Life-history trade-offs among core and transient species regulate local diversity and community structure

Background/Question/Methods

The connection between biodiversity and the commonness and rarity of species is a major research focus in ecology. A recent conceptual framework aims to understand biodiversity by partitioning communities into core species that are abundant and temporally persistent and transient species that are rare and temporally intermittent. Core and transient species have been shown to differ in spatiotemporal turnover, diversity patterns, and importantly, survival strategies targeted at local vs. regional habitat use. We predict that if core and transient species have differing local vs. regional survival strategies, and therefore differ in population-level spatial structure and gene flow, they should also differ predictably in their life-history traits. Specifically, core species should display relatively low dispersal rates, low reproductive effort, high ecological specialization and high survival rates compared to transient species. We present results from 10 years of capture-mark-recapture data (2000-2009) in a diverse rodent community evaluating the linkages between temporal permanence, local abundance, and trade-offs between life-history traits. 

Results/Conclusions

We used temporal permanence (proportion of years present) and average rank of each species to partition the community into three categories: core (present in all years and consistently common; 5 species), transient (present in some years and consistently rare; 5 species) and intermediate (present in all years and consistently rare; 3 species). Core granivorous species had higher survival probability (mean = 0.79 vs. 0.72) and lower probability of making a long distance movement (mean = 0.11 vs. 0.40) than transient granivorous species, and reproductive data suggested that core species also reproduced less often. Core species were arid-adapted specialists, supporting the idea that core species should experience strong local-scale evolutionary pressures and play important function roles in the community. Core species may be responsible for much of the function at a site (e.g., biomass production, nutrient cycling) and may set an upper limit for diversity, but transient species may be primarily responsible for maintaining species richness via subsidies from the regional species pool. We suggest that trait associations among core-transient species may be similar in other systems and will result in differing responses to environmental change among the two groups.