Species traits predict assemblage dynamics at ephemeral resource patches created by carrion

Abstract

Carrion is an ephemeral and spatially patchy resource that supports a diverse subset of species linked to nutrient cycling and the decomposition process. A number of studies have separately documented changes in the diversity of plants, arthropods and vertebrates at individual carcasses, but there are few studies that have examined how functional traits of different groups of organisms underpin their responses to carrion patches. We used a carrion addition experiment to compare changes in composition and functional traits of insect and plant assemblages at carcasses compared with control sites. We found that significant changes in insect assemblage evenness and heterogeneity was associated with species' dispersal traits, and that plant assemblage responses to subsequent soil nitrogen changes was most apparent among graminoids and exotic species. Beetles at carcasses were twice as large as their counterparts at control sites during the first week of carrion decomposition, and also had higher wing loadings. Plants with high specific leaf area responded faster to the carcass addition, and twice as many species recolonised the centre of carcasses in exotic-dominated grassland compared with carcasses in native-dominated grassland. These results provide an example of how traits of opportunist species enable them to exploit patchy and dynamic resources. This increases our understanding of how carcasses can drive biodiversity dynamics, and has implications for the way carrion might be managed in ecosystems, such as appropriate consideration of spatial and temporal continuity in carrion resources to promote heterogeneity in nutrient cycling and species diversity within landscapes.

Figure 1. Effect of carrion on soil and foliar nitrogen.

Carrion increased (a) soil total nitrogen, (b) soil organic nitrogen, and (c) tree foliar total nitrogen relative to control sites. Error bars show mean ± SE.

Figure 2. Differences in plant species richness and traits between carcass centre, carcass edge, and control sites.

(a) Species richness of plants species in exotic grassland compared with native grassland. (b) Specific leaf area of plants in exotic grassland compared with native grassland. (c) Percentage of annuals versus perennials. (d) Percentage of graminoids versus forbs. Error bars show mean ± SE.

Figure 3. Recolonisation of plants 52 weeks after carrion addition.

Very little recolonisation had occurred in the native-dominated grassland sites (a), whereas re-colonisation had progressed further in all exotic-dominated grassland sites (b), reflecting greater tolerance of some exotic species to extremely high nutrients. These examples indicate a different succession trajectory for native versus exotic grassland plant assemblages, with recolonisation occurring over different time scales.

Figure 4. Effect of carrion on beetle and ant diversity.

(a) Species richness and evenness of beetles at carcasses showed a trajectory through time clearly different from control sites at weeks 1, 6 and 12, with a return to similar levels at week 26 (blue arrows). (b) Species richness of ants at carcasses was half that at control sites during week 1 (red arrows), but was then similar to control sites at week 6, 12 and 26 of the experiment. Error bars show mean ± SE.

Figure 5. Effect of carrion on insect assemblage heterogeneity.

Average distance to group centroid, reflecting heterogeneity in composition among samples of (a) beetles and (b) ants from carrion and control treatments. Error bars show mean ± SE.

Figure 6. Differences in insect morphological traits between carcass and control sites.

(a) Beetle species at carrion during week 1 were larger on average than those at control sites. (b) Beetle species at carrion during week 1 had higher wing loadings on average than beetle species at control sites. (c) No differences in ant body size were observed at different stages of carrion decomposition. (d) Macropterous beetles were always more prevalent at carcass sites that control sites. Error bars show mean ± SE.