671,577 research outputs found

    Relative contribution of abundant and rare species to species–energy relationships

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    A major goal of ecology is to understand spatial variation in species richness. The latter is markedly influenced by energy availability and appears to be influenced more by common species than rare ones; species–energy relationships should thus be stronger for common species. Species–energy relationships may arise because high-energy areas support more individuals, and these larger populations may buffer species from extinction. As extinction risk is a negative decelerating function of population size, this more-individuals hypothesis (MIH) predicts that rare species should respond more strongly to energy. We investigate these opposing predictions using British breeding bird data and find that, contrary to the MIH, common species contribute more to species–energy relationships than rare ones

    Less is more: rarity trumps quality in luxury markets

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    The international market for luxury goods has almost doubled since 1990, with a worldwide increase of 10% annually. This trade is fuelled by a great deal of legally and illegally exploited wildlife species, putting enormous pressure on many of them, with potentially irreversible consequences. The dramatic decline of sturgeon populations exploited for their caviar, is a good example: all 27 species are threatened and the most coveted are on the verge of extinction. We aim to identify the mechanism responsible for the continued overexploitation of sturgeon species, despite caviar's ever-increasing price and the imminent loss of these species. Here, we demonstrate consumer preference for rarity over intrinsic quality: customers tasting two caviar samples more often chose the one they thought was rare, although both were identical. In a game theory model, we demonstrate that the most rational behaviour is to rush to consume rare species, even though this precipitates their extinction. We conclude that the human predisposition to place exaggerated value on rarity probably drives the entire market for luxury goods from reptile skins to exotic woods. Our findings suggest that allowing low levels of legal trade will exacerbate the arbitrary value of rare species and thereby stimulate demand. Only a total ban on trade from the wild (with very strict controls) combined with strong support for farmed equivalents will protect rare species

    Habitat Characterization of Five Rare Insects in Michigan (Lepidoptera: Hesperiidae, Riodinidae, Satyridae; Homoptera: Cercopidae)

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    Over 80 species of insects are listed as endangered, threatened, or special concern under Michigan\u27s endangered species act. For the majority of these species, detailed habitat information is scant or difficult to interpret. We describe the habitat of five insect species that are considered rare in Michigan: Lepyronia angulifera (Cercopidae), Prosapia ignipectus (Cercopidae), Oarisma poweshiek (Hesperiidae), Calephelis mutica (Riodinidae), and Neonympha mitchellii mitchellii (Satyridae). Populations of each species were only found within a fraction of the plant communities deemed suitable based upon previous literature. Furthermore, individuals of each species were observed to be closely affiliated with just a few vegetation associations within larger plant communities. Restriction of these species to particular microhabitats was determined to be, in part, due to ecological or behavioral specialization of each insect species. We believe that the most holistic man­agement and conservation practices for these rare insects in Michigan should focus on protecting the integrity of both the plant community and the micro- habitat upon which these species depend

    Updated Conservation Status of Protected Minnesota Caddisflies

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    Seven of the 13 Minnesota Trichoptera species with official protected status were located in the state during 1997-2001, including four species – Agapetus tomus, Asynarchus rossi, Hydroptila novicola, and Polycentropus milaca – not collected in nearly 40 years. Three species – Chilostigma itascae, Oxyethira ecornuta, and Polycentropus milaca – appear rare in Minnesota, two – Agapetus tomus and Asynarchus rossi – appear rare but locally abundant, and two – Hydroptila novicola and Oxyethira itascae – were found throughout northern Minnesota suggesting that they are more abundant than previously thought. Five listed species were not collected during this study and are currently of unknown conservation status. One listed species, Setodes guttatus, almost certainly does not occur in Minnesota and should be delisted

    Estimating sample representativeness in a survey of stream caddisfly fauna

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    Obtaining an adequate and representative sample is a continuing challenge of community ecology. The present study focuses on what sample area represents adequately the structural composition of the caddisfly fauna of a riffle, at a given sampling occasion. Sixty-two Surber samples were collected from a riffle in a second-order reach of the Bernecei Stream (Börzsöny Mountains, Hungary). This data set was used to estimate sample representativeness at different sample sizes (from 1 to 31 Surber samples, 0.09 m2 - 2.79 m2) generated a re-sampling procedure. Sample representativeness was measured with mean Jaccard Coefficient and Bray-Curtis Index between samples for species presence-absence data and abundance data, respectively. We found that a sample size of 2.25 m2 represented well (mean similarity 0.998) the species composition of the caddisfly fauna if rare species were excluded from the analysis. In contrast, sample representativeness of species composition proved to be relatively low (0.719) if rare species were included in the analysis. Curves of sample representativeness based on both raw-, or transformed abundance data were less sensitive to the presence of rare species and showed lower representativeness than sample representativeness based on presence/absence data

