**4210**

###  FS-SRS-4251-4.8

**(Problem 4)**

**[Study plan]{.underline}**

Amphibian Community Succession and Recruitment to Artificial Ponds on
National Forests in Eastern Texas

> **Prepared by:**
>
> **\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ \_\_\_\_\_\_**
>
> **Daniel Saenz Date**
>
> **\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ \_\_\_\_\_\_**
>
> **Richard N. Conner Date**
>
> **Approved by:**
>
> **\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ \_\_\_\_\_\_**
>
> **Ronald E. Thill, Date**
>
> **Project Leader**

**4210**

###  FS-SRS-4251-4.8

**(Problem 4)**

# [September 1999]{.underline}

**[Study Plan Summary]{.underline}**

**[D. Saenz and R. N. Conner]{.underline}**

## Nacogdoches, Texas

Anuran Community Succession and Recruitment to Artificial Ponds on
National Forests in Eastern Texas

Anuran species, frogs and toads, appear to fall along a gradient of
water permanency (length of time a water source is available) where
different species are associated with different portions of the
gradient. Breeding sites may vary from those with extremely short
hydro-periods to permanent water. It is unknown how wildlife ponds
affect anuran populations, but they are now a prominent habitat
component of National Forests and Grasslands in Texas. The ponds, which
are mainly permanent water sources, usually only provide water on one
end of the gradient of water permanency and likely have short and
long-term consequences on both anuran and predator communities. Species
that are dependent on ephemeral water sources for breeding sites might
be displaced over time by species that prefer permanent water. The
objectives of this study are to develop a better understanding of the
dynamics of anuran communities by (1) Developing a model to predict
recruitment rates and persistence of anurans in wildlife ponds in
eastern Texas based on natural history characteristics, such as clutch
size, rate of larval development, and relative abundance, (2)
Determining which species of anurans, other amphibians, and predator
species currently use wildlife ponds in eastern Texas and explore niche
differences between anuran species, (3) Determining the actual
persistence of anurans and species turnover (succession) in wildlife
ponds in eastern Texas, (4) Determining causal mechanisms of anuran
succession in wildlife ponds in eastern Texas using predator/prey
experiments, and (5) Implementing a long term amphibian-monitoring
program at wildlife ponds to explore temporal dynamics of species
composition and regional effects of a globally detected amphibian
decline. Model predictions and field results could give us much insight
on how anurans respond to wildlife ponds. Natural history experiments
may allow us to determine the causal mechanisms involved with
recruitment and persistence of anurans in wildlife ponds. Finally, an
exploratory analysis will be conducted on extensive habitat and life
history data collected in the field component of the study to explore
and contrast ecological niche differences among the anuran species of
the forest communities of eastern Texas. This will help us determine the
key habitat requirements that are critical to individual species.
Initially, the study will require at least two years to collect
preliminary field and laboratory data for the experimental phase,
followed by at least 15 years of monitoring to begin to evaluate
long-term dynamics of anuran communities.

Anuran Community Succession and Recruitment to Artificial Ponds on
National Forests in Eastern Texas

# INTRODUCTION

Ecological succession (the change in community composition over time) is
a well studied phenomenon, especially in plant communities, yet very
little is known about succession in amphibian communities; only a few
studies have focused on this topic (Braz and Joly 1994, Dixon and Heyer
1968, Wiest 1982). The lack of anuran community studies is likely
associated with inherent difficulties in working with amphibians such as
identification of species in the larval stage, fluctuations in natural
populations (Bragg 1960, Pechmann and Wilbur 1994), and differential
distributions across landscapes (Mann et al. 1991). Detectability and
abundances are highly influenced by weather, nocturnal habits, and human
influences such as fragmentation of habitat (Pechmann et al. 1991,
Pechmann and Wilbur 1994). A portable automated recording device, termed
the "froglogger" (Dorcas and Foltz 1991), will hopefully help us
overcome some of the difficulties of working with nocturnal breeding
anurans (frogs, toads, and spadefoots).

