Richard J. Williams

Learn More
Jennifer A. Dunne,* Richard J. Williams and Neo D. Martinez Romberg Tiburon Center, San Francisco State University, Tiburon, CA 94920, USA Santa Fe Institute, Santa Fe, NM 87501, USA *Correspondence: E-mail: Abstract Food-web structure mediates dramatic effects of biodiversity loss including secondary and ‘cascading’ extinctions. We studied(More)
Networks from a wide range of physical, biological, and social systems have been recently described as "small-world" and "scale-free." However, studies disagree whether ecological networks called food webs possess the characteristic path lengths, clustering coefficients, and degree distributions required for membership in these classes of networks. Our(More)
Classic local stability theory predicts that complex ecological networks are unstable and are unlikely to persist despite empiricists' abundant documentation of such complexity in nature. This contradiction has puzzled biologists for decades. While some have explored how stability may be achieved in small modules of a few interacting species, rigorous(More)
It has been suggested that differences in body size between consumer and resource species may have important implications for interaction strengths, population dynamics, and eventually food web structure, function, and evolution. Still, the general distribution of consumer-'resource body-size ratios in real ecosystems, and whether they vary systematically(More)
Water samples were collected in spring, summer, and winter from English rivers in urban/industrial (River Aire and River Calder, Yorkshire, UK) and rural environments (River Thames, Oxfordshire, UK) to study the biodegradation potential of the key steroid estrogen 17beta-estradiol (E2) and its synthetic derivate ethinylestradiol (EE2). Microorganisms in the(More)
Previous studies suggest that food-web theory has yet to account for major differences between marine food webs and the trophic structure of other ecosystems. We examined this issue by analyzing the structure of food webs for Benguela (South Africa), a Caribbean reef, and the Northeast US shelf with 29, 50, and 81 taxa, respectively. Marine webs tend to(More)
While trophic levels have found broad application throughout ecology, they are also in much contention on analytical and empirical grounds. Here, we use a new generation of data and theory to examine long-standing questions about trophic-level limits and degrees of omnivory. The data include food webs of the Chesapeake Bay, U.S.A., the island of Saint(More)
1. Following the development of the relatively successful niche model, several other simple structural food web models have been proposed. These models predict the detailed structure of complex food webs given only two input parameters, the numbers of species and the number of feeding links among them. 2. The models claim different degrees of success but(More)
To predict sewage influent and effluent concentrations of the steroid estrogens 17beta-estradiol, estrone, and 17alpha-ethinylestradiol, a review of human excretion was carried out. This included conjugation and metabolism of the natural and synthetic steroid estrogens within the body, together with quantities excreted in the urine and feces by different(More)