Research

Human impacts on evolutionIMG_4519

Humans are massively restructuring the ecological order of planet Earth. How organisms respond to these rapid anthropogenic changes can help illuminate basic principles regarding how species adapt, or were fortuitously pre-adapted, to novel environments, and give some hints for how humans might stem the biodiversity crisis of the 21st century. My work currently focuses primarily on pre-adaptation to human impacts, and how this filters biological communities living in human dominated landscapes. This research act as a jumping off point to begin to assess ongoing adaptation to anthropogenic impacts (assuming that ongoing adaptation will follow along similar lines as fortuitous pre-adaption).

Why do species survive after habitat conversion?

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Craugastor fitzingeri perched on a bromeliad

As a result of anthropogenic change many species go locally extinct, whereas others benefit tremendously. Many studies document which species die out, and which prosper, but relatively few attempt to seek ecological mechanisms for why they do so. To address these questions I’ve assessed what traits and niche axes are relevant for amphibians, reptiles, and birds to survive post deforestation in the tropics.

To delve into the deep mechanics of survival after habitat conversion I’ve focused in on a pair of closely related neotropical leaf litter frogs in the genus Craugastor that show alternative habitat affinities in mid-elevation southern Costa Rica (based out of the OTS Las Cruces field station); Craugastor crassidigitus is restricted to forest habitat, while Craugastor fitzingeri is found exclusively in open pastures, coffee plantations, urban areas, and very young secondary forest. I’ve honed in on temperature differences between these habitats as the primary driver explain the difference in habitat affiliation between these species. By comparing how temperature structures occupancy and performance ability at multiple spatial scales, from the regional to the individual I demonstrate how evolutionarily novel human interventions in a landscape (i.e. deforestation) interact with species’ temperature affinity to grant some species a preadaptive advantage in human dominated areas.

Community phylogenetics of human-dominated landscapes

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As habitats are converted species that survive may be only represent particular branches of the tree of life. To explore these patterns I delved into a 12 year dataset of Costa Rican birds in neotropical agriculture. The amazing thing about this long term dataset is that we actually could watch temporal dynamics, showing that agriculture unduly favored evolutionarily young species which persisted from year to year in agriculture, and were relatively easily able to recolonize agriculture if they did go extinct. In contrast more ancient species, with few living relatives are quickly extirpated in agriculture, and have a great deal of trouble colonizing these types of habitats. Never-the-less farms with greater vegetative complexity (diversified agriculture) far out performed more industrialized, monoculture farms. Even though the number of species in forest and diversified agriculture is the same (~70 on average), agriculture always decreased representation from across the tree of life (e.g. a loss of 300 million years of unique evolutionary history in converting a forest to diversified agriculture). Yet this loss pails in comparison with the loss incurred by monocultures (a whopping 900 million year loss when compared to forest). Read the study here. I’m currently investigating whether this phenomenon is restricted to birds, or whether reptiles, amphibians, and mammals display similar trends in complex, human-dominated landscapes.

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