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Rare Species (rare + species)

Distribution by Scientific Domains

Life Sciences	85%
Earth and Environmental Science	8%
Humanities and Social Sciences	4%

Distribution within Life Sciences

Ecology & Organismal Biology	32%
Conservation Science	21%
Evolution	10%
Entomology	5%
10 Other Subdomains	32%

Selected Abstracts

Rare Species and the Use of Indicator Groups for Conservation Planning

CONSERVATION BIOLOGY, Issue 3 2003
Joshua J. Lawler
Although tests of the concept have produced varied results, sites selected to address indicator groups can include a high proportion of other species. We tested the hypothesis that species at risk of extinction are not likely to be included in sites selected to protect indicator groups. Using a reserve-selection approach, we compared the ability of seven indicator groups,freshwater fish, birds, mammals, freshwater mussels, reptiles, amphibians, and at-risk species of those six taxa,to provide protection for other species in general and at-risk species in particular in the Middle Atlantic region of the United States. Although sites selected with single taxonomic indicator groups provided protection for between 61% and 82% of all other species, no taxonomic group provided protection for more than 58% of all other at-risk species. The failure to cover at-risk species is likely linked to their rarity. By examining the relationship between a species' probability of coverage by each indicator group and the extent of its geographic range within the study area, we found that species with more restricted ranges were less likely to be protected than more widespread species. Furthermore, we found that although sites selected with indicator groups composed primarily of terrestrial species ( birds and mammals ) included relatively high percentages of those species ( 82,85% ) they included smaller percentages of strictly aquatic species (27,55%). Finally, of both importance and possible utility, we found that at-risk species themselves performed well as an indicator group, covering an average of 84% of all other species. Resumen: Los indicadores de la biodiversidad han sido propuestos como una herramienta potencial en la selección de áreas para conservación cuando la información sobre la distribución de algunas especies es escasa. A pesar de que algunas evaluaciones de este concepto han producido resultados variados, los sitios seleccionados para evaluar grupos indicadores pueden incluir una alta proporción de otras especies. Evaluamos la hipótesis de que las especies en riesgo de extinción probablemente no se incluyan en sitios seleccionados para proteger grupos indicadores. Usando la metodología de selección de reserva, comparamos la capacidad de siete grupos indicadores ( peces de agua dulce, aves, mamíferos, almejas de agua dulce, reptiles, anfibios y especies en riesgo de estos seis taxones ) para proveer protección a otras especies en general y especies en riesgo, en particular, en la región del Atlántico Medio de los Estados Unidos. A pesar de que los sitios con un solo grupo indicador proporcionaron protección para el 61% al 82% de todas las otras especies, ningún grupo taxonómico proporcionó protección para más del 58% de todas las otras especies en riesgo. La incapacidad de proteger especies en riesgo posiblemente se vincule con su rareza. Al examinar la relación entre la probabilidad de cobertura de una especie para cada grupo indicador y la extensión de su rango geográfico dentro del área de estudio, encontramos que las especies con rangos más restringidos tenían menor probabilidad de ser protegidas que las especies de distribución más amplia. Además, encontramos que, a pesar de que los sitios seleccionados con grupos indicadores compuestos principalmente por especies terrestres ( aves y mamíferos ) incluyeron porcentajes relativamente altos de estas especies ( 82%,85% ), éstos incluyeron porcentajes más bajos de especies estrictamente acuáticas ( 27%,55% ). Finalmente, de importancia y posible utilidad, encontramos que las especies en riesgo, por si mismas, funcionaron bien como grupo indicador, abarcando, en promedio, el 84% de todas las otras especies. [source]

International Studbooks for Rare Species of Wild Animals in Captivity

INTERNATIONAL ZOO YEARBOOK, Issue 1 2009
Article first published online: 30 JAN 200
First page of article [source]

Rare Species of Actinomyces as Causative Pathogens in Breast Abscess

THE BREAST JOURNAL, Issue 5 2007
Kaka Hama Attar MRCS
Abstract:, Actinomyces species are commensal flora usually found in the oropharynx, gastrointestinal tract, and female genital tract. Primary actinomycosis of the breast is an unusual condition, where the most commonly isolated pathogen has been Actinomyces israelii. In recent years, other Actinomyces strains have been found associated with breast disease. We present the first reported cases of breast infection caused by the rare species, Actinomyces turicensis and Actinomyces radingae. Both infections displayed chronicity and abscess formation. In the first case, the infection was refractory to recurrent aspirations and initial antibiotic therapy. In the second case, aspiration and prolonged antibiotic therapy was required to overcome the chronic infection. [source]

Why are ferns regularly over-represented on state and provincial rare plant lists?

DIVERSITY AND DISTRIBUTIONS, Issue 6 2006
Matthew Wild
ABSTRACT Several recent studies have suggested that rare species are not randomly distributed throughout plant taxa. This would appear to apply to North American ferns, which are frequently over-represented on local lists of rare plant species. However, such lists often paint a skewed portrait of the true situation because of our tendency to recognize the rarity of well-known and charismatic species while ignoring that of lesser-known or less-appreciated species. In order to verify if this over-representation of ferns is a real and consistent trend throughout local floras in North America, we used data from what we consider to be the most complete and objective available database: NatureServe Explorer (http://www.natureserve.org/explorer/). We compiled data on total vascular plant species, total fern species, as well as rare vascular plant species and rare fern species for each North American subnational (Canadian province or US state) flora. Rare species were defined as those belonging to one of NatureServe's ,at risk' categories. The null hypothesis that the contribution of rare ferns to total rare species did not differ from their contribution to the total vascular flora was assessed using ,2. Out of 64 subnational floras, we obtained significantly higher values than expected in 28 cases, and significantly lower in only one case. Similar trends hold true for individual fern families. These tendencies could be related to several factors of anthropogenic, biological, climatological, evolutionary, and geographical origin. However, we believe that the main reason is related to scale, namely the geopolitical units at which rarity is often studied. Our results illustrate one of the problems of a parochial approach to conservation, where the perceived rarity of an entire taxon is exaggerated because of the scale at which rarity is addressed. [source]

Diversity and composition of Arctiidae moth ensembles along a successional gradient in the Ecuadorian Andes

