Pigment dynamics and autumn leaf senescence in a New England deciduous forest, eastern USA

The leaves of woody plants at Harvard Forest in Central Massachusetts, USA, changed color during senescence; 70% (62/89) of the woody species examined anatomically contained anthocyanins during senescence. Anthocyanins were not present in summer green leaves, and appeared primarily in the vacuoles of palisade parenchyma cells. Yellow coloration was a result of the unmasking of xanthophyll pigments in senescing chloroplasts. In nine red-senescing species, anthocyanins were not detectable in mature leaves, and were synthesized de novo in senescence, with less than 20 m g cm - 2 of chlorophyll remaining. Xanthophyll concentrations declined in relation to chlorophyll to the same extent in both yellow- and red-leaved taxa. Declines in the maximum photosystem II quantum yield of leaves collected prior to dawn were only slightly less in the red-senescing species, indicating no long-term protective activity. Red-leaved species had significantly greater mass/area and lower chlorophyll a / b ratios during senescence. Nitrogen tissue concentrations in mature and senescent leaves negatively correlated to anthocyanin concentrations in senescent leaves, weak evidence for more efficient nitrogen resorption in anthocyanic species. Shading retarded both chlorophyll loss and anthocyanin production in Cornus alternifolia , Acer rubrum , Acer saccharum , Quercus rubra and Viburnum alnifolium . It promoted chlorophyll loss in yellow-senescing Fagus grandifolia . A reduced red : far-red ratio did not affect this process. Anthocyanins did not increase leaf temperatures in Q. rubra and Vaccinium corymbosum on cold and sunny days. The timing of leaf-fall was remarkably constant from year to year, and the order of senescence of individual species was consistent.

Identification, distribution, and probability of infection in sympatric gastropods by digenean parasites at Pa-hay-okee, Everglades National Park using molecules and morphology

In this study, I determined the identity, taxonomic placement, and distribution of digenetic trematodes parasitizing the snails Pomacea paludosa and Planorbella duryi at Pa-hay-okee, Everglades National Park. I also characterized temporal and geographic variation in the probability of parasite infection for these snails based on two years of sampling. Although studies indicate that digenean parasites may have important effects both on individual species and the structure of communities, there have been no studies of digenean parasitism on snails within the Everglades ecosystem. For example, the endangered Everglade Snail Kite, a specialist that feeds almost exclusively on Pomacea paludosa, and is known to be a definitive host of digenean parasites, may suffer direct and indirect effects from consumption of parasitized apple snails. Therefore, information on the diversity and abundance of parasites harbored in snail populations in the Everglades should be of considerable interest for management and conservation of wildlife. Juvenile digeneans (cercariae) representing 20 species were isolated from these two snails, representing a quadrupling of the number of species known. Species were characterized based on morphological, morphometric, and sequence data (18S rDNA, COI, and ITS). Species richness of shed cercariae from P. duryi was greater than P. paludosa, with 13 and 7 species respectively. These species represented 14 families. P. paludosa and P. duryi had no digenean species in common. Probability of digenean infection was higher for P. duryi than P. paludosa and adults showed a greater risk of infection than juveniles for both of these snails. Planorbella duryi showed variation in probability of infection between sampling sites and hydrological seasons. The number of unique combinations of multi-species infections was greatest among P. duryi individuals, while the overall percentage of multi-species infections was greatest in P. paludosa. Analyses of six frequently-observed multiple infections from P. duryi suggest the presence of negative interactions, positive interactions, and neutral associations between larval digeneans. These results should contribute to an understanding of the factors controlling the abundance and distribution of key species in the Everglades ecosystem and may in particular help in the management and recovery planning for the Everglade Snail Kite.

Invasive exotic plant indicators for ecosystem restoration: An example from the Everglades restoration program

We have developed a comprehensive ecological indicator for invasive exotic plants, a human-influenced component of the Everglades that could threaten the success of the restoration initiative. Following development of a conceptual ecological model for invasive exotic species, presented as a companion paper in this special issue, we developed criteria to evaluate existing invasive exotic monitoring programs for use in developing invasive exotic performance measures. We then used data from the selected monitoring programs to define specific performance measures, using species presence and abundance as the basis of the indicator for invasive exotic plants. We then developed a series of questions used to evaluate region and/or individual species status with respect to invasion. Finally, we used an expert panel who had answered the questions for invasive exotic plants in the Everglades Lake Okeechobee model to develop a stoplight restoration report card to communicate invasive exotic plant status. The report card system provides a way to effectively evaluate and present indicator data to managers, policy makers, and the public using a uniform format among indicators. Collectively, the model, monitoring assessment, performance measures, and report card enable us to evaluate how invasive plants are impacting the restoration program and how effectively that impact is being managed. Applied through time, our approach also allows us to follow the progress of management actions to control the spread and reduce the impacts of invasive species and can be easily applied and adapted to other large-scale ecosystem projects.

Disturbance and the rising tide: the challenge of biodiversity management on low-island ecosystems

Sea-level rise presents an imminent threat to freshwater-dependent ecosystems on small oceanic islands, which often harbor rare and endemic taxa. Conservation of these assemblages is complicated by feedbacks between sea level and recurring pulse disturbances (eg hurricanes, fire). Once sea level reaches a critical level, the transition from a landscape characterized by mesophytic upland forests and freshwater wetlands to one dominated by mangroves can occur suddenly, following a single storm-surge event. We document such a trajectory, unfolding today in the Florida Keys. With sea level projected to rise substantially during the next century, ex-situ actions may be needed to conserve individual species of special concern. However, within existing public conservation units, managers have a responsibility to conserve extant biodiversity. We propose a strategy that combines the identification and intensive management of the most defensible core sites within a broader reserve system, in which refugia for biota facing local extirpation may be sought.