Watercress and amphipods: a study of possible resource partitioning.

Abstract

Observations of a number of different species occupying the same habitat suggest that species often reduce interspecific competition by partitioning resources....There has been little research on resource partitioning at an intraspecific level. Therefore, we examined a plant-herbivore system for signs of resource partitioning due to intraspecific competition. In alkaline, spring-fed rivers and streams in northern North America, a generalist amphipod, Gammarus pseudolimnaeus, feeds on leaf litter, algae, and the leaves of watercress, Nasturtium officinale. ...Since dead, yellow leaves of Nasturtium have had most of the toxic chemicals leached out, Gammarus prefer them over the green leaves. We hypothesize that, because of size, and the quantitative nature of Nasturtium's defense chemicals, larger Gammarus will be able to tolerate ingesting green, more toxic leaves.a If we conclude that larger Gammarus are able to utilize the greener leaves, this will suggest that they are able to use a resource that is unavailable to the smaller Gammarus. This would consequently suggest that the Gammarus had partitioned their resources in order to reduce intraspecific competition.