Species effects on ecosystem processes are modified by faunal responses to habitat composition

Abstract

Heterogeneity is a well-recognized feature of natural environments, and the spatial distribution and movement of individual species is primarily driven by resource requirements. In laboratory experiments designed to explore how different species drive ecosystem processes, such as nutrient release, habitat heterogeneity is often seen as something which must be rigorously controlled for. Most small experimental systems are therefore spatially homogeneous, and the link between environmental heterogeneity and its effects on the redistribution of individuals and species, and on ecosystem processes, has not been fully explored. In this paper, we used a mesocosm system to investigate the relationship between habitat composition, species movement and sediment nutrient release for each of four functionally contrasting species of marine benthic invertebrate macrofauna. For each species, various habitat configurations were generated by selectively enriching patches of sediment with macroalgae, a natural source of spatial variability in intertidal mudflats. We found that the direction and extent of faunal movement between patches differs with species identity, density and habitat composition. Combinations of these factors lead to concomitant changes in nutrient release, such that habitat composition effects are modified by species identity (in the case of NH4-N) and by species density (in the case of PO4-P). It is clear that failure to accommodate natural patterns of spatial heterogeneity in such studies may result in an incomplete understanding of system behaviour. This will be particularly important for future experiments designed to explore the effects of species richness on ecosystem processes, where the complex interactions reported here for single species may be compounded when species are brought together in multi-species combinations.

Functional effects of the hadal sea cucumber Elpidia atakama (Echinodermata: Holothuroidea, Elasipodida) reflect small-scale patterns of resource availability

“…In the present study, E. atakama spent 150 min relocating and 267 min feeding (a ratio of 1:1.8), suggesting that resource supply is indeed abundant and that the distance between patches is relatively short (20-40 min travel time, or approximately 10 body length distance). This pattern of movement suggests considerable sensitivity to food concentration (McClintic et al 2008) and implies that the dynamics and organisation of hadal communities are intimately linked to habitat structure and the distribution of resources in ways similar to those found in shallower benthic communities (Levinton and Kelaher 2004;Dyson et al 2007;Bulling et al 2008;Nogaro et al 2008;Godbold et al 2011). Thus, the cumulative response of hadal species to such small-scale variation is likely to influence species contributions to ecosystem properties at much larger scales (Godbold et al 2011).…”

Habitat structure mediates biodiversity effects on ecosystem properties

“…To incorporate habitat heterogeneity, patches were either non-enriched (NE) or enriched (E) with dried, ground U. intestinalis [18,19]. We assembled two heterogeneity configurations (H A and H B ).…”

“…[17,18,44]). As a first step, a linear regression model was applied to check that underlying statistical assumptions were not violated.…”

“…Where components of habitat structure have been considered, species that were previously found to be of minor importance in mediating ecosystem properties in homogeneous experimental systems (e.g. [16,17]) have subsequently been shown to be of much greater importance in equivalent heterogeneous systems [18]. Moreover, the way species interact with their environment has the potential to alter the nature of trophic interactions [19] and the fundamental form of the relationship between biodiversity and ecosystem properties [20,21], rekindling debate over the relevance and capacity of manipulative experiments to inform management, conservation and policy [22][23][24][25][26].…”

Form, function and physics: the ecology of biogenic stabilisation

“…Natural environments tend to be heterogeneous, whereas mesocosm or laboratory studies are generally controlled homogeneous environments (Dyson et al 2007). Natural heterogeneity has been observed to buffer against stressor effects (Godbold et al 2011) or negate patterns observed under laboratory conditions (Bulling et al 2008).…”