DIVERSITY AND DISTRIBUTIONS, Issue 5 2005
Nadine Hilt
ABSTRACT Andean montane rain forests are among the most species-rich terrestrial habitats. Little is known about their insect communities and how these respond to anthropogenic habitat alteration. We investigated exceptionally speciose ensembles of nocturnal tiger moths (Arctiidae) at 15 anthropogenically disturbed sites, which together depict a gradient of forest recovery and six closed-forest understorey sites in southern Ecuador. At weak light traps we sampled 9211 arctiids, representing 287 species. Arctiid abundance and diversity were highest at advanced succession sites, where secondary scrub or young forest had re-established, followed by early succession sites, and were lowest, but still high, in mature forest understorey. The proportion of rare species showed the reverse pattern. We ordinated moth samples by non-metric multidimensional scaling using the chord-normalized expected species shared index (CNESS) index at various levels of the sample size parameter m. A distinct segregation of arctiid ensembles at succession sites from those in mature forest consistently emerged only at high m -values. Segregation between ensembles of early vs. late succession stages was also clear at high m values only, and was rather weak. Rare species were responsible for much of the faunal difference along the succession gradient, whereas many common arctiid species occurred in all sites. Matrix correlation tests as well as exploration of relationships between ordination axes and environmental variables revealed the degree of habitat openness, and to a lesser extent, elevation, as best predictors of faunal dissimilarity. Faunal differences were not related to geographical distances between sampling sites. Our results suggest that many of the more common tiger moths of Neotropical montane forests have a substantial recolonization potential at the small spatial scale of our study and accordingly occur also in landscape mosaics surrounding nature reserves. These species contribute to the unexpectedly high diversity of arctiid ensembles at disturbed sites, whereas the proportion of rare species declines outside mature forest. [source]

Grazing effect on diversity of annual plant communities in a semi-arid rangeland: interactions with small-scale spatial and temporal variation in primary productivity

JOURNAL OF ECOLOGY, Issue 6 2002
Yagil Osem
Summary 1The interactive effect of grazing and small-scale variation in primary productivity on the diversity of an annual plant community was studied in a semiarid Mediterranean rangeland in Israel over 4 years. The response of the community to protection from sheep grazing by fenced exclosures was compared in four neighbouring topographic sites (south- and north-facing slopes, hilltop and wadi (dry stream) shoulders), differing in vegetation, physical characteristics and soil resources. The herbaceous annual vegetation was highly diverse, including 128 species. Average small-scale species richness of annuals ranged between 5 and 16 species within a 20 × 20 cm quadrat, and was strongly affected by year and site. 2Above-ground potential productivity at peak season (i.e. in fenced subplots) was typical of semiarid ecosystems (10,200 g m,2), except on wadi shoulders (up to 700 g m,2), where it reached the range of subhumid grassland ecosystems. Grazing increased richness in the high productivity site (i.e. wadi), but did not affect, or reduced, it in the low productivity sites (south- and north-facing slopes, hilltop). Under grazing, species richness was positively and linearly related to potential productivity along the whole range of productivity. Without grazing, this relationship was observed only at low productivity (< 200 g m,2). 3The effect of grazing along the productivity gradient on different components of richness was analysed. At low productivity, number of abundant, common and rare species all tended to increase with productivity, both with and without grazing. Rare species increased three times compared with common and abundant species. At high productivity, only rare species continued to increase with productivity under grazing, while in the absence of grazing species number in the different abundance groups was not related to productivity. 4In this semiarid Mediterranean rangeland, diversity of the annual plant community is determined by the interaction between grazing and small-scale spatial and temporal variation in primary productivity, operating mainly on the less abundant species in the community. [source]

A long-term study of neighbour-regulated demography during a decline in forest species diversity

JOURNAL OF VEGETATION SCIENCE, Issue 1 2006
Lin Yi-ching
Abstract Question: Did disturbance, no density-dependence of the dominant species, and negative neighbourhood interactions on rare species affect tree demography during a decline in species diversity associated with the increase of Acer saccharum from 1939,2001? Hypotheses: 1. The rise in dominance of A. saccharum was because of its advantage in disturbances and lack of density-dependence of its demography. 2. Rare species were not favoured by disturbances, including those from Dutch elm disease, and demonstrated negative neighbourhood interactions with A. saccharum. Location: Brownfield Woods in Illinois, USA. Methods: Historical maps of trees (, 7.6 cm DBH) from 1939, 1951, 1988, and 2001 in 16 quadrats (48 m × 68 m) were used to compare demography of eight tree species. Effects of disturbances, density-dependence, and neighbourhood interactions on mortality and recruitment of tree species within a 6-m radius of individual target trees were studied. Results: A. saccharum demonstrated a demographic advantage over rare species. It had lower mortality and higher recruitment rates. Disturbances facilitated recruitment of A. saccharum, but did not enhance rare species. Density-dependence of both mortality and recruitment of A. saccharum occurred, but population projection models indicated that ecological conditions became more favourable for A. saccharum in the past 62 years. Furthermore, negative neighbourhood interactions were detected between rare species and A. saccharum. The increase in neighbouring A. saccharum significantly increased mortality and reduced recruitment of the rare species. Conclusions: The general disturbance regime, enhanced by Dutch elm disease, in Brownfield Woods facilitated the rise of dominance of A. saccharum. Meanwhile, rare species declined as a result of their disadvantage in disturbance and negative neighbourhood interactions with A. saccharum. [source]

Spatial distributions of tree species in a subtropical forest of China

OIKOS, Issue 4 2009
Lin Li
The spatial dispersion of individuals in a species is an important pattern that is controlled by many mechanisms. In this study we analyzed spatial distributions of tree species in a large-scale (20 ha) stem-mapping plot in a species-rich subtropical forest of China. O-ring statistic was used to measure spatial patterns of species with abundance >10. ,0,10, the mean conspecific density within 10 m of a tree, was used as a measure of the intensity of aggregation of a species. Our results showed: (1) aggregated distribution was the dominant pattern in the plot. The percentage of aggregated species decreased with increased spatial scale. (2) The percentages of significantly aggregated species decreased from abundant to intermediate and to rare species. Rare species was more strongly aggregated than common species. Aggregation was weaker in larger diameter classes. (3) Seed traits determined the spatial patterns of trees. Seed dispersal mode can influence spatial patterns of species, with species dispersed by both modes being less clumped than species dispersed by animal or wind, respectively. Considering these results, we concluded that seed dispersal limitation, self-thinning and habitat heterogeneity primarily contributed to spatial patterns and species coexistence in the forest. [source]

