Population Densities of Poison Dart Frogs in a Regenerating Tropical Forest
as Measured by the Hayne Estimator
A Thesis Presented
by
Jennifer Rose Bunnell Miller
To the Joint Science Department
Of The Claremont Colleges
In partial fulfillment of
The degree of Bachelor of Arts
Senior Thesis in Organismal Biology
April 2007
TABLE OF CONTENTS
ABSTRACT ................................................................................................................................. 4
INTRODUCTION ......................................................................................................................... 5
MATERIALS AND METHODS ................................................................................................... 14
Study Area........................................................................................................................... 14
Study Species....................................................................................................................... 17
Population Density.............................................................................................................. 19
Distribution ......................................................................................................................... 22
Abiotic Factors.................................................................................................................... 22
RESULTS ................................................................................................................................. 25
Population Densities and Distributions.............................................................................. 25
Rainfall................................................................................................................................ 32
Temperature........................................................................................................................ 33
Time of day.......................................................................................................................... 34
DISCUSSION............................................................................................................................. 37
Hayne Estimator Validity.................................................................................................... 37
Population Densities and Distributions.............................................................................. 41
Temperature........................................................................................................................ 44
Time of Day......................................................................................................................... 45
The Hayne Estimator as a Tool for Monitoring Amphibians ............................................. 46
Conclusions......................................................................................................................... 47
ACKNOWLEDGEMENTS ........................................................................................................... 49
LITERATURE CITED................................................................................................................ 50
2
APPENDICES ............................................................................................................................ 56
3
ABSTRACT
With amphibian populations declining throughout the world, there is an increasing
demand for effective tools to measure species responses to environmental change. This study
investigates the effectiveness of the Hayne Estimator in evaluating the densities of two
species of poison dart frogs in three Costa Rican lowland forest habitats with varying degrees
of recovery from deforestation (selectively-logged riparian forest, post-pasture secondary
forest and non-native bamboo plantation forest). Population densities of Dendrobates
granuliferus and Dendrobates auratus were significantly highest in riparian forest,
substantially lower in bamboo, and very low in secondary forest. This trend corresponds to
previous research on species recolonization after deforestation and subsequent regrowth and
indicates that the Hayne Estimator is well suited for the evaluation of poison dart frogs.
Abiotic factors such as proximity to water, rainfall, temperature and time of day were found
to have some effect on frog sighting frequency. Individuals of both species tended to
aggregate near water, but the proportional distribution of transects according to all habitat
water presence likely negated this effect. Rainfall was unrelated to the sighting frequency of
D. auratus but correlated with the sighting frequency of D. granuliferus. Air temperature did
not impact sighting frequency. Time of day, however, was found to influence the sighting
frequencies of both species, with peaks occurring in the early morning and late afternoon.
The robustness of the Hayne Estimator when used to monitor poison dart frogs suggests that
the technique may be a valuable tool for future conservation research.
4
INTRODUCTION
Since scientists gathered at the First World Congress of Herpetology in 1989 to
address the worldwide decline of amphibian populations, concern for these creatures has
increased at an accelerating rate (Phillips, 1990; Stuart et al., 2004). Now, nearly 2 decades
later, as populations continue to decrease in size and weaken in stability, scientists are calling
for the unprecedented cooperation of all to prevent further loss of amphibian diversity. In
2006, 49 accomplished herpetologists co-authored a forum in Science that announced the
disappearance of 122 species and identified 32.5% of known amphibians as threatened
(Mendelson III et al.). The group asserted that only through the union of “individuals,
governments, foundations, and the wider conservation community” would the escalating rate
of extinctions slow. Their recommendations echo the suggestions of other scientists and
necessitate the implementation of monitoring, surveys, habitat protection and breeding
research colonies in an international effort to ensure the continued existence of amphibians.
Long-term monitoring programs serve as a foundation of restoration ecology planning
because they reflect the responses of at-risk species to environmental change. Knowledge
about the population health of sensitive species in recovering habitats is invaluable to the
conservation community. These studies not only increase the likelihood of successful land
management of protected areas, but they also guide policy towards accurately prioritizing the
protection of land in regions and habitats that are greatly valued for preserving biodiversity.
Without a doubt, Latin America has been more severely impacted by amphibian
declines than any other region in the world (International Union for Conservation of Nature
and Natural Resources [IUCN], 2006). In Central and South America, over 30 genera, 9
families and 1,157 species of amphibians have declined or gone extinct (Young et al., 2001;
5
IUCN, 2006; Pounds et al., 2006). The tropical regions of this area have supported a high
diversity of amphibian species for millennia, leading the region to be classified as a
biodiversity hotspot (Figure 1; Myers et al., 2000; Brooks et al., 2002). When one considers
the increasing rate of new amphibian species discoveries (Donoghue and Alverson, 2000),
the potential number of amphibians that may have been harmed by human activities is
astounding.
Because of the extensive body of tropical ecological research conducted in Costa
Rica, this country has become a paradigm for understanding patterns of species decline in
other tropical locations. Although Costa Rica covers only 0.03% of the planet’s surface, it is
home to 4% of the world’s biodiversity and 3% of the world’s threatened amphibians (IUCN,
2006; World Resources Institute, 2006; National Biodiversity Institute, 2007). To date, one
amphibian species has gone extinct in the country (Bufo periglenes, the golden toad) and 64
species are considered threatened (IUCN, 2006). Although more than one-fifth of Costa
Rican land is protected, it is clear that further action must be taken in order to raise, or at
least sustain, the current level of biodiversity (World Resources Institute, 2006).
Like many other countries throughout the world, Costa Rica has been the site of
rampant deforestation over the past few centuries. However, human habitation has followed a
unique trend within the last several decades. With increasing job opportunities in the urbanbased tourism and textile industries, workers have begun to migrate away from agricultural
areas (Aide and Grau, 2004). Since 1960, the rural population in Latin America and the
Caribbean has dropped by 30%, a trend driven in part by a 20 million person decrease in the
population whose livelihood is based on agriculture, hunting, fishing or
6
Figure 1. The hotspots of the world. Costa Rica is classified as part of the Mesoamerica hotspot, which extends from southern
Mexico to Panama (image from Myers et al., 2000).
7
forestry since 1980 (Food and Agriculture Organization of the United Nations, 2004). While
much of the vacant land has been sold for the expansion of other farms, a substantial amount
has been abandoned, providing an opportunity for regrowth, recolonization and the
reestablishment of natural ecosystems.
While ecologists have extensively explored species’ responses to the degradation of
native habitat, less work has been done on recovering habitats. With the current trend in
Costa Rica favoring natural regrowth, and with the increasing public awareness about the
causes of global warming, a large movement to restore farmed and developed land across the
planet could occur within the next century. Species monitoring programs must be
implemented in order to predict, prepare and assist the associated changes in biodiversity.
In 2001, Pitzer College acquired the Firestone Center, a parcel of land in Costa Rica
that had previously been selectively stripped of forest and converted into a cattle farm and
Figure 2. The Firestone
Reserve, otherwise known as
the Finca la Isla del Cielo, is
owned by Pitzer College and
located near Dominical in
southwestern Costa Rica
(Firestone Center for
Restoration Ecology, 2006).
8
monoculture plantation (Figure 2). A series of changes in ownership has allowed the
Firestone Reserve to have 13 years of continuous natural regeneration. Today, the preserve is
an ideal study site for investigating the process of regrowth. The variation in land patch
quality permits the juxtaposition of species in native riparian habitat versus secondary and
non-native plantations that have had over a decade to recover. The Joint Science Department
of the Claremont Colleges launched a student research program in the summer of 2005 and
has plans to establish long-term monitoring programs to track the regeneration progress.
Since it is unrealistic to study the impacts of human activities on all species in a given
area, indicator species are studied as representatives of a larger group. Indicators may belong
to any taxonomic group, but are commonly characterized by a degree of sensitivity to
disturbance that mirrors the responses of a wide variety of other species (Landres et al.,
1988). Anurans are ideal indicators because all stages of their life cycles are highly
dependent on environmental conditions. Most frogs and toads require a permanent water
source for reproduction, the development of young, and a source of food. Their skins are
permeable to permit survival in water and on land, leaving their bodies vulnerable to the
chemical balance around them. The majority of anurans also consume insects, a group known
to shift radically with a change in vegetation (Gibbs and Stanton, 2001). Based on these
characteristics and others, anurans are especially susceptible to habitat loss, chemical
contamination, climate change and the introduction of exotic species and disease, factors
known as the leading causes of decline in other amphibian species as well (Young et al.,
2001).
Although anurans are prized for the insight they provide regarding the health of an
ecosystem, the creatures are also the arch nemeses of many field scientists. Cryptic and
9
nocturnal, the typical frog or toad is a challenge to study in its natural environment. The
endemic poison dart frogs of Costa Rica, however, provide a colorful alternative to studying
cryptic indicators in the tropics. All members of the family Dendrobatidae are
aposematically colored, diurnally active and easily identified to species. Seventeen species of
Dendrobates have been identified in Central America and more than 100 species are known
to South America (Maxson and Myers, 1985). In addition to the two-continent family
distribution, many poison dart frog species have a range that spans several countries. Data
collected on frogs in one region can thus be readily applied to an entirely different area.
In an effort to measure the biodiversity status in the regenerating Firestone Reserve
habitats, the abundances of two poison dart frog species were measured. Both the granular
Error!
Figure 3. Many frogs utilize camouflage to hide from predators and field scientists alike
(left, Hyla versicolor), whereas Dendrobatids have conspicuous skin color and patterns to
contrast against their background (right, Dendrobates azureus). Their aposematic coloration
conveys to predators the consequences of a quick snack. Photos courtesy of
www.livingunderworld.org and www.webshots.com
10
Figure 4. The study species: Dendrobates granuliferus (top) and Dendrobates auratus
(bottom). Photographs by Keith Christenson.
11
(Dendrobates granuliferus) and the green and black (Dendrobate auratus) poison dart frog
occur naturally on the preserve (Figure 4). The population densities of these species were
assessed in riparian, secondary and bamboo forest habitats during the early wet season of
October 2006. Data were collected and calculated using the Hayne Estimator technique
(Hayne, 1949), which utilizes measurements taken from observations of sighting angle and
distance to each animal. The densities were then applied to approximate frog recolonization
in the secondary and bamboo habitats as compared to the more pristine riparian habitat.
