Print PageA central challenge in community ecology is to understand the connection between biodiversity and ecosystem functioning. The traditional approach in community ecology is based on the premise that predictions can be made by treating a species as a homogenous entity. However, no population is truly homogenous and individuals within a species often vary considerably in their ecology. By far the largest source of this variation between individuals stems from differences in size and ontogenetic stage. The unresolved question is how this variation within species affects the structure and functioning of natural ecosystems. Understanding the consequences of ontogenetic functional diversity for the dynamics of communities and ecosystem processes is critical because it not only determines how the loss of a species affects the functioning of ecosystems, but also how changes in its population structure affect ecosystems. Here we used an experimental approach to test how ontogenetic functional diversity scales up to determine the impact of a species on the structure of communities and ecosystem functioning. By manipulating the stage-structure of key predators in complex experimental pond communities we tested: 1) whether differences in ontogenetic stages lead to quantitative and qualitative differences in their ecological roles and impacts on ecosystem functioning, 2) whether the effects of individual stages are independent, and 3) whether this effect is species specific or general.
Results/Conclusions
Our results indicate that changing the ontogenetic stages within a key predator lead to concurrent changes in the structure and biomass of a complex community and even ecosystem processes such as primary productivity, respiration rates, and decomposition rates. These differences among stages within species were similar or sometimes greater in magnitude compared to differences among species indicating that effects of ontogenetic niche shifts were strong and not species specific. Furthermore, depending on the ecosystem function, the presence of multiple stage classes led to “biodiversity effects”, where the combined effect of stages was not simply the sum of their individual effects. In general, these results indicated that a species’ ecological role and impact on the ecosystem depends on its stage structure (and thus ontogenetic functional diversity). Furthermore, this shows that functional variation among ontogenetic stages within species can scale up to influence the functioning of complex ecosystems. This suggests that we need to account for the “biodiversity within species” when predicting the effect of a species on an ecosystem or how human impacts such as size-selective harvesting will influence natural
