Global Change Biology: The influence of global warming

November 30, 2015

­­­­­Paleontologists report that our planet has experienced five mass extinctions. By most accounts we are living through one more (the subject of last year’s Pulitzer-prize winning The Sixth Extinction, by Elizabeth Kolbert).  With species estimated to be disappearing perhaps 1000 times faster than prior to the arrival of man, the Yale Climate and Energy Institute sponsors talks next week by scientists seeking to understand how global forces like habitat fragmentation and climate change interact to remake life on Earth.

YCEI postdoctoral researcher Marta Jarzyna, a quantitative ecologist, speaks on Monday about changes in avian biodiversity across space and time.  Another ecologist, former YCEI postdoc Adam Rosenblatt, speaks the next day about predator-prey relationships in old field systems, how they respond to stress, and how those responses impact the carbon cycle. Both researchers’ efforts suggest that biologists are shifting their focus from individual species to community- or ecosystem-based studies, with special attention to the functional traits of organisms that contribute to their success or failure.

There is urgency around these questions. A study Jarzyna published in 2015 in Global Change Biology found high turnover in community composition across the 1980 - 2005, time period.  What fate had disappeared species suffered, what had been the cause and what management solutions are indicated to manage threats? 

Answering those questions involves investigating traditional concerns of biologists – about species dispersal, preferred niche habitats, morphological traits and foraging habits – in the context of global change to tell a bigger story.

Consider the thermal tolerances of individual bird species, Jarzyna suggests.  As temperatures in their preferred habitat increase, how do they respond?  Latitudinal or altitudinal migration to cooler latitudes or elevation is one option, but what species must they interact with in the process? Moving ranges might also be impeded by land cover and other landscape characteristics. And what are the consequences for migratory birds that arrive at their summer feeding grounds only to discover that the insects they customarily feed on have hatched early? 

The search for general principles that describe how individual species respond to such challenges drives another trend in biological study: an emphasis on functional traits. Thicker tree bark for added fire protection, heavier seed coatings that resist drought, stronger bills for birds to crack those seeds are examples of adaptive characteristics that confer advantages to different species confronting similar circumstances.  The first trait database for birds and mammals published in 2014 created new opportunities to compare relative threats, adaptive responses, and potential management solutions across biomes.[1]

What Jarzyna finds in that data base, and the precursor data sets she has assembled from Audubon Society Christmas Bird Counts and U.S. government breeding bird surveys, will not comfort bird watchers: though species which have successfully adapted to human civilization and species in fragmented landscapes fare better than species in undisturbed habitat, the difference appears to be only short-term; in the longer-run they are likely to be just as subject to changing climatic conditions.

[1] Wilman, H., Belmaker, J., Simpson, J., de la Rosa, C., Rivadeneira, M.M., and Jetz, W. (2014) EltonTraits 1.0: Species-level foraging attributes of the world’s birds and mammals. Ecology 95, 2027-2027.