The Effect of Temperature and Precipitation on the California Tiger
Salamander
Jodie Ly
ENVS 190A/Thesis
May 14, 2014
Table of Contents
Abstract……………………………………………………………………………………………………………….......2
Introduction…………………………………………………………………………………………….……….……....3
Background………………………………………………………………………………………………………...……4
Life Cycle…………………………………………………………………………………………………………….…....5
Physical Description…………………………………………………………………………………………….…...7
Range and Status……………………………………………………………………………………………………....9
Diet………………………………………………………………………………………………………………………..10
Climate Change Projection……………………………………………………………………………...........…10
The Effect on Habitat…………………………………………………………………………………………….....13
Uplands…………………………………………………………………………………………………….….14
Vernal Pools………………………………………………………………………………………………...14
The Effect of Droughts on Reproduction…………………………………………………………………..17
The Effect on Behavior/Migration……………………………………………………………………….......18
Hybridization with a Bared Tiger Salamander………………………………………………………….19
Conclusion………………………………………………………………………………………………………………20
Reference…………………………………………………………………………………………………………….....22
1
Abstract:
The population of the California Tiger Salamander is decreasing drastically. One of
the major threats to the California Tiger Salamander’s survival is climate change. The
increased temperature and precipitation deficiency directly impacts the life cycle of the
California Tiger Salamander. Climate change affects the salamanders both ecologically and
biologically. They depend heavily on the vernal pools to ensure their survival. Climate
change induces drought which does not allow the vernal pools to become inundated during
the wet season. Desiccation of the vernal pool eliminates the California Tiger Salamanders
breeding site. Not only are they unable to breed, they have a harder time surviving these
harsher, drier conditions. Recently, the California Tiger Salamander has mated with an
invasive species of salamander, the Barred Tiger Salamander from Texas, whom are more
able to adapt to these harsher conditions. Their offspring is a hybrid of the two that have a
higher survival rate than the native California salamander. A change in temperature and
precipitation is directly correlated to population viability of the California Tiger
Salamander.
2
Introduction:
The California Tiger Salamander is an endemic species only found in California. It is
a rare species that is currently endangered and declining in California vernal pools. There
are a plethora of factors that contribute to population decline. One of those factors is
climate change. They are highly susceptible to changes in heat and moisture. Even a small
change can have detrimental impacts on their life history and survival. Understanding how
California Tiger Salamanders respond to changes in temperature and precipitation is
crucial to ensuring their continued existence. This paper describes California Tiger
Salamanders, California’s changing climate, and the effect that temperature and
precipitation have on habitat, reproduction, and distribution. Additionally, the paper will
discuss the connection of climate change with the hybridization of the California Tiger
Salamander and the Barred Tiger Salamander.
Climate change is a complex phenomenon that contributes to species decline
(Blaustein et al., 2010; Parmesan, 2006). Climate change is defined as a change in
temperature and precipitation that affects long term regional and global weather patterns
(Blaustein et al., 2010; Walls et al., 2013). A change in climate will cause species to evolve
biologically and physically. Different Species can tolerate different climate conditions. They
have their own range of temperature and environment conditions that are suitable for
them (Parmesan, 2006). Changes in temperature can pose a threat to a species’ phenology
and distribution (Parmesan, 2006). The rate of climate change has been dramatically
increasing over recent years (Christensen et al., 2007). This has caused temperature
tolerance limits of species to slightly change and species that cannot keep up with change
will decline (Blaustein et al., 2010; Trenham et al., 2001; Walls et al., 2013).
3
The California Tiger Salamander (Ambystoma Californiense) is a rare and
endangered species that was once widespread in California vernal pools (Environmental
Protection Agency, 2010; Trenham et al. 2000). The species was historically abundant
across California but their populations have declined substantially. Global climate change is
putting a lot of stress on the California Tiger Salamander population. They are ectothermic,
which means they are cold blooded amphibians. They are highly sensitive and vulnerable
to changes of temperature and precipitation in their environment. Even the slightest
change can impact their ability to survive (Carey and Alexander, 2003). Because California
Tiger Salamanders have permeable skin, a complex life cycle, and transparent unshelled
eggs (Bolster, CDFW, 2010), they are highly affected by an increase of heat and lack of
moisture.
