Consequences of Dominance: A Review of Evenness Effects on Local and Regional Ecosystem Processes

Abstract

The composition of communities is strongly altered by anthropogenic manipulations of biogeochemical cycles, abiotic conditions, and trophic structure in all major ecosystems. Whereas the effects of species loss on ecosystem processes have received broad attention, the consequences of altered species dominance for emergent properties of communities and ecosystems are poorly investigated. Here we propose a framework guiding our understanding of how dominance affects species interactions within communities, processes within ecosystems, and dynamics on regional scales. Dominance (or the complementary term, evenness) reflects the distribution of traits in a community, which in turn affects the strength and sign of both intraspecifc and interspecific interactions. Consequently, dominance also mediates the effect of such interactions on species coexistence. We review the evidence for the fact that dominance directly affects ecosystem functions such as process rates via species identity (the dominant trait) and evenness (the frequency distribution of traits), and indirectly alters the relationship between process rates and species richness. Dominance also influences the temporal and spatial variability of aggregate community properties and compositional stability (invasibility). Finally, we propose that dominance affects regional species coexistence by altering metacommunity dynamics. Local dominance leads to high beta diversity, and rare species can persist because of source-sink dynamics, but anthropogenically induced environmental changes result in regional dominance and low beta diversity, reducing regional coexistence. Given the rapid anthropogenic alterations of dominance in many ecosystems and the strong implications of these changes, dominance should be considered explicitly in the analysis of consequences of altered biodiversity.

Edge effect on vascular epiphytes in a subtropical Atlantic Forest

“…Cardinale et al (2006) suggested that reductions in richness affect ecosystemic processes such as biomass production and efficacy of resource use. Other properties, such as invasiveness, temporal stability and resilience, have also been associated with richness (Hillebrand et al 2008).…”

From species to communities: the signature of recreational use on a tropical river ecosystem

“…2008). These contrasting results emphasize the need to consider multiple metrics when exploring the potential consequences of anthropogenic impacts.…”

“…However, failure to detect a signature of disturbance in allocation patterns or diversity indices in our data could be interpreted as a sign of some resilience to recreational disturbance in these communities; Hillebrand et al. (2008) suggest that changes in evenness (which should be detectable using these parameters) are more likely to have implications for ecosystem function than differences in species richness. Interpreting the consequences of the changes we have detected for the delivery of ecosystem services is a challenge for the future (Dornelas et al.…”

Predicting species establishment using absent species and functional neighborhoods

“…However, biotic interactions occur at smaller spatial scales than the whole community (Huston, 1999) and abundance can be important in determining interaction outcomes (Hillebrand, Bennett, & Cadotte, 2008). Consequently, multiple samples from the community, each containing distinct information on species abundances, may be more useful in practice.…”