Interactive Effects of Disturbance, Productivity, and Consumer Diversity on the Structure of Prey Communities

Experiments show that consumer diversity can have important effects on the control of prey diversity and abundance. However, theory also indicates that the strength of consumer effects on such properties will vary depending on system productivity and disturbance regime. Using a laboratory-based system composed of ciliate consumers and bacterial prey, I explored the interactive effects of productivity, disturbance, and consumer diversity on prey diversity and trophic-level abundance. Consumer diversity had productivity-dependent effects on bacterial prey that were consistent with theoretical expectations. At low productivity, increasing consumer diversity reduced prey abundance while at high productivity no effects were detected due to compensatory responses among bacteria. In contrast, consumer diversity had weak effects on prey diversity at low productivity but significantly depressed prey diversity at high productivity. Disturbance on consumers enhanced prey diversity but did not alter consumer diversity effects on prey. These results indicate that consumer diversity may play an important role in the regulation of prey communities, but the strength of this effect varies with system productivity. 1. Introduction The relative importance of top-down (consumer) versus bottom-up (resource) effects on prey communities has fueled intense debate and spawned a large body of ecological research [1–5]. The strength of consumer control on trophic-level abundance and the composition of prey has been shown to vary greatly among studies and study systems [5–8]. Such context dependency has prompted investigations into the mechanisms that may mediate top-down effects on the structure of prey assemblages, including the effects of prey defense, stage-structured dynamics, consumer diet breadth, and the form of consumer functional responses [1–3, 9–13]. A parallel body of research has focused on the effects of species loss on ecosystem functioning and biomass yield. Although initially focused on plant species diversity and its effects on primary production and nutrient uptake, several studies have shown that the number of consumer species present within a trophic level can have important impacts on secondary production and the capacity of consumers to control total abundance and diversity of prey assemblages [14–20]. Increasing diversity within a consumer trophic level can theoretically increase total consumer abundance either through niche complementarity among consumers (e.g., via resource partitioning) or through sampling effects (i.e., increased probability of