P. regilla silhouette
Dr. Michael Benard




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Research overview

The goal of my research is to understand how species and populations adapt to and persist in the face of environmental variation. I conduct most of my research on this topic with amphibians. Amphibians are an excellent system in which to investigate these questions. During their larval stage, amphibians may experience a broad range of environmental conditions (e.g., different types of predators, different rates of pond drying). Tadpole traits that confer an advantage in one environmental condition (e.g., high activity improves food intake) may be disadvantageous in another condition (e.g., high activity increases predation risk). This raises the question of how quickly these traits can evolve, and whether evolution of these traits affects the probablity of local extinction. With amphibian larvae, we can study these traits in laboratory, mesocosm, and natural settings. The results of these experiments can be used to build specific models, which can then be tested against long-term field data. The development and testing of these models will improve not only our understanding of basic ecological and evolutionary processes, but will also provide valuable insights into methods for protecting amphibian populations. Developing conservation strategies for amphibians is particularly important, given the alarming rate of global amphibian decline.

Primary Research Areas
1: What causes individual variation in phenotype?

Amphibians exhibit substantial phenotypic plasticity; a single genotype can produce different phenotypes in response to variation in environmental conditions. For instance, I have shown that Pacific Chorus Frogs (Pseudacris regilla) larvae will develop into tadpoles with deep tails when exposed to chemical cues from predatory insects, shallow tails when exposed to chemical cues from predatory fish, and intermediate-depth tails in the absence of chemical cues from predators (Benard 2006 Ecology). In addition to changes in tadpole shape, many amphibians will alter the age and size at which they metamorphose in response to predation risk during the larval stage (Benard 2004 Annual Review of Ecology, Evolution and Systematics). The effects of predation risk in the larval stage can also carry past metamorphosis; Jim Fordyce and I showed that post-metamorphic western toads produced threefold-larger amounts of toxins when they were raised in the presence of predator cues as tadpoles, than western toads raised in the absence of predator cues (Benard and Fordyce 2003 Ecology). Intraspecific phenotypic variation in amphibians is not solely due to phenotypic plasticity. For instance, different families of pacific chorus frogs differ in the extent to which they alter their tail shape in response to cues from different types of predators (Benard, unpublished data).

2: How does natural selection act on phenotypic variation across different environments?

I use laboratory, mesocosm, and field data to study the direction and magnitude of natural selection on phenotypic variation in different environments. For instance, in a series of short-term laboratory trials, I showed that tadpoles with shallow tails were more easily captured by predatory beetles than tadpoles with deep tails. In contrast, tadpoles with deep tails were more easily captured by predatory fish than tadpoles with shallow tails (Benard 2006 Ecology). The existence of this trade-off in survival ability across environments with different predator types provides an explanation for the evolution of predator-specific phenotypic plasticity of tadpole tail shape.

To investigate the strength of natural selection in the wild, I conducted a five-year study of growth and survival in Pacific Chorus frogs (Benard, in review). I found that within a population, there was a strong effect of size at metamorphosis on survival and time to reproduction. Larger metamorphs were more likely to survive than smaller metamorphs. By quantifying the strength of selection, I demonstrated that selection was strong enough to cause a detectable change in size at metamophosis in only a few generations. I also found patterns of conflicting selection on adult frog size (Benard 2007 Journal of Herpetology): larger male pacific treefrogs were more likely to successfuly mate than small frogs, but the large frogs were also more likely to be killed and eaten by predators! Such conflicting directions of natural selection may explain why some traits do not continually evolve in one direction.

3: Does phenotypic variation affect rapidly occurring ecological processes?

One of the major goals of my research program is to determine how changes in the distribution of phenotypes in a population affect population growth rate, dispersal patterns, and ultimately extinction risk. There is good indirect evidence that this is the case. For instance, in a meta-analysis, we found that about half the effects of a predator on prey populations came from trait-mediated indirect effects (Preisser, Bolnick, and Benard 2005 Ecology). There is also good evidence that phenotypic variation affects population-level processes through its effect on dispersal rates (Benard and McCauley 2008 The American Naturalist). I am investigating the importance of phenotypic variation in these processes through a combination of experiments and long-term mark-recapture studies.

Additional Research Interests

In addition to the work described above, I am broadly interested in problems in ecology, evolution, behavior and conservation. As a consequence, I have been involved in research on agricultural land use and reptile diversity (Glor, Flecker, Benard and Power 2001 Biodiversity and Conservation), pesticide exposure and infection risk in amphibians (Davidson, Benard, Shaffer, Parker, O'Leary, Conlon and Rollins-Smith 2007 Environmental Science and Technology), lizard behavior (Hews and Benard 2001 Ethology), and mechanisms of speciation in fish (Near and Benard 2004 Evolution).