The role of predation in shaping biological communities, with particular emphasis to insects

Abstract

Predation in animal communities is the consumption of tissues belonging to another organism. The content of the term predation varies among trophic levels, mode of action and species, and thus several additional terms have been used such as parasitism, herbivory, cannibalism, and larceny. This treatise deals with predation sensu stricto and cannibalism. It was found that in the majority of biotic communities predation by arthropods constitutes the most frequent significant effect as far as competition is concerned, especially in the absence of vertebrate predators. The important predator-prey interaction is addressed via the modelling of the community, a common approach to prediction making on population densities of predator and prey species. Many models have been developed apart from the classical ones of Holling and Lotka-Voltera. LES, Rosenzweig-MacArthur and Luck are newly developed models that predict two paradoxes, namely the paradox of enrichment and the biological control paradox. Models that take into accounts the spatial component such as the reaction-diffusion models allow the investigation of many aspects of the behaviour of the predatorprey system within biotic communities. In terms of the relative importance of predation and competition sensu stricto in shaping insect communities the debate is far from settled. Typically, predation is the energy passed from prey to predator while competition is the modification of the trajectory of energy transfer. In this respect, competition cannot be traced in the fossil record unlike predation, which leaves some detectable traces. In effect, past competition can only be hypothesized. Although the size of predators can be closely related to the size of the attacked prey there are prey species corresponding to two or more predator sizes. These predators belong to two or more assemblages preying on the same prey species. Cannibalism was interpreted as a type of predation. In this view, cannibalism is predation on conspecifics and in this respect it can emerge when competition is low and predators are scarce. In these cases cannibalism is the only mechanism that controls the population densities of organisms. Nevertheless, many authors believe that cannibalism lacks any adaptive significance. The usage of the term 'natural enemy' allowed the inclusion of competitors and predators in a single expression, in the sense that competitors are enemies. In this sense, a prey newcomer cannot invade any biotic community unless it has a difference in its anti-predatory traits from already existing prey species. An advanced form of this interaction is the hypothesis of 'differential diversification' of sister clades that determines the outcome of biotic interaction in evolutionary and ecological time scales. Biodiversity is promoted and maintained by keystone predators. These predators act on numerous or common organisms preventing the dominance of one or a few species. It seems that the higher the rank of the trophic level the greater the difficulty to receive energy from the ecosystem. Thus, increased biodiversity levels are exploited in many ways to attain a firm grasp of energy input in the biological community. Possibly, this is the main cause of the extreme diversity of insect orders. On the other hand, the biodiversity is spatially distributed according to various ecosystem components. Chemical communication, though a primitive way of communication, is heavily employed both in the detection of prey and in the avoidance of predation. The emission of chemical messages and the ability to sense them is so important as to reflect the evolution of the emitter. There is no work on the evolutionary message conferred to the receiver but the alterations needed to emit the chemical message are more sophisticated than the alterations necessary to sense the new blend. The use of chemical messages is tightly connected to the behavioural ecology of insects. Usually, chemistry and morphology are both engaged in the predatory interactions of insects. A number of hypotheses have been proposed to explain these interactions. © 2007 Springer-Verlag Berlin Heidelberg.