8 - Untangling a tangled web  pp. 221-260

Untangling a tangled web

By David H. Wise

Image View Previous Chapter Next Chapter



Introduction

Readers not yet weary of the metaphor may realize that the first six chapters have examined gentle pluckings of the spider's ecological web: field experiments designed to probe the strength of threads connected directly to neighboring actors in the ecological drama. Experimental evidence has been evaluated for food limitation and intraspecific competition, competition between spider species, limitation of spiders by natural enemies, and the impact of spiders upon their prey populations. Most of these interactions yield what conventionally are termed direct effects, though exploitative competition is actually an indirect interaction mediated through impacts on shared prey populations. The last chapter expanded the scope by examining how other components of the environment influence the biotic interactions that have formed the threads of the metaphor. Now it is time to probe consequences of persistent plucking and poking of more-distant regions of the web. What do field experiments reveal about the larger set of connections, links between spiders and other taxa of predators, and organisms on trophic levels several energy-transfer steps away? In short, what do field experiments reveal about indirect effects in complex communities of which spiders are an integral part?

Indirect effects in a simple system

What community could be simpler than two spider species and their prey? David Spiller uncovered both exploitative competition for prey and interference competition in the ecological web comprised of the orb weavers Metepeira grinnelli and Cyclosa turbinata and their prey in a salt marsh (Spiller 1984a,b; Chaps. 4,5).