Research

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Global change and bird distributions in North America

I examine how birds respond to changing vegetation and climate in California and across North America. So far, a key result is that phenological shifts conserve thermal niches in North American birds and reshape expectations for climate-driven range shifts (see news coverage from the New York Times, NPR, Mother Jones, Audubon Magazine, etc). Ongoing projects include a close look at the reorganization of species co-occurrence networks in response to global change, weather effects on bird demography, and an NSF-funded project to understand how climate change impacts the three-level tropic system of trees, caterpillars, and birds using macro-scale North American datasets.

Biodiversity conservation in Peruvian Amazonia and beyond

Deforest White-sandsAs roadbuilding and hydrocarbons development penetrate the western Amazon, rural agriculture often follows. We know very little about the consequences of this process for biodiversity. Therefore, I spent several years surveying birds in slash-and-burn agricultural mosaics near Iquitos, Peru. I show that western Amazonian bird communities are unusually sensitive to agricultural disturbance, and this sensitivity might be predictably related to their extraordinary species richness. I also show that across the neotropics, primary forest bird surveys are consistently biased against sampling the most disturbance-sensitive species in the local species pool. As a consequence, existing studies are likely to overestimate the biodiversity value of disturbed habitats.

Amazonian bird distributions

Landsat of Iquitos 
In the Amazon, dramatic differences in soils and flooding regimes create a highly heterogeneous mosaic of forest types, and nobody understands this better than numerous birds that specialize on particular forest habitats. To understand how differences in vegetation structure, floristics, and flooding regime structure bird communities, I use anthropogenic disturbance as a natural experiment to decouple vegetation formations from the underlying abiotic world. Preliminarily, I have found a dominant role for vegetation structure in governing specialization, and a major role for productivity in determining local species richness.

Stochastic community dynamics

Stochastic community trajectories Ecologists often use ordinary differential equations (ODEs) to understand community dynamics, but real populations fluctuate stochastically. The nature of these fluctuations matters crucially to population dynamics and the maintenance of species diversity. In collaboration with Alex Washburne, I use a combination of simulation and empiricism to gain traction on stochastic community dynamics. Here’s the first paper to result from this line of inquiry.

Quantitative techniques for handling bird survey data

Occupancy modeling is a powerful statistical method for making inference on species distributions despite the possibility of false absences in biodiversity survey data. However, these models are sensitive to a variety of assumptions that may be violated in nature, and our tools to assess the adequacy and fit of these models (particularly hierarchical community occupancy models with species-specific random effects) remain poorly developed. I use simulations to understand how assumption violations might pose serious problems for inference, and to develop robust methods to determine when this is likely to be happening.