Park. This area is monitored by the Sea Turtle Research Team at
the Gumbo Limbo Nature Center.
There have been informal observations of sea turtle nests being attacked by exotic
predaceous ants. The Sea Turtle Research Team at Gumbo Limbo indicated that in such
instances the ants would be classified as “fire ants”, but no further analysis of the ants
was conducted. They also reported that ant mounds or trails would be treated with
Amdro®, specifically when ants were found near or on sea turtle nests.
A total of ten (10) species were observed on the bait cards for the first sampling of
the area. Two of the ten species observed were classified as native to the area. The eight
remaining species were classified as exotic (Table 5).
42
Table 5: List of ant species present in the Boca Raton study site – Initial Survey
Exotic Species
Sites
Native Species
Sites
Solenopsis invicta
3
Dorymyrmex bureni
4
2
Pheidole floridana
1
Tapinoma
melanocephalum
Campanotus sexguttatus
1
Paratrechina
1
longicornis
Forelius pruinosus
1
Nylanderia bourbonica
1
Monomorium floricola
1
Tetramorium
1
bicarinatum
The number of native species was lower than expected despite the high usage of
the beach. The native pyramid ant, Dorymyrmex bureni, was present in four of the twelve
lifeguard tower sites. This species was found in 33% of the sites. Pheidole floridana, was
classified as a native species to this area. It was present in one of the twelve sites,
representing 8% of the total number of active baits (Figure 13). The two native species
were found in a total of four (4) sites, making up 33% of the total number of sites
surveyed.
43
Species Found
Ant Distribution in Boca Raton - Survey I
Tetramorium bicarinatum
Monomorium floricola
Nylanderia bourbonica
Forelius pruinosus
Tapinoma melanocephalum
Paratrechina longicornis
Solenopsis invicta
Campanotus sexguttatus
Pheidole floridana (N)
Dorymyrmex bureni (N)
Dorymyrmex bureni (N)
Pheidole floridana (N)
Campanotus sexguttatus
Solenopsis invicta
Paratrechina longicornis
Tapinoma melanocephalum
Forelius pruinosus
Nylanderia bourbonica
0
1
2
3
Number of Sites
4
5
Monomorium floricola
Tetramorium bicarinatum
Figure 13: Ant Distribution in Boca Raton - Initial Survey. Green bars and (N) denotes
native species, red bars are exotic species.
There were eight ant species that were classified as exotic to this area. Solenopsis
invicta was present in three (3) of the twelve sites on the first sampling. Tapinoma
melanocephalum was present in two (2) of the twelve sites. The other exotic species were
present in one of the twelve sites. The other exotic species were: Campanotus
sexguttatus, Paratrechina longicornis, Forelius pruinosus, Nylanderia bourbonica,
Monomorium floricola and Tetramorium bicarinatum (Figure 13).
5.3.2
Methodology Consistency Analysis
In order to determine if the species present at a surveyed site accurately represent
the distribution of ant species at sea turtle nesting beaches, this study conducted four
44
distinct and independent surveys at the Boca Raton study area. The four different surveys
were conducted on intervals ranging from 5 to 15 days, depending on weather conditions.
Time of day and placement of bait cards were kept constant throughout the different
sampling efforts.
Although variations on species found at each site were observed from one
sampling to the other, overall the species were consistently found in the same sites. It was
observed that the species that did vary were the ones found in least numbers per bait.
These species were not considered “dominant” per each site.
As stated earlier, the surveying efforts in Boca Raton were repeated four times in
order to analyze consistency of results. The initial survey served as a baseline for ant
distribution in this study area. The results for the initial survey are displayed and
discussed in the previous section of this document.
On the second survey, a total of eleven (11) species of ants were observed. Three
(3) of the eleven species were classified as native to the area. The remaining eight (8)
species were classified as being exotic.
