L. Persson

Impact of Intraguild Predation and Stage Structure on Simple Communities along a Productivity Gradient

We analyze the consequences of intraguild predation and stage structure for the possible composition of a three‐species community consisting of resource, consumer, and predator. Intraguild predation, a special case of omnivory, induces two major differences with traditional linear food chain models: the potential for the occurrence of two alternative stable equilibria at intermediate levels of resource productivity and the extinction of the consumer at high productivities. At low productivities, the consumer dominates, while at intermediate productivities, the predator and the consumer can coexist. The qualitative behavior of the model is robust against addition of an invulnerable size class for the consumer population and against addition of an initial, nonpredatory stage for the predator population, which means that the addition of stage structure does not change the pattern. Unless the top predator is substantially less efficient on the bottom resource, it tends to drive the intermediate species extinct over a surprisingly large range of productivities, thus making coexistence generally impossible. These theoretical results indicate that the conditions for stable food chains involving intraguild predation cannot involve strong competition for the bottommost resource.

Gigantic cannibals driving a whole-lake trophic cascade

Trophic cascades have been a central paradigm in explaining the structure of ecological communities but have been demonstrated mainly through comparative studies or experimental manipulations. In contrast, evidence for shifts in trophic cascades caused by intrinsically driven population dynamics is meager. By using empirical data of a cannibalistic fish population covering a 10-year period and a size-structured population model, we show the occurrence of a dynamic trophic cascade in a lake ecosystem, in which the community over time alternates between two different configurations. The intrinsically driven change in the size structure of the fish population from a dominance of stunted individuals to a dominance of gigantic cannibals among adult individuals is the driving force behind distinct abundance switches observed in zooplankton and phytoplankton. The presence of the phase with gigantic cannibals depends critically on the energy they extract from their victims, allowing strong reproduction for a number of years.

Influence of growth history on the accumulation of energy reserves and winter mortality in young fish

In seasonal environments accumulated energy reserves are important to avoid starvation mortality during periods of low resource levels. Here we investigated patterns of energy accumulation and the ...

Size at hatching determines population dynamics and response to harvesting in cannibalistic fish.

We hypothesize that size at hatching strongly affects population dynamics of cannibalistic fish species and is a crucial determinant of how populations respond to selective removal of large individ ...

Body size scalings and the dynamics of ecological systems

This chapter provides an overview of the implications of intraspecific body size scaling for the dynamics of ecological communities. Two trophic configurations have been used to illustrate how different size scalings have profound effects on population dynamics, with strong feedback on overall trophic dynamics. The first example involves a consumer feeding on a resource where the size scaling of foraging rate turn has profound effects on the dynamics of the system and where the dynamics of the system for most parameter values is characterized by nonequilibrium dynamics, driven by cohort competition. The second example involves cannibalism where the scaling of the lower size boundary, for which cannibal–victim interactions take place, has a major effect on dynamics, and where ecological systems may shift among different trophic structures over time. The analysis shows that the size scaling of foraging capacity has important implications for population dynamics and overall trophic dynamics. For consumer–resource interactions, observed body size scalings of foraging and metabolic rate have a strong tendency to lead to nonequilibrium recruit-driven cycles. For both consumer–resource interactions and cannibal–victim interactions, it is also apparent that intraspecific body size scalings and predator–prey body size relationships have important consequences for population and community dynamics.