Because the method assumes that an individual will flush and be readily noticeable as
the observer approaches, the Hayne Estimator is not well designed for the cryptic, nocturnal
habits of most amphibians but has been repeatedly employed to evaluate populations of birds
and mammals (Coulson and Raines, 1985; Pelletier and Krebs, 1997). The conspicuous
coloration and diurnal activity periods of Dendrobatid frogs makes them potentially
appropriate for the Hayne Estimator technique. This study explores the utility of poison dart
frogs as subjects for the Hayne Estimator while investigating the quality of vegetation
regrowth at the Firestone Reserve as a means of supporting native levels of biodiversity.
To account for the impact of abiotic factors on frog sighting frequencies, proximity to
water, as well as correlations with rainfall, air temperature and time of day, were considered.
Because past studies indicate that poison dart frogs do not depend on large bodies of water
(reviewed by Savage, 1968; Vences et al., 2000; Jowers and Downie, 2005), random
distribution was expected. Rainfall and time of day have both been identified as influential
factors, with some Dendrobatids occurring in larger quantities in the presence of rain and in
the early morning and late afternoon (Graves, 1999). Finally, the air temperature was not
12
anticipated to affect sighting frequencies because of its small range due to the tropical
climate.
13
MATERIALS AND METHODS
Study Area
Field research was conducted at the Firestone Center for Restoration Ecology with the
permission of Pitzer College and the Joint Science Department. Claremont Colleges. The
Firestone Reserve is a 60 ha protected preserve of lowland (15m – 303 m) Pacific Moist
Forest in southwestern Costa Rica near Dominical (16.684 N, 51.643 W). The reserve has a
unique history that makes the area a suitable research site for an examination of poison dart
frog populations in regenerating habitats. Beginning around 1950, the property was
completed deforested, with the exception of two precipitous stream canyons within which
circa 100 m wide strips of riparian forest were only selectively logged (Firestone Center for
Restoration Ecology, 2006). The land was utilized as a cattle farm until 1993, when the
property was purchased by Ms. Firestone and converted into a combined sustainable farm
and private biological preserve. At this time, livestock were removed and parts of the land
were replanted with monoculture crops, including 5.9 ha of bamboo (Guadua aculeata, G.
angustifolia, Dendrocalamus asper, and D. latiflorus), 1 ha of bananas (Musa acuminata), 1
ha of black palm (Bactris gasipaes), and 24.7 ha of mixed hardwood tree species.1 The
remaining 27.4 ha were allowed to regenerate naturally. In 2005, the property was donated to
Pitzer College and farming maintenance was abandoned. The land has since been left alone
to regrow and is currently used as a biological reserve for education and research by the
Pitzer Study Abroad Program and the Claremont Colleges Joint Science Department.
The division of the reserve into multiple sub-habitats makes it an ideal location for
the study of biodiversity in recovering natural and non-native vegetation. The Firestone
1
Refer to http://costarica.jsd.claremont.edu/biodiversity/trees.shtml for an up-to-date listing of identified
species.
14
Reserve borders the Hacienda Baru National Wildlife Refuge to form a contiguous 390 ha
sanctuary dedicated to scientific study and eco-tourism with minimal biological impact
(Hacienda Baru National Wildlife Refuge, accessed 2006).
This study focuses on Dendrobatid presence in three types of habitat on the Firestone
Reserve: selectively-logged riparian forest (from hereon referred to as “riparian”), abandoned
pasture (“secondary”) and bamboo plantation (“bamboo”; see Figure 5). The riparian regions
consist of primary forest with tall vegetation and dense canopy cover. The ground in this
habitat is shaded during most of the day and was usually covered by thick leaf litter. No
records are available that describe the method of selective logging in this habitat, leaving no
way to judge whether the land is an accurate standard of natural vegetation. However, the
riparian habitat of the Firestone Reserve is visually indistinguishable from the primary forest
of the Hacienda Baru National Wildlife Refuge. Therefore, the riparian habitat was used in
this study as a representative of natural forest conditions, although it should be recognized
that there are potential influences of the past selective logging that are unmeasured in this
study.
The secondary forest is comprised of lower, thinner trees than the riparian habitat.
Large patches of sunlight are often observed on the ground, causing grasses to replace damp
leaf litter throughout much of the secondary forest (Figure 5). The bamboo habitat features
thick groves of tall culms that provide moderate amounts of shade. Sunlight filters through
the vegetation at a lower intensity than in the secondary forest, and dense, knee-high
vegetation covers the ground around the bamboo. Multiple sources of water exist in all three
sampling habitats. Small and moderate, 1-10 m wide streams run through both the riparian
and secondary forests, while three large ponds border the bamboo habitat.
15
Figure 5. A map of the Firestone Reserve habitats with images of the three habitats of study: bamboo (top left), riparian forest (bottom left) and secondary forest (top right). The
six transects are numbered and differentiated by color. Prominent water sources are represented by light blue symbols (filled polygon = pond; solid line = stream, known location;
dotted line = stream, estimated location [surveyed by McFarlane, 2001 {unpubl. data}]). Photographs by author.
16
Observations were systematically made within each habitat by following the preestablished trails of the reserve as transects for observation. The use of four maintained trails
permitted an accessible and repeatable loop through the forest and covered all three types of
habitat. The trails were divided into six transects of varying lengths, with most transects
covering multiple habitats (Table 1). The order that transects were walked was randomized
when possible so as not to cause unintentional correlations with time. Transects 1 and 4 could
not be shuffled because they provided starting and ending access or connected path loops,
respectively.
Table 1. Length distributions for study transects.
Total
Habitat length (m)
Transect Trail ID* length (m) Riparian Secondary
Bamboo
1
WT
275.9
275.9
0
0
2
B
949.9
84.1
865.8
0
3
C
838.6
721.3
117.3
0
4
B
646.2
194.5
451.7
0
5
BB
985.6
0
236.6
749.0
6
C
100.5
100.5
0
0
*Trail ID corresponding to the survey by McFarlane, 2001 (unpubl. data).
Study Species
The combined Firestone-Hacienda Baru area hosts at least 28 known species of
anurans (M. Ryan, pers. comm.), including Dendrobates granuliferus, the granular poison
dart frog, and D. auratus, the green and black poison dart frog. While both species are
abundant on the Firestone Reserve, D. granuliferus is internationally recognized as a
threatened species due to habitat loss and degradation as well as human harvesting of the
species (IUCN, 2006). The range of D. granuliferus is also limited, covering 5,579 km2 from
17
the mid-western coastal lowlands of Costa Rica to the northern border of Panama (Global
Amphibian Assessment, 2006; IUCN, 2006). Dendrobates auratus is considered to be of
lesser concern, largely because of its greater range of 11,944 km2 from northern Costa Rica
through northern Columbia and higher tolerance of habitat degradation.
Dendrobates granuliferus and D. auratus were selected as study subjects because of
their relevance to amphibian declines and their conspicuous appearances in the field.
Dendrobatids have many natural history characteristics typical of tropical amphibians. All
species are diurnal and commonly live among the low vegetation and leaf litter of moist
forests below elevations of 3,000 m (Savage, 1968). They are considered terrestrial anurans
because their life cycles are independent of large water sources. Dendrobatid eggs are laid on
land and tadpoles are carried on the backs of their parents to temporary puddles of water
among vegetation. Dendrobatids specialize in eating ants but also consume a large quantity
of mites, insects that are also characteristic of the diets of other tropical amphibians such as
Atelopus, Bufo and Bolitoglossus (Toft, 1981; Anderson and Mathis, 1999). They mate
during the wet season like many other tropical amphibians, and they are most active between
May and November (reviewed by Savage, 2002). Because many of the human impacts that
threaten D. granuliferus and D. auratus also affect other tropical amphibians and potentially
other groups of organisms, these two species serve well as indicators of the status of tropical
wildlife populations.
In addition, these species were chosen because their unique aposematic coloration
makes them convenient to study in the field. While many anuran species are nocturnal and
camouflaged to their environments, Dendrobatids are diurnal and have brilliantly colored
skin markings. The coloration serves as a signal to predators, warning them of the toxic
18
alkaloids that can be released from the frogs’ skin glands as a mechanism of defense
(Saporito et al., 2004). The distinctive patterns of D. granuliferus and D. auratus permit easy
sighting of individuals and allowed for a high confidence in the accuracy of the field
techniques used in this study.
Frogs were observed on the Firestone Reserve during the wet season between 6
October and 14 October 2006. The research period corresponded to the Dendrobatid mating
season and the peak of their activity throughout the year (reviewed by Savage, 2002).
Observing at this time guaranteed the highest number of frog sightings possible, leading to
elevated estimates of population densities and an overall optimistic perspective of the
Dendrobatid presence on the Firestone Reserve.
Population Density
The population density of frogs was measured with the Hayne Estimator (Hayne,
1949). To keep measurement technique consistent, all observations were made by the author.
Two sessions of observations typically occurred each day. The first session began at
approximately 7:00 and ended around 11:00 and the second began at approximately 13:30
and ended around 16:30. Transects were walked at a constant speed from start to stop without
pause, except to record frog measurements. Consequentially, transects with many frog
sightings took longer to walk than transects with few sightings.
Each observation followed the same protocol. When a frog was sighted, the observer
immediately took three measurements (Figure 6):
(1) The distance from the observer to the frog’s location at first sighting. Measurements
were made using a Leica Geosytems laser rangefinder accurate to ± 3mm and later
19
trigonomically corrected from incline distances (i.e. from the height of the hand-held
rangefinder) to true plan distances.
(2) The magnetic bearings of the transect and frog, using a Suunto sighting compass
readable to ± 0.5 degrees.
(3) The time of the sighting.
Occasionally, when a frog was observed well beyond the first possible point of contact, the
observer back-tracked her steps until she reached the location where the frog first came into
view. For example, if a frog was first noticed when the observer was directly beside it, the
observer retraced her steps until she could first view the frog amidst the vegetation.
Obscurities due to vegetation occasionally caused sighting difficulties, but errors were most
likely not frequent enough to largely impact data. This technique corrected for the limitation
Figure 6. A visual representation of the
Hayne Estimator data collection
technique, showing the distance from the
observer to the frog (ri) and the
corresponding measured sighting area
(shaded red).
20
of being able to view only one side of a transect at a time.