45
Table 6: List of species found in Boca Raton - Survey II
Exotic Species
Sites
Native Species
Campanotus
Sites
Dorymyrmex
2
2
sexguttatus
bureni
Technomyrmex
Campanotus
2
2
difficilis
floridana
Forelius pruinosus
2
Nylanderia bourbonica
2
Solenopsis invicta
1
Cardiacondyla emeryi
1
Pheidole floridana
Tetramorium
1
bicarinatum
Tetramorium
1
simillimum
46
2
Ant Distribution in Boca Raton - Survey II
Tetramorium simillimum
Dorymyrmex bureni (N)
Tetramorium bicarinatum
Pheidole floridana (N)
Species Found
Nylanderia bourbonica
Campanotus floridana (N)
Forelius pruinosus
Campanotus sexguttatus
Cardiacondyla emeryi
Solenopsis invicta
Technomyrmex difficilis
Solenopsis invicta
Technomyrmex difficilis
Campanotus sexguttatus
Cardiacondyla emeryi
Campanotus floridana (N)
Forelius pruinosus
Pheidole floridana (N)
Nylanderia bourbonica
Dorymyrmex bureni (N)
0
0.5
1
1.5
Number of Sites
2
2.5
Tetramorium bicarinatum
Tetramorium simillimum
Figure 14: Ant Distribution in Boca Raton - Survey II. Green bars and (N)
denotes native species, red bars are exotic species.
Solenopsis invicta was present in one site during this survey. There were four
exotic species present in the greatest number of sites (2). These species were:
Campanotus sexguttatus, Technomyrmex difficilis, Forelius pruinosus and Nylanderia
bourbonica (Figure 14). One of the bait cards (site number 5) was missing at the time of
collecting. Logistic issues at the time of collecting the bait cards may have skewed the
results for this survey. The bait cards were left in site longer than the desired two hours
due to delay on getting to each site.
47
Table 7: List of species found in Boca Raton - Survey III
Exotic Species
Sites
Native Species
Sites
Solenopsis invicta
4
Dorymyrmex bureni
5
Nylanderia bourbonica
2
Pheidole floridana
1
Technomyrmex difficilis
1
Tetramorium simillimum
1
Forelius pruinosus
1
Campanotus sexguttatus
1
Monomorium floricola
1
Tetramorium
bicarinatum
1
On the third survey, a total of 10 species were observed. Two of the ten species
were classified as native while eight were classified as exotic (Table 7). Five sites out of
twelve surveyed (42%) contained native species. Nine sites contained exotic species
(75%). Many species were found in combination with others in one single site.
Solenopsis invicta was present in four (4) out of twelve sites (33% of total sites).
Dorymyrmex bureni was present in five (5) of the twelve sites (42%) (Figure 15).
48
Ant Distribution in Boca Raton - Survey III
Tetramorium bicarinatum
Monomorium floricola
Dorymyrmex bureni (N)
Species Found
Nylanderia bourbonica
Pheidole floridana (N)
Forelius pruinosus
Campanotus sexguttatus
Tetramorium simillimum
Solenopsis invicta
Technomyrmex difficilis
Technomyrmex difficilis
Tetramorium simillimum
Solenopsis invicta
Forelius pruinosus
Campanotus sexguttatus
Nylanderia bourbonica
Pheidole floridana (N)
Monomorium floricola
Dorymyrmex bureni (N)
Tetramorium bicarinatum
0
1
2
3
4
5
6
Number of Sites
Figure 15: Ant Distribution in Boca Raton - Survey III. Green bars and (N) denotes
native species, red bars are exotic species.
On the fourth survey, a total of eleven (11) species were observed. Two of the
eleven species were classified as native to the area. Nine species were classified as exotic
(Table 8).
49
Table 8: List of species found in Boca Raton - Survey IV
Exotic Species
Sites
Native Species
Sites
Solenopsis invicta
3
Dorymyrmex bureni
6
Nylanderia bourbonica
3
Pheidole floridana
1
Tetramorium simillimum
2
Technomyrmex difficilis
1
Campanotus sexguttatus
1
Paratrechina longicornis
1
Monomorium floricola
1
Wasmania auropunctata
1
Tetramorium bicarinatum
1
Native species were present in seven of the twelve sites. Exotic species were
present in ten of the twelve sites. Many species (exotic and native) were found in
combination with other species per site (Figure 16).
