What Is The Principal Cause Of The Present Extinction Spasm

Human activities are associated directly or indirectly with nearly every aspect of the current extinction spasm. The sheer magnitude of the human population has profound implications because of the demands placed on the environment. Population growth, which has increased so dramatically since industrialization, is connected to nearly every aspect of the current extinction event. Amphibians may be taken as a case study for terrestrial organisms. They have been severely impacted by habitat modification and destruction, which frequently has been accompanied by use of fertilizers and pesticides (Hayes et al., 2002). In addition, many other pollutants that have negative effects on amphibians are byproducts of human activities. Humans have been direct or indirect agents for the introduction of exotic organisms. Furthermore, with the expansion of human populations into

44 / David B. Wake and Vance T. Vredenburg new habitats, new infectious diseases have emerged that have real or potential consequences, not only for humans, but also for many other taxa, such as the case of Bd and amphibians (Cunningham et al., 2006). Perhaps the most profound impact is the human role in climate change, the effects of which may have been relatively small so far, but which will shortly be dramatic (e.g., in the sea) (Jackson, Chapter 1, this volume). Research building on the Global Amphibian Assessment database (SN Stuart et al., 2004) showed that many factors are contributing to the global extinctions and declines of amphibians in addition to disease. Extrinsic forces, such as global warming and increased climatic variability, are increasing the susceptibility of high-risk species (those with small geographic ranges, low fecundity, and specialized habitats) (Sodhi et al., 2008). Multiple factors acting synergistically are contributing to the loss of amphibians. But we can be sure that behind all of these activities is one weedy species, Homo sapiens, which has unwittingly achieved the ability to directly affect its own fate and that of most of the other species on this planet. It is an intelligent species that potentially has the capability of exercising necessary controls on the direction, speed, and intensity of factors related to the extinction crisis. Education and changes of political direction take time that we do not have, and political leadership to date has been ineffective largely because of so many competing, short-term demands. A primary message from the amphibians, other organisms, and environments, such as the oceans, is that little time remains to stave off mass extinctions, if it is possible at all.

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