Greg Laden's Blog

Food webs --- the network of trophic (eating) interaction among the many species sharing a habitat or biome -- is a much studied aspect of ecology. Food web and other similar phenomena such as dispersal syndromes are epiphenomena of evolution, resulting from the negotiation of competitive and cooperative interactions among many individuals. Indeed, the food web is the gross-level movement of energy within the ebb and flow of entropy and life-based energy capture. This flow of energy is fundamental to all life systems.

The delicacy or vulnerability of a particular habitat ... the potential susceptibility or resistance to perturbation ... may depend on the details of this network of interactions. If everything ultimately depends on a basal food type that goes extinct, for example, there could be big trouble.

So, just as understanding any aspect of life requires that we examine historically ancient, no longer extant systems, we need to understand ancient food webs. But, a valid study of food webs requires a certain level of detail that is often absent from the data available for ancient systems.

Moments ago, a study of Cambrian food webs came out in PLoS Biology.

From the Author's Summary:

Food webs ... display many regularities in their structure. For example, the distributions of links to prey and links from predators, the percentages of omnivores and herbivores, and the mean trophic level of species change systematically with the number of taxa and feeding links in a web. Such ''scale-dependent'' regularities are formalized by network models based on a few simple ... rules that successfully predict the network structure of complex food webs from a variety of habitats. To explore how long such regularities may have persisted, we compiled and analyzed detailed food-web data for two ancient fossil assemblages from the early Paleozoic, when rapid diversification of multicellular species, body plans, and trophic roles occurred. Our analyses show that for most aspects of network structure, the Early Cambrian Chengjiang Shale and Middle Cambrian Burgess Shale food webs are very similar to modern webs. This suggests that there are strong and enduring constraints on the organization of feeding interactions in ecosystems. However, a few differences, particularly in the Chengjiang Shale web, suggest that some aspects of network structure were still in flux during early phases of de novo ecosystem construction.

In this depiction of the food web of the Burgess Shale from the Middle Cambrian, spheres represent species or groups of species, and the links between them show feeding relationships. The drawing shows a top predator, Anomalocaris, chasing one of its likely prey species, the trilobite Olenoides, with arrows indicating their positions in the food web. Many aspects of the structure of this ancient ecological network are similar to the architecture of modern food webs. (Image: N. D. Martinez. Food-web produced with Network3D software written by R. J. Williams; contact ricw@microsoft.com for more details. Drawings courtesy of Sam Gon III, http://www.trilobites.info.)

The paper can be downloaded here.

Dune, J.A., Williams, R.D., Martinez, N.D., Erwin, D.h., , . (2008). Compilation and Network Analyses of Cambrian Food Webs. PLoS Biology, 6(4), 0001-0016.