SCALE AND FOOD-WEB STRUCTURE - FROM LOCAL TO GLOBAL

A central question in food-web research focuses on the relation between species at different trophic levels and ''scale'' or, in more specific terms, the number of species in food webs. We show that recently advanced scale-dependence hypotheses are consistent with independent data and assumptions connecting properties of the smallest food webs with those of the largest. Consistent with scale dependence, these data and assumptions suggest that mean chain length and the fractions of species at top, intermediate, and basal trophic levels depend on the number of species within ''local'' (i.e., small-scaled) webs with 2 to 10(2) species. Our analysis also suggests that the fractions of species in different trophic levels become asymptotically stable for regionally to globally scaled food webs with 10(4) to 10(7) species, respectively. A new hypothesis for the behavior of mean chain length in regional to global webs is also advanced. Our analyses specify for the first time specific functional forms for the effects of scare on food-web structure that take into account recently demonstrated scale dependencies at the local scale as well as estimates of biodiversity at regional and global scales. Rates of change over specific ranges are described as well as numerical estimates of asymptotes.