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Eco-evolutionary dynamics of community self-organization through ontogenetic asymmetry

Final Report Summary - ECOEVODEVO (Eco-evolutionary dynamics of community self-organization through ontogenetic asymmetry)

This project focuses on the aspect of life that the majority of animal species are characterized by a life history full of complexities. Individuals need to grow during their life, sometimes over impressive ranges of body size, and these changes in body size change their energy requirements for subsistence, growth and reproduction. In many species these changing energy demands are met by changing the use of available resources during juvenile development (ontogeny) or by changing the habitat individuals live in. Examples of the former are piscivorous fish species that start out eating zooplankton as newborn but switch to hunting for other fish when large. Examples of the latter are amphibians with an aquatic, juvenile life stage and a terrestrial, adult life stage and species of salmonoids that migrate from the river to the ocean and back for growth and reproduction, respectively. In this project the possible drivers are investigated that have resulted in the evolution of such life cycle complexities and the consequences of such complex life cycles for population persistence and community structure.

With increasing body size the efficiency changes, with which individuals can use available resources to grow or reproduce, often resulting in asymmetric competition between juveniles and adults when they forage on a shared resource. We have theoretically shown that natural selection would by default minimize such asymmetric competition, which occurs when individuals of different sizes are equally efficient in their use of available energy. Other types of interactions that individuals are engaged in disrupt this evolutionary tendency. For example, cannibalism of larger individuals on smaller conspecifics can be shown to evolve and give rise to evolutionary coexistence in the same population of a slow, large-sized cannibalistic life history type and a faster growing smaller non-cannibalistic life history type. The evolution of cannibalism also promotes population persistence if a species switches resources during its life history from feeding on a basic, shared resource early in life and hunting for prey later on.

In this project we have also shown that a change in diet during juvenile development is likely to evolve when an alternative resource is available in abundance, but that adaptation to this new foraging niche will not occur if it has negative effects for the foraging success as a newborn. This trade-off between early and large foraging success thus impedes the evolution of an ontogenetic niche shift. However, our studies have also revealed that if alternative resources are available in abundance a change in resource use is expected to evolve hand in hand with metamorphosis, during which process individuals invest stored energy to change their morphology and thereby their foraging efficiency. Metamorphosis thus breaks up the trade-off between early and late foraging. Once metamorphosis is fixated in the population, deterioration of either the juvenile or adult habitat is likely to lead to population extinction rather than to the evolution of an alternative life history, in which the metamorphosis is skipped (paedomorphosis, direct development). Metamorphosis is hence an evolutionary dead end.

Other studies in the project have focused on the plasticity of individuals to adopt different life history strategies, for example salmonoid species, in which part of the population migrates out to the marine environment before reproduction, while an other part of the population stays behind and completes its juvenile phase in freshwater. In general these studies have shown that under a given set of environmental conditions only one of the possible life history strategies is really successful and hence supports population persistence, but that the environmental conditions determines which is this productive strategies. These findings suggest that the coexistence of alternative life history strategies may ensure population persistence in the face of changing environmental conditions. Above all, this ERC project has emphasized and revealed the importance of the impact of population dynamics on the life history that individuals can realize. This feedback from the population and community toward the individual level mostly determines population persistence and evolution as well as community structure.

The project has been theoretical in nature and used population dynamic models to answer fundamental questions in ecology and evolutionary biology. As part of the project a generic methodology and software package was developed to analyze population dynamic models that explicitly represent complex life histories of individual organisms. As such these models contrast with the classic models in ecology that tend to ignore individual life history altogether. The tools developed are made publicly available as open-source software.

Research results have been presented in a large number of presentations by team members at national and international conferences in Europe (the Netherlands, France, England, Germany) and the United States. These are conferences in the field of evolutionary biology, ecology, and theoretical biology, attesting of the interdisciplinary nature of the project. As part of the ERC project an international course was furthermore organized to educate early-career scientists from a variety of countries to use the structured population models that this ERC project focused on.