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Science 22 July 2005:
Vol. 309. no. 5734, p. 532
DOI: 10.1126/science.309.5734.532h
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This Week in Science

An evaluation by Ceballos et al. (p. 603; see the news story by Stokstad) of global conservation priorities and conflicts for an entire animal group, the land mammals, shows that at least 15% of Earth's land surface is needed for the conservation of 10% of the geographic ranges of the great majority of mammal species. A variety of approaches to conservation will be necessary in different areas and for different taxa, ranging from protected reserves to management of human-dominated landscapes. How is animal population size regulated? Sibly et al. (p. 607; see the Perspective by Reynolds and Freckleton) analyze population time series from 1780 data sets that cover four of the major taxonomic groups of animals. Most populations do not grow exponentially to carrying capacity, as previously assumed. Instead, growth rate is strongly adjusted by density-dependent factors and slows long before carrying capacity is achieved. Despite the differences in evolutionary history, metabolism, and body size, species in all four groups generally show strong density dependence at low population levels that falls off at high population levels.




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Science. ISSN 0036-8075 (print), 1095-9203 (online)