    Neighborhood and community interactions determine the spatial pattern of tropical tree seedling survival

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    Factors affecting survival and recruitment of 3531 individually mapped seedlings of Myristicaceae were examined over three years in a highly diverse neotropical rain forest, at spatial scales of 1–9 m and 25 ha. We found convincing evidence of a community compensatory trend (CCT) in seedling survival (i.e., more abundant species had higher seedling mortality at the 25-ha scale), which suggests that density-dependent mortality may contribute to the spatial dynamics of seedling recruitment. Unlike previous studies, we demonstrate that the CCT was not caused by differences in microhabitat preferences or life history strategy among the study species. In local neighborhood analyses, the spatial autocorrelation of seedling survival was important at small spatial scales (1–5 m) but decayed rapidly with increasing distance. Relative seedling height had the greatest effect on seedling survival. Conspecific seedling density had a more negative effect on survival than heterospecific seedling density and was stronger and extended farther in rare species than in common species. Taken together, the CCT and neighborhood analyses suggest that seedling mortality is coupled more strongly to the landscape-scale abundance of conspecific large trees in common species and the local density of conspecific seedlings in rare species. We conclude that negative density dependence could promote species coexistence in this rain forest community but that the scale dependence of interactions differs between rare and common species

    Protracted speciation revitalizes the neutral theory of biodiversity.

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    Understanding the maintenance and origin of biodiversity is a formidable task, yet many ubiquitous ecological patterns are predicted by a surprisingly simple and widely studied neutral model that ignores functional differences between species. However, this model assumes that new species arise instantaneously as singletons and consequently makes unrealistic predictions about species lifetimes, speciation rates and number of rare species. Here, we resolve these anomalies - without compromising any of the original models existing achievements and retaining computational and analytical tractability - by modelling speciation as a gradual, protracted, process rather than an instantaneous event. Our model also makes new predictions about the diversity of incipient species and rare species in the metacommunity. We show that it is both necessary and straightforward to incorporate protracted speciation in future studies of neutral models, and argue that non-neutral models should also model speciation as a gradual process rather than an instantaneous one

    Creating ultracold molecules by collisions with ultracold rare gas atoms in an optical trap

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    We study collisions of para-H2_2 with five rare gas atomic species (He, Ne, Ar, Kr and Xe) over the range from 1 K to 1 ÎĽ\mu K and evaluate the feasibility of sympathetic cooling H2_2 with ultracold ground state rare gas atoms co-trapped within a deep optical trap. Collision cross-sections over this large temperature range show that all of these species could be used to cool H2_2 to ultracold temperatures and that argon and helium are the most promising species for future experiments.Comment: 5 pages, 1 figure, 1 table, submitted for publicatio

    Neutral Theory and Relative Species Abundance in Ecology

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    The theory of island biogeography[1] asserts that an island or a local community approaches an equilibrium species richness as a result of the interplay between the immigration of species from the much larger metacommunity source area and local extinction of species on the island (local community). Hubbell[2] generalized this neutral theory to explore the expected steady-state distribution of relative species abundance (RSA) in the local community under restricted immigration. Here we present a theoretical framework for the unified neutral theory of biodiversity[2] and an analytical solution for the distribution of the RSA both in the metacommunity (Fisher's logseries) and in the local community, where there are fewer rare species. Rare species are more extinction-prone, and once they go locally extinct, they take longer to re-immigrate than do common species. Contrary to recent assertions[3], we show that the analytical solution provides a better fit, with fewer free parameters, to the RSA distribution of tree species on Barro Colorado Island (BCI)[4] than the lognormal distribution[5,6].Comment: 19 pages, 1 figur

    Data on the terrestrial Isopoda fauna of the AlsĂł-hegy, Aggtelek National Park, Hungary

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    Field surveys in dolines of AlsĂł-hegy, Aggtelek Karst (Hungary) yielded 10 terrestrial isopod species. Despite of the relatively low species richness, we would like to emphasize the high naturalness of the area indicated by the presence of endemic and rare species
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