EVOLUTION, Issue 1 2003
NICK J. B. ISAAC
Abstract., Explaining the uneven distribution of species among lineages is one of the oldest questions in evolution. Proposed correlations between biological traits and species diversity are routinely tested by making comparisons between phylogenetic sister clades. Several recent studies have used nested sister-clade comparisons to test hypotheses linking continuously varying traits, such as body size, with diversity. Evaluating the findings of these studies is complicated because they differ in the index of species richness difference used, the way in which trait differences were treated, and the statistical tests employed. In this paper, we use simulations to compare the performance of four species richness indices, two choices about the branch lengths used to estimate trait values for internal nodes and two statistical tests under a range of models of clade growth and character evolution. All four indices returned appropriate Type I error rates when the assumptions of the method were met and when branch lengths were set proportional to time. Only two of the indices were robust to the different evolutionary models and to different choices of branch lengths and statistical tests. These robust indices had comparable power under one nonnull scenario. Regression through the origin was consistently more powerful than the t -test, and the choice of branch lengths exerts a strong effect on both the validity and power. In the light of our simulations, we re-evaluate the findings of those who have previously used nested comparisons in the context of species richness. We provide a set of simple guidelines to maximize the performance of phylogenetically nested comparisons in tests of putative correlates of species richness. [source]

Cost-Efficiency of Decaying Wood as a Surrogate for Overall Species Richness in Boreal Forests

CONSERVATION BIOLOGY, Issue 1 2006
ARTTI JUUTINEN
biodiversidad; gestión de bosques; indicadores de riqueza de especies; seleccion de sitios Abstract:,Decaying wood is one of the most important elements for species richness in boreal forests. We tested how well reserve selection based on the amount and quality of decaying wood results in a representation of four ecologically different taxa (beetles, birds, wood-inhabiting fungi, and vascular plants). We also compared the cost-efficiency of the use of dead-wood indicators with comprehensive species inventory. Our database included 32 seminatural old-forest stands located in northern Finland. Decaying wood was a relatively good indicator of saproxylic species but not overall species richness. Even though dead wood did not reflect accurately overall species richness, our results indicated that the use of decaying wood as an indicator in site selection was more cost-efficient than using information from large-scale species inventories. Thus, decaying wood is a valuable surrogate for species richness, but other cost-efficient indicators that reflect the requirements of those species which are not dependent on decaying wood should be identified. Resumen:,La madera en descomposición es uno de los elementos importantes para la riqueza de especies en bosques boreales. Probamos como resulta la selección de reservas con base en la cantidad y calidad de madera en descomposición en la representación de cuatro taxa ecológicamente distintos (escarabajos, aves, hongos habitantes en la madera y plantas vasculares). También comparamos la rentabilidad del uso de indicadores de madera muerta con inventarios integrales de especies. Nuestra base de datos incluyó 32 sitios de bosque maduro seminatural localizados en el norte de Finlandia. La madera en descomposición fue un indicador relativamente bueno de especies saproxílicas pero no de la riqueza total. Aunque la madera en descomposición no reflejó la riqueza total con precisión, nuestros resultados indicaron que el uso de madera en descomposición como un indicador en la selección de sitios fue más rentable que el uso de información de inventarios de especies de gran escala. Por lo tanto, la madera en descomposición es un sustituto valioso de la riqueza de especies, pero se deben identificar otros indicadores rentables que reflejen los requerimientos de aquellas especies que no dependen de la madera en descomposición. [source]

Beyond Species Richness: Community Similarity as a Measure of Cross-Taxon Congruence for Coarse-Filter Conservation

