Food webs: reconciling the structure and function of biodiversity

Abstract

The global biodiversity crisis concerns not only unprecedented loss of species within communities, but also related consequences for ecosystem function. Community ecology focuses on patterns of species richness and community composition, whereas ecosystem ecology focuses on fluxes of energy and materials. Food webs provide a quantitative framework to combine these approaches and unify the study of biodiversity and ecosystem function. We summarise the progression of foodweb ecology and the challenges in using the food-web approach. We identify five areas of research where these advances can continue, and be applied to global challenges. Finally, we describe what data are needed in the next generation of food-web studies to reconcile the structure and function of biodiversity.Reconciling the study of biodiversity and ecosystem function We are experiencing two interrelated global ecological crises. One is in biodiversity, with unprecedented rates of species loss across all major ecosystems, combined with greatly accelerated biotic exchange between landmasses [1]. Consequently, spatial and temporal patterns of species occurrence are being fundamentally altered by extinction and invasion. The second crisis concerns the regulation of ecological processes and the ecosystem services they provide. Processes such as primary production and nutrient cycling have been severely altered by human activities [1].Our understanding of biodiversity comes largely from a sound theoretical and empirical basis provided by community ecology, including core concepts such as niche segregation [2] and Island Biogeography [3,4]. Early studies of individual species' habitat preferences and physiological tolerances have been complemented by studies of interspecific interactions from field surveys and experiments. Applications such as conservation management depend largely on mapping of community patterns and studies of habitat occupancy and preferences. More recently, habitat models have been applied, and the advent of simple and cheap molecular markers has allowed quantification of important community assembly (see Glossary) processes such as dispersal [5]. In community ecology the unit of study is the individual, population, or species, consistent with other sub-disciplines such as behavioural and population biology. Review GlossaryAssembly: the set of processes by which a food web is rebuilt after disturbance or the creation of new habitat. Bioenergetics: the flow and transformation of energy in and between living organisms and between living organisms and their environment. Cascade model: a food-web model which assumes hierarchical feeding along a single niche axis, with each species allocated a probability of feeding on taxa below it in the hierarchy. Community web: a food web intended to include all species and trophic links that occur within a defined ecological community. 'Species' in this sense might involve various degrees of aggregation or division of biological species. Compartmentalisation: the property by which one subset of sp...

Biodiversity and ecosystem functioning in dynamic landscapes

“…Traditional BEF experiments most frequently manipulate the richness of one trophic level and keep constant the diversity of the other ( prey or consumer) trophic levels, whereas in natural systems, biodiversity varies at both (or even across more than two) levels [24]. This simultaneous variation is triggered by (i) independent responses of species groups across trophic levels to environmental changes, and (ii) interdependent responses of the species groups to the biodiversity of the other level, such as predator and prey groups that covary in density and diversity.…”

“…In real-world ecosystems, however, the clear separation between consumer and prey biodiversity effects is blurred by the complex structure of food webs [33]. While the group of autotrophs with their mineral resources are well defined, consumers of higher trophic levels often distribute their feeding interactions across resources of multiple trophic levels [24,33]. Hence, the dynamics of resource and consumer populations comprise feedback mechanisms via intraguild predation links that alter the functional consequences of biodiversity change [9,34,35].…”

Concomitant predation on parasites is highly variable but constrains the ways in which parasites contribute to food web structure

“…Food webs also connect biodiversity to ecosystem functions by integrating patterns and processes from individual to community scales (Thompson et al . 2012). In particular, the overall structure of food webs has been directly tied to ecosystems' responses to environmental change (Thompson & Townsend 2003, 2005a; Tylianakis et al .…”

Disentangling higher trophic level interactions in the cabbage aphid food web using high-throughput DNA sequencing

“…The structure of the two food webs was described and compared using standard food web connectedness descriptors, namely taxa richness, trophic links, connectance, ratio of prey to consumer and food web vulnerability (Thompson et al 2012). Hyperparasitism rates (i.e.…”

“…4). Brevicoryne brassicae food web structure in native (UK) and invaded (NZ) ranges, and connectedness descriptors (see Bersier et al 2002 andThompson et al 2012), based on the molecular study of aphid mummies (N=99). Full circles represent trophic levels identified to species level based on COI DNA sequences (>98% BLAST similarity) and full circles with disrupted borders represent MOTUs which could not be identified down to species based on the Genbank and BOLD databases.…”