The Knutson-Vandenberg (KV) Act (1930) allowed for some of the proceeds
from timber sales on federal lands to be used for wildlife habitat
improvement. A portion of this KV money has been used to build wildlife
ponds throughout most of the South including national forests in eastern
Texas. These wildlife ponds, which typically hold water year-round, have
an unknown affect on anuran communities, but provide an excellent
opportunity to study amphibian breeding phenology, amphibian recruitment
to newly created habitats, and amphibian community succession.

Newly constructed wildlife ponds are initially devoid of anurans. Anuran
species that typically breed in ephemeral sites (sites that are
typically dry at least part of the year) should be the first species to
reach and breed in these ponds. These species are more likely to use new
breeding sites because their life histories suggest that they should be
more evenly distributed (spatially) than other species and have a higher
probability of finding the new ponds faster. As the ponds age, the
number of species that prey on amphibian larvae should increase; these
predators will eliminate species that lack predator defenses. Both fish
and dragonfly larvae are know to negatively impact some amphibian larval
populations (Brockelman 1969) and are common in wildlife ponds.

Species associated with permanent water will likely colonize the ponds
more slowly than other species because they are likely tied to
historically permanent breeding sites. When the species associated with
permanent water arrive, they should be able to coexist with predators
and become the dominant amphibian species using older ponds. There are
some species of anurans that exhibit phenotypic plasticity, enabling
them to metamorphose at smaller sizes, alter spatial distribution,
reduce activity in the presence of predators, or release an alarm
substance from their skin that triggers conspecifics to "move away",
potentially avoiding predators (Skelly 1997, Skelly and Werner 1990, Van
Buskirk 1988, Petranka 1989, Wilbur and Fauth 1990). These species might
be able to breed in either ephemeral or permanent ponds and could be
found in both new and old ponds.

It is of particular interest to determine the exact mechanisms driving
anuran community composition at any given time during the succession of
a wildlife pond. This will clarify how different pond ages effect anuran
populations and help focus on which management strategies might best be
used to attain the anuran species diversity and species richness
objectives desired by managers. Additionally, the research would provide
insight on undescribed natural history traits of some anuran species
enhancing our ability to understand and manage this hard-to-study group
of organisms.

##### OBJECTIVES

1.  Develop a model to predict recruitment rates and persistence of
    anurans in wildlife ponds in eastern Texas based on natural history
    characteristics, such as clutch size, rate of larval development,
    and relative abundance.

2.  Determine which species of anurans, other amphibians, and predator
    species currently use wildlife ponds in eastern Texas and explore
    niche differences between anuran species.

3.  Determine the actual persistence of anurans and species turnover
    (succession) in wildlife ponds in eastern Texas.

4.  Determine causal mechanisms of anuran succession in wildlife ponds
    in eastern Texas using predator/prey experiments.

5.  Begin a long-term amphibian monitoring program at wildlife ponds to
    explore temporal dynamics of species composition and regional
    effects of a globally detected amphibian decline.

# METHODS

**Objective 1.** (Model)

Initially, a simulation model will be developed using Stella^®^ Modeling
software to make predictions on recruitment and succession in ponds from
1 to 10 years of age, ages comparable to existing artificial ponds in
eastern Texas. Rate of larval development, clutch size, and relative
abundance of each species will be used as objective data for the model.
We will run 30 repetitions of the model to determine mean abundance
levels for each species over the ten-year timeframe. The model will be
evaluated with actual field data described in objectives 1 and 2. Actual
colonization and persistence in the ponds will be compared to the model
output. The model will also be evaluated with our behavioral and our
succession experiments in objective 3.

## Model assumptions:

The primary assumptions of the model are that rates of larval
development and relative abundance directly affect recruitment rates to
newly created habitat. The basis for this assumption is that the shorter
the larval stage the more evenly distributed (spatially) the species is
likely to be across the landscape, whereas species with longer larval
stages will be clumped near permanent water. A distribution value will
be developed from the length of the larval stage and combined with
relative abundance to compute a recruitment probability index for each
species.

Rate of larval development has been positively correlated with predation
rates (Skelly 1997) and will be used to compute a predation rate for
each species. The assumption is that the shorter the larval stage of a
species, the more susceptible that species is to predation from fish and
aquatic invertebrate predators. Anuran species less susceptible to
predation can "afford" a longer larval stage. Fish and aquatic
invertebrate predators will occur more frequently in older ponds than in
newer ponds because they need time to become established.

