On nestedness in ecological networks
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2010-01-01
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Abstract
Questions: Are interaction patterns in species interaction networks different from what one expects by chance alone? In particular, are these networks nested - a pattern where resources taken by more specialized consumers form a proper subset of those taken by more generalized consumers? Organisms: Fifty-nine and 42 networks of mutualistic and host-parasitoid interactions, respectively. Analytical methods: For each network, the observed degree of nestedness is compared with the distribution of nestedness values derived from a collection of 1000 random networks. Those networks with nestedness values lower than 95% of all random values are considered 'unusually nested'. The analysis considers two different metrics of nestedness and five different network randomization algorithms, each of which differs in the ecological assumptions imposed. Results: Most ecological networks are unusually nested when compared with loosely constrained random networks. Comparisons with highly constrained networks temper these findings, but we still report a significant preponderance of nested networks (typically those with the most species). Conclusions: Bascompte et al. (2003) previously showed most observed mutualistic networks to be unusually nested. Later work using more ecologically realistic randomization algorithms cast doubt on those results. Across the largest set of species interactions considered to date, we conclude that an unexpectedly large number of interaction networks are patterned in a non-random manner. © 2010 Stuart L. Pimm.
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Stuart L. Pimm
Stuart Pimm is a world leader in the study of present-day extinctions and what can be done to prevent them. His research covers the reasons why species become extinct, how fast they do so, the global patterns of habitat loss and species extinction and, importantly, the management consequences of this research. Pimm received his BSc degree from Oxford University in 1971 and his Ph.D. from New Mexico State University in 1974. Pimm is the author of over 350 scientific papers and five books. He is one of the most highly cited environmental scientists. Pimm wrote the highly acclaimed assessment of the human impact to the planet: The World According to Pimm: a Scientist Audits the Earth in 2001. His commitment to the interface between science and policy has led to his testimony to both House and Senate Committees on the re-authorization of the Endangered Species Act. He was worked and taught in Africa for nearly 30 years on elephants, most recently lions — through National Geographic’s Big Cats Initiative — but always on topics that relate to the conservation of wildlife and the ecosystems on which they depend. Other research areas include the Everglades of Florida and tropical forests in South America, especially the Atlantic Coast forest of Brazil and the northern Andes — two of the world's "hotspots" for threatened species. His international honours include the Tyler Prize for Environmental Achievement (2010), the Dr. A.H. Heineken Prize for Environmental Sciences from the Royal Netherlands Academy of Arts and Sciences (2006), the Society for Conservation Biology’s Edward T. LaRoe III Memorial Award (2006), and the Marsh Award for Conservation Biology, from the Marsh Christian Trust (awarded by the Zoological Society of London in 2004). Sigma Xi, The Scientific Research Society, awarded him the William Proctor Prize for Scientific Achievement in 2007. In 2019, he won the International Cosmos Prize, which recognised his founding and directing Saving Nature, www.savingnature.org, a non-profit that uses donations for carbon emissions offsets to fund local conservation groups in areas of exceptional tropical biodiversity to restore their degraded lands.
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