The meaning of functional trait composition of food webs for ecosystem functioning

Abstract

One contribution of 17 to a theme issue 'Biodiversity and ecosystem functioning in dynamic landscapes'. There is a growing interest in using trait-based approaches to characterize the functional structure of animal communities. Quantitative methods have been derived mostly for plant ecology, but it is now common to characterize the functional composition of various systems such as soils, coral reefs, pelagic food webs or terrestrial vertebrate communities. With the everincreasing availability of distribution and trait data, a quantitative method to represent the different roles of animals in a community promise to find generalities that will facilitate cross-system comparisons. There is, however, currently no theory relating the functional composition of food webs to their dynamics and properties. The intuitive interpretation that more functional diversity leads to higher resource exploitation and better ecosystem functioning was brought from plant ecology and does not apply readily to food webs. Here we appraise whether there are interpretable metrics to describe the functional composition of food webs that could foster a better understanding of their structure and functioning. We first distinguish the various roles that traits have on food web topology, resource extraction (bottom-up effects), trophic regulation (top-down effects), and the ability to keep energy and materials within the community. We then discuss positive effects of functional trait diversity on food webs, such as niche construction and bottom-up effects. We follow with a discussion on the negative effects of functional diversity, such as enhanced competition (both exploitation and apparent) and topdown control. Our review reveals that most of our current understanding of the impact of functional trait diversity on food web properties and functioning comes from an over-simplistic representation of network structure with welldefined levels. We, therefore, conclude with propositions for new research avenues for both theoreticians and empiricists.

Bringing Elton and Grinnell together: a quantitative framework to represent the biogeography of ecological interaction networks

“…But one could develop the model further to integrate such traits, inspired by the framework developed by Gravel et al (2016). It corresponds to the Grinnellian dimension of the niche.…”

“…As mentioned earlier, Gravel et al (2016) proposed to represent the occurrence of interactions based on some trait-matching rules (given by a function of the type P L T T E ( )| , , ijy i y jy y ) and the co-distribution of traits (corresponding to P T T E ( , | ) iy jy y ). In this context, both the Eltonian and Grinnellian dimensions of the niche could be represented.…”

Biodiversity and ecosystem functioning in dynamic landscapes

“…Metrics are dovetailed to describe the functional diversity of complex food webs and the consequences for food web structure, resource use efficiency, trophic regulation, and the cycling of energy and materials in the community. This network approach opens exciting new avenues for future research on species traits and BEF in multi-trophic communities [47]. Tackling BEF in complex natural communities thus requires understanding the importance of various species traits and population characteristics, including (i) the population-averaged body mass, (ii) population abundance (or biomass density); and (iii) the stoichiometry (i.e.…”

“…For example, one article in this special issue [47] illustrates the application of trait-based approaches to characterize the functional structure of complex networks. Metrics are dovetailed to describe the functional diversity of complex food webs and the consequences for food web structure, resource use efficiency, trophic regulation, and the cycling of energy and materials in the community.…”

Functional Rarity: The Ecology of Outliers

“…Complementing this, quantifying functional rarity must include the extent to which species traits, used as proxies to represent functions, trophic links and niche axes [42][43][44][45][46][47], are more or less distinct or redundant within local communities or larger-scale species assemblages [40,48,49] (Box 1).…”