The location of each frog was recorded relative to a surveyed map of the reserve
paths. A survey of current habitat borders was mapped during the study period and overlaid
on the original path survey. Survey information was used to relate frog sighting to habitat
type for use in the Hayne Estimator. Total transect length and average segment (i.e. the
distance between transect turns) length were also collected from the survey.
The population densities of D. granuliferus and D. aruatus for each observation
session were calculated for each habitat using the unmodified Hayne Estimator:
Dh =
n ⎛1
⎜
2L ⎝ n
n
1⎞
i= t
i
∑ r ⎟,
⎠
where Dh is the Hayne density estimate, n is the number of animals observed, L is the
transect length, and ri is the sighting distance to the ith animal. The standard deviation was
calculated by taking the square root of the variance, calculated as:
⎡
n ⎛
⎞2 ⎤
1
⎢
∑⎜ r − R⎟ ⎥⎥
⎠
⎝
2 ⎢ var(n)
,
Variance(DH ) ≈ DH ⎢ 2 + i= t 2 ,
n
R n (n −1) ⎥
⎢
⎥
⎢⎣
⎥⎦
where R is the mean of the reciprocal of the sighting distances and calculated as:
R=
1
n
n
1
i= t
i
∑r ,
Circular statistics on sighting angles were computed using the StatistiXL Excel AddIn (http://www.statistixl.com/). Population densities were analyzed with VassarStats (Lowry,
2007) for statistical differences between the species and habitats using One-Way Independent
ANOVA and Tukey HSD tests.
21
Distribution
To relate frog sightings to actual geographical features, ArcGIS Version 9.1 was used
to project the Firestone trail survey into a satellite image of the Firestone Reserve (obtained
from Digital Globe, Inc.) with reference to GPS coordinates collected at the site. Habitat
zones were constructed using several older habitat maps of the reserve as well as records of
current habitat boundaries taken during the study. Frog sighting points were imported and
displayed with graduated symbols to represent point densities. Water sources (streams and
ponds) were approximated and drawn by hand according to the trail survey (McFarlane,
2001, unpubl. data) and satellite image.
The proximity of each sighting to water was determined using COMPASS software
(Version 5.05; Fish, 2005) The straight-line distance between each sighting location and the
closest water source was measured and then correlated to the number of frogs sighted at the
location using a linear regression calculated with VassarStats (Lowry, 2007).
Abiotic Factors
To determine whether the transect distribution proportionally represented the amount
of water in each habitat, an analysis of transect-resource proportionality was conducted using
measurements from the Firestone maps created with ArcGIS to compare the ratio of the
habitat area within 50 m of a water source to the total habitat area versus the transect length
(by habitat) to the total transect length (by habitat). In other words,
area of habitat within 50m of water tran sec t length in habitat within 50m of water
:
total area of habitat
total length of tran sec t in habitat
22
Rainfall and air temperature (from now on referred to as “reserve temperature”) were
measured every 2 hours by a Davis Weatherlink meteorological station on the Firestone
Reserve. Average reserve temperature was calculated for each increment as the arithmetic
mean of the high and low temperatures. To test for a correlation between reserve temperature
and the frog sighting frequency, data were analyzed using a linear regression calculated with
Vassar Stats (Lowry, 2007). VassarStats was also used to determine whether a correlation
existed between rainfall and frog sighting frequency with a Pearson’s chi-square 2x2
contingency table test. To evaluate overall trends in frog sighting frequency, data from both
species were combined and compared to the time of sighting.
The air temperature in each habitat (from now on referred to as “habitat temperature”)
was measured using four temperature loggers (Stow Away XTI). One logger was attached to
a tree in each habitat and the sensor was oriented to hang freely (Figure 7). The loggers were
positioned so that they received light levels typical of the particular habitat (i.e. not in full
sunlight). A fourth control logger was set in a deforested meadow on the reserve to measure
the highest possible daily temperature (i.e. full sunlight). Loggers were set to record data for
each day and night of the study period and measured the habitat temperature every 5 or 20
minutes, depending on the format available on the logger. Temperature data from all the days
in the study period were averaged to find the 24-hour mean temperature fluctuation for each
habitat. The fluctuations of all habitats were then compared to determine whether a large
difference in temperature in any of the habitats may have influenced poison dart frog activity
levels.
23
Figure 7. Locations of the temperature loggers in each habitat: bamboo (left top), secondary
(bottom left), riparian (top right) and exposed meadow (bottom right). Photographs by
author.
24
RESULTS
Inconsistencies in data collected at the start of the study period have led to the
exclusion of several days of data from the final analysis. The number of frog sightings in the
first three days was significantly lower than sightings during the remainder of the observation
days (an average of 6 ± 6 observed frogs/km in contrast with 85 ± 39 observed frogs/km).
Additionally, no significant differences were found in abiotic factors such as rainfall or
temperature between the first 3 days and the subsequent days of observation. The lack of
disparity suggests that the initial low number of sightings was likely a result of the observer’s
learning period. A test run was not conducted ahead of time, leading the observer to learn the
sighting and measurement techniques during the official study period. Therefore, only data
from 9 October through 14 October 2006 were included in the analysis (Appendix A). Data
collected from 6 October to 8 October are listed in Appendix B but are not considered valid
data or incorporated into the thesis.
Population Densities and Distributions
A total of 166 D. granuliferus and 109 D. auratus were observed, resulting in a total
sample size of 275 frogs. The average population densities for both species were larger in the
riparian forest than in the secondary or bamboo habitats (Figure 8). For D. granuliferus, the
riparian density was estimated to be 68 times greater than the secondary density and 23 times
greater than the bamboo density. The D. auratus riparian density estimate was 155 times
greater than the secondary density but only three times greater than the bamboo density.
Bamboo densities were larger than secondary densities for both species, with density for D.
granuliferus in bamboo reaching an estimate that was three times larger than for secondary
25
forest and the density for D. auratus in bamboo estimated to be 47 times larger than in
secondary forest. ANOVA analysis indicated significant effects of habitats on densities for
both D. granuliferus and D. auratus (F = 20.31, df = 2, P < 0.0001; F = 28.62, df = 2, P <
0.0001, respectively).
2.2
2
1.8
Density (frogs/ha)
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
Riparian
Secondary
Bamboo
Habitat Type
Figure 8. Average population densities of D. granuliferus (solid) and D. auratus (open) by
habitat. Vertical lines represent one standard deviation.
26
Population density trends differed through habitats between the two poison dart frog
species. The presence of D. granuliferus was nearly twice that of D. auratus in the riparian
forest, while the density of the D. auratus was more than four times larger than in the
bamboo. The population densities of both species in the secondary forest were very low,
although results indicated that D. granuliferus was sighted more often than D. auratus.
Tukey HSD tests found densities of riparian versus secondary habitats and riparian versus
bamboo habitats to be significantly different, but secondary versus bamboo habitats to be not
significant (P < 0.01, P < 0.01, P > 0.5, respectively).
A clear correlation between the number of frog sightings and proximity to water was
apparent for both species (Figure 9). Analysis with a linear regression indicated a significant
negative relationship between the number of sightings and the distances of the sighting
locations to a water source (y = -0.0476x + 13.478, df = 1, r2 = 0.207, P < 0.01). Three
particularly dense clusters of frog sightings are apparent in the riparian and secondary
habitats near streams, while sightings in the bamboo habitat did not appear to be correlated to
water (Figure 10).
The distributions of D. granuliferus and D. auratus were generally very similar.
Individuals of both species were found simultaneously at the same locations on multiple
occasions. Only two locations throughout the study site indicated the dominating presence of
one species without the other (Figure 11). For one, there is a distinct difference in the number
of D. auratus (n = 8) found in bamboo compared to D. granuliferus (n = 2). However, the
small sample size undermines the strength of this disparity. A second conspicuous
dissimilarity in distribution occurred on the southernmost stream where the trail dips towards
the southern stream.
27
35
30
Number of sightings
25
20
15
10
y = -0.0476x + 13.478
2
r = 0.2072
5
0
0
50
100
150
200
250
300
Distance to water source (m)
Figure 9. A scatterplot showing the negative relationship between the number of sightings
(D. granuliferus and D. auratus combined) and the distance of the sighting location to a
water source in all three habitats. A linear trend line has been fit to the dat
28
Figure 10. Distribution of all frog sightings through the habitats of the reserve (D. granuliferus and D. auratus combined). Where multiple frogs were seen in the same location,
sighting frequencies are symbolized by graduated circles (see legend). Prominent water sources are represented by blue symbols (filled polygon = pond; solid line = stream, known
location; dotted line = stream, estimated location [surveyed by McFarlane, 2001 {unpubl. data}]).
29
Figure 11a. Distribution of Dendrobates granuliferus sightings through the habitats of the reserve. Where multiple frogs were seen in the same location, sighting frequencies are
symbolized by graduated circles (see legend). Prominent water sources are represented by light blue symbols (filled polygon = pond; solid line = stream, known location; dotted
line = stream, estimated location [surveyed by McFarlane, 2001 {unpubl. data}]).
30
Figure 11b. Distribution of Dendrobates auratus sightings through the habitats of the reserve. Where multiple frogs were seen in the same location, sighting frequencies are
symbolized by graduated circles (see legend). Prominent water sources are represented by light blue symbols (filled polygon = pond; solid line = stream, known location; dotted
line = stream, estimated location [surveyed by McFarlane, 2001 {unpubl. data}]).
31
Rainfall
No significant correlations were found between rainfall (i.e. rain falling at the time of
observation) and D. auratus sightings (Pearson=1.41, P=0.24). A significant correlation was
found for D. granuliferus sightings (Pearson=5.53, P=0.02), indicating that the frequency of
frog sighting increased in the absence of rainfall and decreased during rainfall (Figure 12).
Number of transects with frogs observed
60
50
40
30
20
10
0
Present
Absent
Rainfall status at time of observation
Figure 12. A bar graph showing the negative correlation between rainfall (rain falling when
frogs observed) and D. granuliferus sightings (open bars = transects on which frogs were
observed; shaded bars = transects on which frogs were not observed).
32
Temperature
Regression analyses found no significant relationship between temperature and frog
sightings for either D. granuliferus or D. auratus (y = -0.0031x + 0.0962, df = 17, P > 0.05,
r2 = 0.1378; y = -0.0012x + 0.0434, df = 17, P > 0.05, r2 = 0.0587, respectively). Temperature
varied only 7ºC according to the Firestone meteorological station during the time of
observation and ranged from 23ºC and 30ºC.
