Document: DAV-3-56-40

Giant cannibals emerge from size-structured population dynamics.

CLAESSEN, D.* ^1,2, A.DE ROOS ¹ and L.PERSSON ²

University of Amsterdam, The Netherlands ¹
Umea University, Sweden ²

Abstract:
Cannibals and their victims often share common resources and thus potentially compete. Smaller individuals are often competitively superior to larger ones because of size-dependent scaling of foraging and metabolic rates, while larger ones may use cannibalism to counter this competition. We studied the interplay between cannibalism and competition using a size-structured population model, in which all individuals consume a shared resource, but larger ones may cannibalize smaller conspecifics. In the model, intercohort competition caused single-cohort cycles when cannibalism was absent. Moderate levels of cannibalism reduced intercohort competition, enabling coexistence of many cohorts. More voracious cannibalism, in combination with competition, produced large-amplitude cycles and a bimodal population size-distribution with many small and few giant individuals. These coexisting ``dwarfs'' and ``giants'' had very different life histories, resulting from a reversal in importance of cannibalism and competition. The population structure at time of birth determined whether individuals suffered severe cannibalism with the few survivors reaching giant sizes, or suffered intense intracohort competition, with all individuals remaining small. These model results agreed remarkably well with empirical data on perch population dynamics. We argue that the induction of cannibalistic giants in piscivorous fish is a population dynamic, emergent phenomenon that requires a combination of size-dependent cannibalism and competition.

Keywords: size-dependent cannibalism, competition, size-structured population dynamics, growth bottleneck, ontogenetic niche shift

This abstract is being presented at: 3:30 PM in session:
ANIMAL ECOLOGY