Body-masses, food-web structure, animal diversity and ecosystem functioning
The distribution of body masses across species in general and the scaling of resource body mass with consumer body mass in particular have strong implications for food-web structure, community stability and ecosystem functioning. In this talk, I will present a novel global data base on consumer and resource body masses, which was compiled based on the collaboration among a global group of food-web scientists. The data allows unprecedented analyses of consumer-resource body-mass relationships across different interaction types (predators and herbivores), ecosystem types, movement types and species' metabolic categories. Together, these analyses provide deepened insight into the body-mass structure of natural communities and their consequences for the network structure of food webs.
These principles of food-web structures are used to formulate generic network models using consumer and resource body mass distributions as the only input parameter. These network models are used to predict the consequences of varying the diversity of animal consumers for different ecosystem functions (primary productivity, herbivory, predation, carbon respiration). Prior studies suggested that increasing animal diversity can lead to higher primary productivity via trophic cascades or to lower primary productivity if intra-guild predation dampens the top-down pressure on plants. In the food-web simulations, we found that despite higher intraguild predation in more diverse animal communities, both the exploitation rates on plants and the animal community biomass increased. Unexpectedly, this did not negatively affect the plant community biomass because of a dynamic adjustment of the community body-size structure, which exhibited a shift towards larger, and thus energetically more efficient, species in more diverse communities. The plasticity of community body-size structure reconciles the debate on the consequences of animal species loss on primary productivity.