Species coexistence and predictability mediated by functional equivalence as documented in an experimental approach

KRUK, C., SEGURA, A. M., SARTHOU, F., NOGUEIRA, L., CABRERA, C. & G. BEAMUD

San Michele all’Adige (Trento)

Congreso; 16th Workshop of the International Association of Phytoplankton Taxonomy and Ecology (IAP); 2011

<!-- @page { margin: 2cm } P { margin-bottom: 0.21cm } -->Phytoplankton responses to environmental change are predictable when grouping species using global indicators (i.e., chlorophyll a). However, the specific composition is difficult if not impossible to know in advance. Here, we use a morphology-based functional groups (MBFG) approach and show that community structure and coexistence of species depends on specific traits related to species ecological aptitude. We carried out experiments with natural communities and analyzed the succession under different nutrient, temperature and predation levels. We evaluated the temporal variation in total chlorophyll and phycocyanin and the composition in terms of species and MBFG. Total biomass (chlorophyll) and cyanobacteria (phycocyanin) developed most in high nutrients and high temperature treatments. However, different cyanobacteria species with similar morphological traits can alternatively dominate or coexist in similar environmental conditions. For example under high nutrients, high temperature, and absence of large herbivores, large filamentous high S/V potentially toxic cyanobacteria (MBFG III) dominate. However, we found either Planktothrix agardhii, Pseudanabaena spp., Cylindrospermopsisraciborskii or other taxa dominating or coexisting. This suggests that MBFG do indeed contain functionally equivalent and therefore interchangeable species. In line with the emergent neutrality theory, this means that selection is acting on functional groups and the identity of a particular species within such groups could be essentially random. The MBFG approach integrates individual traits which can be related to ecological processes at the community level at different temporal scales and independently from geographical location. Within MBFG, species showed similar responses to the environmental conditions and therefore might be similarly affected by impact and restoring human activities. Thus MBFG constitute a useful summarizing tool to disentangle the effects of anthropogenic impacts on phytoplankton responses.