Jasmijn Hillaert, Martijn L. Vandegehuchte, Thomas Hovestadt, Dries Bonte
Body size can be thought of as a “master trait” as it has an effect on most aspects of an organism’s life, including behaviour, physiology and life history. It not only determines how much energy an individual organism needs to consume to maintain life functions, it also affects its mobility. Thus, there is an optimal size for both prey and predator and a preferred body size ratio, which balances the success of the predator in catching and consuming prey against the success of the prey in avoiding predation. Habitat fragmentation and habitat loss may increase the need to move between patches when resources are limited and can therefore influence the evolution of body size.
We built a mechanistic individual based model to understand shifts in body size in a simple prey-predator system. Our model linked vital rates and movement to body size at maturity. The model was designed for terrestrial arthropods but should be generally applicable, at both the population and community level. The model helps us to understand how the interactions between food availability (bottom-up control) and predation (top-down control) influence the prey. We showed that these feedbacks select for larger predators with habitat loss and habitat fragmentation, but that, unlike in environments without predators, prey sizes are not affected. As large predators are more mobile, increased body sizes enables predators to more easily move from patch to patch to hunt prey.
Realised predator-prey body size ratios thus increase with habitat fragmentation. As such deviations from the optimal ratio weaken food web interactions, they are anticipated to decrease food web stability under habitat fragmentation.