In today’s Academic Minute, Dr. Gareth Russell of the New Jersey Institute of Technology reassesses the number of endangered tropical bird species.
Gareth Russell is an associate professor of biological sciences at the New Jersey Institute of Technology where his research seeks to understand how complex ecological systems work. His lab applies information-based statistics to ecology and employs Bayesian methods to estimating survivorship and related curves.
Dr. Gareth Russell – Habitat and Endangered Birds
Human activities result in many species seeing their habitat — the special environment they live in — reduced to a fraction of its former extent. This is a problem on its own, but is made worse when remaining habitat is scattered in isolated fragments. A species' survival depends on the sizes of these fragments, and on whether individuals can move between them, that is, on their separation. Ecologists bring these ideas together mathematically in metapopulation theory, but this theory has not been used when identifying species at risk of extinction. This is despite that fact that habitat fragmentation is acknowledged to be a risk factor.
One reason is that to apply the theory to the real world, we must map out all the fragments. This used to be difficult, but advances in remote sensing technology mean that much of the globe is now well mapped, and patches of different habitat easy to identify. We are in a position to upgrade our methods. To demonstrate this, we applied metapopulation theory to 127 forest-dwelling bird species living in the Atlantic Forest of Brazil, a 1600-mile strip of once-forested coastal mountains centered on Rio de Janeiro. The forest now covers less than ten percent of its former area, in thousands of fragments. These are, famously, rich in endemic bird species — those found there and nowhere else. Many of the species are already listed as being in danger of extinction, but we wanted to see what the new method would say.
From the distribution of remaining habitat for each species, we calculated a number called metapopulation capacity. The vast majority of species had either very small, or quite large, metapopulation capacity, creating a straightforward link between fragmentation and extinction risk. But while the small-capacity group does contain most of the species already listed as at risk, almost exactly half of the group are currently deemed not at risk, even though they have similarly reduced and fragmented habitat. We believe that these species need to be reevaluated. More generally, we show that extinction risk assessment can be made more quantitative and consistent by adapting existing mathematical models to modern and widely available environmental mapping technology.