Clutch size is also an important factor because some organisms might be
able to persist by producing more offspring than predators can consume.
Incidental predation from birds, snakes, mammals, and other predators
will be assumed equal among different age ponds.

**Objective 2.** (Actual pond use)

A series of ponds were constructed on the Davy Crockett National Forest
from the mid 1980s to the mid 1990s. The ponds were approximately 10
meters wide and 20 meters long with a maximum depth of 1.6 meters
sloping to a minimum depth of 0.6 meters. Five ponds of the same
dimensions will be constructed on the Stephen F. Austin Experimental
Forest in Nacogdoches County, Texas, in April 2000.

Four ponds, ranging in age from five to 15 years on the Davy Crockett
National Forest and four new ponds on the Stephen F. Austin Experimental
Forest, will be monitored continuously for two years using frogloggers
(Dorcas and Foltz 1991). Frogloggers will record anuran calls nightly
for 1 minute every hour for the first six hours after sunset, the period
of time when anurans are likely to be most vocal, on 90-minute capacity
audiotapes. The tapes will be analyzed in the lab, the anuran calls
identified using Elliott (1992), and all information transcribed to data
sheets.

Tadpoles will be collected monthly, from 15 different ponds ranging in
age from five to 15 years old in the Davy Crockett National Forest and
the five new ponds on the Stephen F. Austin Experimental Forest, by
seining and with minnow traps. Tadpole sampling will be conducted
concurrently with the froglogger data recording periods. All collected
tadpoles will be preserved in 10 percent formalin in the field. They
will then be returned to the lab and identified to species using Altig
and Ireland (1984) and Altig and Johnston (1986). The specimens will be
deposited in the Texas Cooperative Wildlife Collection at Texas A&M
University at the end of the study.

Arthropods will be sampled monthly with seines and minnow traps,
preserved in 70 % ethanol, and identified in at the lab using Merritt
and Cummings (1984). Fish will be sampled while seining the ponds and
identified in the field where they will be immediately released alive
into the ponds in which they were caught so that the vertebrate predator
base will not be depressed or eliminated. Invertebrate predators should
be able to adequately rebuild populations after destructive sampling.

Forest vegetation measurements will be taken in five randomly chosen
11.2-m-radius plots in the forest stands within 25 m of each pond.
Height of overstory and midstory vegetation will be measured using a
clinometer. Stand age will be determined by coring five dominant or
co-dominant overstory trees with increment borers at breast height and
counting annual growth rings; three years will be added to correct for
the time the tree takes to grow to breast height. Canopy closure will be
ocularly estimated using a 4 cm diameter by 12 cm hollow tube. Soil type
for each site will be determined from U.S. Forest Service GIS layers.
Air temperature and relative humidity will be continuously monitored
using Hobo temperature loggers. Overstory and understory basal area
will be determined using a one-factor metric prism. Finally, we will
calculate foliage density of vegetation from ground level to 2 m using a
density board as described by MacArthur and MacArthur (1961).

Pond water chemistry and other limnological data will also be collected
monthly at each site. Ages of each pond will be verified by referring to
records on excavation dates provided by the U.S. Forest Service.
Dissolved oxygen, pH, conductivity and water temperature will be
measured monthly using portable hydro-probes. Turbidity will be
calculated using a Secchi disc.

**Objective 3.** (Species turnover in wildlife ponds)

Anurans will be sampled as described above (objective 2) using
frogloggers for breeding adults and seines and traps for larvae. No
long-term data on anuran use of wildlife ponds exists, therefore,
community composition in old and new ponds will be concurrently examined
to provide a "snapshot" view of anuran community succession.

**Objective 4.** (Mechanisms of succession)

A series of three different experiments will be conducted on the larvae
of the 12 common anuran species that occur within Houston and
Nacogdoches counties. Egg masses or tadpoles will be collected within
eastern Texas and will be kept alive in the lab until they are used in
the experiments. Tadpoles will be fed a ration of a mixture of 1 part
rabbit food (18% crude protein) and 5 parts tropical fish flakes (48%
crude protein). One day's ration of food is equivalent to 10 percent of
a tadpoles body-weight.