No large temperature differences were found between the riparian, secondary and
bamboo habitats. The temperatures of the study habitats consistently remained within 1˚ of
each other (Figure 13). In contrast, temperatures recorded in the deforested meadow
remained higher than in the study habitats, peaking at 6.6˚C higher than in the other habitats.
The temperature loggers indicated that the temperature in the three study habitats ranged
from 22.5˚C to 28˚C while the temperature in the deforested meadow ranged from 23.5˚C to
34.0˚C.
33
36
Average air temperature (˚C)
34
32
30
Bamboo
Secondary
Riparian
Deforested meadow
28
26
24
22
22
:0
0
18
:0
0
20
:0
0
14
:0
0
16
:0
0
10
:0
0
12
:0
0
8:
00
6:
00
4:
00
2:
00
0:
00
20
Time
Figure 13. Mean daily temperature fluctuations in each study habitat and control
environment (deforested meadow).
Time of day
To evaluate overall trends in frog sighting frequency, data from both species were
combined and compared to the time of sighting (Figure 14). A large increase in the sighting
frequency was observed in the early morning (7:00 to 8:00), followed by relatively constant
rates in the later morning and early afternoon (8:00 to 12:00 and 13:00 to 14:00; no data was
collected from 12:00 to 13:00). From 14:00 to 15:00, a sharp decrease in sighting frequency
34
occurred, followed by a substantial increase in the late afternoon (16:00 to 17:00) and a sharp
decrease in the mid afternoon (14:00 to 15:00).
Data separated by species show less extreme patterns of change over time. Sighting
frequency of D. granuliferus peaked in the early morning (7:00 to 8:00) and rose again in the
later morning (10:00 to 11:00) and mid afternoon (15:00 to 17:00), but remained
approximately constant at all other times of the day (Figure 15). Dendrobates auratus
sighting frequency also peaked in the early morning (7:00 to 8:00) but remained relatively
constant throughout the rest the day, with low dips in activity in the mid morning (10:00 to
11:00) and mid afternoon (14:00 to 15:00).
Frog sighting frequency (frogs/m)
0.16
0.14
0.12
0.1
0.08
0.06
0.04
0.02
0
7:00
8:00
9:00
10:00
11:00
13:00
14:00
15:00
16:00
Time
Figure 14. Total frog sighting frequency over time (D. granuliferus and D. auratus
combined). Vertical lines indicate one standard deviation.
35
Gran/m vs. Time
Frog sighting frequency (frogs/m)
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
7:00
8:00
9:00
10:00
11:00
13:00
14:00
15:00
16:00
Time
Frog sighting frequency (frogs/m)
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
7:00
8:00
9:00
10:00
11:00
13:00
14:00
15:00 16:00
Time
Figure 15. Sighting frequency of D. granuliferus (top) and D. auratus (bottom) over time.
Vertical lines indicate one standard deviation.
36
DISCUSSION
Hayne Estimator Validity
The Hayne Estimator makes several assumptions that were met to the fullest extent
possible (Hayne, 1949):
(i)
Animals are distributed randomly and independently throughout the area of
study.
(ii)
Animals on the transect line are observed with a probability of one.
(iii) Sightings are independent events.
(iv)
Animals are motionless until stimulated to flush by the observer.
(v)
Each animal has a specific circle of detection in which the animal will flush
when stimulated by the observer’s presence.
(vi)
The mean sighting angle between the observer’s path and the animal is 32.7˚.
(vii) Animals are not counted more than once.
(viii) Distances are measured without error.
(ix)
Sighting conditions remain consistent during the study.
Assumption i challenges the instinctive nature of wild animals to cluster near
beneficial resources and when mating. Since breeding pairs of D. granuliferus and D. auratus
only come into contact for a short period during courting and amplexus (Dunn, 1941;
Summers et al., 1999), mating was not believed to substantially impact overall frog
distribution during the study. Additionally, because most organisms prefer to have easy
access to water, food, shelter and other similar necessities, animals disperse non-randomly.
However, the quantity of a given resource in a study site can be proportionally represented by
the amount of transect length that includes the particular resource. Both D. granuliferus and
37
D. auratus tended to be sighted more often when closer to a water source (Figure 9); in fact,
50% of frogs were observed within 50 m of a water source. An analysis of transect-resource
proportionality was conducted using measurements from the Firestone maps created with
ArcGIS to compare the ratio of the habitat area within 50 m of a water source to the total
habitat area versus the transect length (by habitat) to the total transect length (by habitat). In
other words,
area of habitat within 50m of water tran sec t length in habitat within 50m of water
:
total area of habitat
total length of tran sec t in habitat
Riparian habitat yielded a habitat : transect water ratio of 1.00, secondary habitat yielded a
ratio of 0.70 and bamboo habitat yielded a ratio of 0.88 (Table 2). Generally, the transects in
all three habitats were found to be distributed proportionally and represented the amount of
water in each habitat, therefore accurately reflecting a proportional number of frog sightings
between the habitats. The lower ratio of the secondary habitat is an indicator that this habitat
contained fewer water sources than the others and may be a primary cause of the low number
of frog sightings (n = 2). The high ratios in all habitats suggests that the distribution of the
transects throughout the study site upheld assumption i of the Hayne Estimator.
Table 2. Analysis results of the transect-resource proportionality test.
Habitat type
Riparian
Secondary
Bamboo
Proportion of habitat
area within 50 m of
water
0.71
0.15
0.23
Proportion of transect
length within 50 m of
water
0.70
0.21
0.26
Ratio of habitat to
transect proportions
1.00
0.70
0.88
38
The consistency of sighting method maintained assumption ii. Because this project
was carried out in a tropical rainforest, the density of vegetation was unpredictable and
variable in different areas of the transects. Consequentially, the probability of sighting a frog
declined quickly as one moved farther away from the center of the trail. However, brush did
not tend to obstruct the transect itself and frogs sitting directly on the path were visually and,
often, audibly conspicuous.
Sightings were treated as independent events (iii) by counting each frog as an
individual observation, even if frogs were within close proximity to each other. However, the
study was conducted during the wet season, when poison dart frogs mate (Savage, 2002).
The aggregating of frogs may have altered the normal distribution of frogs throughout the
study site, but the effect of mating on the data has not been explored.
Assumptions iv and v are well suited for the study of poison dart frogs. When
approached, both D. granuliferus and D. auratus typically remained motionless or hopped
slowly until the observer was within about 3 m. At this point, the frog increased its rate of
movement until hidden by vegetation or at a location determined safe by the frog.
Occasionally frogs remained stationary despite the close proximity of the observer;
measurements in these cases were taken from the first possible sighting location as
determined by the observer. The density of vegetation may have had some impact on the
observer’s ability to see frogs, e.g. the bamboo habitat had less vegetation within 2 m of the
ground than the riparian or secondary forests. This may have biased the data, causing more
sightings to occur in the bamboo. However, only 10 frogs were observed in the bamboo,
while 261 and 4 frogs were seen in the riparian and secondary forests, respectively. The large
39
difference in frog sightings between riparian forest and bamboo habitats suggests that overall
trends are apparent regardless of the potential sighting error due to vegetation densities.
Assumption vi has been the cause of much debate because limitations in the field
cause many experiments to yield a mean sighting angle larger than 32.7˚ (Robinette et al.,
1974; Burnham et al., 1980). Alterations to the Hayne Estimator have been explored in a
number of studies (Gates, 1969; Burnham and Anderson, 1976; Burnham, 1979; Hayes and
Buckland, 1983). The Modified Hayne’s Estimator proposed by Burnham and Anderson
(1976) allows mean sighting angles of up to 45˚ through the introduction of a scalar into the
traditional Hayne Estimator. Because the mean sighting angle of all frogs in my study was
29.2 ± 4.1˚, which is not substantially different than the theoretical value of 32.7˚, the
unmodified Hayne Estimator was selected for density calculations.
Assumption vii also corresponds to the ideal transect for the Hayne Estimator: a
perfectly straight line on which animals are not counted more than once due to overlap in
observation area. While the transects were composed of curves, the sighting distances were
much smaller than segment lengths. The mean frog sighting distance was 1.2 ± 2.0 m, while
the mean surveyed trail segment length was 17.9 ± 8.1 m (COMPASS mapping software;
Fish, 2005). Since the mean sighting distance and mean trail segment length are more than
eight standard deviations apart, the trails can be treated as a series of short, straight transects.
Assumptions viii and xi were met by the study technique. Mean sighting distance was
measured using a Leica Geosystems laser rangefinder accurate to ± 3 mm from a constant
height. Magnetic bearings of the transect and frog were measured with a Suunto sighting
compass readable to ± 0.5 degrees. The low and consistent errors of these instruments
ensured the credibility of their measurements. All observations were carried out under the
40
same relative conditions. The effects of rainfall, humidity, temperature and time have been
accounted for and their influences will be discussed.
Population Densities and Distributions
Statistical results indicated that the population densities of both D. granuliferus and
D. auratus were significantly higher in riparian habitat than they were in secondary or
bamboo habitats. This is not surprising that population. Primary forest provides the natural
flora for which poison dart frogs are best adapted. Leaf litter is plentiful and provides
opportunities for water conservation, protection and foraging. Arthropod communities are
known to shift with habitat fragmentation (Gibbs and Stanton, 2001); perhaps the riparian
forest supports more preferred prey as compared to the secondary or bamboo habitats. While
in the field, I observed that the riparian forest tended to have higher canopy growth due to the
presence of more mature trees (original growth as compared to 13-year growth in secondary
and bamboo habitats) and provide more shade than did secondary or bamboo forests. These
factors may have been favored by poison dart frogs because of the decreased rate of
evaporative water loss, as well as greater buildup of leaf litter.
The densities recorded in the secondary and bamboo habitats were too low to detect a
statistically significant difference between these habitats. While no formal conclusions can be
reached, higher densities were measured in the bamboo than the secondary forest. This may
have been due to lower light penetration in the bamboo than the secondary forest, causing
leaf litter to be moister and more highly preferred by poison dart frogs. Frogs might avoid
dryer areas in favor of moister conditions where thermoregulation and moisture retention
would be less energetically expensive. The fact that the distribution of both frogs favored
41
areas close to water further supports this idea (Figure 9). Additionally, it is possible that the
bamboo habitat may provide appropriate nutrients for prey species that the secondary forest
vegetation lacks. Further study of frog densities in secondary and non-native bamboo habitats
is needed to test these hypotheses. If the difference in frog densities increases between these
two habitats with a greater sample size, then bamboo should be further explored as a
sustainable crop in Costa Rica.