Background:
The California Tiger Salamander is a member of the Ambystomatidae – a family of
the mole salamander. Like the mole salamanders, they spend their adult life in
underground burrows until the time of breeding (Bolster, CDFW, 2010). California Tiger
Salamanders inhabit grasslands or open woodlands with vernal pools (Environmental
Protection Agency, 2010), since they require both aquatic and terrestrial environments to
complete their life-cycle. They are known as one of the most significant, yet difficult species
to study in the California vernal pools complex. Therefore, to understand the impacts of
temperature and precipitation on California Tiger Salamanders, it is necessary to
understand their life history and status.
4
Life Cycle:
California Tiger Salamanders go through a biphasic life cycle, having both aquatic
and terrestrial stages (Figure 1) (Environmental Protection Agency, 2010). Eggs are laid
during winter when adult California Tiger Salamanders migrate to the pool to breed during
the fall and winter rain (Trenham et al., 2000). It takes about two to four weeks for eggs to
hatch after being laid and a minimum of ten weeks to complete metamorphosis from egg to
larvae (East Contra Costa County, 2006). Adult California Tiger Salamanders are nocturnal
species that spend rest of their time in underground burrows sheltering and hibernating
during the warm and dry seasons of summer and autumn. During the night of the first rain
of the season, adults migrate from upland to vernal pools to mate and breed at the ponds.
Then they migrate back to the underground burrows after breeding. This usually takes
place between November and May (Bolster, CDFW, 2010). During the breeding season, it is
not uncommon to see very large numbers of California Tiger Salamanders in the breeding
pond. Males are usually the first to arrive to the breeding pond and the last to leave while
females are the last to arrive to the pond and the earliest to leave (Loredo and Vuren,
1996). Dispersal from the breeding ponds is not as synchronized as the arrival.
Eggs are found in October to March, attached to aquatic vegetation (Loredo and
Vuren, 1996). Larvae are mainly detected in March to August in breeding ponds (Loredo
and Vuren, 1996). They consume zooplankton and other aquatic invertebrates as they
mature (Bolster 2010). When larvae are ready for metamorphosis, they change to
terrestrial juvenile California Tiger Salamander during late spring to summer.
5
After the first summer, they resemble adults but smaller in size. Juvenile California
Tiger Salamanders usually complete their metamorphosis between May and July (Trenham
et al., 2000) and migrates to upland regions. Like the adults, they will settle in underground
burrows (Environmental Protection Agency, 2010) until they reach sexual maturity, which
takes about two to five years (Bolster, CDFW, 2010). Breeding does not occur every year; it
depends on the timing of the seasons and suitable breeding conditions for females. Once
they breed, they produce a plethora of eggs; however, many of these eggs are unable to
reach sexual maturity (Loreda and Vuren, 1996; East Contra Costa County, 2006; Trenham
et al., 2000). The surviving individuals of California Tiger Salamanders can live up to ten
years or more (Trenham et al., 2000).
Figure 1: Life cycle of California Tiger Salamander (Jewett, 2004)
6
Physical Description:
The California Tiger Salamander has four developmental stages: egg, larvae,
juvenile, and adult. The California Tiger Salamander’s eggs are found submerged in
breeding ponds and cluster together within some aquatic plants for protection (Loredo and
Vuren, 1996). They are transparent in color with a thick gelatinous layer surrounding them
(Figure 2) (California Herps, 2014; Loredo and Vuren, 1996). During the aquatic stage,
larvae are olive in color with fine dark stippling and have gills (Figure 3) (Stanford
University, 2014). After a few months, the larvae transform into juveniles and migrates
upland. Juveniles have a light olive color with some visible stippling and they no longer
have gills (Figure 4). This marks the completion of the aquatic stage and the transition into
terrestrial stage. Adult California Tiger Salamander can reach between six to eight inches in
length (Environmental Protection Agency, 2010). They have black bodies with numerous
pale yellow and white spots on their body including their stomach. They also have large
rounded head, small eyes, blunt snout and side-to-side flattened tail (Figure 5) (Bolster,
CDFW, 2010; California Herps, 2014).
