Parasites reduce food web robustness because they are sensitive to secondary extinction as illustrated by an invasive estuarine snail

Kevin D Lafferty,Armand M Kuris

doi:10.1098/rstb.2008.0220

Abstract

A robust food web is one in which few secondary extinctions occur after removing species. We investigated how parasites affected the robustness of the Carpinteria Salt Marsh food web by conducting random species removals and a hypothetical, but plausible, species invasion. Parasites were much more likely than free-living species to suffer secondary extinctions following the removal of a free-living species from the food web. For this reason, the food web was less robust with the inclusion of parasites. Removal of the horn snail, Cerithidea californica, resulted in a disproportionate number of secondary parasite extinctions. The exotic Japanese mud snail, Batillaria attramentaria, is the ecological analogue of the native California horn snail and can completely replace it following invasion. Owing to the similarities between the two snail species, the invasion had no effect on predator–prey interactions. However, because the native snail is host for 17 host-specific parasites, and the invader is host to only one, comparison of a food web that includes parasites showed significant effects of invasion on the native community. The hypothetical invasion also significantly reduced the connectance of the web because the loss of 17 native trematode species eliminated many links.

Highlights

One way to measure the stability of a network, such as the Internet, is to simulate how the network responds to the addition or removal of nodes (Albert et al 2000)
Because the loss of one host species, the California horn snail, Cerithidea californica, led to a disproportionate number of secondary parasite species extinctions, we investigated a plausible scenario for the extirpation of the California horn snail from the Carpinteria Salt Marsh (CSM)
Three trematode species were sensitive to secondary extinctions because they depended on a single host species at two stages of their life cycle

Summary

Introduction

One way to measure the stability of a network, such as the Internet, is to simulate how the network responds to the addition or removal of nodes (Albert et al 2000). In food webs, removing all of a consumer’s resources will lead to its indirect extinction Such secondary extinctions are more likely to result from the extirpation of highly connected resource species, especially prey species that have many predators (Sole & Montoya 2001; Allesina & Bodini 2004; Quince et al 2005). The Carpinteria Salt Marsh (CSM) estuary food web (Lafferty et al 2006b) is a topological web that, similar to most other food webs, depicts links between predators and prey (87 free-living species). This food web is expandable to include 47 parasite species at CSM, making it currently the food web with the most complete inclusion of parasites.

Methods

Results

Conclusion