Proceedings of the Royal Society of London B (http://dx.doi.org/10.1098/rspb.2009.0413)
ROBERT R. DUNN (1), NYEEMA C. HARRIS (1), ROBERT K. COLWELL (2), LIAN PIN KOH (3),
NAVJOT S. SODHI (4,5)
1Department of Biology, North Carolina State University, Raleigh, NC 27607, USA, 2Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, CT 06269-3043, USA, 3Institute of Terrestrial Ecosystems, ETH Zu¨ rich, CHN G74.2, Universitatstrasse 16, 8092 Zurich, Switzerland, 4Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore 117543, Republic of Singapore, 5Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, US
Author for media correspondence: Robert R. Dunn, Rob_Dunn "at" ncsu.edu
Scientists have been warning of an impending sixth mass extinction event for decades, but most of our efforts to understand extinctions and their dynamics have focused on charismatic groups of organisms (the big-eyed, warm and fuzzy species of the world). In a new paper we argue that the bulk of the global biodiversity at risk of extinction could be parasites and mutualists rather than charismatic flagship species like the panda or polar bear. The loss of a host species, such as a mammal, often leads to the loss of affiliated species that depend on this host for survival -- a phenomenon called ‘coextinction’. And since the diversity of affiliated species -- which may include viruses, ticks, lice and bacteria, and butterflies, but also mutualists such as the crops pollinated by honey bees or the bees themselves-- is several orders of magnitude greater than that of their hosts, the absolute numbers of co-extinctions are also expected to be far greater than the number of extinctions of host species. But why should we care? We argue that the loss of parasites and mutualists bears consequences just as great as those of the loss of their hosts, including the loss of biological diversity and diversification, co-evolutionary history, and unique species traits. But perhaps most worrisome of the consequences of coextinction is the possibility that declines in ‘natural’ host species could drive parasite species to switch onto alternative hosts, which would in turn escalate the rate of emerging pathogens and parasites both for humans and our domesticated animals and plants. Put simply, when a host becomes rare, its parasites and mutualists have two choices, jump ship to another host or go extinct. Either situation is a problem. We urge more research effort be invested to study the phenomenon of coextinction, which is both the least understood aspect of species loss and, we argue, most insidious threat to global biodiversity and human well-being (PDF).
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