50
Species Found
Ant Distribution in Boca Raton - Survey IV
Tetramorium bicarinatum
Wasmania auropunctata
Monomorium floricola
Nylanderia bourbonica
Tetramorium simillimum
Technomyrmex difficilis
Paratrechina longicornis
Solenopsis invicta
Campanotus sexguttatus
Pheidole floridana (N)
Dorymyrmex bureni (N)
Dorymyrmex bureni (N)
Pheidole floridana (N)
Campanotus sexguttatus
Solenopsis invicta
Paratrechina longicornis
Technomyrmex difficilis
Tetramorium simillimum
Nylanderia bourbonica
0
1
2
3
4
5
6
7
Number of Sites
Monomorium floricola
Wasmania auropunctata
Figure 16: Ant Distribution in Boca Raton - Survey IV. Green bars and (N) denotes
native species, red bars are exotic species.
The species found in greatest abundance (number of individuals greater than 100)
when bait was shared with other species were classified as “dominant” over the other
species. In some cases, the bait cards contained only one species of ant. These species
were considered “dominant” as well (Table 9). “N/A” indicates that the bait was either
missing or with no ants present.
51
Table 9: Comparison per site between the four sampling efforts in Boca Raton, FL Species observed based on abundance of individuals
Exotic
Survey 1
Survey 2
Survey 3
Survey 4
Solenopsis
invicta
Nylanderia
bourbonica
Tetramorium
simillimum
Tetramorium
bicarinatum
Campanotus
sexguttatus
Technomyrmex
difficilis
Forelius
pruinosus
Monomorium
floricola
Paratrechina
longicornis
Tapinoma
melanocephalum
Wasmania
auropunctata
Cardiacondyla
emeryi
Native
3
1
4
3
1
2
2
3
1
1
2
1
1
1
1
1
2
1
1
2
1
1
2
1
Dorymyrmex
bureni
Pheidole
floridana
Campanotus
floridana
1
1
1
1
1
1
2
1
1
Survey 1
Survey 2
Survey 3
Survey 4
4
2
5
6
1
2
1
1
2
52
Overall, the species observed at each bait card are consistently found in the sites.
There are some general variations in the results obtained, which was expected due to
weather condition and time that the bait was left at each site. Although it may not be
possible to determine dominance, it is reasonable to assume that these species are
currently distributed in this area. Therefore, based on these results, the bait method used
to survey ants in this study has shown consistent results in the species observed. Its aim
was to survey for dominant ant species in the area.
5.3.3
Possible Threats to Sea Turtle Hatchlings
Several studies have indicated that RIFAs are a threat to ground nesting birds and
reptiles (Greenwood, Palmer, & Richardson, 2010; Parris et al., 2002; Wetterer et al.,
2007; Wetterer & Hara, 2002). There have been reports about fire ant attacks on sea turtle
hatchlings. These attacks happen either at the time of emergence or soon as the turtles
have pipped. Ants can also monitor the egg chamber as a way of “knowing” when it is
appropriate to swarm the nest. Fire ants can forage as far as mid-beach, so nests far from
the vegetation can still be affected by ant attacks (Krahe, 2005; Wetterer et al., 2007).
In 2012, the same year when the ant distribution survey was conducted for this
study, Gumbo Limbo Nature Center reported a total of 1143 nests along the entire stretch
of beach monitored by their Sea Turtle Research Team (Rusenko et al., 2012). The
presence of RIFAs poses a significant threat to the survival ability of sea turtle hatchlings
because they are most vulnerable to predators at that stage.
53
This study was able to determine which sites were most likely to have RIFAs.
Solenopsis invicta was observed in five of the twelve sites in Boca Raton. This data was
geo-referenced in ArcGIS and combined with the data obtained by Gumbo Limbo Nature
Center (Rusenko et al., 2012) on sea turtle nests for the 2012 nesting season. Considering
that sea turtle hatchlings are potential targets for RIFAs attacks, the presence of
Solenopsis invicta (RIFAs) can be considered a threat to sea turtle nesting and hatchling
survival and success (Figure 17).