> **Experiment 1.** (Activity and predator avoidance)
>
> Each species will be tested in independent trials for the activity
> experiments. We will conduct five different sets of trials for each
> species which will include a range of tadpole sizes (ages) for each
> species.
>
> Thirty 3-qt plastic tubs will be gridded into 4 parallel equal cells
> and filled with 2 liters of dechlorinated water (see Fig. 1). A small
> enclosure will be placed on one end
>
> (cell 1) of the tub where an odonate (dragonfly larvae) predator will
> be placed. Half of the trials will not include a predator (n = 15),
> but these tubs will still include the small empty enclosure. Four
> tadpoles will be places into each of the 30 tubs (15 with an odonate
> larvae and 15 without a predator) and will be allowed to acclimate for
> one hour. No food will be provided during this experiment. After
> acclimatization, each tub will be sampled by recording the exact
> position of each tadpole and the number of tadpoles moving in each tub
> the instant the tub is first viewed. Each tub will be observed every
> 30 minutes for 5 pseudoreplications. We will preserve all of the
> tadpoles in 10% formalin immediately after the trials and measure
> snout-vent and total length to the nearest 0.01 mm. Measurements of
> length will permit us to test for effects of size on movement and
> response to predators.
>
> **Experiment 2.** (Affinity of species to seek cover)
>
> The affinity of each species to seek cover will be tested during five
> different sets of independent trials. An effort will be made to use
> tadpoles of different sizes in each set of experiments to determine if
> tadpole size influences their affinity to seek cover.
>
> Thirty 3-qt plastic tubs will be gridded into 4 equal quadrants and
> filled with 2 liters of dechlorinated water (see Fig. 2). Quadrants 1
> and 4 will each contain equal
>
> amounts (three pieces) of artificial aquarium plant to provide cover
> for the tadpoles. A small enclosure will be placed in the center of
> the tub where an odonate predator will be placed. Four tadpoles will
> be places into each of the 30 tubs (15 with an odonate larvae in the
> small enclosure and 15 without a predator in the small enclosure) and
> will be allowed to acclimate for one hour. No food will be provided
> during this experiment. After acclimatization, each tub will be
> sampled by recording the exact position of each tadpole in each tub
> the instant the tub is first viewed. Each tub will be observed every
> 30 minutes for 5 pseudoreplications. We will preserve all of the
> tadpoles in 10% formalin immediately after the trials and measure
> snout-vent and total length to the nearest 0.01mm, permitting us to
> test for effects of size on tadpole use of cover in the presence and
> absence of predators.
>
> **Experiment 3.** (Predator/prey succession experiments)
>
> Auran species that overlap seasonally in their larval stages will be
> tested together for survival rates at three different levels of cover
> and predator density. The cover and predator levels will simulate
> three pond successional stages: new, middle-aged, and old. Trials will
> be conducted in forty 1 m diameter wading pools filled with
> approximately 50 liters of dechlorinated water. Ten control pools will
> contain only water. Ten "new" pools will each contain no cover and 25
> odonate larvae, a low predator level. Ten "middle-aged" pools will
> contain 25 pieces of artificial aquarium plant and 50 odonate larvae.
> Ten "old" pools will contain 50 pieces of artificial aquarium plant,
> 50 odonate larvae, and 10 green sunfish (*Lepomis cyanellus*)
> approximately 6-8 cm in length.
>
> Twenty tadpoles of each species will be placed in each pool and fed a
> four-day ration (as described above) of food. After four days an
> additional three-day ration (based on initial tadpole weight) will be
> added to each pool. At the end of the seven-day period, the trial will
> end and all of the tadpoles in the pools will be counted to determine
> survivorship. An effort will be made to use tadpoles of approximately
> the same size for all of the species to control for affect of size on
> predation rates. Experiments will be conducted individually during
> winter, spring, and summer to encompass the different breeding seasons
> of the various anuran species.

**Objective 5.** (Long-term monitoring)

Initial sampling will be conducted with frogloggers in the Stephen F.
Austin Experimental Forest and the Davy Crockett National Forest as
described in objective 2. These data will be used as the baseline for a
long-term monitoring program at amphibian breeding ponds. Additional
sites may be added in the future to increase repetition and geographic
coverage. The recordings will be used to build a long-term database on
population fluctuations over time and detailed information on breeding
season dynamics and pond use for each species.