Rare species in communities of tropical insect herbivores: pondering the mystery of singletons

OIKOS, Issue 3 2000
Vojtech Novotný
The host specificity, taxonomic composition and feeding guild of rare species were studied in communities of herbivorous insects in New Guinea. Leaf-chewing and sap-sucking insects (Orthoptera, Phasmatodea, Coleoptera, Lepidoptera and Hemiptera-Auchenorrhyncha) were sampled from 30 species of trees and shrubs (15 spp. of Ficus, Moraceae, six spp. of Macaranga and nine species of other Euphorbiaceae) in a lowland rain forest. Feeding trials were performed with all leaf-chewers in order to exclude transient species. Overall, the sampling produced 80,062 individuals of 1050 species. The species accumulation curve did not attain an asymptote, despite 950 person-days of sampling. Rare species, defined as those found as single individuals, remained numerous even in large samples and after the exclusion of transient, non-feeding species. There was no difference among plant species in the proportion of rare species in their herbivore communities, which was, on average, 45%. Likewise, various herbivore guilds and taxa had all very similar proportions of rare and common species. There was also no difference between rare and common species in their host specificity. Both highly specialised species and generalists, feeding on numerous plants, contributed to the singleton records on particular plant species. Predominantly, a species was rare on a particular host whilst more common on other, often related, host species, or relatively rare on numerous other host plants, so that its aggregate population was high. Both cases are an example of the "mass effect", since it is probable that such rare species were dependent on a constant influx of immigrants from the other host plants. These other plants were found particularly often among congeneric plants, less so among confamilial plants from different genera and least frequently among plants from different families. There were also 278 very rare species, found as one individual on a single plant species only. Their host specificity could not be assessed; they might have been either very rare specialists, or species feeding also on other plants, those that were not studied. The former possibility is unlikely since monophagous species, collected as singletons at the present sampling effort, would have existed at an extremely low population density, less than 1 individual per 10 ha of the forest. [source]

Ectomycorrhizal fungal communities at forest edges

JOURNAL OF ECOLOGY, Issue 2 2005
IAN A. DICKIE
Summary 1Ectomycorrhizal fungi are spatially associated with established ectomycorrhizal vegetation, but the influence of distance from established vegetation on the presence, abundance, diversity and community composition of fungi is not well understood. 2We examined mycorrhizal communities in two abandoned agricultural fields in Minnesota, USA, using Quercus macrocarpa seedlings as an in situ bioassay for ectomycorrhizal fungi from 0 to 20 m distance from the forest edge. 3There were marked effects of distance on all aspects of fungal communities. The abundance of mycorrhiza was uniformly high near trees, declined rapidly around 15 m from the base of trees and was uniformly low at 20 m. All seedlings between 0 and 8 m distance from forest edges were ectomycorrhizal, but many seedlings at 16,20 m were uninfected in one of the two years of the study. Species richness of fungi also declined with distance from trees. 4Different species of fungi were found at different distances from the edge. ,Rare' species (found only once or twice) dominated the community at 0 m, Russula spp. were dominants from 4 to 12 m, and Astraeus sp. and a Pezizalean fungus were abundant at 12 m to 20 m. Cenococcum geophilum, the most dominant species found, was abundant both near trees and distant from trees, with lowest relative abundance at intermediate distances. 5Our data suggest that seedlings germinating at some distance from established ectomycorrhizal vegetation (15.5 m in the present study) have low levels of infection, at least in the first year of growth. Distance from established vegetation represents an important gradient for ectomycorrhizal fungi, with different species occupying distinct niches along this gradient. This provides support for niche differentiation as a factor contributing to ectomycorrhizal fungal diversity. 6Ectomycorrhizal infection of seedlings is spatially complex, with high infection and high fungal diversity near trees, high infection but lower diversity at intermediate distances, and low infection and low fungal diversity distant from trees. This spatial complexity should be considered as a factor potentially influencing the establishment of ectomycorrhizal vegetation. [source]

Quantifying Plant Population Persistence in Human-Dominated Landscapes

CONSERVATION BIOLOGY, Issue 4 2008
DAWN M. LAWSON
Base de Datos de la Diversidad Natural de California; conservación de plantas; crecimiento de la población; especies en peligro; paisajes urbanos Abstract:,We assessed population performance of rare plants across a gradient from rural to urban landscapes and evaluated 2 hypotheses central to strategic conservation planning: (1) population performance declines with increasing human dominance and (2) small populations perform poorly relative to larger ones. Assessing these hypotheses is critical to strategic conservation planning. The current conservation paradigm adheres to the well-established ecology theory that small isolated populations, particularly those in human-dominated landscapes, are the least likely to succeed over the long term. Consequently, conservation planning has strongly favored large, remote targets for protection. This shift in conservation toward ecosystem-based programs and protection of populations within large, remote systems has been at the expense of protection of the rarest of the rare species, the dominant paradigm for conservation driven by the endangered species act. Yet, avoiding conservation of small populations appears to be based more on theoretical understanding and expert opinion than empiricism. We used Natural Heritage data from California in an assessment of population performance of rare plants across a landscape with an urban-rural gradient. Population performance did not decrease in urban settings or for populations that were initially small. Our results are consistent with a pattern of few species extinctions within these landscapes over the past several decades. We conclude that these populations within compromised landscapes can contribute to overall biodiversity conservation. We further argue that conservation planning for biodiversity preservation should allocate relatively more resources to protecting urban-associated plant taxa because they may provide conservation benefit beyond simply protecting isolated populations; they may be useful in building social interest in conservation. Resumen:,Evaluamos el funcionamiento de la población de plantas raras a lo largo de un gradiente de paisajes rurales a urbanos y evaluamos 2 hipótesis centrales para la planificación estratégica de la conservación: (1) declinaciones en el funcionamiento poblacional con el incremento de la dominancia humana y (2) las poblaciones pequeñas funcionan pobremente en relación con las grandes. La evaluación de estas hipótesis es crítica para la planificación estratégica de la conservación. El paradigma actual de la conservación se adhiere a la teoría ecológica bien establecida que propone que las poblaciones pequeñas aisladas, particularmente en paisajes dominados por humanos, tienen menor probabilidad de sobrevivir a largo plazo. Consecuentemente, la planificación de la conservación ha favorecido objetivos grandes y remotos. Este cambio hacia programas de conservación basados en ecosistemas y la protección de poblaciones en sistemas extensos y remotos ha sido a costa de la protección de las especies más raras entre las raras, el paradigma dominante en la conservación conducida por el acta de especies en peligro. No obstante, la evasión de la conservación de poblaciones pequeñas parece estar basada más en entendimiento teórico y en la opinión de expertos que en el empirismo. Utilizamos datos del Patrimonio Natural de California en una evaluación del funcionamiento de plantas raras en un paisaje con un gradiente urbano a rural. El funcionamiento de la población no decreció en sitios urbanos o en poblaciones que eran pequeñas inicialmente. Nuestros resultados son consistentes con un patrón de extinción de especies en estos paisajes en las últimas décadas. Concluimos que estas poblaciones en paisajes comprometidos pueden contribuir a la conservación de la biodiversidad en general. También argumentamos que la planificación de la conservación para la preservación de la biodiversidad debería asignar más recursos para la protección de taxa de plantas asociadas a ambientes urbanos porque pueden proporcionar beneficios de conservación más allá de simplemente proteger poblaciones aisladas; pueden ser útiles para construir el interés social por la conservación. [source]