54
Figure 17: Sea Turtle Nests and Fire Ant Presence in Boca Raton, Fl - 2012
55
Solenopsis invicta can forage very large areas, depending on colony size. The
foraging territory can be adjusted based on food availability, but it may also be strongly
related to the number of workers and territory size. Studies have indicated that colony
ranges from 12 to 197 m2 (Dhami, 2008). Based on this information and the data obtained
on sea turtle nests, fire ants may pose significant threat to hatchlings if population density
of the invasive species is not kept under control.
5.4 Statistical Analysis
When comparing the number of sites with native and exotic species surveyed in
2006 against those surveyed in 2010 at Sandy Point, St. Croix, USVI, the p-value
obtained using the chi-squared formula was 0.26, which is greater than the critical alpha
value of 0.05. This indicates that the ratio of native and exotic species was not
significantly different at Sandy Point from the 2006 survey to the 2010 survey. The table
below indicates the observed values and the expected values used in this analysis (Table
10). The bar graph was used to indicate the frequency of native and exotic species during
each of the surveyed periods (Figure 18).
56
Table 10: Observed (O) versus Expected (E) sites with native and exotic species in 2006
and 2010 - Sandy Point, St. Croix, USVI (P>0.05)
Observed
Natives Exotics
Total Surveyed Sites
2006
18
23
33
2010
30
31
60
Grand Total
48
54
93
Expected
Year/Sites
Natives Exotics
Total Surveyed Sites
2006
17.03
19.16
33
2010
30.97
34.84
60
Grand Total
48
54
93
p-value
0.26
57
Frequency of Native and Exotic Species per number of
sites - Sandy Point Survey 2006 vs. 2010
Species
Exotics
2010
Natives
2006
0
5
10
15
20
25
30
35
Number of Sites
Figure 18: Graph of frequency of native versus exotic species – the Sandy Point ant
survey in 2006 against the Sandy Point ant survey in 2010
Since Solenopsis invicta and Solenopsis geminata are the two species of fire ants
present in St. Croix, this study investigated the frequency that they were observed. The
survey conducted in 2006 observed Solenopsis geminata in 11 sites, and Solenopsis
invicta was observed in 5 sites. In 2010, Solenopsis geminata was detected in 13 sites
while Solenopsis invicta was still detected in 5 sites in Sandy Point, St. Croix. The ratio
of sites with Solenopsis invicta and Solenopsis geminata surveyed at Sandy Point in 2006
did not significantly differ from the 2010 survey. The p-value obtained from the chisquare test was 0.82, which is greater than 0.05. This indicates that the number of sites
containing Solenopsis invicta and Solenopsis geminata at Sandy Point did not vary
significantly from the 2006 survey to the 2010 survey. The table below indicates the
observed values and the expected values used in this analysis (Table 11). The bar graph
58
shows the frequency of Solenopsis invicta and Solenopsis geminata at Sandy Point during
the 2006 and the 2010 surveys (Figure 19).
Table 11: Observed (O) and Expected (E) number os sites containing Solenopsis invicta
and Solenopsis geminata in 2006 and 2010 - Sandy Point, St. Croix, USVI(P>0.05)
Observed
S. geminata
S. invicta
Total Surveyed
Sites
2006
11
5
16
2010
13
5
18
Grand Total
24
10
34
Expected
S. geminata
S. invicta
Total Surveyed
Sites
2006
11.29
4.71
16
2010
12.71
5.29
18
Grand Total
24
10
34
p-value
0.82
59
Frequency of Solenopsis invicta and Solenopsis
geminata - Sandy Point Survey 2006 vs. 2010
Species
S. invicta
2010
2006
S. geminata
0
5
10
15
Number of Sites
Figure 19: Graph of frequency of Solenopsis invicta and Solenopsis geminata per number
of sites – the Sandy Point survey in 2006 against the Sandy Point survey in 2010
The two sites surveyed in St. Croix for this study are remarkably different from
each other. While Sandy Point is sought for tourism, Jack Bay is more secluded. The
present study investigated if this difference could be detected in the ant distribution of
each area. The results of the chi-squared test indicated that the ratio of native species
versus exotic species at Sandy Point was significantly different than that of Jack Bay, St.
