My research falls under two categories:
1) Identifying mechanisms of species declines
2) Researching strategies to reduce future species declines

Mechanisms of species declines

Hybridization drives species declines by causing the genetic erosion of species. I have used surveys and mathematical models to elucidate the poorly understood mechanisms underlying the hybridization of previously reproductively isolated threespine stickleback fish species from Enos Lake, British Columbia, Canada.  In the past, strong selection against hybrids which are morphologically intermediate between the two parental species formed the basis of postmating reproductive isolation.

Measuring the morphology of stickelbacks using geometric morphometrics.

Measuring the morphology of sticklebacks using geometric morphometrics.

My work showed that following a major ecological change to the lake likely precipitated by the introduction of an invasive crayfish, this strong selection against hybrids was no longer functioning, and stickleback hybrids were present in high numbers (Behm et al. 2010).

In collaboration with theoretician, Tucker Gilman, we built a mathematical model investigating how ecological disturbances to premating isolating mechanisms can cause species declines due to hybridization in systems like the sticklebacks. We demonstrated that even weak ecological disturbances may result in hybridization and the permanent loss of the parental species (Gilman and Behm 2011).

Habitat Loss
For my dissertation, I was funded in part as a National Science Foundation Fellow with the ‘Biodiversity and Sustainable Development in Southwest China’ IGERT (Integrative Graduate Education Research and Traineeship) Program at the University of Wisconsin-Madison, and as a Fulbright Fellow.  I conducted my research in Xishuangbanna, Yunnan Province, China at the Xishuangbanna Tropical Botanic Garden in collaboration with Chen Jin and Yang Xiaodong.

Rubber plantation field experiment.

Rubber plantation field experiment.

Since the mid-1970s, two-thirds of the native lowland rainforests in Xishuangbanna have been converted to rubber tree plantations.  Because Xishuangbanna is part of the Indo-Burma biodiversity hotspot and a frog diversity hotspot within China, this land conversion has the potential to cause massive habitat loss for a large number of species.  I conducted a series of experiments and surveys to determine whether frogs were using rubber plantations as habitat.

I found that while several frog species did use rubber plantations for their adult habitat needs, no species bred there, despite the abundance of aquatic sites.  This means that because no species can complete their entire lifecycle in rubber plantations, rubber plantations do constitute habitat loss for the frog species in Xishuangbanna (Behm et al. 2013).

Left: Polypedates leucomystax communal nest; Right: normal sized single nest.

Left: Polypedates leucomystax communal nest; Right: normal sized single nest.

The frog species in Xishuangbanna have not been well-studied and as a result, we don’t know much about them.  Through my surveys with my student field assistants, I observed never-before documented natural history activities which resulted in several natural history notes.  For example, my assistants and I recorded group breeding activity in the treefrog Polypedates leucomystax (Behm et al. 2012). Usually, females oviposit single clutches of eggs, however, on several occasions we observed large communal nests.  These communal nests were observed during an especially dry rainy season, so its possible that forming communal clutches is a strategy to reduce desiccation of clutches.    

Invasive Species
In addition to the conversion of rainforests into rubber plantations, frogs in Xishuangbanna also have to cope with invasive tilapia fish which predate tadpoles in breeding pools.

Mesocosms used in experiments.

Mesocosms used in experiments.

I conducted a set of mesocosm experiments to determine whether three common tadpole species exhibited predator-induced phenotypic plasticity in response to invasive tilapia.

Left: Control tadpole not exposed to predators; Right: tadpole exposed to tilapia predators.  Exposure to tilapia results in longer and thicker tails relative to control.

Left: Control tadpole not exposed to predators; Right: tadpole exposed to tilapia predators. Exposure to tilapia results in longer and thicker tails relative to control.

Despite a lack of evolutionary history with tilapia, all three tadpole species exhibited phenotypic plasticity in traits following non-lethal exposure to tilapia predators.  However, for two of the tadpole species, plasticity in traits unexpectedly translated into decreased survival with tilapia during predation trials.  This means that plastic responses for these species may be maladaptive.

Competitive Interactions
The tadpoles in Xishuangbanna live in species-rich communities at high densities.  My student, Devin Edmonds, conducted an experiment to measure inter- and intraspecific competition among three common tadpole species. Upon analyzing the data, we realized the absence of a standard statistical framework for analyzing data from such experiments that have issues of non-independence (because two species are in one experimental unit) and heteroscedasticity. Therefore, I developed a statistical framework for extracting the data of interest (in this case strengths of inter- and intraspecific competition) from datasets that lack independence and have heteroscedasticity (Behm et al. 2013). My analyses showed that by not properly accounting for these issues, we would have made different ecological conclusions regarding the interactions between species.  I have since applied this framework to the analysis of data from an arbuscular mycorrhizal fungi competition experiment (Engelmoer et al. 2013).

Tadpoles in a pool at high density (gray patches are tadpoles, brown is the ground)

Tadpoles in a pool at high density – gray patches are tadpoles, brown is the ground. 

Diagram showing interactions among species that were extracted using the statistical framework.

Diagram showing interactions among species that can be extracted using the statistical framework.








Strategies to reduce future species declines

Biodiversity Footprinting
In a project funded in part by the Amsterdam Global Change Institute, I am collaborating with Roggebot Estate, a non-profit organization in the Netherlands, to construct a ‘biodiversity neutral’ conference center.  Similar to the idea of carbon neutral, the goal of biodiversity neutral is to have no net impact on biodiversity with respect to building materials used and systems involves in running the building (e.g., energy, water, waste).  The ultimate goal of the project is to develop a framework that can be used by other organizations with similar biodiversity neutral goals.