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Thirty years of forest census at Barro Colorado and the importance of immigration in maintaining diversity.

ABSTRACT: The neutral theory of community ecology can predict diversity and abundances of tropical trees, but only under the assumption of steady input of new species into the community. Without input, diversity of a neutral community collapses, so the theory's predictions are not relevant unless novel species evolve or immigrate. We derive analytically the species input needed to maintain a target tree diversity, and find that a rate close to 1.0 x 10(-4) per recruit would maintain the observed diversity of 291 species in the Barro Colorado 50-ha tree plot in Panama. We then measured the rate empirically by comparing species present in one complete enumeration of the plot to those present five years later. Over six census intervals, the observed rate of input was 0.6 x 10(-4) to 1.8 x 10(-4) species per recruit, suggesting that there is adequate immigration of novel species to maintain diversity. Species interactions, niche partitioning, or density-dependence, while they may be present, do not appear to enhance tree species richness at Barro Colorado.

SUBMITTER: Condit R

PROVIDER: S-EPMC3511510 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature

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Thirty years of forest census at Barro Colorado and the importance of immigration in maintaining diversity.

Condit Richard R Chisholm Ryan A RA Hubbell Stephen P SP

PloS one 20121130 11

The neutral theory of community ecology can predict diversity and abundances of tropical trees, but only under the assumption of steady input of new species into the community. Without input, diversity of a neutral community collapses, so the theory's predictions are not relevant unless novel species evolve or immigrate. We derive analytically the species input needed to maintain a target tree diversity, and find that a rate close to 1.0 x 10(-4) per recruit would maintain the observed diversity ...[more]

PMID: 23226222

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Project description:BackgroundSand flies (Diptera, Psychodidae, Phlebotominae) in the genus Lutzomyia are the predominant vectors of the protozoan disease leishmaniasis in the New World. Within the watershed of the Panama Canal, the cutaneous form of leishmaniasis is a continuous health threat for residents, tourists and members of an international research community. Here we report the results of screening a tropical forest assemblage of sand fly species for infection by both Leishmania and a microbe that can potentially serve in vector population control, the cytoplasmically transmitted rickettsia, Wolbachia pipientis. Knowing accurately which Lutzomyia species are present, what their evolutionary relationships are, and how they are infected by strains of both Leishmania and Wolbachia is of critical value for building strategies to mitigate the impact of this disease in humans.Methodology and findingsWe collected, sorted and then used DNA sequences to determine the diversity and probable phylogenetic relationships of the Phlebotominae occurring in the understory of Barro Colorado Island in the Republic of Panama. Sequence from CO1, the DNA barcoding gene, supported 18 morphology-based species determinations while revealing the presence of two possible "cryptic" species, one (Lu. sp. nr vespertilionis) within the Vespertilionis group, the other (Lu. gomezi) within the Lutzomyia-cruciata series. Using ITS-1 and "minicircle" primers we detected Leishmania DNA in 43.3% of Lu. trapidoi, 26.3% of Lu. gomezi individuals and in 0% of the other 18 sand fly species. Identical ITS-1 sequence was obtained from the Leishmania infecting Lu. trapidoi and Lu. gomezi, sequence which was 93% similar to Leishmania (viannia) naiffi in GenBank, a species previously unknown in Panama, but recognized as a type of cutaneous leishmaniasis vectored broadly across northern and central South America. Distinct strains of the intracellular bacterium Wolbachia were detected in three of 20 sand fly species, including Lu. trapidoi, in which it frequently co-occurred with Leishmania.ConclusionsBoth morphological and molecular methods were used to examine an assemblage of 20 sand fly species occurring in the forests of the Panama Canal area. Two of these species, members of separate clades, were found to carry Leishmania at high frequency and hence are likely vectors of leishmaniasis to humans or other mammal species. A single Leishmania species, identified with high confidence as Le. naiffi, was carried by both species. That Le. naiffi is known to cause cutaneous lesions in South America but has hitherto not been reported or implicated in Panama opens the possibility that its range has recently expanded to include the Isthmus or that it occurs as a recent introduction. The occurrence of Leishmania and Wolbachia in Lu. trapidoi identifies one important vector of the disease as a potential target for gene introductions using Wolbachia population sweeps.

Project description:Ecological communities are structured in response to spatial and temporal variation of numerous factors, including edaphic conditions, biotic interactions, climatic patterns and disturbance regimes. Widespread anthropogenic factors such as timber harvesting can create long-lasting impacts, obscuring the relationship between community structure and environmental conditions. Minimally impacted systems such as old-growth forests can serve as a useful ecological baseline for predicting long-term compositional shifts. We utilized decadal tree species sampling data (1979-2010) divided into three strata (understory, midstory, overstory) to examine temporal changes in relative abundances and spatial distributions of dominant taxa, as well as overall shifts in community composition, in a relatively pristine Appalachian old-growth forest in eastern Kentucky, USA. Quercus and Carya species persisted mainly as mature canopy trees with decreasing juvenile recruitment, especially in mesic areas. In contrast, Acer, Fagus, and other mesophytic species were abundant and spatially widespread in subcanopy layers suggesting these species are more likely to recruit in gap-scale canopy openings. In the overstory, mesophytic species were spatially restricted to lower and mid-slope mesic habitats. Temporal changes in community composition were most evident in the understory and tended to be greater in mesic areas, a trend seemingly driven by recruitment failure among xerophytic species. In subcanopy vegetation we discovered a loss of distinction through time among the ecological community designations established following the 1979 survey (Chestnut oak, Mixed mesophytic, and Beech). The overstory was more stable through time, suggesting a storage effect where long-lived trees have maintained a particular community composition through time in areas where regeneration opportunities are minimal under current environmental conditions. Overall, sitewide canopy succession is occurring slowly in the absence of major disturbance, and topography-driven environmental variation appears to have an important local-scale filtering effect on communities.

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Thirty years of forest census at Barro Colorado and the importance of immigration in maintaining diversity.

Publications

Thirty years of forest census at Barro Colorado and the importance of immigration in maintaining diversity.

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