Beyond Reaping the First Harvest: Management Objectives for Timber Production in the Brazilian Amazon

CONSERVATION BIOLOGY, Issue 4 2007
DANIEL J. ZARIN
manejo de bosques; producción sostenida; sustentabilidad; tala de impacto reducido Abstract:,Millions of hectares of future timber concessions are slated to be implemented within large public forests under the forest law passed in 2006 by the Brazilian Congress. Additional millions of hectares of large, privately owned forests and smaller areas of community forests are certified as well managed by the Forest Stewardship Council, based on certification standards that will be reviewed in 2007. Forest size and ownership are two key factors that influence management objectives and the capacity of forest managers to achieve them. Current best ecological practices for timber production from Brazil's native Amazon forests are limited to reduced-impact logging (RIL) systems that minimize the environmental impacts of harvest operations and that obey legal restrictions regarding minimum diameters, rare species, retention of seed trees, maximum logging intensity, preservation of riparian buffers, fire protection, and wildlife conservation. Compared with conventional, predatory harvesting that constitutes >90% of the region's timber production, RIL dramatically reduces logging damage and helps maintain forest cover and the presence of rare tree species, but current RIL guidelines do not assure that the volume of timber removed can be sustained in future harvests. We believe it is counterproductive to expect smallholders to subscribe to additional harvest limitations beyond RIL, that larger private forested landholdings managed for timber production should be sustainable with respect to the total volume of timber harvested per unit area per cutting cycle, and that large public forests should sustain volume production of individual harvested species. These additional requirements would improve the ecological sustainability of forest management and help create a stable forest-based sector of the region's economy, but would involve costs associated with lengthened cutting cycles, reduced harvest intensities, and/or postharvest silviculture to promote adequate growth and regeneration. Resumen:,Bajo la nueva ley forestal aprobada en 2006 por el Congreso Brasileño, millones de hectáreas de bosques públicos están destinadas a constituir futuras concesiones madereras. Millones de hectáreas adicionales de extensos bosques privados y áreas reducidas de bosques comunitarios están certificadas por el Forest Stewardship Council por su buen manejo, con base en estándares de certificación que serán revisados en 2007. La extensión y tenencia del bosque son dos factores clave que influyen en los objetivos de manejo y en la capacidad de los manejadores para alcanzarlos. Las mejores prácticas ecológicas actuales para la producción de madera en los bosques de la Amazonía Brasileña están limitadas a sistemas de tala de impacto reducido (TIR) que minimizan los impactos ambientales de las operaciones de cosecha y que obedecen restricciones legales en relación con los diámetros mínimos, las especies raras, la retención de árboles semilla, la máxima intensidad de tala, la preservación de amortiguamientos ribereños, la protección del fuego y la conservación de vida silvestre. En comparación con la cosecha convencional, depredadora, mediante la cual se obtiene >90% de la producción de madera en la región, la TIR dramáticamente reduce el daño y ayuda a mantener la cobertura del bosque y la presencia de especies de árboles raras, pero los actuales lineamientos de TIR no aseguran que el volumen de madera removida pueda ser sostenido en futuras cosechas. Consideramos que es contraproducente esperar que los pequeños propietarios suscriban límites a la cosecha más allá de la TIR; que los bosques privados manejados para la producción de madera debieran ser sustentables respecto al volumen total de madera cosechada por unidad de área por ciclo de corte; y que los bosques públicos deberían sustentar el volumen de producción de especies individuales. Estos requerimientos adicionales mejorarían la sustentabilidad ecológica del manejo de bosques y ayudaría a crear un sector forestal estable en la economía regional, pero implicarían costos asociados con la prolongación de los ciclos de corte, la reducción de las intensidades de cosecha y/o la silvicultura postcosecha para promover el crecimiento adecuado y la regeneración. [source]

Susceptibility of Common and Rare Plant Species to the Genetic Consequences of Habitat Fragmentation