> **ANALYSES**

**Objective 1.** (Model)

Mean abundance levels will be computed for each species over time and
graphically plotted. No statistical analyses will be required to achieve
objective 1.

**Objective 2.** (Actual pond use)

Presence and absence data will be used to empirically demonstrate anuran
use of wildlife ponds. We will use a Principle Component Analysis (PCA)
as a data reduction technique to identify habitat components that are
associated with each individual species and to graphically contrast
ecological differences among species. Only components with an eigen
value greater than 1 will be used to contrast niche relationships of
species on the new orthogonal variables constructed by the PCA.

**Objective 3.** (Species turnover in wildlife ponds)

Abundance data obtained from the frogloggers and by sampling with traps
and seines at different age ponds will be graphically displayed and
visually compared to the results of the simulation model. Spearman-rank
correlation analysis will be calculated to explore possible similarities
between population dynamics as projected by the model with real-world
data.

**Objective 4.** (Mechanisms of succession)

**Experiment 1.** (Activity and predator avoidance)

> We will use a two-way factorial anova (predator presence or absence ×
> tadpole size) and a Bonferroni multiple-range test to compare activity
> levels among species and among size-classes within a species in both
> the presence and absence of predators. We will test the hypotheses
> that neither tadpole size nor the presence of predators affects
> tadpole activity and that activity levels do not differ among species.
>
> We will also use a two-way factorial anova (predator presence or
> absence × tadpole size) and a Bonferroni multiple-range test to
> examine the effect of predator presence on tadpole spatial arrangement
> among species and among size-classes within species. The mean distance
> between cells with filled predator cages and tadpoles will be
> contrasted with the mean distance between cells with empty predator
> cages and tadpoles. Thus, we will test the hypotheses that the
> presence of a predator has no effect on the spatial distribution of
> tadpole species during all stages of larval development and that the
> spatial arrangement of different species does not differ in the
> presence or absence of predators.
>
> **Experiment 2.** (Affinity to cover)
>
> We will use a two-way factorial anova (predator presence or absence ×
> tadpole size) and a Bonferroni multiple-range test to compare the
> effect of predator presence on the use of cover among species and
> among size-classes within a species. We will test the hypotheses that
> neither tadpole size nor the presence of predators affects the amount
> of cover used by tadpoles and the amount of cover used does not differ
> among species.
>
> **Experiment 3.** (Predator/prey succession experiments)
>
> A two-way factorial anova (artificial pond succession stage \[habitat
> complexity and predator density\] × tadpole species) and a Bonferroni
> multiple range-test will be used to determine difference in the
> survival of different anuran species under three different artificial
> pond successional regimes. We will test the hypotheses that different
> stages of pond succession have no effect on the rates of predation on
> anuran species and predation rates do not differ among species.

**Objective 5.** (Long-term monitoring)

Anuran abundance levels, temperature, and relative humidity will be
monitored over time using the same methods described in objective 2 and
graphically displayed to visually observe population trends. After
sufficient data are collected, trend analyses will be calculated to
determine population deviations from a stable population level. This
information should provide added insight to the anuran community
succession in wildlife ponds. In addition, the long-term database will
provide information to calculate the effects of weather conditions on
anuran activity and potentially provide insight on global climate change
and its effect on anuran abundance.

**SCHEDULE OF RESEARCH**

Sampling will commence in the spring 2000 and continue for at least two
years, for objectives 1 though 4. The sufficiency of data will then be
evaluated to determine whether additional years of data collection are
necessary. The succession experiments will begin as soon as adequate
breeding data are collected for each species. The long-term monitoring
will be conducted for at least 15 years to provide adequate information
on anuran population trends.

**PRESENTATION OF RESULTS**

A final report will be completed upon termination of the study in the
form of a Ph.D. dissertation. Results will be presented at appropriate
scientific meetings and submitted to scientific journals for
publication.

# SAFETY

Several safety hazards will be encountered while conducting this study,
including noxious plants, venomous animals, and heat. All personnel will
be alerted to these hazards. A job hazard analysis is attached
(Appendix).