The bias of both species’ distributions towards areas near water is intriguing. Three
particularly dense clusters of sightings occurred on the transects: at the intersection of several
streams near the eastern reserve border of the reserve; around the midpoint of the
northernmost east-west stream in the northern region of the reserve; and at the western end of
the southernmost east-west stream (Figure 10). All of these clusters occur near or
immediately adjacent to water sources. Previous studies have not documented poison dart
frogs as requiring large water sources for survival; rather, poison dart frogs are thought to be
unique among anurans because they utilize water from small pools of rainwater among the
leaf litter (reviewed by Savage 1968; Vences et al., 2000; Jowers and Downie, 2005). Instead
of laying eggs in permanent ponds, Dendrobatids are thought to lay their eggs on land and
carry their larvae to small pools of water in the folds of leaves, where tadpoles remain until
they become adults. This lifestyle supports random and independent distribution of poison
dart frogs throughout the Firestone Reserve. My data, however, indicate a strong correlation
between the number of sightings and the proximity to a permanent water source (Figure 9).
Other observations of poison dart frogs aggregating near large water sources have not been
previously documented in published literature.
42
A severe shortage of rainfall during October 2006 may have also influenced frog
behavior. When in Costa Rica, the author encountered many native Costa Ricans who
remarked on the atypical lack of rain. Their observations were confirmed by a simple
comparison of the total precipitation in October of 2005 and October 2006. A 502.2 cm
difference occurred between the two years, with 2005 receiving 772.4 cm and 2006 receiving
270.2 cm of rainfall (Firestone Reserve Weatherlink). The unseasonably dry weather may
have led poison dart frogs to alter their behavior, perhaps motivating them to congregate
around large water sources. The dryer environment could have stimulated some frogs to
withdraw beneath damp leaf litter as during the dry season of the year, thus reducing the
number of exposed, observable frogs and the density estimates recorded in this study.
Rainfall
Insignificant correlations between rainfall and sighting frequency for D. auratus and
significant negative correlations for D. granuliferus are inconsistent with previous
conclusions about tropical anuran species. Extensive research indicates that most frog species
increase activity during periods of rainfall (Aichinger, 1987; Duellman, 1995; Gottsberger
and Gruber, 2004). Our results conversely suggest that the activity of D. granuliferus
increased without rain and decreased with rain. The disparity between conclusions may be
caused by the limitations of study conditions. The inconsistency of rainfall during the study
period led to twice the number of transects to be observed when rain was absent than when
rain was present, which may account for the greater probability for frogs observed in the
absence of rainfall.
43
Temperature
The relative consistency of temperature during the study was expected of the tropical
setting. The average daily reserve temperature ranged only 7°C during the study period.
Observations were conducted during the daylight hours, during which the reserve
temperature range was merely 4°C. The temperature range during the observation period was
stable and moderate enough to not affect frog activity.
Considering the limited potential for temperature differences, it is not surprising that
the average daily habitat temperature of all three study habitats remained within 1°C of each
other. The only point at which a difference occurred was for the riparian habitat around 13:00
(Figure 13). At this point the temperature decreased 2°C within 2 hours, a trend that the other
two study habitats as well as the control habitat followed at a more gradual rate. The sudden
change in riparian temperature was likely due to the sun shifting and creating a completely
shaded environment around the temperature logger, or some other similar situation
unrepresentative of the overall temperature in the habitat.
The fact that the riparian, secondary and bamboo regions had approximately the same
average habitat temperature while the deforested meadow temperature averaged a higher
temperature suggests that the loggers received the same amount of sunlight in each of the
study habitats. Although field observations by the author indicated that vegetation was
densest in the riparian forest and sparsest in the secondary forest, results imply that the
amount of light penetration was approximately the same in all of the study habitats. This
finding provides an intriguing conclusion: that sunlight, or at least temperature, differences
were not the main cause of distribution bias towards the riparian forest and away from the
secondary forest. Perhaps there were substantial differences between vegetation coverage to
44
cause moisture and plant species composition differences, but not enough to cause
differences in temperature.
Time of Day
Differences in sighting frequency over the day echo the conclusions of other studies
on poison dart frog activity. Studies have shown that D. auratus has bimodal peaks of
activity around 7:00 and 17:00 (Jaeger and Hailman, 1981; Graves, 1999). High activity
levels in D. pumilio, a species whose biology is often compared to D. granuliferus, were
previously found to be limited to the morning between 8:00 and 9:00 (Graves, 1999). The
activity levels (represented by sighting frequency) of both D. granuliferus and D. auratus in
my study were found to be higher in the early morning when examined on the species level
(Figure 15). When species data were combined, a rise in activity in the late afternoon was
also observed (Figure 14).
The increase in activity during the early morning could be product of multiple factors.
Environmental conditions may be more favorable to frog activity due to higher ground
moisture levels from unevaporated nightly rainfall, lower light levels or decreased
temperature levels, leading to slower rates of evaporative water loss. Additionally, arthropod
activity may be higher during this time of the day, allowing frogs to expend less energy when
foraging (Basset et al., 2001). Finally, frogs could simply be hungry from a night spent
beneath leaf litter and commence feeding with the first morning light.
45
The Hayne Estimator as a Tool for Monitoring Amphibians
Based on the results of the study, the Hayne Estimator appears to be a useful tool for
measuring population densities of poison dart frog species. The pattern of density estimates
among habitats is consistent with the results of past studies on deforestation and population
densities. Although this study did not deal directly with positive or negative estimate bias,
many case studies have found the Hayne Estimator to overestimate population densities due
to its inability to account for a larger detection angle than 32.7º (Gates, 1969; Burnham and
Anderson, 1976; Hayes and Buckland, 1983). The results presented here did not reflect these
restrictions, further confirming the success of the Hayne Estimator field technique with
poison dart frogs in the forests of Costa Rica.
Additional studies using the Hayne Estimator and similar tools are needed to further
explore the effects of deforestation and subsequent re-growth on amphibian populations. The
results of this project suggest that poison dart frog population densities are higher in
selectively-logged riparian forests than secondary or non-native bamboo forests. Despite over
a decade of unrestricted natural regrowth, secondary forests showed substantially lower
population densities of both D. granuliferus and D. auratus. Nevertheless, the higher
presence of Dendrobatids in bamboo compared to the lack of presence in secondary forest
suggest that bamboo plantations may provide an interim solution in the process of restoring
canopy cover to deforested lands. Future studies could evaluate similar parameters in other
poison dart frog species to expand our understanding of the sensitivity of this group to habitat
destruction. Similarly, it would be relevant to examine areas of recovering forest of various
ages to investigate the length of time necessary for frogs to repopulate areas at normal
densities.
46
Conclusions
A powerful result of this study is that 13 years is an inadequate amount of time to
regenerate suitable habitat for poison dart frogs. Riparian forest most likely supported the
strongest frog presence because the selective logging preserved enough native vegetation to
support frog populations. As past studies have shown, secondary regrowth tends to feature a
distinct species composition and, as a result of reduced competition with native organisms,
an abundance of exotic species (Aide et al., 2000; Walker, 2000).
Empty and fertile from years with manure, livestock pastures are particularly
vulnerable to invasive species. A study on the vegetation species composition of 71 tropical
abandoned cattle pastures in Puerto Rico found that the density, basal area, aboveground
biomass and species richness of the secondary forest sites matched old growth forest areas
after 40 years of regeneration (Aide et al., 2000). Of the colonists, exotic species were some
of the most abundant species in the secondary forests, although not all maintained their
presence permanently. Similarly in New Zealand, an abandoned sheep and rabbit pasture
showed increased species richness and biodiversity over 4 years of monitoring, a
consequence of the introduction of exotic species (Walker, 2000). In both cases, the longterm effect of the invasive flora depended on the species’ life-history characteristics and
abilities to persist through the rigorous competition of succession.
Despite the drastic impacts that exotic species can have on an ecosystem, there are
certain situations in which invasive species are the best alternative. In a site so badly affected
by human activity that native vegetation refuses to grow, exotics can prepare the earth for
native recolonization by increasing and stabilizing topsoil organic matter and boosting
nitrogen levels (Lamb, 1998). Such may have been the case with the bamboo plantation on
47
the Firestone Reserve, since more poison dart frogs were found in the bamboo than in the
secondary forest. Innumerable factors contribute to the outcome of forest recovery, the most
significant often being land-use history, time since abandonment, vegetation cover, rate and
type of seed dispersal, and spatial variables such as elevation and slope (Aragon and Morales,
1988; Holl, 1999). Managers must carefully weigh the unique qualities of each site, for they
may have important effects on the presence of sensitive groups such as poison dart frogs and
should serve as important criteria in predicting the success of recovering ecosystems to
maintain biodiversity.
Perhaps the most significant message from this study’s results is that the
reestablishment of biodiversity takes time. If the densities and distributions of D.
granuliferus and D. auratus serve as accurate indicators of the overall fauna of the reserve,
then it is clear that the Firestone Reserve is at the very beginning of a long process, despite
having been dedicated to natural regeneration for over a decade. How long must we wait
before we can accurately reclassify an area as natural? The answer will most likely never be
finite or universal, but rather unique to each restoration site. With the help of monitoring
programs that track regeneration over time, we will continue to refine our understanding of
reforestation and restore or, at the very least, stabilize biodiversity in these areas.
48
ACKNOWLEDGEMENTS
I am deeply appreciative of Professor McFarlane for his inspiration, guidance, humor
and endless support through my intellectual journey. I am also thankful of Professor Preest
for her assistance with editing, methodology and equipment and Professor Thomson for her
guidance with statistical analysis. My intimacy with Costa Rican poison dart frogs could not
have occurred without financial support from the Claremont McKenna College Dean of
Students, the Roberts Environmental Center, the Claremont Colleges Joint Science
Department and the Firestone Reserve. Additionally, I express my thanks to Carol Brandt of
the Pitzer College Costa Rica Study Abroad Program for accommodating me at the Firestone
Center while I conducted research. I extend my appreciation to the staff of Joint Science and,
in particular, the Organismal Biology Department for providing me with the biological
foundation to create this thesis. Finally, thanks to my family and friends for their
encouragement through all.