CONSERVATION BIOLOGY, Issue 3 2007
OLIVIER HONNAY
diversidad genética; endogamia; fragmentación de hábitat; sistema reproductivo; tamaño poblacional Abstract:,Small plant populations are more prone to extinction due to the loss of genetic variation through random genetic drift, increased selfing, and mating among related individuals. To date, most researchers dealing with genetic erosion in fragmented plant populations have focused on threatened or rare species. We raise the question whether common plant species are as susceptible to habitat fragmentation as rare species. We conducted a formal meta-analysis of habitat fragmentation studies that reported both population size and population genetic diversity. We estimated the overall weighted mean and variance of the correlation coefficients among four different measures of genetic diversity and plant population size. We then tested whether rarity, mating system, and plant longevity are potential moderators of the relationship between population size and genetic diversity. Mean gene diversity, percent polymorphic loci, and allelic richness across studies were positively and highly significantly correlated with population size, whereas no significant relationship was found between population size and the inbreeding coefficient. Genetic diversity of self-compatible species was less affected by decreasing population size than that of obligate outcrossing and self-compatible but mainly outcrossing species. Longevity did not affect the population genetic response to fragmentation. Our most important finding, however, was that common species were as, or more, susceptible to the population genetic consequences of habitat fragmentation than rare species, even when historically or naturally rare species were excluded from the analysis. These results are dramatic in that many more plant species than previously assumed may be vulnerable to genetic erosion and loss of genetic diversity as a result of ongoing fragmentation processes. This implies that many fragmented habitats have become unable to support plant populations that are large enough to maintain a mutation-drift balance and that occupied habitat fragments have become too isolated to allow sufficient gene flow to enable replenishment of lost alleles. Resumen:,Las poblaciones pequeñas de plantas son más propensas a la extinción debido a la pérdida de variación genética por medio de la deriva génica aleatoria, el incremento de autogamia y la reproducción entre individuos emparentados. A la fecha, la mayoría de los investigadores que trabajan con erosión genética en poblaciones fragmentadas de plantas se han enfocado en las especies amenazadas o raras. Cuestionamos si las especies de plantas comunes son tan susceptibles a la fragmentación del hábitat como las especies raras. Realizamos un meta análisis formal de estudios de fragmentación que reportaron tanto tamaño poblacional como diversidad genética. Estimamos la media general ponderada y la varianza de los coeficientes de correlación entre cuatro medidas de diversidad genética y de tamaño poblacional de las plantas. Posteriormente probamos si la rareza, el sistema reproductivo y la longevidad de la planta son moderadores potenciales de la relación entre el tamaño poblacional y la diversidad genética. La diversidad genética promedio, el porcentaje de loci polimórficos y la riqueza alélica en los estudios tuvieron una correlación positiva y altamente significativa con el tamaño poblacional, mientras que no encontramos relación significativa entre el tamaño poblacional y el coeficiente de endogamia. La diversidad genética de especies auto compatibles fue menos afectada por la reducción en el tamaño poblacional que la de especies exogámicas obligadas y especies auto compatibles, pero principalmente exogámicas. La longevidad no afectó la respuesta genética de la población a la fragmentación. Sin embargo, nuestro hallazgo más importante fue que las especies comunes fueron tan, o más, susceptibles a las consecuencias genéticas de la fragmentación del hábitat que las especies raras, aun cuando las especies histórica o naturalmente raras fueron excluidas del análisis. Estos resultados son dramáticos porque muchas especies más pueden ser vulnerables a la erosión genética y a la pérdida de diversidad genética como consecuencia de los procesos de fragmentación que lo se asumía previamente. Esto implica que muchos hábitats fragmentados han perdido la capacidad para soportar poblaciones de plantas lo suficientemente grandes para mantener un equilibrio mutación-deriva y que los fragmentos de hábitat ocupados están tan aislados que el flujo génico es insuficiente para permitir la reposición de alelos perdidos. [source]

Metropolitan Open-Space Protection with Uncertain Site Availability

CONSERVATION BIOLOGY, Issue 2 2005
ROBERT G. HAIGHT
acceso público; Chicago; modelo de selección de sitio; optimización; representación de especies Abstract:,Urban planners acquire open space to protect natural areas and provide public access to recreation opportunities. Because of limited budgets and dynamic land markets, acquisitions take place sequentially depending on available funds and sites. To address these planning features, we formulated a two-period site selection model with two objectives: maximize the expected number of species represented in protected sites and maximize the expected number of people with access to protected sites. These objectives were both maximized subject to an upper bound on area protected over two periods. The trade-off between species representation and public access was generated by the weighting method of multiobjective programming. Uncertainty was represented with a set of probabilistic scenarios of site availability in a linear-integer formulation. We used data for 27 rare species in 31 candidate sites in western Lake County, near the city of Chicago, to illustrate the model. Each trade-off curve had a concave shape in which species representation dropped at an increasing rate as public accessibility increased, with the trade-off being smaller at higher levels of the area budget. Several sites were included in optimal solutions regardless of objective function weights, and these core sites had high species richness and public access per unit area. The area protected in period one depended on current site availability and on the probabilities of sites being undeveloped and available in the second period. Although the numerical results are specific for our study, the methodology is general and applicable elsewhere. Resumen:,Planificadores urbanos adquieren espacios abiertos para proteger áreas naturales y proporcionar acceso público a oportunidades de recreación. Debido a presupuestos limitados y a la dinámica de los mercados de terrenos, las adquisiciones se llevan a cabo secuencialmente en función de la disponibilidad de fondos y sitios. Para atender estas características de la planificación, formulamos un modelo de selección de sitios de dos períodos con dos objetivos: maximizar el número esperado de especies representado en sitios protegidos y maximizar el número esperado de personas con acceso a sitios protegidos. Ambos objetivos fueron maximizados con un límite superior en la superficie protegida en los dos períodos. El balance entre la representación de especies y el acceso público fue generado por el método de ponderación de programación de multiobjetivos. La incertidumbre fue representada con un conjunto de escenarios probabilísticos de la disponibilidad de sitios en una formulación lineal-integral. Para demostrar el modelo, utilizamos datos para 27 especies raras en 31 sitios potenciales en el oeste del Condado Lake, cerca de la ciudad de Chicago. Cada curva tenía forma cóncava y la representación de especies descendió a medida que incrementó la accesibilidad pública, con un menor equilibrio en niveles altos del presupuesto para el área. Varios sitios fueron incluidos en soluciones óptimas independientemente de las funciones de ponderación de los objetivos, y estos sitios tuvieron alta riqueza de especies y acceso público por unidad de área. La superficie protegida en el período uno dependió de la disponibilidad de sitios y de las probabilidades de que los sitios no fueran desarrollados y de su disponibilidad en el segundo período. Aunque los resultados numéricos son específicos a nuestro estudio, la metodología es general y aplicable en otros sitios. [source]

Consumers' taste for rarity drives sturgeons to extinction

CONSERVATION LETTERS, Issue 5 2008
Agnès Gault
Abstract The international market for luxury goods puts pressure on many wildlife species, with potentially irreversible consequences for many of them. Although classical economic theory suggests that trade alone would not drive a rare species to extinction, in practice numerous species are being threatened by overexploitation. This is for example the case for sturgeons, exploited for their caviar, of which all 27 species are threatened with extinction. We performed a caviar-tasting experiment, combined with a modeling approach merging ecological theory and psychosociology. This allowed us to demonstrate that the human predisposition to place exaggerated value on rarity drives sturgeons' overexploitation, despite caviar's ever-increasing price and the imminent loss of these species. These findings suggest that this mechanism probably drives the entire market for wildlife based luxury goods. [source]

Why are ferns regularly over-represented on state and provincial rare plant lists?