CONSERVATION BIOLOGY, Issue 1 2004
JEFFREY C. SU
Species richness is only one measure of species diversity, however, and recent studies suggest that investigations of cross-taxon congruence should consider a broader range of assessment techniques. The cross-taxon congruence of community similarity between sites among taxa has rarely been examined and may be the most relevant measure of species diversity in the context of coarse-filter conservation strategies. We examined cross-taxon congruence patterns of species richness and community similarity (Bray-Curtis similarity) among birds, butterflies, and vascular plants in montane meadow habitats in the Greater Yellowstone Ecosystem. Although patterns of species richness (Spearman rank correlation) varied between taxa, we consistently found a positive correlation in community similarity (Mantel test) between all pair-wise comparisons of the three taxa (e.g., sites with similar bird communities also had similar butterfly communities). We suggest that the success of a surrogate taxon depends on the technique used to assess surrogacy and the specific approach to conservation planning. In the context of coarse-filter conservation, measures of community similarity may be more appropriate than measures of species richness. Furthermore, the cross-taxon congruency of community similarity in our study suggests that coarse-filter conservation may be tenable in montane meadow communities. Resumen:,El uso de un taxón sustituto en la planeación de la conservación se ha vuelto cuestionable porque información reciente sugiere que la correlación de riqueza de especies entre pares de taxones es altamente variable taxonómica y geográficamente. Sin embargo, la riqueza de especies es solo una medida de la diversidad de especies, y estudios recientes sugieren que las investigaciones de congruencia trans-taxón debieran considerar una mayor variedad de técnicas de evaluación. La congruencia trans-taxón de la similitud de comunidades entre sitios entre taxones rara vez se ha examinado y puede ser la medida de diversidad de especies más relevante en el contexto de las estrategias de conservación de grano grueso. Examinamos patrones de congruencia trans-taxón de riqueza de especies y similitud de comunidades (similitud Bray-Curtis) en aves, mariposas y plantas vasculares en hábitats de praderas montanas en el Ecosistema Greater Yellowstone. Aunque los patrones de riqueza de especies (correlación Spearman de rangos) variaron entre especies, encontramos consistentemente una correlación positiva en la similitud de la comunidad (prueba de Mantel) entre todas las comparaciones de pares de los tres taxones (es decir, los sitios con comunidades similares de aves también tenían comunidades similares de mariposas). Sugerimos que el éxito de un taxón sustituto depende de la técnica utilizada para evaluar la sustitución y el abordaje específico de la planeación de conservación. En el contexto de la conservación de grano grueso, pueden ser más apropiadas las medidas de similitud de comunidades que las medidas de riqueza de especies. Más aun, la congruencia trans-taxón de similitud de comunidades en nuestro estudio sugiere que la conservación de grano grueso puede ser justificable en comunidades de praderas montanas. [source]

Impact of Forest Fragmentation on Understory Plant Species Richness in Amazonia

CONSERVATION BIOLOGY, Issue 2 2003
Julieta Benítez-Malvido
In Central Amazonia, 9 to 19 years after fragmentation, we recorded species richness and net seedling recruitment rate in forest fragments of 1, 10, and 100 ha and in continuous forest. In 1991 all seedlings 5,100 cm tall within permanent 1-m2 plots in fragments and continuous forest were counted and grouped into tree, liana, palm, and herb life-form classes. In 1993 we manually removed all seedlings that were <1 m tall from the permanent plots. Six years and 5 months later ( 1999 ), all new seedlings recruited into the plots were counted, grouped into different life forms, and classified into distinct morphospecies. The species richness of recruited tree, liana, herb, and palm seedlings was lower in forest fragments than in continuous forest, with the 1-ha fragment having the poorest species richness. The total number of recruited individuals was 40% less than that previously present for all life forms, except lianas. Liana recruitment was 7% to 500% higher than the original abundance in the forest fragments and continuous forest. In general, species similarity was higher among fragments than between fragments and continuous forest, with the 1-ha fragment being less similar. Species rank/abundance curves showed that continuous forest species in all life forms tended to disappear in forest fragments, whereas common species in forest fragments were absent from continuous forest. Overall, our results suggest that the life-form composition and structure of the regenerative plant pool in fragments were shifting toward a species-poor seedling community. Losses of understory species diversity, but especially of tree seedlings, threaten the maintenance of rainforest biodiversity and compromise future forest regeneration. Resumen: La fragmentación de las selvas tropicales afecta severamente a a los árboles de gran porte, sin embargo, su efecto sobre otros estadíos y formas de vida de las plantas es poco conocido. En la Amazonia central, de 9 a 19 años después de la fragmentación, se registró la riqueza de especies y la tasa neta de reclutamiento de plántulas en fragmentos de selva de 1, 10, y 100 ha y en selva contínua. En 1991, todas las plántulas de 5,100 cm de altura dentro de cuadrantes permanentes de 1-m2 en los fragmentos y en la selva contínua, fueron contadas y agrupadas en diferentes formas de vida: árboles, lianas, palmas y hierbas. En 1993 se removieron manualmente todas las plántulas <1 m de altura dentro de los cuadrantes. Seis años y cinco meses más tarde (1999) se contaron todas las plántulas reclutadas dentro de los cuadrantes, se agruparon en diferentes formas de vida v se clasificaron en morfoespecies distintivas. La riqueza de especies de plántulas reclutadas en todas las formas de vida fue menor en los fragmentos que en la selva contínua, con el fragmento de 1 ha presentando la menor riqueza de especies. El número total de individuos reclutados fue 40% menor que los previamente presentes para todas las formas de vida, excepto lianas. El reclutamiento de lianas fué de 7 a 500% mayor que la abundancia original en los fragmentos y en la selva contínua. En general la similitud de especies fué mayor entre fragmentos que entre fragmentos y selva contínua, con el fragmento de 1-ha siendo el menos similar. Las curvas de rango/abundancia de especies, mostraron que las especies de selva contínua en todas las formas de vida tendieron a desaparecer de los fragmentos, mientras que las especies comunes en los fragmentos estuvieron ausentes en la selva contínua. En general, nuestros resultados sugieren que la composición de formas de vida y la estructura del banco regenerativo en fragmentos tienden a convertirse en una comunidad de plántulas pobre en especies. La pérdida de diversidad de especies del sotobosque, pero especialmente de plántulas de árboles, amenaza el mantenimiento de la biodiversidad y pone en peligro la regeneración futura de la selva. [source]

