Biocomplexity Project: A Synthetic Approach to Phytotelmata Communities

Background on Phytotelmata Communities Recently it has become clear that a full understanding of the factors controlling communities will require understanding of processes that occur at different spatial and temporal scales. Models of communities at large scales assume that, at the local and short-term scales, ecological processes such as competition and predation will be most important for determining individual behaviors, reproduction, and survival. At regional or longer scales, factors like migration, habitat destruction and extinction, and evolutionary history may be more important determinants of population growth rates and persistence. However, very few studies have explored community structure across many scales. Two factors have made this a particularly difficult experimental problem. First, many communities are large and extremely complex. Even defining community boundaries can be difficult. Second, most communities vary dramatically in response to climatic and historical factors at any large scale, making it difficult to partition the effects of various regional factors. Phytotelmata communities provide a unique situation in which to explore communities at a variety of scales. The pitcher plant Sarracenia purpurea occurs from northern Florida up the eastern seaboard, then across the northern midwest. In Canada, the species occurs across the continent, from Labrador to British Columbia. Each individual plant may have from 1 to 15 or more cup-shaped leaves that fill with rainwater and attract insect prey. The taxonomy of this species is the subject of some current debate. In general, the species is generally divided into a northern (S. purpurea purpurea) and southern (S. purpurea venosa) subspecies, with the southern subspecies having generally redder leaves and more obvious red veins running through the leaf. Recently, Naczi and his colleagues (Naczi et al. 1999) have proposed that the southernmost populations are actually a separate species, based on features such as the generally pinker flowers, shorter flowering scapes, and several aspects of the pitcher morphology. The leaves of Sarracenia purpurea serve as a specialized habitat for a number of species, creating a unique community type. In particular, three dipterans, a mite, and a rotifer are apparently specialists, occurring almost exclusively in the leaves of S. purpurea. One of these, the mosquito Wyeomyia smitthii has been the subject of a number of previous ecological and evolutionary studies, especially those of Bradshaw and Holzapfel's group at the University of Oregon. The rest of the community has been previously studied in specific locations but never systematically studied over any range. The studies of dynamics within individual leaves ("local dynamics") have demonstrated several consistent patterns. First, the communities are highly variable within any population of Sarracenia purpurea. The underlying cause of this variation is unknown but may be related to variation in bottom-up forces (variation among leaves in prey capture rate) and/or top-down forces (predation by mosquito larvae on protozoa and rotifers). Several experiments have shown that prey availability and mosquito abundance can both affect these communities of phytotelmata (e.g., Cochran-Stafira and Von Ende 1998, Kneitel and Miller in press). Other studies have demonstrated that -- Selection on life-history traits in Wyeomyia smithii occurs on latitudinal gradients that appear to be largely related to photoperiod and phenology. Recent evidence even suggests that global warming affects recent evolution in mosquito populations (William Bradshaw and Christine Holzapfel). -- Midges can rip apart dead insects, increasing bacterial activity, positively affecting the rest of the community (Stephen Heard). -- Rotifers and other phytotelmata are important for processing nitrogen sources that ultimately benefit the pitcher plant itself (Aaron Ellison and Leszek Bledszki). -- Some protozoan species are migration limited, while others are limited more by local conditions within each leaf (Tom Miller, Jamie Kneitel, and Jean Burns). We proposed that that these communities are ideal for studying how communities were structured at distinct spatial scales. At the smallest scale, the leaf itself, we do have some knowledge of the basic species interactions that can structure these communities, but little work has compared how communities vary at larger scales, that is among sites and across larger geographic areas. We feel that this approach will allow us to create further testable hypotheses about how communities are assembled, how community dynamics are affected by history and habitat, and how species in communities coevolve.