Diversity and composition of Arctiidae moth ensembles along a successional gradient in the Ecuadorian Andes

Subpopulations of Cryptocephalus beetles (Coleoptera: Chrysomelidae): geographically close but genetically far

DIVERSITY AND DISTRIBUTIONS, Issue 1 2003
R. W. Piper
Abstract. The leaf beetles Cryptocephalus coryli, C. decemmaculatus and C. nitidulus are of conservation concern and are included on the UK Biodiversity Action Plan. The distinctiveness of the disjunct remaining populations of these beetles was compared to that of more continuously distributed Cryptocephalus species. This was carried out with a view to defining evolutionary significant units (ESUs) in the rare species. A portion of the cytochrome b gene, an intergenic spacer and partial tRNA was analysed from 93 specimens of Cryptocephalus beetle (Coleoptera: Chrysomelidae). Considerable sequence divergence was apparent in all the species, even at an intersite scale when the distances between sampled localities were very small (< 1 km). Intrapopulation, intersite and interpopulation divergence observed in the rare species was reflected in the species that have a more continuous distribution, implying that dispersal ability in these species is poor and gene flow can be impeded by relatively trivial barriers to dispersal. The evidence suggests that the disjunct populations of the rare Cryptocephalus species can, tentatively, be considered as ESUs. This has important implications for management strategies and reintroductions. [source]

Heterogeneity, speciation/extinction history and climate: explaining regional plant diversity patterns in the Cape Floristic Region

DIVERSITY AND DISTRIBUTIONS, Issue 3 2002
R. M. Cowling
Abstract. This paper investigates the role of heterogeneity and speciation/extinction history in explaining variation in regional scale (c. 0.1,3000 km2) plant diversity in the Cape Floristic Region of south-western Africa, a species- and endemic-rich biogeographical region. We used species-area analysis and analysis of covariance to investigate geographical (east vs. west) and topographic (lowland vs. montane) patterns of diversity. We used community diversity as a surrogate for biological heterogeneity, and the diversity of naturally rare species in quarter degree squares as an indicator of differences in speciation/extinction histories across the study region. We then used standard statistical methods to analyse geographical and topographic patterns of these two measures. There was a clear geographical diversity pattern (richer in the west), while a topographic pattern (richer in mountains) was evident only in the west. The geographical boundary coincided with a transition from the reliable winter-rainfall zone (west) to the less reliable non-seasonal rainfall zone (east). Community diversity, or biological heterogeneity, showed no significant variation in relation to geography and topography. Diversity patterns of rare species mirrored the diversity pattern for all species. We hypothesize that regional diversity patterns are the product of different speciation and extinction histories, leading to different steady-state diversities. Greater Pleistocene climatic stability in the west would have resulted in higher rates of speciation and lower rates of extinction than in the east, where for the most, Pleistocene climates would not have favoured Cape lineages. A more parsimonious hypothesis is that the more predictable seasonal rainfall of the west would have favoured non-sprouting plants and that this, in turn, resulted in higher speciation and lower extinction rates. Both hypotheses are consistent with the higher incidence of rare species in the west, and higher levels of beta and gamma diversity there, associated with the turnover of species along environmental and geographical gradients, respectively. These rare species do not contribute to community patterns; hence, biological heterogeneity is uniform across the region. The weak topography pattern of diversity in the west arises from higher speciation rates and lower extinction rates in the topographically complex mountains, rather than from the influence of environmental heterogeneity on diversity. [source]

Spatiotemporal patterns of seed dispersal in a wind-dispersed Mediterranean tree (Acer opalus subsp. granatense): implications for regeneration

ECOGRAPHY, Issue 1 2007
Lorena Gómez-Aparicio
Seed dispersal can severely limit the quantity of plant recruits and their spatial distribution. However, our understanding of the role of dispersal in regeneration dynamics is limited by the lack of knowledge of seed deposition patterns in space and time. In this paper, we analyse the spatiotemporal variability of seed dispersal patterns in the Mediterranean maple, Acer opalus subsp. granatense, by monitoring seed rain along two years at a broad spatial scale (2 mountain ranges, 2 populations per range, 4 microhabitats per population). We quantified seed limitation and its components (source and dispersal limitation), and explored dispersal limitation in space by analysing dispersal distances, seed aggregation, and microhabitat seed distribution. Acer opalus subsp. granatense was strongly seed-limited throughout the gradients explored, being always dispersal limitation much higher than source limitation. The distribution of seeds with distance from adult individuals was leptokurtic and right-skewed in all populations, being both kurtosis and skewness higher the year of the highest seed production. Dispersal distances were shorter than expected by random in the four populations, which suggests distance-limited dispersal. Dispersal patterns were highly aggregated and showed a preferential direction around adults. At the microhabitat scale, most seeds accumulated under adult maples. However, there were no more seeds under trees and shrubs other than maple than in open interspaces, implying that established vegetation does not disrupt patterns of seed deposition by physically trapping seeds. When compared with patterns of seedling establishment, limited dispersal ability and inter-annual spatial concordance in seed rain patterns suggest that several potentially safe sites for recruitment have a very low probability of receiving seeds in most maple populations. These findings are especially relevant for rare species such as Acer opalus subsp. granatense, and illustrate how dispersal studies are not only crucial for our understanding of plant population dynamics but also to provide conservation directions. [source]

The effect of sample size and species characteristics on performance of different species distribution modeling methods