Hypolithic community shifts occur as a result of liquid water availability along environmental gradients in China's hot and cold hyperarid deserts

ENVIRONMENTAL MICROBIOLOGY, Issue 2 2007
Stephen B. Pointing
Summary Hypolithic cyanobacterial communities occur in hot and cold hyperarid environments but the physical factors determining their diversity are not well understood. Here we report hypolithic diversity and colonization of a common quartz substrate at several hyperarid locations in the ancient deserts of north-western China, that experience varying mean annual temperature, rainfall and concomitant availability of liquid water in soil. Microscopy and enrichment culture resulted only in Chroococcidiopsis morphotypes which were ubiquitous, but community phylogenetic analysis revealed considerable cyanobacterial and heterotrophic bacterial diversity. Species Richness and Shannon's Diversity Index displayed a significant positive linear correlation with availability of liquid water but not temperature or rainfall alone. Several taxonomic groups occurred only in specific climatically defined locations, while for Chroococcidiopsis, Deinococcus and Phormidium location specific lineages within these genera were also evident. Multivariate analysis was used to illustrate pronounced community shifts due to liquid water availability, although these did not significantly affect the predicted functional relationships within any given assemblage in either hot or cold, wet or dry hyperarid deserts. This study clearly demonstrates that availability of liquid water, rather than temperature or rainfall per se is the key determinant of hypolithic diversity in hyperarid locations, and furthermore that functionally similar yet taxonomically distinct communities occur, characterized by the presence of taxa that are specific to defined levels of aridity. [source]

Effects of Restoration on Plant Species Richness and Composition in Scandinavian Semi-Natural Grasslands

RESTORATION ECOLOGY, Issue 3 2004
Regina Lindborg
Abstract Plant species richness in rural landscapes of northern Europe has been positively influenced by traditional management for millennia. Owing to abandonment of these practices, the number of species-rich semi-natural grasslands has decreased, and remaining habitats suffer from deterioration, fragmentation, and plant species decline. To prevent further extinctions, restoration efforts have increased during the last decades, by reintroducing grazing in former semi-natural grasslands. To assess the ecological factors that might influence the outcome of such restorations, we made a survey of semi-natural grasslands in Sweden that have been restored during the last decade. We investigated how plant species richness, species density, species composition, and abundance of 10 species that are indicators of grazing are affected by (1) the size of the restored site, (2) the time between abandonment of grazing and restoration, (3) the time elapsed since restoration, and (4) the abundance of trees and shrubs at the restored site. Only two factors, abundance of trees and shrubs and time since restoration, were positively associated with total species richness and species density per meter square at restored sites. Variation in species composition among restored sites was not related to any of the investigated factors. Species composition was relatively similar among sites, except in mesic/wet grasslands. The investigated factors had small effects on the abundance of the grazing-indicator species. Only Campanula rotundifolia responded to restoration with increasing abundance and may thus be a suitable indicator of improved habitat quality. In conclusion, positive effects on species richness may appear relatively soon after restoration, but rare, short-lived species are still absent. Therefore, remnant populations in surrounding areas may be important in fully recreating former species richness and composition. [source]

Restoration of Species Richness in Abandoned Mediterranean Grasslands: Seeds in Cattle Dung

RESTORATION ECOLOGY, Issue 3 2003
Juan Traba
Abstract Endozoochory has proven to be a highly effective mechanism in the dispersal of viable seeds in Mediterranean grasslands. We studied the effect of cattle dung application on species richness, particularly on the reintroduction of species lost after abandonment. Sown and control plots were monitored for 3 years after dung sowing. We found a significant increase in small-scale richness, which may be attributed to the treatment, with the inclusion of species detected in the dung and in the grazed pasture. The differences in richness and floristic composition diminished over time. This experiment proves the potential utility of this treatment for the restoration of species richness in abandoned pastures, although supplementary steps are necessary, including further sowing and/or shrub cutting in subsequent years. [source]

Bayesian Estimation of Species Richness from Quadrat Sampling Data in the Presence of Prior Information