49
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55
APPENDICES
Appendix A. Frog sighting data from 9 October to 14 October 2006. For species, Gran = Dendrobates granuliferus (granular poison
dart frog) and GB = Dendrobates auratus (green and black poison dart frog).
Date
10/9
10/9
10/9
10/9
10/9
10/9
10/9
Transect
1
6
6
3
3
3
3
Start
Time
7:00
7:13
7:13
7:20
7:20
7:20
7:20
10/9
10/9
10/9
10/9
10/9
10/9
10/9
10/9
10/9
10/9
10/9
10/9
10/9
10/9
3
3
3
3
3
3
3
3
4
4
4
4
4
4
7:20
7:20
7:20
7:20
7:20
7:20
7:20
7:20
8:15
8:15
8:15
8:15
8:15
8:15
End
Time
7:13
7:20
7:20
8:13
8:13
8:13
8:13
8:13
8:13
8:13
8:13
8:13
8:13
8:13
8:13
8:47
8:47
8:47
8:47
8:47
8:47
Observ.
Frog
Path
Time Species Bearing (˚) Bearing (˚)
7:17
Sighting
Angle (˚)
Modified
Dist. (m)
7:28
7:46
7:46
7:48
GB
Gran
Gran
Gran
Gran
Gran
313
320
36
26
138
241
284
311
53
53
225
216
29
9
17
27
87
25
1.18
0.90
1.18
1.08
0.54
1.21
7:49
7:50
7:52
7:53
8:00
8:01
8:02
8:05
8:24
8:26
8:27
8:28
8:30
8:32
Gran
Gran
GB
Gran
Gran
Gran
GB
GB
Gran
Gran
Gran
Gran
Gran
Gran
144
172
193
258
110
195
229
221
181
198
286
293
262
196
186
153
156
208
120
185
203
203
232
230
230
230
230
240
42
19
37
50
10
10
26
18
51
32
56
63
32
44
0.90
1.04
0.84
0.95
0.38
1.26
1.29
1.59
0.99
1.07
1.07
1.38
1.61
1.04
Location
Habitat
C71
C71
C25
C25
C26
C26
west of
C26
C27
C27
C28
C29
C29-C30
C31
C31
B24
B24
B24
B24
B24
B23
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
56
Date
10/9
10/9
10/9
Transect
4
4
5
Start
Time
8:15
8:15
8:44
End
Time
8:47
8:47
9:02
Observ.
Frog
Path
Time Species Bearing (˚) Bearing (˚)
8:32
Gran
196
240
8:34
Gran
216
248
8:47
GB
239
265
Sighting
Angle (˚)
44
32
26
Modified
Dist. (m)
1.04
1.24
1.22
10/9
10/9
10/9
10/9
4
4
4
4
9:02
9:02
9:02
9:02
9:30
9:30
9:30
9:30
9:10
9:12
9:14
9:15
Gran
Gran
Gran
Gran
255
85
7
3
213
65
29
52
42
20
22
49
1.27
1.29
1.24
1.15
10/9
10/9
10/9
10/9
10/9
10/9
10/9
10/9
10/9
10/9
10/9
10/9
10/9
10/9
10/9
10/9
10/9
10/9
10/9
4
4
4
2
2
1
1
6
6
6
3
3
3
3
3
3
3
3
3
9:02
9:02
9:02
9:30
9:30
9:50
16:16
16:28
16:28
16:28
16:35
16:35
16:35
16:35
16:35
16:35
16:35
16:35
16:35
9:30
9:30
9:30
9:50
9:50
10:02
16:28
16:35
16:35
16:35
17:14
17:14
17:14
17:14
17:14
17:14
17:14
17:14
17:14
9:16
9:18
9:18
9:47
9:48
Gran
Gran
Gran
GB
GB
90
53
9
319
43
59
73
73
12
68
31
20
64
53
25
16:20
16:30
16:31
16:31
16:35
16:40
16:44
16:49
16:50
16:51
16:53
17:00
17:00
GB
Gran
Gran
Gran
GB
Gran
Gran
Gran
GB
GB
GB
Gran
Gran
234
14
340
343
221
221
240
132
230
288
320
322
324
300
326
322
293
203
203
178
170
258
279
305
7
340
66
48
18
50
18
18
62
38
28
9
15
45
16
1.34
1.24
0.96
1.51
1.20
Location
B23
B23
BB24
B23 (10m
uphill)
B23
B24
B24
B24 (20m
downhill)
B28
B28
B92
B92
Habitat
Riparian
Riparian
Bamboo
Riparian
Secondary
Secondary
Riparian
Riparian
1.46
1.17
1.11
0.96
1.54
1.63
1.39
1.27
1.36
1.15
0.97
1.22
1.68
WT2
C72
C72
C72
C31
C31
C30
C31
C40
C53
C56
C26
C26
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
57
Date Transect
10/9
3
10/9
3
10/9
3
10/10
1
10/10
2
10/10
4
10/10
5
10/10
4
10/10
4
10/10
4
10/10
4
10/10
4
10/10
4
10/10
3
10/10
3
10/10
3
10/10
3
10/10
3
10/10
3
10/10
3
10/10
3
10/10
3
10/10
3
10/10
3
10/10
3
10/10
3
10/10
3
10/10
3
Start
Time
16:35
16:35
16:35
7:47
7:52
8:21
8:43
9:10
9:10
9:10
9:10
9:10
9:10
9:32
9:32
9:32
9:32
9:32
9:32
9:32
9:32
9:32
9:32
9:32
9:32
9:32
9:32
9:32
End
Time
17:14
17:14
17:14
7:50
8:20
8:42
9:07
9:32
9:32
9:32
9:32
9:32
9:32
10:22
10:22
10:22
10:22
10:22
10:22
10:22
10:22
10:22
10:22
10:22
10:22
10:22
10:22
10:22
Observ.
Frog
Path
Time Species Bearing (˚) Bearing (˚)
17:02
GB
318
260
17:05
GB
162
208
17:06
GB
146
208
9:15
9:16
9:17
9:18
9:19
9:21
9:45
9:47
9:48
9:48
9:50
9:50
9:51
9:55
9:56
9:58
10:01
10:01
10:03
10:05
10:10
Gran
Gran
Gran
Gran
Gran
Gran
GB
Gran
GB
Gran
GB
GB
GB
GB
GB
Gran
GB
Gran
GB
Gran
Gran
118
4
28
126
110
359
116
26
311
187
202
201
286
184
70
29
167
151
145
193
281
63
47
58
53
61
59
118
66
289
154
154
153
339
175
31
64
121
115
111
206
254
Sighting
Angle (˚)
58
46
62
Modified
Dist. (m)
0.95
1.02
1.51
Location
C57
C26
C26
Habitat
Riparian
Riparian
Riparian
55
43
30
73
49
60
2
40
22
33
48
48
53
9
39
35
46
36
34
13
27
1.19
1.29
1.04
0.96
1.05
1.51
1.23
1.16
1.00
1.19
1.41
1.25
1.44
0.87
0.99
1.07
1.27
1.06
1.08
1.36
0.87
B23
B24
B24
B24
B26
B26
C24
C27
C52
C27
C27
C26
C26
C25
C25
C25-24
C22
C22
C22
C20
Tag 20
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
58
Date
Transect
Start
Time
End
Time
Observ.
Frog
Path
Time Species Bearing (˚) Bearing (˚)
Sighting
Angle (˚)
Modified
Dist. (m)
10/10
10/10
10/10
10/10
3
3
3
3
9:32
9:32
9:32
9:32
10:22
10:22
10:22
10:22
10:11
10:20
10:21
10:21
Gran
Gran
Gran
Gran
203
340
150
162
279
330
185
191
76
10
35
29
0.93
1.05
0.80
0.66
10/10
10/10
10/10
10/10
3
3
6
6
9:32
9:32
10:23
10:23
10:22
10:22
10:35
10:35
9:41
9:44
10:25
10:28
Gran
Gran
Gran
Gran
132
217
93
73
157
118
105
105
25
99
12
32
1.05
0.86
1.10
0.80
10/10
10/10
10/10
10/10
10/10
10/10
10/10
10/10
6
6
3
3
3
3
3
3
10:23
10:23
10:35
11:01
11:01
11:01
11:01
11:01
10:35
10:35
11:00
11:50
11:50
11:50
11:50
11:50
10:30
10:31
10:50
11:10
11:13
11:14
11:15
11:16
Gran
Gran
Gran
Gran
Gran
Gran
GB
GB
62
100
183
45
150
202
113
348
111
125
150
55
141
176
103
311
49
25
33
10
9
26
10
37
0.93
0.48
1.03
1.15
0.94
0.50
0.85
0.83
10/10
10/10
10/10
10/10
10/10
3
3
3
3
3
11:01
11:01
11:01
11:01
11:01
11:50
11:50
11:50
11:50
11:50
11:17
11:17
11:17
11:20
11:20
Gran
Gran
Gran
GB
Gran
276
279
335
66
65
247
257
32
54
54
29
22
57
12
11
0.51
1.00
0.97
1.44
1.43
Location
(50m
uphill)
C52
C46
C37
C37
Tag 18
(50m past)
C29
C71
C71-C72
C7271(closer
to 72)
C72-71
C26
C25
C23
C22
C22-21
C23
C24-C25
(closer to
C24)
C25
C26
C26
C26
Habitat
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
59
Date
Transect
Start
Time
End
Time
Observ.
