Print PageA major focus in recent ecological research has been to elucidate if and when the details of biological interactions play a critical role in producing observed patterns of diversity. These patterns take many forms, but among the most commonly studied macroecological patterns are the species-abundance distribution (SAD), the species-area relationship (SAR) and the species-time relationship (STR). Macroecology has increasingly become an important and popular approach in ecology. However, because it often ignores the inherent complexity within biological systems in its attempt to find generality across systems, its utility has been increasingly questioned. This has generated an important question: are macroecological patterns contingent on the specific networks of interactions among ecological particles or do patterns emerge from interactions regardless of the details of interactions? We generated rank-abundance distributions (RADs), SARs and STRs using annual plant census data (1989-2008) at a long-term experimental site where communities differ in an important biotic interaction, seed predation. Rodent seed predation strongly influences species composition and density of individuals in the winter annual community, but not the summer annual community. Fenced plots constrain rodent access in one of three ways: 1) all rodents have access, 2) large-bodied rodents (Dipodomys spp.) removed, and 3) all rodents removed.
Results/Conclusions
Although seed predation alters plant community composition (Permanova, winter, p=0.0001, summer, p=0.0002), there was no detectable difference in RAD or SAR shape among experimental treatments. We compared RADs using chi-squared tests (winter and summer, all p values>0.05) and compared the slopes and intercepts of SARs (ANOVA, winter slope, p=0.13 intercept, p=0.13, summer slope, p=0.56, intercept, p=0.59). However, slopes and intercepts of STRs differed significantly in the winter and summer annual community (ANOVA, winter slope p=0.072, winter intercept p<0.0001, summer slope p=0.042, summer intercept p=0.0001). Our results suggest that static patterns, which represent only a snapshot of species diversity in time, may not be strongly influenced by the details of biotic interactions. In contrast, dynamic patterns may be more likely to capture the effects of altered biotic interactions on species richness. Our research is unique in that we have combined a local-scale experimental approach with a spatiotemporal macroecological approach to understand species richness. Further syntheses of macroecology and experimental data may lead to a more robust understanding of when biological details are necessary for predicting spatial and temporal patterns of diversity.