BIOMETRICS, Issue 3 2006
Jérôme A. Dupuis
Summary We consider the problem of estimating the number of species of an animal community. It is assumed that it is possible to draw up a list of species liable to be present in this community. Data are collected from quadrat sampling. Models considered in this article separate the assumptions related to the experimental protocol and those related to the spatial distribution of species in the quadrats. Our parameterization enables us to incorporate prior information on the presence, detectability, and spatial density of species. Moreover, we elaborate procedures to build the prior distributions on these parameters from information furnished by external data. A simulation study is carried out to examine the influence of different priors on the performances of our estimator. We illustrate our approach by estimating the number of nesting bird species in a forest. [source]

Rapid Recovery of Biomass, Species Richness, and Species Composition in a Forest Chronosequence in Northeastern Costa Rica

BIOTROPICA, Issue 5 2009
Susan G. Letcher
ABSTRACT Secondary forests are a vital part of the tropical landscape, and their worldwide extent and importance continues to increase. Here, we present the largest chronosequence data set on forest succession in the wet tropics that includes both secondary and old-growth sites. We performed 0.1 ha vegetation inventories in 30 sites in northeastern Costa Rica, including seven old-growth forests and 23 secondary forests on former pastures, ranging from 10 to 42 yr. The secondary forest sites were formerly pasture for intervals of <1,25 yr. Aboveground biomass in secondary forests recovered rapidly, with sites already exhibiting values comparable to old growth after 21,30 yr, and biomass accumulation was not impacted by the length of time that a site was in pasture. Species richness reached old-growth levels in as little as 30 yr, although sites that were in pasture for > 10 yr had significantly lower species richness. Forest cover near the sites at the time of forest establishment did not significantly impact biomass or species richness, and the species composition of older secondary forest sites (>30 yr) converged with that of old growth. These results emphasize the resilience of tropical ecosystems in this region and the high conservation value of secondary forests. [source]

Impact of Flooding on the Species Richness, Density and Composition of Amazonian Litter-Nesting Ants

BIOTROPICA, Issue 5 2009
Amy L. Mertl
ABSTRACT Litter-nesting ants are diverse and abundant in tropical forests, but the factors structuring their communities are poorly known. Here we present results of the first study to examine the impact of natural variation in flooding on a highly diverse (21 genera, 77 species) litter-nesting ant community in a primary Amazonian forest. Fifty-six 3 × 3 m plots experiencing strong variation in flooding and twenty-eight 3 × 3 m terra firme plots were exhaustively searched for litter-nesting ants to determine patterns of density, species richness and species composition. In each plot, flooding, litter depth, twig availability, canopy cover, plant density, percent soil nitrogen, carbon, and phosphorus were measured. Degree of flooding, measured as flood frequency and flood interval, had the strongest impact on ant density in flooded forest. Flooding caused a linear decrease in ant abundance, potentially due to a reduction of suitable nesting sites. However, its influence on species richness varied: low-disturbance habitat had species richness equal to terra firme forest after adjusting for differences in density. The composition of ant genera and species varied among flood categories; some groups known to contain specialist predators were particularly intolerant to flooding. Hypoponera STD10 appeared to be well-adapted to highly flooded habitat. Although flooding did not appear to increase species richness or abundance at the habitat scale, low-flooding habitat contained a mixture of species found in the significantly distinct ant communities of terra firme and highly flooded habitat. [source]

Bat Species Richness in Atlantic Forest: What Is the Minimum Sampling Effort?