Frog
Path
Time Species Bearing (˚) Bearing (˚)
Sighting
Angle (˚)
Modified
Dist. (m)
10/10
10/10
10/10
10/10
10/10
10/10
10/10
10/10
10/10
10/10
10/10
10/10
3
3
3
3
3
3
3
3
3
3
3
3
11:01
11:01
11:01
11:01
11:01
11:01
11:01
11:01
11:01
11:01
11:01
11:01
11:50
11:50
11:50
11:50
11:50
11:50
11:50
11:50
11:50
11:50
11:50
11:50
11:23
11:23
11:28
11:30
11:30
11:31
11:39
11:39
11:39
11:39
11:40
11:40
Gran
GB
Gran
GB
GB
GB
Gran
GB
GB
GB
Gran
GB
46
333
52
53
282
355
59
49
51
72
52
61
22
351
45
28
308
357
44
47
22
49
47
51
24
18
7
25
26
2
15
2
29
23
5
10
1.12
1.23
1.32
1.27
1.00
0.86
1.62
1.62
1.23
0.85
1.04
1.30
10/10
10/10
10/10
10/10
10/10
10/10
10/10
10/10
10/10
10/10
10/10
10/10
10/10
3
3
3
6
6
1
1
6
6
3
3
3
3
11:01
11:01
11:01
11:50
11:50
11:56
14:57
15:12
15:12
15:16
15:16
15:16
15:16
11:50
11:50
11:50
11:56
11:56
12:02
15:05
15:16
15:16
15:50
15:50
15:50
15:50
11:40
11:47
11:49
11:51
11:55
GB
Gran
Gran
GB
Gran
76
142
149
349
247
92
121
121
323
300
16
21
28
26
53
15:14
15:16
15:40
15:41
15:43
15:46
Gran
GB
Gran
GB
Gran
GB
320
187
317
151
49
75
298
222
317
211
98
111
22
35
0
60
49
36
0.89
1.04
0.91
0.94
0.91
Location
C27 (100m
down)
C27
C27
C27
C28
C29-C30
C31
C31
C31-Tag18
Tag18-C32
C38
C28
C51-C53
(30m from
C53)
C56
C56
C70
C72-71
Habitat
Riparian
Riparian
Riparian
Riparian
Riparian
1.00
0.97
0.70
0.99
0.90
1.20
C72-71
Tag 20
C55
C26
C26
C25
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
60
Date Transect
10/10
3
10/10
3
10/10
5
10/10
5
10/10
4
10/10
4
10/10
4
10/10
4
10/10
4
10/10
4
10/10
2
10/11
1
10/11
6
10/11
6
10/11
6
10/11
3
10/11
3
10/11
3
10/11
3
10/11
3
10/11
3
10/11
3
10/11
3
10/11
4
10/11
5
10/11
4
10/11
2
10/11
1
Start
Time
15:16
15:16
16:15
16:15
16:22
16:22
16:46
16:46
16:46
16:46
17:05
7:04
7:11
7:11
7:11
7:17
7:17
7:17
7:17
7:17
7:17
7:17
7:17
7:50
8:22
8:47
9:02
9:20
End
Time
15:50
15:50
16:46
16:46
16:15
16:15
17:05
17:05
17:05
17:05
17:20
7:11
7:16
7:16
7:16
7:49
7:49
7:49
7:49
7:49
7:49
7:49
7:49
8:10
8:45
9:02
9:20
9:30
Observ.
Frog
Path
Time Species Bearing (˚) Bearing (˚)
15:18
Gran
29
62
15:40
Gran
225
205
16:40
GB
3
34
16:41
GB
92
68
16:08
Gran
246
279
16:11
Gran
305
250
16:55
Gran
245
205
16:55
Gran
5
42
16:50
Gran
23
52
16:54
Gran
41
68
17:10
Gran
122
81
7:13
7:14
7:15
7:40
7:41
7:42
7:43
7:44
7:45
7:20
7:23
8:00
8:40
8:50
GB
Gran
GB
GB
GB
Gran
Gran
GB
GB
Gran
Gran
Gran
GB
Gran
357
303
312
293
336
122
190
110
61
58
73
189
19
135
333
335
280
257
282
219
131
95
73
69
100
237
58
61
Sighting
Angle (˚)
33
20
31
24
33
55
40
37
29
27
41
Modified
Dist. (m)
1.01
0.88
0.88
0.99
0.74
0.81
1.26
0.94
0.92
0.84
1.15
Location
C25-C24
C21
BB24
BB25
B26
B24
B24
B25
B27
B28
B56
Habitat
Riparian
Riparian
Bamboo
Bamboo
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
24
32
32
36
54
97
59
15
12
11
27
48
39
74
1.25
1.25
1.07
1.13
0.98
1.06
0.96
0.87
1.12
1.39
1.06
1.01
0.96
1.01
C72
C72-C71
C72-71
C57-56
C52
C26
C26
C25
C25-C27
C24
C22
B24
BB23
B23
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Bamboo
Riparian
61
Date Transect
10/11
1
10/11
6
10/11
10/11
10/11
10/11
10/11
10/11
10/11
10/11
10/11
10/11
10/12
10/12
10/12
10/12
10/12
10/12
10/12
10/12
10/12
10/12
10/12
10/12
10/12
10/12
3
3
3
3
3
4
5
4
2
1
1
2
4
4
4
4
4
4
5
4
4
4
3
3
Start
Time
13:37
13:42
13:46
13:46
13:46
13:46
13:46
14:16
14:31
14:58
15:12
15:26
7:05
7:12
7:35
7:35
7:35
7:35
7:35
7:35
8:00
8:27
8:27
8:27
8:47
8:47
End
Time
13:42
13:46
14:15
14:15
14:15
14:15
14:15
14:31
14:58
15:12
15:26
15:31
7:12
7:33
7:56
7:56
7:56
7:56
7:56
7:56
8:27
8:46
8:46
8:46
9:43
9:43
Observ.
Frog
Path
Time Species Bearing (˚) Bearing (˚)
Sighting
Angle (˚)
Modified
Dist. (m)
Location
Habitat
Riparian
Riparian
Riparian
Riparian
Riparian
13:46
14:02
14:02
14:03
14:10
GB
Gran
Gran
Gran
GB
193
170
113
72
20
203
201
181
78
84
10
31
68
6
64
1.02
0.90
0.94
1.06
1.12
Tag 20
(10m on
transect 3)
C26
C25
C24
C24
14:43
GB
76
50
26
1.16
BB44
Bamboo
7:46
7:46
7:47
7:48
7:44
7:45
8:14
8:35
8:37
8:38
9:00
9:00
Gran
Gran
Gran
Gran
Gran
Gran
Gran
Gran
Gran
Gran
GB
Gran
220
212
340
336
189
290
193
89
114
28
252
252
251
265
261
261
233
230
193
59
65
86
278
278
31
53
79
75
44
60
0
30
49
58
26
26
1.15
1.24
0.80
1.17
1.07
1.09
0.70
1.24
1.12
0.97
0.65
0.62
B27
B27-B26
B26
B26
C26
B26
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Bamboo
Riparian
Riparian
Riparian
Riparian
Riparian
B24-B26
B26
B27
C21
C21
62
Date Transect
10/12
3
10/12
3
10/12
3
10/12
3
10/12
3
10/12
3
10/12
3
10/12
3
10/12
3
10/12
3
10/12
3
10/12
3
10/12
3
10/12
3
10/12
3
10/12
3
10/12
3
10/12
3
10/12
6
10/12
6
10/12
1
10/13
1
10/13
6
10/13
3
10/13
3
10/13
3
10/13
3
10/13
3
Start
Time
8:47
8:47
8:47
8:47
8:47
8:47
8:47
8:47
8:47
8:47
8:47
8:47
8:47
8:47
8:47
8:47
8:47
8:47
9:43
9:43
9:46
7:17
7:25
7:29
7:29
7:29
7:29
7:29
End
Time
9:43
9:43
9:43
9:43
9:43
9:43
9:43
9:43
9:43
9:43
9:43
9:43
9:43
9:43
9:43
9:43
9:43
9:43
9:46
9:46
9:52
7:25
7:29
8:14
8:14
8:14
8:14
8:14
Observ.
Frog
Path
Time Species Bearing (˚) Bearing (˚)
9:03
GB
332
290
9:04
GB
313
290
9:10
Gran
262
271
9:12
GB
263
250
9:12
Gran
299
248
9:16
GB
85
48
9:16
GB
62
48
9:16
Gran
342
347
9:16
Gran
356
347
9:16
Gran
348
247
9:16
Gran
344
347
9:22
GB
325
347
9:25
GB
45
6
9:40
Gran
312
313
9:41
Gran
53
11
9:43
Gran
61
94
8:55
Gran
74
105
8:55
Gran
342
349
9:45
GB
97
97
9:46
GB
85
181
7:31
7:46
7:46
7:46
7:26
Gran
Gran
Gran
GB
GB
301
158
147
155
176
279
196
196
196
212
Sighting
Angle (˚)
42
23
9
13
51
37
14
5
9
101
3
22
39
1
42
33
31
7
0
96
Modified
Dist. (m)
1.30
1.09
1.69
1.70
1.32
1.32
1.56
1.05
1.73
1.87
2.18
0.71
1.53
0.73
1.14
0.92
0.95
1.38
1.04
1.05
Location
C22
C22
C24
C24
C24-C25
C26
C26
C27
C27
C27
C27
C27
C27
C29-C30
Tag 18
C51
C51-C52
Tag 20
C71
Habitat
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
22
38
49
41
36
1.10
1.16
1.15
1.52
1.41
C52-C51
C26
C26
C26
C26
Riparian
Riparian
Riparian
Riparian
Riparian
63
Date Transect
10/13
3
10/13
3
10/13
3
10/13
3
10/13
3
10/13
3
10/13
3
10/13
3
10/13
3
10/13
3
10/13
4
10/13
5
10/13
5
10/13
4
10/13
2
10/13
1
10/13
1
10/13
2
10/13
4
10/13
5
10/13
4
10/13
4
10/13
4
10/13
4
10/13
4
10/13
4
10/13
4
10/13
4
Start
Time
7:29
7:29
7:29
7:29
7:29
7:29
7:29
7:29
7:29
7:29
8:15
8:31
8:31
9:14
9:25
9:43
14:02
14:12
14:32
14:48
15:13
15:13
15:13
15:13
15:13
15:13
15:13
15:13
End
Time
8:14
8:14
8:14
8:14
8:14
8:14
8:14
8:14
8:14
8:14
8:31
8:53
8:53
9:23
9:43
9:45
14:12
14:32
14:47
15:13
15:35
15:35
15:35
15:35
15:35
15:35
15:35
15:35
Observ.