# ENVIRONMENTAL EFFECTS

The implementation and activities of this study will have no significant
negative effect on the human environment or the habitat used by the
amphibians.

**PERMITS**

No permits are required to work with these species. Habitat sampling
will be nondestructive.

BUDGET

[FY02]{.underline} [FY03]{.underline}

[FUNDING NEEDS:]{.underline}

#### Wildlife Biologist \$15,000 \$15,000

[Field technician]{.underline} \$10,000 \$10,000

[Transportation]{.underline} \$3,000 \$3,000

[Supplies]{.underline} \$3,000 \$3,000

TOTALS \$31,000 \$31,000

**LITERATURE CITED**

Altig, R., and P. H. Ireland. 1984. A key to the salamander larvae and
larviform adults of the United States and Canada. Herpetologica
40(2):212-218.

Altig, R., and G. F. Johnston. 1986. Major characteristics of
free-living anuran tadpoles. Smithsonian Herpetological Information
Service No. 67.

Brag, A. N. 1960. Population fluctuation in the amphibian fauna of
Cleveland County, Oklahoma during the past twenty-five years. The
Southwestern Naturalist 5(3):165-169.

Braz, E., and P. Joly. 1994. Micro-habitat use, resource partitioning
and ecological succession in a size-structured guild of newt larvae (g.
Triturus, Caudata, Amphibia). Arch. Hydrobiology 131(2):129-139.

Brockelman, W. Y. 1969. An analysis of density effects and predation in
Bufo americanus tadpoles. Ecology 50:632-644.

Dixon, J. R., and W. R. Heyer. 1968. Anuran succession in a temporary
pond in Colima, Mexico. Bulletin of the Southern California Academy of
Science 67:129-137.

Dorcas, M. E., and K.D. Foltz. 1991. Environmental effects on anuran
advertisement calling. Am. Zool. 31:111A.

Elliot, L. 1992. The calls of frogs and toads, eastern and central North
America. Lang Elliott, NatureSound Studio, Ithaca New York.

Knutson-Vandenberg Act. 1930. Financial sources, uses, and conditions of
the Knutson-Vandenberg fund, established under section 3 of the Act of
June 9. 16 U.S.C. 576b.

MacArthur, R. H. and J. W. MacArthur. 1961. On bird species diversity.
Ecology 42:594-598.

Mann, W., P. Dorn, and R. Brandl. 1991. Local distribution of
amphibians: the importance of habitat fragmentation. Global Ecology and
Biogeography Letters 1:36-41.

Merritt R. W., and K. W. Cummings. 1984. An introduction to the aquatic
insects of North America. 2nd ed. Kendal/Hunt publishing Co. Dubuque,
Iowa.

Pechmann, J. H. K., D. E. Scott, R. D. Smelitsch, J. P. Caldwell, L. J.
Vitt, and J. W. Gibbons. 1991. Declining amphibian populations: the
problem separating human impacts from natural fluctuations. Science
253:892-895.

Pechmann, J. H. K., and H. M. Wilbur. 1994. Putting declining amphibian
populations in perspective: natural fluctuations and human impacts.
Herpetologica 50(1):65-84.

Petranka, J. W. 1989. Response of toad tadpoles to conflicting chemical
stimuli: predator avoidance versus "optimal" foraging. Herpetologica
45(3):283-292.

Skelly, D. K. 1997. Tadpole communities: Pond permanence and predation
are powerful forces shaping the structure of tadpole communities.
American Scientist 85:36-45.

Skelly, D. K., and E. E. Werner. 1990. Behavioral and life-history
responses of larval American toads to an Odonate predator. Ecology
71(6):2313-2322.

SAS Institute Inc. 1988. SAS/STAT user's guide, release 6.03 edition.
SAS Institute Inc., Cary, North Carolina.

Van Buskirk, J. 1988. Interactive effects of dragonfly predation in
experimental pond communities. Ecology 69:857-867.

Wiest, J. A. Jr. 1982. Anuran succession at temporary ponds in a post
oak-savanna region of Texas. US Fish and Wildlife Service wildlife
research report 13:39-47.

Wilbur, H. M., and J. E. Fauth. 1990. Experimental aquatic food webs:
interactions between two predators and two prey. American Naturalist.
135:176-204.