Placing biodiversity and ecosystem functioning in context: environmental perturbations and the effects of species richness in a stream field experiment

Abstract

Greater biodiversity is often associated with increased ecosystem process rates, and is expected to enhance the stability of ecosystem functioning under abiotic stress. However, these relationships might themselves be altered by environmental factors, complicating prediction of the effects of species loss in ecosystems subjected to abiotic stress. In boreal streams, we investigated effects of biodiversity and two abiotic perturbations on three related indices of ecosystem functioning: leaf decomposition, detritivore leaf processing efficiency (LPE) and detritivore growth. Replicate field enclosures containing leaves and detritivore assemblages were exposed to liming and nutrient enrichment, raising pH and nutrient levels. Both treatments constitute perturbations for our naturally acidic and nutrient-poor streams. We also varied detritivore species richness and density. The effects of the abiotic and diversity manipulations were similar in magnitude, but whereas leaf decomposition increased by 18% and 8% following liming and nutrient enrichment, respectively, increased detritivore richness reduced leaf decomposition (6%), detritivore LPE (19%) and detritivore growth (12%). The detritivore richness effect on growth was associated with negative trait-independent complementarity, indicating interspecific interference competition. These interactions were apparently alleviated in both enriched and limed enclosures, as trait-independent complementarity became less negative. LPE increased with detritivore density in the monocultures, indicating benefits of intra-specific aggregation that outweighed the costs of intra-specific competition, and dilution of these benefits probably contributed to lowered leaf decomposition in the species mixtures. Finally, the effects of liming were reduced in most species mixtures relative to the monocultures. These results demonstrate how environmental changes might regulate the consequences of species loss for functioning in anthropogenically perturbed ecosystems, and highlight potential influences of biodiversity on functional stability. Additionally, the negative effects of richness and positive effects of density in our field study were opposite to previous laboratory observations, further illustrating the importance of environmental context for biodiversity-ecosystem functioning relationships.

Intraspecific traits change biodiversity effects on ecosystem functioning under metal stress

“…Our study highlights the importance of environmental context to explain the variability of results when examining biodiversity-ecosystem functioning relationships as found previously by others (Mckie et al 2009;Pascoal et al 2010). Manipulating 1-4 aquatic hyphomycete species, Pascoal et al (2010) showed that the exposure to zinc attenuated the positive effects of species richness on leaf decomposition.…”

Headwater reservoirs weaken terrestrial‐aquatic linkage by slowing leaf‐litter processing in downstream regulated reaches

“…Flow reduction is also related to a decrease of the total taxa richness and shredder abundance (Death et al, 2009), which is also supported in our study. Species loss might impact ecosystem functioning by reducing the overall capacity of the biota to maintain a process at a given rate (McKie et al, 2009). Furthermore, as leaf litter decomposition in headwater streams represents the main input of energy within the system (Wallace et al, 1997), secondary species loss and further impairment of the ecosystem might easily be predicted in regulated headwater streams.…”

No evidence for leaf‐trait dissimilarity effects on litter decomposition, fungal decomposers, and nutrient dynamics

“…In contrast, by enclosing detritivores in litter-containing microcosms, Vos et al (2013) could distinguish between feeding on single and multiple litter species. Similar experiments would have to be conducted in streams (McKie et al 2009) to test whether consumermediated litter dissimilarity effects could arise at the stream-reach scale rather than at the litterbag scale examined in the present study.…”