Frog
Path
Time Species Bearing (˚) Bearing (˚)
7:46
GB
186
212
7:48
Gran
186
210
7:51
Gran
258
219
7:51
Gran
263
219
7:51
Gran
138
171
7:57
Gran
59
75
7:57
Gran
306
75
8:00
GB
64
69
8:02
GB
121
100
8:13
Gran
273
213
Sighting
Angle (˚)
26
24
39
44
33
16
129
5
21
60
Modified
Dist. (m)
1.29
0.87
1.26
1.48
1.10
0.89
0.38
1.14
0.86
1.18
Location
C26
C26
C26
C26
C26
C25-C24
C25-24
C24
C22
C2-C1
Habitat
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
8:43
8:50
GB
GB
351
341
313
21
38
40
1.31
0.61
BB3
BB24
Bamboo
Bamboo
14:14
14:42
GB
Gran
324
251
291
279
33
28
1.08
1.04
B96
B24
Riparian
Riparian
15:16
15:17
15:17
15:17
15:17
15:17
15:19
15:19
Gran
Gran
Gran
Gran
Gran
Gran
Gran
GB
84
80
73
65
150
150
99
135
61
62
62
62
90
90
80
85
23
18
11
3
60
60
19
50
1.07
1.23
1.47
1.78
1.37
1.37
1.61
1.60
B24-26
B26
B26
B26
B27
B27
B27-B28
B27-B28
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Secondary
Secondary
64
Date Transect
10/13
3
10/13
3
10/13
3
10/13
3
10/13
3
Start
Time
15:55
15:55
15:55
15:55
15:55
End
Time
16:18
16:18
16:18
16:18
16:18
Observ.
Frog
Path
Time Species Bearing (˚) Bearing (˚)
15:43
GB
310
350
15:46
GB
305
289
15:46
GB
7
340
15:47
Gran
222
250
15:47
GB
237
250
10/13
3
15:55
16:18
15:50
Gran
310
10/13
10/13
10/13
10/13
10/13
10/13
10/13
10/13
10/13
10/13
10/13
10/13
10/13
10/13
10/13
10/13
10/13
10/13
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
6
15:55
15:55
15:55
15:55
15:55
15:55
15:55
15:55
15:55
15:55
15:55
15:55
15:55
15:55
15:55
15:55
15:55
16:18
16:18
16:18
16:18
16:18
16:18
16:18
16:18
16:18
16:18
16:18
16:18
16:18
16:18
16:18
16:18
16:18
16:18
16:29
15:50
15:50
15:50
15:57
15:58
16:01
16:01
16:01
16:05
16:06
16:06
16:14
16:14
16:17
16:17
15:43
15:43
16:21
GB
GB
GB
GB
Gran
GB
GB
GB
Gran
GB
GB
GB
Gran
Gran
Gran
GB
GB
Gran
290
37
20
5
20
40
45
25
299
299
355
327
327
315
92
70
70
95
Sighting
Angle (˚)
40
16
27
28
13
Modified
Dist. (m)
1.09
1.20
0.88
1.08
1.06
250
60
0.89
250
355
345
345
340
5
5
2
245
245
25
345
345
360
134
112
102
122
40
42
35
20
40
35
40
23
54
54
30
18
18
45
42
42
32
27
0.98
1.14
1.01
1.30
1.02
1.47
1.52
1.32
1.13
1.21
0.94
1.01
1.01
1.14
1.09
1.18
1.22
1.09
Location
C21
C21-C22
C21
C24
C24
C25-C24,
closer to
C25
C25-C24,
closer to
C25
C27
C28
C28
C29
C30
C30
C31
C31
C31
C34
C35
C35
C43
C44-C46
C52-C51
C52-C51
Habitat
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
65
Date Transect
10/13
6
10/13
6
10/13
6
10/13
1
10/14
1
10/14
6
10/14
6
10/14
3
10/14
3
10/14
3
10/14
3
10/14
3
10/14
3
10/14
3
10/14
3
10/14
3
10/14
3
10/14
3
10/14
3
10/14
3
10/14
4
10/14
5
10/14
4
10/14
2
10/14
1
10/14
1
10/14
6
10/14
3
Start
Time
16:18
16:18
16:18
16:29
7:15
7:20
7:20
7:30
7:30
7:30
7:30
7:30
7:30
7:30
7:30
7:30
7:30
7:30
7:30
7:30
8:03
8:16
8:40
8:57
9:15
13:30
13:35
13:40
End
Time
16:29
16:29
16:29
16:33
7:20
7:29
7:29
8:02
8:02
8:02
8:02
8:02
8:02
8:02
8:02
8:02
8:02
8:02
8:02
8:02
8:16
8:40
8:51
9:15
9:18
13:35
13:43
14:19
Observ.
Frog
Path
Time Species Bearing (˚) Bearing (˚)
16:26
GB
125
154
16:26
GB
125
154
16:26
Gran
145
205
Sighting
Angle (˚)
29
29
60
Modified
Dist. (m)
1.13
1.71
1.10
Location
Habitat
Riparian
Riparian
Riparian
7:25
7:26
9:31
7:44
7:46
7:46
7:47
7:48
7:48
7:49
7:50
7:50
7:55
7:56
7:56
Gran
GB
Gran
GB
GB
GB
Gran
Gran
GB
GB
Gran
Gran
Gran
GB
Gran
320
203
204
162
203
166
180
129
232
125
53
52
182
94
114
268
234
250
162
182
182
158
168
208
148
71
72
117
109
99
52
31
46
0
21
16
22
39
24
23
18
20
65
15
15
1.14
1.08
0.79
1.07
1.16
2.00
1.22
1.07
0.88
1.02
0.88
1.40
1.18
1.20
1.20
C56
C28
C27-28
C27-28
C27
C27
C26
C26
C25
C25-24
C22
C22
C22-21
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
8:44
Gran
13
58
45
1.23
B24-26
Riparian
13:40
14:02
Gran
Gran
310
102
284
192
26
90
0.59
1.25
bridge
C30
Riparian
Riparian
66
Date Transect
10/14
3
10/14
3
10/14
3
10/14
3
10/14
3
10/14
3
Start
Time
13:40
13:40
13:40
13:40
13:40
13:40
End
Time
14:19
14:19
14:19
14:19
14:19
14:19
Observ.
Frog
Path
Time Species Bearing (˚) Bearing (˚)
14:03
GB
126
151
14:03
GB
134
176
14:03
Gran
94
155
14:04
Gran
150
195
14:06
GB
25
46
14:06
Gran
123
46
Sighting
Angle (˚)
25
42
61
45
21
77
Modified
Dist. (m)
0.92
0.95
0.85
1.02
1.18
0.85
10/14
3
13:40
14:19
14:07
Gran
33
72
39
0.48
10/14
3
13:40
14:19
14:08
GB
46
72
26
0.92
10/14
10/14
10/14
10/14
10/14
10/14
10/14
10/14
10/14
3
3
3
3
4
5
4
2
1
13:40
13:40
13:40
13:40
14:20
14:35
15:27
15:45
16:00
14:19
14:19
14:19
14:19
14:35
15:42
15:42
16:00
16:05
14:08
14:16
13:59
14:01
Gran
GB
GB
GB
23
44
44
145
67
66
66
107
Gran
Gran
97
357
58
54
44
22
22
38
0
39
57
1.12
1.19
1.30
0.52
0.00
0.63
1.01
15:17
15:30
Location
C29
C27
C27
C26-27
C25
C25
C25-24,
closer to 25
C25-24,
closer to 25
C25-24,
closer to 25
C25-24
C25-24
C22
BB13
B24
Habitat
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Riparian
Bamboo
Riparian
67
Appendix B. Frog sighting data from 6 October to 8 October 2006 (omitted from analysis). Under “species, Gran = Dendrobates
granuliferus (granular poison dart frog) and GB = D. auratus (green and black poison dart frog).
Date Transect
10/6
1
10/6
2
10/6
4
10/6
5
10/6
4
10/6
3
10/6
1
10/6
3
10/6
4
10/6
5
10/6
4
10/6
2
10/6
1
10/7
1
10/7
2
10/7
4
10/7
1
10/7
5
10/7
4
10/7
4
10/7
4
10/7
2
10/7
1
10/7
3
10/7
1
10/7
1
Start
Time
6:15
6:30
7:32
8:10
9:03
9:35
14:25
14:40
15:12
15:32
16:00
16:28
16:45
6:13
6:20
6:52
7:13
7:15
7:45
7:45
7:45
7:55
8:15
8:20
9:05
10:14
End
Time
6:27
7:25
8:00
8:50
9:25
10:15
14:35
15:10
15:28
16:00
16:16
16:45
16:50
6:20
6:50
7:10
7:28
7:43
8:17
8:17
8:17
8:15
8:23
9:00
9:12
10:20
Observ.
Time
Frog
Path
Species Bearing (˚) Bearing (˚)
Sighting
Angle (˚)
Modified
Dist. (m)
Location
Habitat
8:25
GB
72
135
63
1.24
BB38
Bamboo
9:47
GB
14
14
0
1.51
B56
Riparian
7:14
GB
355
328
37
0.77
WT1
Riparian
7:55
7:55
8:02
Gran
Gran
Gran
21
22
36
67
67
71
46
45
35
1.37
1.38
1.05
B24
B24
B24-26
Riparian
Riparian
Riparian
8:40
GB
101
147
46
1.05
C23
Riparian
68
Date Transect
10/7
3
10/7
3
Date Transect
10/7
3
10/7
3
10/7
2
10/7
1
10/8
1
10/8
3
10/8
4
10/8
5
10/8
4
10/8
2
10/8
1
10/8
4
Start
Time
10:26
10:26
Start
Time
10:26
10:26
11:10
11:35
9:15
9:26
9:59
10:19
10:45
11:03
11:25
14:30
End
Time
11:07
11:07
End
Time
11:07
11:07
11:34
11:43
9:20
9:58
10:17
10:44
11:02
11:25
11:31
?
Observ.
Time
10:30
10:50
Observ.
Time
10:50
10:58
Frog
Path
Species Bearing (˚) Bearing (˚)
Gran
99
68
Gran
84
62
Frog
Path
Species Bearing (˚) Bearing (˚)
GB
71
80
GB
107
79
Sighting
Angle (˚)
31
22
Sighting
Angle (˚)
9
28
Modified
Dist. (m)
1.49
1.14
Modified
Dist. (m)
1.27
1.03
Location
C24
C24-C25
Habitat
Riparian
Riparian
Location
C25
C25
Habitat
Riparian
Riparian
9:40
Gran
356
30
34
1.02
C25
Riparian
14:40
Gran
360
55
55
1.17
B24
Riparian
69