ECOGRAPHY, Issue 5 2006
Pilar A. Hernandez
Species distribution models should provide conservation practioners with estimates of the spatial distributions of species requiring attention. These species are often rare and have limited known occurrences, posing challenges for creating accurate species distribution models. We tested four modeling methods (Bioclim, Domain, GARP, and Maxent) across 18 species with different levels of ecological specialization using six different sample size treatments and three different evaluation measures. Our assessment revealed that Maxent was the most capable of the four modeling methods in producing useful results with sample sizes as small as 5, 10 and 25 occurrences. The other methods compensated reasonably well (Domain and GARP) to poorly (Bioclim) when presented with datasets of small sample sizes. We show that multiple evaluation measures are necessary to determine accuracy of models produced with presence-only data. Further, we found that accuracy of models is greater for species with small geographic ranges and limited environmental tolerance, ecological characteristics of many rare species. Our results indicate that reasonable models can be made for some rare species, a result that should encourage conservationists to add distribution modeling to their toolbox. [source]

The significance of geographic range size for spatial diversity patterns in Neotropical palms

ECOGRAPHY, Issue 1 2006
Holger Kreft
We examined the effect of range size in commonly applied macroecological analyses using continental distribution data for all 550 Neotropical palm species (Arecaceae) at varying grain sizes from 0.5° to 5°. First, we evaluated the relative contribution of range-restricted and widespread species on the patterns of species richness and endemism. Second, we analysed the impact of range size on the predictive value of commonly used predictor variables. Species sequences were produced arranging species according to their range size in ascending, descending, and random order. Correlations between the cumulative species richness patterns of these sequences and environmental predictors were performed in order to analyse the effect of range size. Despite the high proportion of rare species, patterns of species richness were found to be dominated by a minority of widespread species (,20%) which contained 80% of the spatial information. Climatic factors related to energy and water availability and productivity accounted for much of the spatial variation of species richness of widespread species. In contrast, species richness of range-restricted species was to a larger extent determined by topographical complexity. However, this effect was much more difficult to detect due to a dominant influence of widespread species. Although the strength of different environmental predictors changed with spatial scale, the general patterns and trends proved to be relatively stabile at the examined grain sizes. Our results highlight the difficulties to approximate causal explanations for the occurrence of a majority of species and to distinguish between contemporary climatic factors and history. [source]

Patterns of commonness and rarity in central European birds: reliability of the core-satellite hypothesis within a large scale

ECOGRAPHY, Issue 4 2002
David Storch
The frequency distribution of species' area of occupancy is often bimodal, most species being either very rare or very common in terms of number of occupied sites. This pattern has been attributed to the nonlinearity associated with metapopulation dynamics of the species, but there are also other explanations comprising sampling artifact and frequency distribution of suitable habitats. We tested whether the bimodal frequency distribution of occupied squares in central European birds could be derived solely from the frequency distribution of species population sizes (i.e. the sampling artifact hypothesis) or from the spatial distribution of their preferred habitats. Both models predict high proportion of very common species, i.e. the right side of frequency distribution. Bimodality itself is well predicted by models based on random placement of individuals according to their abundances but neither model predicts the observed prevalence of rare species. Even the combined models that assume random placement of individuals within the squares with suitable habitat do not predict such a high proportion of rare species. The observed distribution is more aggregated, rare species occupying a smaller portion of suitable habitat than predicted on the basis of their abundance. The pattern is consistent with metapopulation processes involving local population extinctions. The involvement of these processes is supported by two further observations. First, species rarity is associated with significant population trend and/or location on the edge of their ranges within central Europe, both situations presumably associated with metapopulation processes. Second, suitable habitats seem to be either saturated or almost unoccupied, which is consistent with the predictions of the metapopulation model based on nonlinear dynamics of extinction and colonization. Although the habitat suitability is an important determinant of species distribution, the rarity of many species of birds within this scale of observation seems to be affected by other factors, including local population extinctions associated with fragmentation of species' habitats. [source]

Distributions of forest birds and butterflies in the Andaman islands, Bay of Bengal: nested patterns and processes

ECOGRAPHY, Issue 1 2002
Priya Davidar
The distributional patterns of forest birds and butterflies in the Andaman islands, an oceanic chain located off SE Asia, were tested for nestedness. Both taxa were highly nested. Nestedness could be due to colonization or extinction processes, area or distance effects or nestedness of habitats. Nestedness in forest bird distributions were strongly influenced by area and habitat related factors. Habitats were significantly nested in all three island groups, however most strongly for the North Andamans. However forest bird distributions in the North Andamans, as indicated by row order in the packed matrix, was not correlated with habitat diversity, suggesting that habitat related factors alone cannot account for these patterns. Other causal influences could be passive sampling, where common and abundant species and habitats are more likely to have a widespread distribution than rare species and habitats. The nested subset pattern seen in two unrelated taxa suggests that the Andamans are extinction dominated and that the protection of forests on large islands is critical for the conservation of its biodiversity. [source]

Community structure of arboreal caterpillars within and among four tree species of the eastern deciduous forest

ECOLOGICAL ENTOMOLOGY, Issue 6 2003
Keith S. Summerville
Abstract., 1.,A seasonally replicated experimental design was used to address the question of how differences within and among host tree species affect arboreal caterpillar communities. 2.,Seasonal variation influenced caterpillar community composition most significantly, and the similarity among caterpillar assemblages did not necessarily follow the pattern of phylogenetic relatedness among host trees. 3.,Species richness and abundance of caterpillars were higher on oaks and maples than on American beech. Diversity partitioning models revealed that , diversity was only occasionally greater or less than expected by chance alone. 4.,When , diversity was significant, values tended to be greater than expected by chance among replicate trees within each species and lower than expected by chance among the four tree species. 5.,Differences among trees appeared important for determining patterns of species presence/absence for rare species and influencing patterns of species dominance within caterpillar assemblages. Differences among tree species had a significant effect on overall lepidopteran community composition and mean species diversity (i.e. , diversity). 6.,Because , diversity of caterpillars among host trees was lower than expected by chance, host specificity within the Lepidoptera may be less prevalent than thought previously. [source]

Allee effects in biological invasions

ECOLOGY LETTERS, Issue 8 2005
Caz M. Taylor
Abstract Understanding the dynamics of small populations is obviously important for declining or rare species but is also particularly important for invading species. The Allee effect, where fitness is reduced when conspecific density is low, can dramatically affect the dynamics of biological invasions. Here, we summarize the literature of Allee effects in biological invasions, revealing an extensive theory of the consequences of the Allee effect in invading species and some empirical support for the theory. Allee effects cause longer lag times, slower spread and decreased establishment likelihood of invasive species. Expected spatial ranges, distributions and patterns of species may be altered when an Allee effect is present. We examine how the theory can and has been used to detect Allee effects in invasive species and we discuss how the presence of an Allee effect and its successful or unsuccessful detection may affect management of invasives. The Allee effect has been shown to change optimal control decisions, costs of control and the estimation of the risk posed by potentially invasive species. Numerous ways in which the Allee effect can influence the efficacy of biological control are discussed. [source]