Figure 2: Eggs of California Tiger Salamander (California Herps, 2014)
7
Figure 3: Larvae Stage of juvenile California Tiger Salamander (Bolster, CDFW, 2010)
Figure 4: Metamorphosis stage of California Tiger Salamander (Bolster, CDFW, 2010)
Figure 5: Adult California Tiger Salamander (Bolster, CDFW, 2010)
8
Range & Status:
California Tiger Salamanders are scattered throughout California. They are limited
to the grasslands and foothills throughout the central valley of Central California with
disjoint outlier populations in the southern part of Santa Barbara County and in Sonoma
County (Figure 6) (Bolster, 2010; Environmental Protection Agency, 2010; Trenham et al.,
2000). In Shaffer et al. (2004) study, Shaffer and his colleagues identified six genetically
and geographically sets of California Tiger Salamander populations. Among the six, two
populations are geographically secluded and genetically distinct from the others. The two
populations are found in Sonoma County and Santa Barbara County (Shaffer et al., 2004).
The California Tiger Salamander populations in both Sonoma County and Santa Barbara
County are considered as separate distinct population segments (DPS) because of genetic
differences between each population (Environmental Protection Agency, 2010). While the
remaining four populations show a coherent of genetic intermixing at their shared
boundaries, they are classified as one whole populations of Central California (Bolster,
2010). Because most of the grasslands and foothills that contain vernal pools have been
targets of conversion for agricultural expansion and urbanization, they have been listed as
threaten species for two reasons: habitat loss and habitat fragmentation (Davidson et al.,
2002; East Contra Costa County, 2006).The population in Santa Barbara County and
Sonoma County are currently endangered meaning they are at risk of extinction (USFW
Species Profile, 2014). In Central California, they are currently threatened, which means
they are threatened by extinction (USFW Species Profile, 2014). Currently, the U.S. Fish and
Wildlife Service is monitoring populations of California Tiger Salamanders in each three
distinct population segments (Environmental Protection Agency, 2010).
9
Figure 6: Range of California Tiger Salamander (USFW, 2014)
Diet:
California Tiger Salamanders feed on invertebrates. Hatchlings feed on zooplankton,
but as they mature, they start feeding on larger aquatic invertebrates. Older larvae feed on
aquatic invertebrates like snails and tadpoles. Juveniles and adults feed mainly on a variety
of terrestrial invertebrates (Bolster, CDFW, 2010). They mostly find food during the night
when the temperature is much cooler during the night (Environmental Protection Agency,
2010).
Climate Change Projection:
The Intergovernmental Panel of Climate Change (IPCC) projects that North America
will be getting warmer with an increase of two degree Celsius of surface air temperature
10
(Christensen et al., 2007). The IPCC suggests there will be an overall increase in
temperature along with a possible change in annual precipitation in North America. As
stated before, the IPCC models predict an increase in temperature and change in annual
precipitation but also predict an increase of spatial variability of precipitation (Christensen
et al., 2007). This will cause uncertainty of predicting precipitation in that area that lies on
the boundary of North America due to the complexity of the regional climate and
contrasting projections across models (Christensen et al., 2007). California lies between
that boundary of possible increased and decreased of precipitation (Figure 7) (Christensen
et al., 2007).
Figure 7: The map shows the annual, December January February (DJF), June July August (JJA) temperature and
precipitation change over North America climate projections. Top row is the annual mean, DJF, JJA temperature changes
between the years 1980 to 1999, and 2080 to 2099. The middle is same as the top but instead of temperature change, it is
the changes in precipitation. The bottom row is the a projection showing possible increase in precipitation in North
America (Christensen et al., 2007)
11
Bell et al., (2004) predicted a decrease in mean annual precipitation throughout
California except for the northern part, where an increase of rainfall is predicted (Bell et al.,
2004). The assumption was that there will be minimal change in mean rainfall per day;
however, some scenarios projected that there will be a few days that might rain, as well as
a decrease in heavy rainfall events (Figure 8 and Table 1) (Bell et al., 2004). California will
receive fewer showers and longer duration of drought conditions. These models indicate
that the location determines the amount of precipitation it receives.