BIOTROPICA, Issue 2 2003
Helena Godoy Bergallo
ABSTRACT Species lists are sources of information for studies of both conservation and macroecology. It is, however, important to differentiate between relatively complete lists and extremely incomplete ones. The aim of this study was to evaluate how sampling effort typically used in inventories affects the number of bat species captured in areas of Atlantic Forest in southeastern Brazil. We also evaluated if the number of sampled sites, size of the sampled area, and sampling effort (net hours) affect species richness. We used previously reported data from studies in Rio de Janeiro, São Paulo, and Minas Gerais States, and our own data collected during 1989 and 2001. Nonlinear models fit well the data for Rio de Janeiro and Minas Gerais States and all states together, but not for São Paulo State. Genera richness showed a similar pattern to that of species richness. The model used to explain the relationship between species richness and size of the study area, number of sites, and sampling effort sampled was significant. The number of sites sampled explained a significant part of the variation observed; however, other variables contributed nothing to the model, suggesting that capturing beta diversity is the most important aspect of biodiversity surveys for bats, and that increasing net hours at a given location is much more inefficient than distributing net hours across locations. We suggest 1000 captures as the minimum necessary when sampling with mist nets to capture the majority of phyllostomid species for a given site (alpha diversity). In addition, we suggest that shifting the position of the mist nets between nights will increase the probability of capturing more species. RESUMO As listas de espécies são fontes de informações para estudos, tanto de conservação quanto de macroecologia. Entretanto, é importante diferenciar entre listas relativamente completas daquelas seriamente incompletas. O objetivo deste estudo foi avaliar como o esforco amostral mínimo tipicamente usado em inventários afeta o número de especies de morcegos capturados em áreas de Mata Atlãntica do sudeste do Brasil. Nós também avaliamos se o número de pontos amostrados, o tamanho da área amostrada e o esforço de captura (hora-rede) afetam a riqueza de espécies. Nós usamos dados disponíveis de estudos desenvolvidos nos estados do Rio de Janeiro, São Paulo e Minas Gerais, e os nossos próprios dados coletados de 1989 a 2001. Modelos não-lineares se ajustaram para os estados do Rio de Janeiro e Minas Gerais e todos os estados juntos, mas não para o Estado de São Paulo. A riqueza de g,neros mostrou o mesmo padrão da riqueza de espécies. O modelo usado para expliçãr a relacao entre riqueza de espécies e tamanho da área de estudo, número de pontos amostrados e esforço amostral foi significative. O número de pontos amostrados explicou uma parte significante da variação observada. Contudo, as outras variáveis não contribuiram para o modelo, sugerindo que capturar a diversidade Beta é o aspecto mais importante de inventários de biodiversidade para morcegos, e que o aumento de horas-rede numa dada localidade é muito mais ineficiente do que distribuir horas-rede entre localidades. Nós sugerimos 1000 capturas como o mínimo necessário para amostrar, com redes de neblina, a maioria das espécies de filostomídeos de uma dada área (diversidade Alfa). Adicionalmente, sugerimos que mudando a posição das redes entre noites aumentará a probabilidade de capturar um maior número de espéciesS. [source]

Multispecies and Multiscale Conservation Planning: Setting Quantitative Targets for Red-Listed Lichens on Ancient Oaks

CONSERVATION BIOLOGY, Issue 3 2010
HEIDI PALTTO
bosque de encino maduro; cantidad de hábitat; encino antiguo; escala espacial; líquenes en la lista roja Abstract:,Species occurrence in a habitat patch depends on local habitat and the amount of that habitat in the wider landscape. We used predictions from empirical landscape studies to set quantitative conservation criteria and targets in a multispecies and multiscale conservation planning effort. We used regression analyses to compare species richness and occurrence of five red-listed lichens on 50 ancient oaks (Quercus robur; 120,140 cm in diameter) with the density of ancient oaks in circles of varying radius from each individual oak. Species richness and the occurrence of three of the five species were best explained by increasing density of oaks within 0.5 km; one species was best explained by the density of oaks within 2 km, and another was best predicted by the density of oaks within 5 km. The minimum numbers of ancient oaks required for "successful conservation" was defined as the number of oaks required to obtain a predicted local occurrence of 50% for all species included or a predicted local occurrence of 80% for all species included. These numbers of oaks were calculated for two relevant landscape scales (1 km2 and 13 km2) that corresponded to various species responses, in such a way that calculations also accounted for local number of oaks. Ten and seven of the 50 ancient oaks surveyed were situated in landscapes that already fulfilled criteria for successful conservation when the 50% and 80% criteria, respectively, were used to define the level of successful conservation. For cost-efficient conservation, oak stands in the landscapes most suitable for successful conservation should be prioritized for conservation and management (e.g., grazing and planting of new oaks) at the expense of oak stands situated elsewhere. Resumen:,La ocurrencia de especies en un parche de hábitat depende del hábitat local y de la cantidad de ese hábitat en un paisaje más amplio. Utlizamos predicciones de estudios de paisaje empíricos para definir criterios y objetivos de conservación cuantitativos en un esfuerzo de planificación de la conservación para múltiples especies y escalas. Utilizamos análisis de regresión para comparar la riqueza y ocurrencia de especies de cinco líquenes en la lista roja sobre 20 encinos antiguos (Quercus robur; 120,140 cm de diámetro) con la densidad de encinos antiguos en círculos de radio variable desde cada encino individual. La riqueza y ocurrencia de tres de las cinco especies fue mejor explicada por el incremento de la densidad de encinos en 0.5 km; una especie fue mejor explicada por la densidad de encinos en 2 km, y la otra fue mejor pronosticada por la densidad de encinos en 5 km. Los números mínimos de encinos antiguos requeridos para una "conservación exitosa" fueron definidos como el número de encinos requeridos para obtener una ocurrencia local pronosticada de de 50% para todas las especies incluidas o una ocurrencia local pronosticada de 80% para todas las especies incluidas. Estos números de encinos fueron calculados para dos escalas de paisaje relevantes (1 km2 y 13 km2) que correspondieron a las respuestas de varias especies, de tal modo que los cálculos también incluyeron el número local de encinos. Diez y siete de los 50 encinos antiguos estaban situados en paisajes que ya cumplían criterios para conservación exitosa cuando los criterios de 50% y 80%, respectivamente, fueron usados para definir el nivel de conservación exitosa. Para una conservación redituable, los bosques de encinos en los paisajes más aptos para la conservación exitosa deberían ser priorizados para conservación y manejo (e. g., pastoreo y siembra de encinos nuevos) a costa de bosques de encino situados en otros lados. [source]

