Species diversity and trade-offs in pitcher plant (Sarracenia purpurea) inquiline communities

Understanding the factors that enable species to coexist and the resulting patterns of diversity remains one of the prominent goals of ecology. These factors can be separated into two distinct scales in most communities. At the local community scale, resource levels and species interactions (competition and predation) can regulate species abundances. At the regional scale, processes such as dispersal can affect community dynamics. Traditionally, coexistence of species in communities has been explained by niche differences: trade-offs in species traits that allow each species do well under certain circumstances. However what is much less recognized is that these trade-offs must occur at very specific spatial scales in order to promote coexistence. The purpose of this study is to better understand how these different factors (local processes, regional processes, and species traits) affect species abundances and coexistence at different scales.; The inquiline community (bacteria, protozoans, rotifers, and mosquito larvae) found in the water-filled leaves of the pitcher plant, Sarracenia purpurea, is a model system in which to examine community dynamics at different spatial scales. The boundaries of the local community are distinct and the species that inhabit this community have short generation times and are easily manipulated. Manipulative experiments were used to quantify the relative effects of predators and resources in this community. Local community dynamics (bacteria and protozoan abundance and diversity) were strongly affected by resource addition, but predation affected only specific groups of species. Increases in dispersal frequency among communities, increased protozoan regional diversity and had a hump-shaped relationship with protozoan local diversity. The hump-shaped relationship was suppressed when a predator was present in the local community. The most common protozoan and rotifer species exhibited trade-offs in predator tolerance and competitive ability in different resource environments, indicating coexistence most likely occurs at the heterogeneous-regional scale. In addition, life-history traits (growth rate, carrying capacity, and size) were correlated with species-interaction traits. Species-specific differences also resulted in differential effects on the adjacent trophic levels (bacteria abundance and larval growth). Local and regional processes interacted with species-specific traits to produce the patterns of abundance and diversity observed in this unique community.