How is global warming impacting montane organisms? 

Climate change is changing where species live, how they time events in their annual cycle, and how they interact with other species. We know a fair bit about climate change's impact on temperate zone environments (e.g. North America, Europe), but almost nothing for tropical species. This is unfortunate, as the vast majority of biodiversity is found in the tropics, and tropical species may respond differently to climate change than temperate species. Inspired by Jared Diamond's 1960s studies of New Guinean birds, my wife Alexandra Class Freeman and I recently resurveyed the avifaunas of two mountains originally surveyed by Diamond. We found that most bird species have moved rapidly upslope associated with warming temperatures, though we don't yet understand why some species have shifted far upslope while others have not. Finally, we combined our data with other recent studies to suggest that tropical species in general are 'strong responders' to global warming, more sensitive than temperate zone species to small temperature increases.

Alexandra and I enjoy a last minute of sunshine atop the summit of Mt. Karimui before navigating the treacherous trail (cleared the day before!) back down to our field camp

Alexandra and I enjoy a last minute of sunshine atop the summit of Mt. Karimui before navigating the treacherous trail (cleared the day before!) back down to our field camp

Why do montane species specialize on narrow elevational zones? 

One of the most obvious and interesting facets of species is that they do not live everywhere. Explaining why this is so -- the abiotic and biotic factors that limit species' distributions -- is a primary goal of ecologists and biogeographers. Interesting distributions occur everywhere, but I am particularly fascinated by the fact that tropical montane birds typically inhabit only a narrow elevational band. I find it astonishing that I can walk uphill through forest where a given species is absent, to forest where that species is abundant, and finally to forest that again lacks the species all in the course of 15 minutes of hard hiking. This despite the fact that the forest appears similar throughout (at least to my human eyes) and that it would be easy for birds to fly to upper or lower elevations. So why don't they? Is it a Goldilocks scenario where other places are too hot or too cold? Or perhaps birds live where their preferred food is most abundant? I am particularly interested in the hypothesis that biotic interactions such as relationships with predators and competitors limit the elevational distributions of tropical birds. I am currently exploring this hypothesis using a combination of approaches, including phylogenetic analyses and field competition experiments.

 

Steep and lush: Bird species generally inhabit narrow elevational zones on tropical mountains

Steep and lush: Bird species generally inhabit narrow elevational zones on tropical mountains

Natural history of poorly known birds

A stunning female Gold-ringed Tanager near her nest

A stunning female Gold-ringed Tanager near her nest

As a naturalist, I enjoy learning more about where species live, what they eat, how they interact with other species, how they attract mates and how they raise their babies. In short, what makes a species tick -- it's natural history. Ecology is built on understanding the natural history of organisms, and I have been fortunate to study the natural history (particularly breeding biology) of many tropical birds. For example, I found an active nest of the lovely Gold-ringed Tanager in Colombia's Choco cloud forests, and was able to document that multiple adults bring food to provision Gold-ringed Tanager nestlings -- this species is a cooperative breeder. Modern ecology is conducted in a hypothesis-testing framework, but both generating testable hypotheses and conducting comparative analyses rely on accurate and thorough natural history information. For example, global analyses of cooperative breeding currently suggest cooperative breeding to be rare in tropical birds. New natural history data for poorly known tropical birds may challenge this assumption, potentially altering the conclusions of hypothesis-testing analyses of the phylogenetic and environmental drivers of cooperative breeding.