Vertebrate Ranging Scale and Tree Dynamics in a Congo Forest

Wildlife Conservation Society, Bronx NY

Investigators

Abstract

A central question in community ecology is how species diversity will typically respond to the removal of a one or a few species. Are species highly redundant so that the loss of one species is easily compensated for by other, functionally equivalent species? Or, do species tend to play unique functional roles so that the loss of one species can propagate out to cause a catastrophic loss of diversity. These questions assume ever greater practical importance as the global wave of extinctions accelerates. And, although some progress has been made in simple model systems, we still have a vague understanding of more complex communities with dynamics that evolve over large temporal and spatial scales. It is not clear whether anthropogenically induced extinction of individual species will generally cascade across these communities. Most notably, we have little ability to predict how the mounting loss of the largest mammals to hunting is likely to affect diversity in tropical forests, which are home to a large proportion of the world's species. The primary focus of this study will be the collection of empirical data linking the ranging behavior of terrestrial mammals to tree species diversity in a Congo forest. The study site typifies tropical forests worldwide in that its mammals act both as seed dispersers for a species rich guild of spatially rare trees and seed predators of a species poor guild of spatially aggregated trees. Even though mammals of many body sizes disperse and predate the same tree species, they may not be functionally redundant because mammalian body size is highly correlated with ranging scale. Thus, large mammals are particularly mobile seed predators that are drawn to dense stands of the species poor guild from great distances. Large mammals also tend to disperse seeds over a great area, which provides a number of benefits to mutualists in the species rich tree guild, including escape from predators & pathogens. Consequently, local extinction of large mammals may well tip the competitive balance between guilds, triggering a loss of diversity in the species rich tree guild that propagates out through a myriad of dependent plants and animals, including smaller mammalian seed dispersers. This project will include both animal and vegetation studies and use a combination of ground and remote sensing methods. Aerial video and satellite imagery at several resolutions will be used to develop detailed maps of the distribution of the two tree guilds over a large scale. Line transect methods will then be used to quantify how the spatial grain of mixing between the two tree guilds influences both fruit availability and the spatial distribution of mammals varying in body size from mice to elephants. Trapping studies on rodents, the first GPS telemetry study on several duiker species, and the first telemetry study of any kind on red river hogs will quantify how body size influences the spatio-temporal pattern of fruit availability within an animal's home range. And an attempt will be made to identify a set of individual tree species using high-resolution digital photography and aerial videography. If this proves successful, it will allow the first large- scale scale study of tropical tree distribution and phenology. The empirical data collected in the study will be used to parameterize coupled, spatially explicit models of animal ranging and vegetation dynamics with the goal of predicting how large mammal extirpation is likely to affect tree species diversity. In addition to addressing basic theoretical issues, data collected in this project will be of direct value to wildlife management, both guiding management at the study site and informing park planning and sustainable hunting programs across the region. Remote sensing methodologies developed in this project will also provide the tools for studying how the wave of logging currently sweeping Central Africa is likely to affect tree species diversity. And African personnel trained and employed in the study will bolster feeble research and management capacity in the region.