Effects of Conversion of Dry Tropical Forest to Agricultural Mosaic on Herpetofaunal Assemblages

CONSERVATION BIOLOGY, Issue 2 2008
IRERI SUAZO-ORTUÑO
atributos de vulnerabilidad; bosque tropical seco; ensambles herpetofaunísticos; modificación del hábitat; mosaico agrícola Abstract:,We explored the impact of forest conversion to agricultural mosaic on anuran, lizard, snake, and turtle assemblages of Neotropical dry forests. Over 2 years, we sampled 6 small watersheds on the west coast of Mexico, 3 conserved and 3 disturbed. The disturbed watersheds were characterized by a mosaic of pastures and cultivated fields (corn, beans, squash) intermingled with patches of different successional stages of dry forest. In each watershed, we conducted 11 diurnal and nocturnal time-constrained searches in 10 randomly established plots. We considered vulnerability traits of species in relation to habitat modification. Eighteen anuran, 18 lizard, 23 snake, and 3 turtle species were recorded. Thirty-six species (58%) occurred in both forest conditions, and 14 (22%) and 12 species (19%) occurred only in the conserved and disturbed sites, respectively. Assemblages responded differently to disturbance. Species richness, diversity, and abundance of lizards were higher in disturbed forests. Anuran diversity and species richness were lower in disturbed forest but abundance was similar in both forest conditions. Diversity, richness, and abundance of turtles were lower in disturbed forest. The structure and composition of snake assemblages did not differ between forest conditions. We considered species disturbance sensitive if their abundance was significantly less in disturbed areas. Four anuran (22%), 2 lizard (11%), and 3 turtle (100%) species were sensitive to disturbance. No snake species was sensitive. The decline in abundance of disturbance-sensitive species was associated with the reduction of forest canopy cover, woody stem cover, roots, and litter-layer ground cover. Anuran species with small body size and direct embryonic development were especially sensitive to forest disturbance. An important goal for the conservation of herpetofauna should be the determination of species traits associated with extinction or persistence in agricultural mosaics. Resumen:,Exploramos el impacto de la conversión de bosques a mosaico agrícola sobre ensambles de lagartijas, serpientes y tortugas de bosques Neotropicales secos. Durante 2 años muestreamos 6 cuencas pequeñas, 3 conservadas y 3 perturbadas, en la costa occidental de México. Las cuencas perturbadas se caracterizaron por un mosaico de pastizales y campos cultivados (maíz, frijol, calabaza) entremezclados con parches de bosque seco en diferentes etapas sucesionales. En cada cuenca, realizamos 11 búsquedas diurnas y nocturnas en 10 parcelas establecidas aleatoriamente. Consideramos los atributos de vulnerabilidad de especies en relación con la modificación del hábitat. Registramos 18 especies de lagartijas, 23 de serpientes y 3 de tortugas. Treinta y seis especies (58%) ocurrieron en ambas condiciones de bosque, y 14 (22%) y 12 (19%) especies solo ocurrieron en los sitios conservados y perturbados, respectivamente. Los ensambles respondieron a la perturbación de manera diferente. La riqueza de especies, la diversidad y la abundancia de lagartijas fueron mayores en los bosques perturbados. La diversidad y riqueza de especies de anuros fueron menores en el bosque perturbado pero la abundancia fue similar en ambas condiciones de bosque. La diversidad, riqueza de especies y abundancia de tortugas fueron menores en el bosque perturbado. La estructura y la composición de los ensambles de serpientes no difirieron entre condiciones de bosque. Consideramos que las especies eran sensibles a la perturbación si su abundancia fue significativamente menor en las áreas perturbadas. Cuatro (22%) especies de anuros, 2 (11%) de lagartijas y 3 (100%) de tortugas fueron sensibles a la perturbación. Ninguna especie de serpiente fue sensible. La declinación en la abundancia de especies sensibles a la perturbación se asoció con la reducción en la cobertura del dosel, de tallos leñosos, raíces y hojarasca. Las especies de anuros de cuerpo pequeño y desarrollo embrionario directo fueron especialmente sensibles a la perturbación del bosque. La determinación de atributos de las especies asociadas con su extinción o persistencia en mosaicos agrícolas debería ser una meta importante para la conservación de la herpetofauna. [source]

