MEASURING THE FUNCTIONAL DIVERSITY OF FOOD WEBS

This chapter reviews the concept of functional diversity as it applies to single trophic levels and then extends the concept to food webs. One component of biodiversity that measures the extent of resource use differences among species is functional diversity. It may also explain and predict ecosystem functioning more accurately than does species richness. Experiments, mostly in plant communities, show that variation in functional diversity can have substantial effects on ecosystem functioning, though effects appear contingent upon factors such as spatial scale and environmental conditions. Functional diversity explained more variance in decomposition rate than in respiration rate, suggesting that a single measure of functional diversity will not be able to explain or predict all ecosystem processes. Different information about the species and/or different measures of diversity may be required for different functions, or diversity may have less functional significance for some ecosystem processes compared to others. Decades of research show that multiple factors determine the distribution of biomass and productivity in a food web. More research demonstrates the importance of the identity of trophic groups for ecosystem processes, perhaps more so than the diversity of trophic strategies. Another example of why functional diversity may not predict food web functioning is provided by studies of interactions among different trophic levels.