Contribution of rarity and commonness to patterns of species richness

ECOLOGY LETTERS, Issue 2 2004
Jack J. Lennon
Abstract There is little understanding in ecology as to how biodiversity patterns emerge from the distribution patterns of individual species. Here we consider the question of the contributions of rare (restricted range) and common (widespread) species to richness patterns. Considering a species richness pattern, is most of the spatial structure, in terms of where the peaks and troughs of diversity lie, caused by the common species or the rare species (or neither)? Using southern African and British bird richness patterns, we show here that commoner species are most responsible for richness patterns. While rare and common species show markedly different species richness patterns, most spatial patterning in richness is caused by relatively few, more common, species. The level of redundancy we found suggests that a broad understanding of what determines the majority of spatial variation in biodiversity may be had by considering only a minority of species. [source]

RELATIVE ABUNDANCE AND THE SPECIES-SPECIFIC REINFORCEMENT OF MALE MATING PREFERENCE IN THE CHRYSOCHUS (COLEOPTERA: CHRYSOMELIDAE) HYBRID ZONE

EVOLUTION, Issue 12 2005
Merrill A. Peterson
Abstract Most studies of reinforcement have focused on the evolution of either female choice or male mating cues, following the long-held view in sexual selection theory that mating mastakes are typically more costly for females than for males. However, factors such as conspecific sperm precedence can buffer females against the cost of mating mistakes, suggesting that in some hybrid zones mating mistakes may be more costly for males than for females. Thus, the historical bias in reinforcement research may underestimate its frequency. In this study, we present evidence that reinforcement has driven the evolution of male choice in a hybrid zone between teh highly promiscuous lealf beetles chyrsochus cobaltinus and C. auratus, the hybrids of which have extremely low fitness. In addition, there is evidence for male choice in these beetles and that male mating mistakes may be costly, due to reduced opportunities to mate with conspecific females. The present study combines laboratory and field methods to quantify the strenght of sexual isolation, test the hypothesis of reproductive character displacement, and assess the link between relative abundance and the strenght of selection against hybridization. We document that, while sexual isolation is weak, it is sufficient to produce positive assortative mating. In addtion, reproductive character displacement was only detected in the relatively rare species. The strong postzygotic barriers in this system are sufficient to generate the bimodality that characterizes this hybrid zone, but the weak sexual isolation is not, calling into question whether strong prezygotic isolation is necessary for the maintenance of bimodality. Growing evidence that the cost of mating mistakes is sufficient to shape the evolution of male mate choice suggests that the reinforecement of male mate choice may prove to be a widespread occurrence. [source]

Diel variation in the seagrass ichthyofaunas of three intermittently open estuaries in south-eastern Australia: implications for improving fish diversity assessments

FISHERIES MANAGEMENT & ECOLOGY, Issue 2 2001
S. P. Griffiths
Diel variation in the ichthyofaunas associated with Zostera capricorni Ascherson was investigated in three intermittently open estuaries in the Illawarra region, New South Wales. Each estuary showed differing diel shifts in fish assemblages, which appeared to be related to estuary size. In the largest estuary (Lake Illawarra) significantly more species were caught during the night than the day for all months. In contrast, there was little diel variation in the fish assemblages at Werri Lagoon and Shellharbour Lagoon, although many species were only caught during the night at both estuaries. The distinct diel changes at Lake Illawarra was thought to be attributable to the relatively deep channels adjacent to the seagrass beds which are better habitats for larger fishes compared with the shallow sand bars without deep channels throughout the two smaller estuaries. The composition of fish species within the three estuaries were significantly different, although each assemblage was characterised by large numbers of small-sized fish (<100 mm FL) indicating the importance of intermittently open estuaries as fish habitats. It was concluded that night sampling provided a more complete picture of the ichthyofaunas associated with Z. capricorni. As a result, inclusion of night sampling in fish diversity assessments would increase the chance of catching diurnally rare species and therefore attain a better representation of the true community structure. [source]

Bryozoan populations reflect nutrient enrichment and productivity gradients in rivers

FRESHWATER BIOLOGY, Issue 11 2009
HANNA HARTIKAINEN
Summary 1. The hypothesis that nutrient enrichment will affect bryozoan abundance was tested using two complementary investigations; a field-based method determining bryozoan abundance in 20 rivers of different nutrient concentrations by deploying statoblast (dormant propagule) traps and an experimental laboratory microcosm study measuring bryozoan growth and mortality. These two methods confirmed independently that increased nutrient concentrations in water promote increases in the biomass of freshwater bryozoans. 2. Statoblasts of the genus Plumatella were recorded in all rivers, regardless of nutrient concentrations, demonstrating that freshwater bryozoans are widespread. Concentrations of Plumatella statoblasts were high in rivers with high nutrient concentrations relative to those with low to moderate nutrient concentrations. Regression analyses indicated that phosphorus concentrations, in particular, significantly influenced statoblast concentrations. 3. Concentrations of Lophopus crystallinus statoblasts were also higher in sites characterised by high nutrient concentrations. Logistic regression analysis revealed that the presence of L. crystallinus statoblasts was significantly associated with decreasing altitude and increasing phosphorus concentrations. This apparently rare species was found in nine rivers (out of 20), seven of which were new sites for L. crystallinus. 4. Growth rates of Fredericella sultana in laboratory microcosms increased with increasing nutrient concentration and high mortality rates were associated with low nutrient concentrations. 5. Our results indicate that bryozoans respond to increasing nutrient concentrations by increased growth, resulting in higher biomasses in enriched waters. We also found that an important component of bryozoan diets can derive from food items lacking chlorophyll a. Finally, bryozoans may be used as independent proxies for inferring trophic conditions, a feature that may be especially valuable in reconstructing historical environments by assessing the abundance of statoblasts in sediment cores. [source]