PARENT SESSION
Symposium 2: Soil Biodiversity: Scaling from microbe to ecosystem
Organized by: A Fitter, C Kennan, and H Jones
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 517 B, Level 5, Palais des congrès de Montréal

Species richness, functional traits and facilitation: Unraveling the role of invertebrate diversity in soil.

Wolters, Volkmar¹, ¹ Justus-Liebig-University, Giessen

ABSTRACT- The functional implication of the enormous invertebrate richness in soil still is an unresolved problem of ecology. 'Facilitation' is key in this context - an old but widely ignored concept of ecology that emphasizes the important influence of positive interactions on the organization and performance of natural communities. Invertebrates and microbiota in soil provide an excellent case for this type of interaction. Edaphic invertebrates impact microbial performance by (i) shaping the microbial community, (ii) incorporating and redistributing various materials, and (iii) altering distal factors controlling microbial performance. Soil microbiota, in turn, affect invertebrates by (i) altering the quantity and availability of essential resources, (ii) affecting the physico-chemical environment, and (iii) interacting directly. Not all of these interactions are 'positive' at the level of the individual species, but the cumulative outcome very often is considered to facilitate essential ecosystem processes (e.g. decomposition, N transfer, C storage). Most of our knowledge on the functional implications of biotic interactions in soil still is anecdotic. It is thus very difficult to predict the consequence of changes in species richness, resource conditions or specific interactions for processes taking place at higher spatio-temporal scales. Recent evidence suggests, however, that invertebrate effects in soil relate to certain functional traits rather than to the presence or absence of a certain species. This confirms the 'step hypothesis' predicting that (i) even a small share of species with key traits dramatically increases the probability of a functional effect when species get lost, (ii) the loss of function is related to the variety of key traits, and (iii) it is very difficult to detect a relationship between species richness and function by studying 'random communities', since the chance of misinterpreting the results as an 'idiosyncratic' relationship between species richness and function is high (Wolters 2001, Eur J Soil Biol 37, 221-227.). Here I provide a number of case studies underpinning this concept. Despite the rather crude approach to diversity-function relationships in soil suggested by the step hypothesis, species richness strongly affects the persistence of a function under conditions of environmental change, since the number of species performing this function determines its ecological range. Moreover, facilitation opens another backdoor for species richness, because the 'functional strength' of a trait very often depends on mutualistic interactions with other species.

Key words: soil, species richness, functional traits