Demographic source-sink dynamics in Vaccinium elliottii Elliott’s blueberry (Vaccinium elliottii) occurs in dry upland as well as flood-prone bottomland forests throughout the southeastern United States. These contrasting habitats differ significantly in water table depth, light levels, and soil pH and nutrient levels, which should result in divergent selection on phenotypic traits. However, Vaccinium elliottii is not locally adapted to these distinct habitats. Rather, our results are consistent with demographic source-sink dynamics, in which adaptation to a marginal habitat is constrained by continual immigration from a benign habitat (Anderson & Geber, 2010). Theory predicts that selection should favor trait values that enhance fitness in the source habitat (upland forests) at the expense of trait values that are advantageous in the sink habitat (bottomland forests); essentially, V. ellioittii should exhibit traits specialized to dry upland conditions. Paradoxically, V. elliottii families showed a high degree of plasticity in foliar, ecophysiological, and rooting traits (Anderson, Sparks & Geber, 2010). We propose that phenotypic plasticity can be maintained despite demographic source-sink dynamics if: (1) plasticity is adaptive within the source habitat, and/or (2) plasticity is a phylogenetic artifact and genetic variation for plasticity is low, or the costs of plasticity are negligible. Indeed, genotypic selection analyses revealed few costs to plasticity and indicated that plasticity in some traits is beneficial under drought conditions, a stress associated with the source habitat (Anderson, in preparation). Our field experiment has been ongoing from 2005 to the present, during which time we have monitored phenotypes and fitness components in this long-lived woody perennial. Our future research in this system will apply ecogenomic tools to investigate the genetic basis of phenotypic plasticity. Seed dispersal by fish Seed dispersal is a critical stage in the life history of plants. It determines the initial pattern of juvenile distribution, and influences community dynamics, species diversity and gene flow among populations. One major group of vertebrates has been largely overlooked in studies of seed dispersal: fruit-eating fishes (Horn et al., 2011). During the lengthy annual flooded season, hundreds of species of frugivorous fish move into South American floodplain forests and consume fallen fruits and seeds. We have investigated the seed dispersal activities of frugivorous fishes in Pacaya-Samiria National Reserve (Peruvian Amazon), the Brazilian Pantanal, and the Rio Caqueta (Colombian Amazon). These species disperse massive quantities of seeds of a large proportion of the flora, which can germinate in seasonally flooded habitats after floodwaters recede (Anderson et al., 2009 and Correa et al., in press). The extensive mobility of large-bodied species such as Colossoma translates into extremely long distance seed dispersal, which rivals seed dispersal by Asian elephants and African hornbills (Anderson, Nuttle, Saldaña Rojas, Pendergast and Flecker, 2011). Our seed dispersal model incorporates seed loss to inhospitable habitats, which is likely to occur in nearly all systems when frugivores visit habitats that are not suitable for germination. Since these fish spend the vast majority of their time in flooded forests and savannahs, few seeds are lost to permanent bodies of water, such as rivers or oxbow lakes. Large fruit-eating fish species are highly overexploited throughout their ranges. Overfishing has likely biased the age structure of populations to younger fish, with unknown implications for plant community dynamics and the maintenance of diversity in Amazonian floodplains. In collaboration with Drs. Sandra Correa , Jerry Penha, Catia Nunes da Cunha, Pablo Stevenson, Pia Parolin, Agostinho Catella, and Edwin Córdoba, we are currently dissecting the ecological and evolutionary consequences of overexploitation of fruit-eating fish in the Brazilian Pantanal and the Colombian Amazon. Our study integrates data on fish behavior, plant ecology and fisheries to test whether commerical fisheries target the best seed dispersers (generally larger, older fish). We are also establishing a series of exclosures in wetland habitats in the Pantanal to connect the seed dispersal activities of fish (flooded season) with plant regeneration and seedling diversity (dry season). We have also have studied regeneration dynamics in two species of tropical trees (Anderson, 2009), and flooding tolerance of a shrub in cypress-tupelo swamps (Anderson, Landi and Marks, 2009). We have co-authored reviews of the Janzen-Connell hypothesis (Carson et al., 2008), ecogenomic techniques for investigating plant defenses against herbivores (Anderson and Mitchell-Olds, 2011), the evolutionary genetics of plant adaptation (Anderson et al., 2011), and evolutionary responses of plants to global change (Anderson et al., 2012).
