DynaCom (Sp 7)
The rates at which species disperse among local communities can play a crucial role in maintaining metacommunity diversity and stability. The distance over which an animal can actively disperse while through areas of unsuitable habitat depends on both the speed of travel and duration of the dispersal bout. Larger-bodied animals benefit from reduced mass-specific metabolic costs (i.e. better metabolic efficiencies per unit of body mass) and higher absolute rates of metabolic activity than smaller-bodied animals. Animal movement speeds are therefore expected to scale positively with body mass according to a power-law; however, results from a recent global meta-study indicate that the realised maximum speeds of animals follow a hump-shaped relationship and that this scaling relationship further varies between movement modes (flying, running, swimming) and feeding types (carnivores, omnivores, herbivores, detritivores). As animals typically travel at a fraction of their maximum speed during dispersal, it remains unclear how the rate of active dispersal scales in relation to fundamental traits such as body size, movement mode, and feeding type.
The aim of this study is twofold: (1) Using empirical data from vertebrate movement studies, a meta-study will be used to analyse how travel speeds and dispersal bouts scale with body mass, and in relation to movement mode and feeding type. The model will provide the basis for trait-based predictions of dispersal rates for actively dispersing animals. Due to the paucity of movement data from invertebrate movement studies, it will be necessary to corroborate whether similar trait-based constraints apply to the active dispersal rates of invertebrates. Experimental mesocosms equipped with arrays of RFID (radio-frequency identification) readers allow the real-time movements and dispersal rates of tagged terrestrial invertebrates to be related to their traits (e.g. body mass, feeding type). (2) Replicate mesocosm experiments in which patch size and the degree of isolation vary across treatments will be used to test for the combined effects of animal movement traits and spatial network configuration on the rates of active dispersal within invertebrate metacommunities. Together, the mechanistic insights gained from this study are expected to improve the estimation of animal dispersal rates across fragmented habitats and contribute towards a more predictive framework for understanding the effects of spatial processes on metacommunity organisation.
The colonization process of islands or habitat patches consists of several sub-processes like dispersal, establishment, immigration or emigration. The DynaCom subproject 7.2 concentrates on the underlying mechanisms of emigration.
We want to investigate the qualitative trait dependence of emigration, which is energetics of emigration. The stability and diversity of food webs is driven by the ratio of energy intake (feeding) and energy use (metabolic demands). The energy intake will be measured within a functional response framework. Moreover, the energy loss (metabolism) makes calculation of the energetic budget of an individual possible. The energy intake depends on resource quality, which is stoichiometry (e.g. compensatory feeding with decreasing food quality) as well as food quantity and predation risk. The experiments will be performed as microcosm experiments.
We will measure the effect of both bottom up by resource quality (stoichiometry) and quantity (resource density in a patch) as well as top down pressure by predators of different body masses. We will have three different experimental parts:
- 1 Functional response + assimilation efficiency
- 2 Respiration rate
- bottom-up effects on emigration (resource quality + quantity)
- top-down effects on emigration (predation pressure)
Thus, the hypotheses are the following:
(a) Increasing resource quality (i.e. stoichiometry) will lead to decreased feeding and decreased emigration rates. (part I)
(b) Emigration of consumers is driven by the top down pressure of their predators. (part II).
We will use terrestrial isopods as study organisms representing consumers and several predatory macro-invertebrates of different body masses.
Additionally, we will cooperate with the Ecotron project. Here we can look at moving patterns of macro-invertebrates between different patches of leaf litter of different stoichiometric quality (ash, oak, birch and mountain ash), which are separately arranged or all mixed up.