Dynasym

A symbiosis represents the physical association of individuals from different species, which may have positive, negative or no effects on the fitness of both partners resulting in e.g. mutualism, parasitism or commensalism. Such forms of symbiosis have been considered as fixed among distinct species pairs but recent evidence reveals that the form of symbiosis may change depending on the abiotic or biotic conditions (the context). The aim of SP2 is to gain novel and general insights into how the form of symbiosis depends on the densities, frequencies and traits of the symbiosis partners, and how the form of symbiosis influences the population and trait dynamics and the feedback between the form of symbiosis and trait and population dynamics. This will contribute to general theory building in community ecology by integrating aspects of eco-evolutionary dynamics and food web theory into the framework of context-dependent symbiosis. Therefore, we will implement mathematical models that account for the essential features of the ciliate-algae symbioses experimentally studied in SP1 and SP4. More specifically, we want to develop and analyse a basic food web model to reveal general processes underlying context-dependent changes in the strength and form of a symbiosis under different environmental conditions (light, nutrients, bacteria) (WP1). We will extend this basic food web model to allow individual organisms, in particular the host and the algal endosymbiont, to adjust their functional properties to changing conditions and to determine the effect of this flexibility on population dynamics and the form of symbiosis (WP2). Furthermore, we want to extend the basic food web model to incorporate (1) an additional grazer, which implies a kind of protective symbiosis and may be tested experimentally, (2) a top predator feeding on ciliates but not on free-living algae enhancing the mortality and thus the costs of endosymbionts, and/or (3) another competing free-living alga that may reduce the benefits of the host from endosymbiosis.