43,954 research outputs found
Estimating sample representativeness in a survey of stream caddisfly fauna
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
Relative contribution of abundant and rare species to species–energy relationships
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
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
Protracted speciation revitalizes the neutral theory of biodiversity.
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
Data on the terrestrial Isopoda fauna of the AlsĂł-hegy, Aggtelek National Park, Hungary
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
Oxycheila binotata Gray (Coleoptera: Carabidae: Cicindelinae), information on a little known taxon from Colombia
Two specimens of Oxycheila binotata Gray (Coleoptera: Carabidae: Cicindelinae) in the Field Museum of Natural History offer additional information on the morphology and distribution of this rare species. One of the specimens, a female, is considered to be the first known specimen of this species
Neutral Theory and Relative Species Abundance in Ecology
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
Where less may be more: how the rare biosphere pulls ecosystems strings
Rare species are increasingly recognized as crucial, yet vulnerable components of Earth’s ecosystems. This is also true for microbial communities, which are typically composed of a high number of relatively rare species. Recent studies have demonstrated that rare species can have an over-proportional role in biogeochemical cycles and may be a hidden driver of microbiome function. In this review, we provide an ecological overview of the rare microbial biosphere, including causes of rarity and the impacts of rare species on ecosystem functioning. We discuss how rare species can have a preponderant role for local biodiversity and species turnover with rarity potentially bound to phylogenetically conserved features. Rare microbes may therefore be overlooked keystone species regulating the functioning of host-associated, terrestrial and aquatic environments. We conclude this review with recommendations to guide scientists interested in investigating this rapidly emerging research area
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