Figure 8: The hydrologic basins of California shown here from the California Department of Water Resources (1998)
Regional Climate Models (Bell et al., 2004). It connects to Table 1 shown below.
Table 1: The changes in annual precipitation and the frequency of an extreme event in a day (Bell et al., 2004). This table
illustrates a decrease in both total rainfall and number of rain days of California and a possible increase of one day
extreme wet event.
12
Climate change will result in global temperature increases of two degree Celsius
(Christensen et al., 2007). The increase of global temperature is significantly alternating the
climate, which result in more extreme and unpredictable weather occurring in California.
This is a complex factor that is posing a threat to the California Tiger Salamander, affecting
its distribution and population dynamics, directly and indirectly. Changes in temperature
and precipitation pattern may influence local weather patterns and extreme weather
events that are detrimental to the California Tiger Salamanders, putting them at high risk of
mortality. Since California Tiger Salamanders are highly sensitive to their environment,
slight changes in temperature will put stress on them, causing an alternation of their
reproduction and migration.
The Effect on Habitat:
The California Tiger Salamander requires two habitats to complete its life cycle,
uplands and vernal pools. The California Tiger Salamander require temporary seasonal
vernal pools to reproduce with surrounding terrestrial migration and dispersal land that
contains underground rodent burrows to serve as underground shelter (Bolster, 2010).
These habitats play a vital role in their life history and in maintaining a healthy number in
terms of population. These habitats must properly exist to sustain a vital population of
California Tiger Salamander. Climate change, as well as land use changes, threatens habitat
loss and vernal pool environmental conditions.
13
Uplands
A change in temperature and precipitation alters the upland ecosystem where the
California Tiger Salamander spends its time in underground burrows. Active underground
burrows are considered an important upland habitat for the California Tiger Salamander
(Loredo et al., 1996; Trenham et al., 2000; Trenham, 2001). Because California Tiger
Salamanders are poor diggers, they depend on the burrows of the California Ground
Squirrels (Environmental Protection Agency, 2010). They share a commensalism
relationship with the California Ground Squirrel where they benefit from each other
without harming each other (Loredo et al., 1996; Trenham, 2001). The California Ground
Squirrel’s underground burrows are important habitats for California Tiger Salamander
adults and juveniles who are prone to desiccation or heat stress (Loredo et al., 1996;
Trenham et al., 2000). Underground burrows must be maintained by the squirrel in order
to prevent it from collapsing during harsh weather conditions (Loredo et al., 1996;
Trenham et al., 2000). If the burrows collapse, California Tiger Salamanders must find
other available underground burrows within their geographical range. The California Tiger
Salamander may migrate further away outside of its current range. Loredo et al., (1996)
noticed having active squirrels maintaining underground burrows during severe weather
conditions, are essential to sustaining a viable population of California Tiger Salamanders. .
Vernal Pools
Vernal pools are crucial aquatic habitats that house many unique aquatic species. In
California, vernal pools are primary breeding sites for the California Tiger Salamander.
Pond size influence productivity. Wang et al., (2011) indicates larger vernal pools can
14
support a larger population. However, as climate changes, vernal pools will be altered,
which will directly and indirectly affect their viability.
Vernal pools are distinctive seasonal ephemeral wetlands that receive water from
precipitation and runoff according to the timing (Keeley and Zeldler, 1998). The limited
duration of standing water is the defining feature of vernal pools (Zedler, 2003). The
inundated phase can vary greatly in duration, ranging from no ponding water at all for
several consecutive years to inundation for fifty to ninety days in a rainy year (Bauder,
2005). Vernal pools are distinct from other seasonal wetlands that they lack water input
from drainage and are entirely dependent on input from precipitation (Keeley and Zedler,
1998). Vernal pools are unique ecosystems that are well adapted to the Mediterranean
climate. Four stages that describe vernal pools are wetting phase, inundation phase,
waterlogged terrestrial phase and the drought phase (Keeley and Zeldler, 1998). This
indicates that vernal pools are vital ecosystems for supporting rare and endemic species
that are adapted to wet winters and dry summers. The three key elements that determine
healthy vernal pools are the source of water, the duration of the inundation and
waterlogged phases, and the timing of the phases (Keeley and Zeldler, 1998). There is great
unpredictability in the amount of precipitation and the pattern between the years because
of the variability of climate change. This unpredictability can have a dramatic effect on the
vernal pool habitat, since the total amount of seasonal precipitation is the most important
factor that affects the ponding in vernal pools (Bauder, 2005).
