My research program is focused on understanding the mechanisms underlying species distributions and applying this knowledge to predict the impacts of environmental change on biodiversity. I work in both tropical and temperate ecosystems and take advantage of the natural changes found along elevational gradients to address my research questions.


Fig 1. Tolerance breadth of beetles by realized seasonality. Symbol colors represent species from the dung beetle tribes Phanaeini (black), Dichotomini (gray), Canthonini (white) and carrion beetles in the genus Nicrophorus (hatched). Shapes represent beetles from Ecuador (squares), Costa Rica (diamonds), Argentina (triangles) and USA (circles).

Seasonality, thermal physiology and range size

In previous work, I explored the impact of seasonality in temperature on the physiology and range size of tropical and temperate dung and carrion beetles. Specifically, I trapped beetles along broad elevational gradients in Ecuador, Argentina, Costa Rica, and the US to understand diversity patterns. I then tested the thermal tolerance of beetles across four closely-related groups to understand the processes behind the patterns I observed. I demonstrated that both thermal tolerance (Fig. 1) and elevational range size increased with seasonality across all four beetle groups, but realized seasonality – the temperature variation restricted to the months each species is active – was a better predictor of both thermal tolerance and range size than was annual seasonality (Sheldon & Tewksbury 2014). My results support a more mechanistic framework linking variation in realized temperature to evolutionary history, physiology, and distributions.

Climate change across latitude

A major component of my research has been applying a mechanistic understanding of species distributions to help us predict the impacts of climate change on biodiversity. In one study, collaborators and I created a model simulating range shifts in response to climate change for diverse groups of endotherms (birds and mammals) and ectotherms (dung beetles, frogs, lizards and snakes) from tropical and temperate regions (Sheldon et al. 2011). Our model explicitly integrated geographic patterns of projected warming with geographic variation in elevational range size. Because our model relied on empirical data of elevational range size for a variety of taxa, we were able to compare differences among taxa as well as differences within taxa across latitude to create a global projection of the impacts of climate change. We found that, due to smaller elevational ranges at low latitudes tropical communities appear to be more sensitive to temperature increases compared with temperate communities. In addition, we found greater change in communities for ectotherms compared to endotherms. Our work was highlighted in the Editors’ Choice section of Science Magazine (25 November 2011:1033).

Southern Masked-weaver building a nest, South Africa.

Natural History

Natural history is the cornerstone of ecology, and thus, it is an integral part of my work. I have published on patterns of seed rain in tropical forests and the breeding biology of birds and butterflies. I am currently working on a paper describing phenological patterns of tropical epiphytes. I support natural history work as a member of both the Yanayacu Natural History Research Group and the Natural History Network.

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