Don Shepard's Research
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My general research
interest is the ecology, evolution, behavior, and conservation of amphibians
and reptiles.
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Current Projects
Phylogeography of the Plethodon ouachitae complex in the Ouachita Mountains
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Salamanders of the Plethodon ouachitae complex occur at high elevations in the Ouachita Mountains of west-central Arkansas and southeast Oklahoma. Because these salamanders are restricted to high elevations, many populations may be isolated by intervening low valleys, creating a "sky island" situation where gene flow or reproduction among populations on different mountains cannot occur. Previous work using allozymes (Duncan and Highton, 1979) found significant genetic variation among populations on different mountains, and it would not be surprising if the number of distinct taxa within this complex is considerably higher than the three currently recognized species. Frank Burbrink, Kelly Irwin, and I are sampling the region more intensively and using DNA sequence data to analyze patterns of genetic diversification and assess species boundaries. As of March 2008, we have collected and sequenced the cyt b and ND4 mitochondrial genes (1816 bp) for about 280 P. ouachitae from 55 localities throughout the Ouachita Mountains. We have finished writing our first paper on P. ouachitae and will be submitting it soon. We are continuing to collect and sequence P. fourchensis and P. caddoensis in Spring and Fall 2008 to assess lineage diversity in those species. Additionally, we are examing morphological variation, looking at several nuclear loci, and using ecological niche modeling to better understand species diversity in this group. |
Survey and Inventory of the Brazilian Cerrado Herpetofauna
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The Cerrado is Brazil's second largest
biome and is currently one of South America's most threatened ecosystems
due to rapid agricultural expansion. Little is known about the Cerrado
herpetofauna, but recent work has shown that diversity is much higher
than previously thought. I am assisting Dr. Laurie
Vitt and Dr. Jan
Caldwell in their NSF funded project in collaboration with Dr. Guarino
Colli and his graduate students at the University of Brasilia (UnB)
to survey the amphibians and reptiles in several regions and study their
ecology. Click
here for more about this project.
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Diet Composition and Overlap between Recently Metamorphosed Southern Leopard Frogs (Rana sphenocephala) and Crawfish Frogs (Rana areolata)
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Larval anurans often occur at very
high densities and much research has focused on interspecies competition
within this life stage. Anuran density can also be high during the period
immediately following metamorphosis, which could lead to intense competition
between species that metamorphose simultaneously . Rana sphenocephala
and Rana areolata overlap in distribution entirely, often breed
concurrently in the same habitats, metamorphose during the same time
period, and are morphologically similar, thus the potential for interspecies
competition is high. During June and July of 2003,
John Crawford and I collected recently metamorphosed frogs of the
two species and compared morphology and diet. We found that both species
were similar in body size, although head morphological variables increased
at a faster rate relative to body size in R. areolata. Both species
ate primarily hemipterans, beetles, and spiders, and exhibited significant
dietary overlap. Manuscript currently in review.
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Continued Range Expansion of the Green Treefrog (Hyla cinerea)
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Historically, the Green Treefrog in Illinois
was known only from the extreme southern tip of the state (Smith, 1961.
Ill. Nat. Hist. Surv. Bull. 28:1-298), but has expanded its range northward
and eastward over the last several decades (Redmer et al., 1999.
Ill. Nat. Hist. Surv. Bull. 36:37-66). Since 1999, Mike
Redmer, Ben Jellen, and I have been documenting the continued expansion
of this species' range and have found many new localities, several of
which are considerably farther north than previously recorded. We are
using ecological niche modeling to predict the range of the Green Treefrog
in Illinois to determine where favorable conditions exist for this species
and see how far this species should be expected to expand its range.
