Abstract
The aim of this proposal is to test consequences of realistic biodiversity loss for the ability of communities to cope with disturbance and adapt to environmental change, i.e. community resilience. In the last decade it has been shown that random loss of diversity reduces important ecosystem functions, such as primary production and carbon storage. However, in general little is known about consequences of diversity loss for ecosystem resilience and thereby for the ability of communities to keep their functions while environmental conditions change. In particular, very little is known about how realistic diversity loss affects essential community functioning and resilience. We argue that in natural communities two extinction scenarios dominate: stochastic loss of the rare species - natural extinctions - and loss of the dominant species through human exploitation. We hypothesize (1) that ecosystem functioning is driven by the dominant best competitor, but that in a diverse community rare subdominant species can compensate for the loss of such a dominant species; (2) that rare species are essential for the ability for the community to reorganise and keep essential functioning while environmental conditions change; (3) that regional diversity of rare species is important to keep community functioning after loss of dominant species from environmental change. To test these hypotheses, we will establish metacommunities each consisting of connected local communities with marine benthic microalgae. Among the metacommunities we will manipulate the degree of connectedness, and within the metacommunities we will expose the local communities to disturbance by removing biomass at different rates. In this experimental design species in the metacommunities will coexist by patch-dynamics which is so far a neglected mechanism maintaining diversity when it comes to biodiversity-ecosystem functioning experiments. Consequences of species loss will be determined by manipulating the total number of species available within the metacommunities ? the regional diversity ? changing the subset of species that can re-colonize local habitats after disturbances and replace species lost to environmental stress. The different regional species pools will be constructed by removing the rare species ? mimicking natural species loss ? obtained from realistic frequency distribution of species which is based on natural assembly rules. In a series of experiments we will test effects of losing different levels of rare species for the ability of the metacommunity to 1) compensate for loss of species with a high value for ecosystem function by removing the most dominant species ? mimicking human exploitation, and 2) maintaining community function under environmental stress by exposing the communities to both continuous and gradual temperature stress.
Netherlands