Beyond Species Richness: Community Similarity as a Measure of Cross-Taxon Congruence for Coarse-Filter Conservation

Spatiotemporal changes of beetle communities across a tree diversity gradient

DIVERSITY AND DISTRIBUTIONS, Issue 4 2009
Stephanie Sobek
Abstract Aim, Plant and arthropod diversity are often related, but data on the role of mature tree diversity on canopy insect communities are fragmentary. We compare species richness of canopy beetles across a tree diversity gradient ranging from mono-dominant beech to mixed stands within a deciduous forest, and analyse community composition changes across space and time. Location, Germany's largest exclusively deciduous forest, the Hainich National Park (Thuringia). Methods, We used flight interception traps to assess the beetle fauna of various tree species, and applied additive partitioning to examine spatiotemporal patterns of diversity. Results, Species richness of beetle communities increased across the tree diversity gradient from 99 to 181 species per forest stand. Intra- and interspecific spatial turnover among trees contributed more than temporal turnover among months to the total ,-beetle diversity of the sampled stands. However, due to parallel increases in the number of habitat generalists and the number of species in each feeding guild (herbivores, predators and fungivores), no proportional changes in community composition could be observed. If only beech trees were analysed across the gradient, patterns were similar but temporal (monthly) species turnover was higher compared to spatial turnover among trees and not related to tree diversity. Main conclusions, The changes in species richness and community composition across the gradient can be explained by habitat heterogeneity, which increased with the mix of tree species. We conclude that understanding temporal and spatial species turnover is the key to understanding biodiversity patterns. Mono-dominant beech stands are insufficient to conserve fully the regional species richness of the remaining semi-natural deciduous forest habitats in Central Europe, and analysing beech alone would have resulted in the misleading conclusion that temporal (monthly) turnover contributes more to beetle diversity than spatial turnover among different tree species or tree individuals. [source]

Spatial congruence between ecotones and range-restricted species: implications for conservation biogeography at the sub-continental scale

DIVERSITY AND DISTRIBUTIONS, Issue 3 2009
Berndt J. Van Rensburg
ABSTRACT Aim, To examine whether at a sub-continental scale range-limited species tend to occur close to areas of transition between vegetation boundaries more often than expected by chance. Location, South Africa and Lesotho. Methods, We examined the relationship between the distance of a grid square to ecological transition areas between vegetation types and both avian and frog range-limited species richness in the quadrat. We used quadrats at a spatial resolution of quarter degree (15, × 15,, 676 km2). Spatial congruence between areas representing range-restricted species and those representing ecological transition zones was assessed using a random draw technique. Results, Species richness and range size rarity are generally negatively correlated with distance to transition areas between vegetation communities when analysed for the whole region for both groups. Although this relationship becomes weaker after controlling for environmental energy and topographical heterogeneity, the explanatory power of distance to transition areas remains significant, and compared to the different biomes examined, accounts for most of the variation in bird richness (20%), frog richness (18%), range-restricted bird species (17%) and range-restricted frog species (16%) in the savanna biome. The random draw technique indicated that areas representing range-restricted species were situated significantly closer in space to those areas representing transition areas between vegetation communities than expected by chance. Main conclusions, We find that at the sub-continental scale, when examined for South Africa, areas of transition between vegetation communities hold concentrations of range-limited species in both birds and frogs. We find that South African endemic/range-limited birds and frogs are located closer to ecological transition zones than endemics and non-endemics combined. This has important implications for ongoing conservation planning in a biogeographical context. [source]

Satellite sleuthing: does remotely sensed land-cover change signal ecological degradation in a protected area?

DIVERSITY AND DISTRIBUTIONS, Issue 2 2009
T. A. Waite
ABSTRACT Aim, We evaluate whether remotely sensed land-cover change within a newly protected area signalled human-driven ecological degradation. Vegetation density changed in a quarter of pixels during the first 13 years (1986,1999) following the sanctuary's formal enclosure, with many patches showing a decrease in density. We use on-the-ground data collected in 2006 in 132 random plots to explore whether these changes in vegetation density reliably signalled latent shifts in local diversity of woody plants and whether they could be attributed to illicit activities including fuel wood collection and livestock grazing. Location, Kumbhalgarh Wildlife Sanctuary, Rajasthan, India. Results, Species richness, species sharing, species assemblages, and incidence of invasive and useful species were statistically similar among plots in which vegetation density had decreased, increased or remained similar. Likewise, intensity of disturbance associated with human activities was similar across these plot types. Main conclusions, Our data provide no clear evidence that local changes in vegetation density signalled latent shifts in local diversity of woody plants. They also fail to reveal any clear association between local changes in vegetation density and human-related activities. Finding no evidence that land-cover change led to biotic erosion, we reflect on the utility of resource-use bans in protected areas, particularly those embedded within historically coupled human-nature systems. [source]

