Habitat-mediated cannibalism and microhabitat restriction in the stream invertebrate Gammarus pulex

Abstract

In cannibalistic species, small individuals often shift habitats to minimize risk of predation by larger conspecifics. The availability of diverse size-structured habitats may mediate the incidence of cannibalism by larger individuals on smaller individuals and increase fitness of smaller individuals. We tested these hypotheses in a series of laboratory studies with Gammarus pulex, a freshwater amphipod inhabiting substrates with varying interstitial pore space sizes. In the absence of larger, potentially cannibalistic individuals, small Gammarus actively used all pore space sizes offered. They used only substrates containing food and preferred food items that provided cover to food items that did not. In the presence of larger G. pulex, small individuals almost exclusively used smaller pore spaces from which larger individuals were excluded. Small individual survival was significantly lower in the presence of larger Gammarus than in controls without larger individuals regardless of substrate size, but availability of mixed pore sizes significantly increased survival. Food consumption and growth per individual were not affected by the presence of larger individuals or substrate composition. Our results suggest that the distribution and availability of complex and high-quality habitats may affect the occurrence and significance of cannibalism in size-structured populations.

Substrate preferences of coexisting invasive amphipods, Dikerogammarus villosus and Dikerogammarus haemobaphes, under field and laboratory conditions

“…Within predatory and cannibalistic species, sizeasymmetric predation may have significant effects for community dynamics (Benoît et al 2000;Kinzler et al 2009) and smaller individuals often select habitats to avoid conspecific predation (McGrath et al 2007;De Gelder et al 2016). Adult amphipods often inhabit large stony substrates with smaller individuals seeking refuge in suitable substrate crevices or macrophytes to shelter (Boets et al 2010;Kobak et al 2015).…”

“…Substrate preferences often reflect the body size and age/life stage of an individual; with intra and inter-specific spatial separation being observed among many populations of amphipods (McGrath et al 2007). Optimum substrates are typically heterogeneous with the particle size or interstitial spaces between them being similar to that of the organisms' body size (Platvoet et al 2009b;De Gelder et al 2016).…”

The long-term effects of invasive signal crayfish (Pacifastacus leniusculus) on instream macroinvertebrate communities

“…This taxon has been widely cited as adopting various avoidance strategies in order to evade inter and intra-specific predation, including enhanced drift and locomotion, vertical migration and increased use of refuges (Andersson et al, 1986;McGrath et al, 2007;Haddaway et al, 2014).…”

Dietary Preference ofGammarus pulexandAsellus aquaticusduring a Laboratory Breeding Programme for Ecotoxicological Studies

“…Whatever the mechanism, the outcome of this difference in response is that reduction in food quality has a greater impact on the energy balance of A. aquaticus than that of G. pulex, resulting in less energy being available. G. pulex may also resort to cannibalism in experimental situations when insufficient/inappropriate nutritional supplements are available [16], which could hinder a laboratory breeding programme.…”