Information Technology Reference
In-Depth Information
previous work in the eld of ecological networks. We will instead rst briey discuss
the state of the eld, emphasizing eorts and conclusions in understanding the
systems' structural properties. We then discuss examples of investigations of the
networks' dynamics, followed by what we believe to be some of the most exciting
unanswered questions regarding the dynamic behavior, both for the near and far
term.
14.2. Food Webs
The tremendous diversity of ecosystems around the globe is apparent to even the
most casual of observers. These ecosystems can dier in the population, sizes, and
type of species present, the type of environment, the assembly history, and the rate
of change. This diversity poses a very real challenge to the development of a general
understanding of community dynamics.
Food webs are a description of who eats whom in an ecosystem [Sugihara (1984);
Cohen et al. (1990)]. The food webs reported in the literature appear increasingly
complex [Cohen et al. (1990); Pimm (2002); Pascual and Dunne (2006)]. Under-
standing the structure of food webs is of great importance because it provides in-
sights into, for example, how ecosystems behave under perturbations [Berlow (1999);
Chapin et al. (2000); McCann (2000)].
14.2.1. The structure of food webs
Recent research on the structure of food webs has lead to a solution to the problem
of developing a general understanding: there exist a number of universal features
that hold for a large number of empirical food webs [Camacho et al. (2002); Dunne
et al. (2002b); Cohen et al. (2003); Bascompte and Melian (2005); Stouer et al.
(2005); Pascual and Dunne (2006); Stouer et al. (2006); Camacho et al. (2007);
Stouer et al. (2007); Allesina et al. (2008); Dunne et al. (2008); Petchey et al.
(2008); Williams and Martinez (2008)]. These quantitative patterns describe the
most highly-resolved empirical food webs available in the literature (Fig. 14.1).
The most remarkable aspect of this result is that there were no a priori reasons to
believe that the food webs studied have anything in common; in fact, the food webs
studied have dierent sizes (ranging from 25 to 155 species), the species themselves
are dierent, the empirical data was collected by dierent investigators, and they
come from a variety of environments located across the globe | lakes, streams,
deserts, rain forests, estuaries, bays, and islands.
Relying upon this \universality" found in food webs, scientists have begun to
reach a consensus on their static structural characteristics [Pascual and Dunne
(2006); Williams and Martinez (2008); Allesina et al. (2008)]. These universal pat-
terns demonstrate that there may indeed be fundamental principles which act as
the determinants of food-web structure. Reinforcing this conclusion is a study by
Dunne et al. (2008) which demonstrated that Cambrian food webs also exhibit the