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Survey and Inventory of Amphibians and Reptiles of the Wildlife Management Areas of Oklahoma
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The wildlife management areas of Oklahoma offer some of the best maintained and most undisturbed natural habitats in the state. With the increasing threat of development and urbanization, these areas will play a critical role in conserving the state's diverse flora and fauna. However, no detailed information currently exists on the species that occur in these areas and this baseline data is needed for effective management and in order to gauge the impact of future habitat modifications. Over the next several years, Dr. Laurie Vitt, Dr. Jan Caldwell, and all of the herpetology students at the Oklahoma Museum of Natural History are intensively surveying several wildlife management areas for amphibians and reptiles to generate species lists, assess relative abundances, and collect data on species' ecology. Check out the project webpage. |
Some Recent Projects
Predation on Lizards: Effects of Habitat and Body Shape
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Predation is a major selective force in the evolution of morphological characteristics of organisms. Visually oriented predators (e.g. birds) develop search images for prey using features such as pattern and the body contour and outline. Lizards that rely on crypsis as a defense have body shapes that enhance their ability to avoid detection whereas lizards that depend on flight possess body shapes that promote rapid locomotion. In December 2004, I used clay models to test whether predator attack rates varied among lizards of four different body shapes. I conducted this experiment in three Cerrado habitats in Brazil with different vegetative characteristics to examine potential differences in attack rates among habitats. Predator attacks did not differ among the model shapes, but did differ among habitats. Predator attacks were most frequent in the most structurally complex habitat and were higher in more exposed microhabitats (Can you tell which lizards on the left are real and which ones are models?). Related publication: Shepard, 2007. Herpetologica. (pdf) |
Evolutionary Ecology of Foam-nesting Frogs of the Genus Leptodactylus
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Frogs of the genus Leptodactylus deposit their eggs in foam nests; however, nest deposition site and the extent to which larvae develop in the foam nest vary among species. Foam nests may be deposited on the water surface, on land at the margins of water, in burrows below ground adjacent to water, or in burrows below ground away from water. Larvae may enter water shortly after hatching or after an extended period in the foam nest, or they may complete development within the foam nest independent of water. Reproductive modes are hypothesized to have a phylogenetic basis, but data to evaluate this are lacking for most species of Leptodactylus. In 2003, Dr. Jan Caldwell and I studied the reproductive ecology of Leptodactylus labyrinthicus at a locality in the Cerrado region of Brazil. We found that foam nests were deposited on land about 2 m from the water's edge. Less than 20% of the eggs in nests developed and tadpoles remained in the nest after hatching, feeding on the undeveloped eggs. Heavy rains washed tadpoles out of foam nests and into adjacent ponds where they then fed on the eggs of other frogs, primarily small hylids. Related publication: Shepard and Caldwell, 2005. Copeia. (pdf) |
Ecology and Behavior of Copperheads (Agkistrodon contortrix)
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Copperheads (Agkistrodon contortrix) are a common inhabitant of forests throughout the southern and eastern U.S. Many aspects of their ecology and behavior have been well studied, but many other aspects remain unexplored. Because ecology can vary geographically within a species, population level studies across a species range are important. Additionally, basic demographic data are typically lacking for many snake species because of their secretive nature. During the spring and summer of 2003, I conducted a demographic study on a copperhead population in eastern Oklahoma as well as making general observations on their ecology. The venomous copperhead is responsible for many snake bites each year throughout the U.S. and is often stereotyped as aggressive and quick to bite. John Crawford and I examined copperhead defensive behavior to determine the intrinsic and extrinsic factors that influence snake defensive responses. Manuscript currently in review. |
Body Size, Age, Growth, and Alternative Mating Tactics in Toads: Satellite Males are Smaller but not Younger than Calling Males
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Alternative mating tactics occur in many species. In toads, non-calling males parasitize calling males and attempt to intercept females. These satellite males are usually smaller in size than the calling males they parasitize and this has led to the assumption that because they are smaller, they are also younger. Chris Leary and I analyzed size and age data on caller and satellite Bufo cognatus and Bufo woodhousii and found that although callers were larger in size than satellites, they were not different in age. The size difference between callers and satellites of the same age was the result of different growth trajectories, with callers growing faster. Related publication: Leary et al., 2005. Anim. Behav. (pdf) |
Ecology and Conservation of the Eastern Massasauga (Sistrurus c. catenatus)
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Started in 1999, this project is a
long-term study on all aspects of the life history and ecology of the
eastern massasauga at Carlyle Lake, Illinois. (With Dr. Chris
Phillips, Mike Dreslik, and Ben Jellen of the Illinois
Natural History Survey). We are currently working on several manuscripts
on various topics related to this project as well as continuing our
mark-recapture study.
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Road Mortality of Reptiles around Carlyle Lake, Illinois