Vernal pools are vulnerable to climate change and may be limited due to the
dependence on water availability controlled by outside factors (Bauder, 2005). Climate
changes that affect seasonaility can causes dramatic changes in the form of vernal pools
15
ecosystem but also disrupt the system’s function (Pyke, 2005). Slight changes in
temperature alter the seasons, causing variation in season lengths (Bauder, 2005; Pyke,
2005). It can lead to a mismatch between key elements in vernal pools. The vernal pools
accumulate water when first rains occur during winter and spring, and change in volume in
response to the variation of weather patterns. During a single season, pools may fill and dry
several times. As temperatures rise, there will be an increase in evapotranspiration loss
which will result a long period of drought and a delayed of rainfall (Blaustein et al., 2010).
When there is a year of extreme drought, some vernal pools may not fill at all. This will
cause a failure of California Tiger Salamander larvae to fail and develop into juveniles
before the ponds dry up (Loredo and Vuren 1996). A more severe cause will be a complete
loss of vernal pools altogether or may undergo serious and irreversible changes due to a
delay in rainfall and extended drought during each season.
McMenamin et al. (2008) conducted a study in the northern part of Yellowstone
National Park that studied the correlation of climate change and wetland desiccation on
native species. They observed 4 native amphibians in Yellowstone National Park, the
conditions of the weather and 46 vernal pools (McMenamin et al., 2008). McMenamin and
his colleagues obtain climate and hydrological records to view recent changes in water
availability and weather conditions, and to correlate it with the survivorship of the four
native amphibians.
One of the four native amphibians being studied is the blotched tiger salamander
(Ambystoma tigrinum melanostictum) which is from the same family of Amystoma with the
California Tiger Salamander and has a similar lifecycle. The study showed there is a linkage
of climate change and wetland desiccation because there is evidence that indicates that
16
ponds have been completely dried up in Yellowstone National Park (McMenamin et al.,
2008). As a result, there was a decline in all 4 native species (Figure 9). The results show
that the blotched tiger salamanders are highly affected by the increase of temperature and
extreme drought. This indicates the California Tiger Salamander may experience the same
result as blotched tiger salamanders. There will be a decline in populations as extreme
drought occurs and as temperature increases.
Figure 9: Number of species present in ponds (on the left) and Number of each four specie populations (on the right)
present in ponds during 1992-1993 and 2006-2008. The left graph illustrates the number of locations containing species
during 1992-1993 and 2006-2008. The right graph illustrates the number of populations of each species during 19921993 and 2006-2008 (McMenamin et al., 2008). The left graph shows a decrease of amphibians present in ponds that are
not dried up yet. The right graph shows which each species populations and the number between 1992-1993 and 20062008.
The Effect of Droughts on Reproduction:
Water availability is associated with the California Tiger Salamander’s reproduction
(Trenham et al., 2000; Walls et al., 2013). However, changes in temperature may influence
the total amount of precipitation that may impact their reproduction. For successful
reproduction to occur there must be an abundance of water available in the vernal pools,
since the total amount of precipitation received is an important factor for maintaining a
sufficient amount of water in the breeding pools (Bauder, 2005). Lack of precipitation will
17
result in reproductive failure and the ability to develop into juveniles. This also results in
high mortality of the California Tiger Salamander’s egg because they are unshelled and
require sufficient water coverage in order to spawn to hatchlings (Bolster, CDFW, 2010;
Loredda and Vuren, 1996; Trenham et al., 2000; Walls et al., 2013). The population will
continue to decline if there is not enough successful reproduction.
The Effect on Behavior/Migration:
Behavior and migration may be influenced by the change in temperature and
precipitation (Blaustein et al., 2010; Walls et al., 2013). When California Tiger Salamanders
went through the stresses of temperature and precipitation, their behavior and action will
be abnormal which can affect their life cycles and increase the risk of population decline
(Trenham, 2001; Walls et al., 2013).