Croix. The p-value was 0.007, which is less than the alpha critical value of 0.05 (Table
12). The bar graph indicates the frequency at which native and exotic ant species were
observed in Jack Bay versus Sandy Point (Figure 20). The two species of fire ants,
Solenopsis invicta and Solenopsis geminata, were not detected in Jack Bay. This can
possibly be related to the environmental conditions of the area, but further study is
needed in order to investigate this matter.
60
Table 12: Observed (O) and Expected (E) number of sites with native and exotic species
in Sandy Point and Jack Bay (P<0.05)
Observed
Natives
Exotics
Total Surveyed
Sites
Sandy Point
30
31
60
Jack Bay
11
1
12
Grand
41
32
72
Total
Expected
Natives
Exotics
Total Surveyed
Sites
Sandy Point
34.17
26.67
60
Jack Bay
6.83
5.33
12
Grand Total
41
32
72
p-value
0.007
61
Species
Frequency of Native and Exotic Species per
number of sites - Sandy Point vs. Jack Bay, St.
Croix, USVI
Exotics
Jack Bay
Natives
Sandy Point
0
10
20
30
40
Number of Sites
Figure 20: Graph of frequency of native and exotic species in Sandy Point and Jack Bay,
St. Croix
The same comparative analysis was conducted for the two study areas in South
Florida – Pompano Beach and Boca Raton. A slight difference was expected to be
observed between the two areas because Pompano Beach appears to be more impacted by
anthropogenic use than Boca Raton. The surveyed area in Pompano Beach does not have
any dune vegetation while the surveyed area in Boca Raton does. However, the results
obtained with the chi-squared test indicated that the ratio of native and exotic species was
not significantly different between the two areas. The p-value was 0.32, which is greater
than the critical alpha value of 0.05 (Table 13). The frequency of native and exotic
species surveyed in Pompano Beach and Boca Raton is given by the bar graph below
(Figure 21). When comparing the number of sites where Solenopsis invicta was detected,
the two areas were not significantly different. The p-value was 0.48, which is greater than
the critical alpha value of 0.05 (Table 14). The frequency of Solenopsis invicta in
Pompano Beach and Boca Raton is given by the bar graph below (Figure 22).
62
Table 13: Observed (O) and Expected (E) number of sites with native and exotic species
in Pompano Beach and Boca Raton (P>0.05)
Observed
Natives
Exotics
Total Surveyed Sites
Pompano Beach
6
6
12
Boca Raton
4
9
12
Grand Total
10
15
24
Expected
Natives
Exotics
Total Surveyed Sites
Pompano Beach
5
7.5
12
Boca Raton
5
7.5
12
Grand Total
10
15
24
p-value
0.32
63
Frequency of Native and Exotic Species per number of
sites - Pompano Beach, FL vs. Boca Raton, FL
Species
Exotics
Boca Raton
Pompano Beach
Natives
0
2
4
6
8
10
Number of Sites
Figure 21: Graph of frequency of native and exotic species in Pompano Beach and Boca
Raton
64
Table 14: Observed (O) and Expected (E) number of sites with Solenopsis invicta in
Pompano Beach and Boca Raton survey areas (P>0.05)
Observed
S. invicta
Total Surveyed
Sites
Pompano Beach
5
12
Boca Raton
3
12
Grand Total
8
24
Expected
S. invicta
Total Surveyed
Sites
Pompano Beach
4
12
Boca Raton
4
12
Grand Total
8
24
p-value
0.48
65
Frequency of Solenopsis invicta in Pompano Beach
and Boca Raton
Species
Boca Raton
Pompano Beach
Boca Raton
Pompano Beach
0
2
4
6
Number of Sites
Figure 22: Graph of frequency of Solenopsis invicta in Pompano Beach and Boca Raton,
FL
The survey conducted in Boca Raton was replicated four times to determine
consistency in surveying methods. Although some variation is expected, the overall
outcome was not expected to vary significantly among replicate surveys. The results
obtained with the chi-squared test indicated that there is no significant difference in the
ratio of native and exotic species among the four replicate surveys. The p-value was 0.70,
which is greater than the critical alpha value of 0.05 (Table 15). The frequency of native
and exotic species in Boca Raton for all four replicates is given by the bar graph below
(Figure 23). When comparing the number of sites where Solenopsis invicta was detected,
the four replicates did not indicate significant differences. The p-value was 0.63, which is
greater than the alpha critical value of 0.05 (Table 16). The frequency of Solenopsis
invicta when comparing the four replicates is given by the bar graph below (Figure 24).
