PARENT SESSION
Contributed Oral Session 10: Aquatic Trophic Systems I
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 519 B, Level 5, Palais des congrès de Montréal
Interactive effects of habitat diversity and cannibalism on fitness of a stream-dwelling invertebrate.
McGrath, Kathleen*,1, 2, Peeters, Edwin1, Scheffer, Marten1, 1 Wageningen University, Wageningen, The Netherlands2 Pacific Northwest National Laboratory (PNNL)/Battelle, Richland, WA, USA
ABSTRACT- We hypothesized that the availability of diverse size-structured habitats would mediate the incidence of cannibalism by larger individuals on smaller individuals as well as affect fitness characteristics associated with growth of the smaller individuals. We tested these hypotheses in a series of laboratory studies with Gammarus pulex, a freshwater amphipod of slow-flowing streams throughout western Europe. G. pulex resides in substrate interstitial pore spaces that vary in size with substrate size and condition. In the absence of larger, potentially predatory individuals, small Gammarus demonstrated a weak preference for large pore spaces but 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. Survival of small individuals was lower in the presence of larger Gammarus than in controls without larger individuals regardless of substrate size, but availability of mixed pore sizes significantly (p<0.0001) increased survival (large pores, with predators: 10.0%; large pores, without predators: 97.5%; mixed pores, with predators: 46.7%; mixed pores, without predators: 97.5%). We were unable to confirm our hypothesis that large individual presence would reduce small individual growth. This may be because survival of small individuals was size-selective favoring the largest individuals, or, surviving small individuals demonstrated compensatory growth. Our study has implications for population dynamics of cannibalistic species, and suggests that anthropogenic activities such as stream channelization and sedimentation resulting in habitat homogenization may affect size-mediated processes such as cannibalism in aquatic invertebrate species.
Key words: cannibalism, substrate, habitat diversity, body size