During the stressful conditions of high temperature and low moisture, California
Tiger Salamanders will hide in an underground burrow and will reduce their activity
(Blaustein et al., 2010) until the stressful condition is more suitable for reproduction. An
example is the study conducted by Loreda and Vuren (1996). Their study was a three year
observation of a breeding pond of California Tiger Salamanders at the Concord Naval
Weapon station in Contra Costa County. They observed the reproduction traits of California
Tiger Salamander for three seasons (Loreda and Vuren, 1996). From their three season
study, they noticed that the females did not migrate to breeding ponds during their normal
mating season due to lack of precipitation (Loreda and Vuren, 1996). Instead, the female
18
will skip the breeding season and wait until the next suitable mating season (Bolster,
CDFW, 2010).
Hybridization with a Barred Tiger Salamander:
Climate change is predicted to introduce and spread invasive species into the region
that may become a problem to native species (Blaustein et al., 2010). A slight change in
temperature and precipitation can alter the condition of the ecosystem which favors
invasive species. The term “Invasive Species” is defined as exotic (alien or non-native)
species whose introduction or propagation threatens the environment. Invasive species are
sometimes brought in voluntarily to take out specific species, and sometimes involuntarily.
Barred tiger salamanders (A. tigrinum mavortium) are an invasive species that
introduced in California for about 60 years (Fitzpatrick and Shaffer, 2007a). Bait dealers
imported thousands of Barred Tiger Salamander larvae from Texas to use it as fishing baits
(Fitzpatrick and Shaffer, 2007a). These salamanders have very high tolerance to drier
conditions because the climate in Texas is drier than California. The Barred Tiger poses a
serious threat to the native California Tiger Salamander because they are interbreeding
with the native California Tiger Salamander and are producing viable and fertile offspring
(Bolster, CDFW, 2010). The hybrid offspring have higher survival rates than the native
California Tiger Salamander and the Barred Tiger Salamander (Fitzpatrick and Shaffer,
2007a). Hybrid salamanders tend to have better fitness conditions than the native
California tiger salamanders and able to withstand the changes in the ecosystem
19
(Fitzpatrick and Shaffer, 2007a). The hybrid tiger salamanders tend to reduce native
California growth and survival rate (Bolster, CDFW, 2010).
The Barred Tiger Salamander and the hybrid salamander have a different lifecycle. The
Barred Tiger Salamander is able to reproduce sexually at an earlier stage of life than the
California Tiger Salamander. The Barred Tiger Salamander was able to forgo the
metamorphosis stage and become sexually mature during the larval stage, which is called
paedomorphs stage (Bolster, CDFW, 2010). Because they forgo the paedomorphs stage,
they are able to reproduce sooner, which could benefits population size. As more
hybridization occurs, the populations of California Tiger Salamanders will diminish.
Conclusion:
Climate changes are expected to change pool hydrology and, as a result, the
distributions, populations, and interactions of species. It also indirectly introduces exotic
species that favor the change in environment. To make matters worse, agriculture
expansion and urbanization have already destroyed most of the vernal pools and upland
area or subdivided them into isolated patches. Nearly 90% of California vernal pools have
disappeared (CDFW, 2014). Because of climate change, these separated patches will be
uninhabitable for the California Tiger Salamander.
Climate change is a huge factor that is currently posing a threat to the California
Tiger Salamander. Changes in temperature and precipitation are affecting their ecosystem,
reproduction, and distribution. However, a more severe threat to the California Tiger
Salamander is the interaction with other stressors such as invasive species like the Barred
20
Tiger Salamander. Other stressors such as contaminants, diseases, habitat fragmentation
and much more also harm the California Tiger Salamander. It is important to continue
researching more about the California Tiger Salamander’s interaction with other stressors
and more research on the California Tiger Salamander’s activities and habitat in order to
understand the complex interaction they have with their habitat.
Temperature and precipitation affect the California Tiger Salamanders directly and
indirectly. Therefore, preventing further declines and restoring populations to healthy
numbers necessitate more research on the understanding of behavior and proper habitat
conditions.
21
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