66
Table 15: Observed (O) and Expected (E) number of sites with Solenopsis invicta in
Pompano Beach and Boca Raton survey areas (P>0.05)
Observed
Natives
Exotics
Total Surveyed Sites
BR1
4
9
12
BR2
4
8
12
BR3
5
9
12
BR4
7
10
12
Grand
20
36
48
Total
Expected
Natives
Exotics
Total Surveyed Sites
BR1
5
9
12
BR2
5
9
12
BR3
5
9
12
BR4
5
9
12
Grand
20
36
48
Total
p-value
0.70
67
Frequency of Native and Exotic Species per number of sites Pompano Beach, FL vs. Boca Raton, FL
Replicates
BR4
BR3
Exotics
BR2
Natives
BR1
0
2
4
6
8
10
12
Number of Sites
Figure 23: Graph of frequency of native and exotic species in Boca Raton
68
Table 16: Observed (O) and Expected (E) number of sites with Solenopsis invicta in the
Boca Raton survey area – four replicates (P>0.05)
Observed
S. invicta
Total Surveyed Sites
BR1
3
12
BR2
1
12
BR3
4
12
BR4
3
12
11
48
Grand Total
Expected
S. invicta
Total Surveyed Sites
BR1
2.75
12
BR2
2.75
12
BR3
2.75
12
BR4
2.75
12
11
48
Grand Total
p-value
0.63
69
Frequency of Solenopsis invicta in Boca Raton
Replicates
BR4
BR3
BR1
BR2
BR2
BR3
BR4
BR1
0
1
2
3
4
5
Number of Sites
Figure 24: Graph of frequency of Solenopsis invicta in Boca Raton - four replicates
70
6
FINAL REMARKS
The red imported fire ants impact a wide range of organisms, from native ant
communities to endangered species such as the sea turtles nesting in South Florida and
the U.S Virgin Islands. Mitigation efforts are required in order to control the spread of the
species in areas where it is present, and avoid introduction to areas where the species is
currently absent, like Jack Bay, St. Croix, USVI.
Efforts to control the RIFA’s impact on sea turtle hatchlings are on-going. The
Sea Turtle Research Team at Gumbo Limbo Nature Center periodically treats for fire ants
if they are detected near sea turtle nests. The U.S Fish and Wildlife office in St. Croix
also monitors for fire ant attacks on hatchlings.
However, a more concerted effort is needed in accurately identifying fire ants and
determining whether or not the species is dominant in the area. The study of the
distribution of an invasive species such as the RIFA can serve as a baseline to determine
critical areas that need to be tackled in terms of control as well as areas that need to be
monitored to keep these invasive ants from spreading. Knowing where the fire ants
currently are can provide insight for future range expansions.
71
The methodology used in these surveys is the one most commonly used when
surveying for dominant species of ants. Although variations on species detected occur,
the likelihood of species found in one survey of an area not to be there in subsequent
surveys is small. Moreover, there is a need to conduct baseline ant distribution surveys in
other areas where sea turtles nest because – with globalization and climate change – it is
likely that Solenopsis invicta will be introduced to other sea turtle nesting beaches.
72
7
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