Species richness of helminth parasites in Mexican amphibians and reptiles

DIVERSITY AND DISTRIBUTIONS, Issue 4 2002
Gerardo Pérez-Ponce de León
Abstract. Amphibians and reptiles represent an important group of vertebrates in Mexico; on a global scale 10% of the biodiversity of these groups is found in the country, attaining extraordinarily high levels of endemism (60.7% and 53.7%, respectively). However, fewer than 20% of the known species of amphibians and reptiles in Mexico have been surveyed for helminths, so the inventory is far from complete. We assembled a data base that includes a total of 1246 records (entries) of which 460 correspond to helminths in amphibians and 786 to helminths in reptiles. In total, only 41 species of amphibians (14% of those occurring in Mexico) and only 118 species of reptiles (17% of those occurring in Mexico) have been studied for helminth parasites. From amphibians, 119 species of helminths belonging to 60 genera have been recorded, while 239 species of helminths representing 113 genera have been described from Mexican reptiles. One feature of the distribution of helminths of Mexican amphibians and reptiles is its asymmetry, as seen in representation of helminth groups, host groups and geographical range. However, such statistical asymmetry might be an artefact of sampling effort. Based on our data, we estimate that if all the herpetofauna of Mexico could be studied in the following years, approximately 827 additional species of helminths from amphibians and approximately 1403 from reptiles would be described. [source]

Grasshopper (Orthoptera: Acridoidea) species diversity in the Pampas, Argentina

DIVERSITY AND DISTRIBUTIONS, Issue 2 2000
María Marta Cigliano
Abstract., A study was conducted to describe the major features of geographical and temporal variation in the diversity of grassland grasshopper species (Orthoptera: Acridoidea) in different sites of the Pampas, Argentina. Species richness and relative abundance were assessed at 12 sites in eastern La Pampa and western Buenos Aires provinces, from 1994 through 1999. Mean species richness at the regional level was 10, and 34 grasshopper species were collected throughout of the study. Comparison with grasshopper species diversity from the Great Plains of North America is discussed. An evaluation of the proportions of species in each of the three distribution groups (broad, intermediate and narrow) revealed that, over all sites, broadly distributed species made up 14.7% of species composition and intermediately and narrowly distributed species made up 26.5% and 58.8%, respectively. The three top-ranked species in the studied sites were Dichroplus elongatus, D. pratensis and Staurorhectus longicornis. Results showed that, contrary to what was expected, one of the widely distributed species in the region (i.e. Baeacris punctulatus) does not always constitute one of the most abundant species. Finally, the loss of one of the historically most common species in the Pampas, D. maculipennis, is also discussed. [source]

Species richness of marine Bryozoa in the continental shelf and slope off Argentina (south-west Atlantic)

DIVERSITY AND DISTRIBUTIONS, Issue 1 2000
Juan López Gappa
Abstract., A total of 246 marine bryozoan species was recorded within an area of the south-west Atlantic between 35° and 56°S, and between the coast of Argentina and 50°W. The distribution pattern of benthic stations surveyed during the most important cruises in the area shows that the sampling effort has been biased towards southern shelf areas off Santa Cruz and Tierra del Fuego, as well as around the Malvinas (Falkland) islands. The littoral zone, Patagonian gulfs and the continental shelf off Chubut, Río Negro and Buenos Aires state received less attention, and should be surveyed more intensively in the future. Only 2% of the species can be regarded as non-indigenous, all of them inhabiting biofouling communities in harbour environments. With the exception of some thoroughly surveyed localities, the number of species recorded for different areas of the coast, shelf and slope is estimated to be just a small fraction of the actual number of species present. A distinct diversity gradient was found, with species-rich stations located only in the southern shelf. Highest diversity occurred in shelf areas dominated by coarse sediments, and along a high-productivity shelf-break front. A remarkable decrease in species richness was found in inner and middle shelf areas off Chubut, Río Negro and Buenos Aires state. This pattern may be related to the Pacific origin of the Magellanic fauna, since the diversity of bryozoans is higher in the Pacific than in the Atlantic Ocean. The trend of species richness is, however, overemphasized by the fact that the least diverse faunistic assemblage occurs in areas where surveys have been relatively less frequent. An up-to-date checklist of species recorded for the study area is included. [source]

Integrating highly diverse invertebrates into broad-scale analyses of cross-taxon congruence across the Palaearctic

ECOGRAPHY, Issue 6 2009
Andreas Schuldt
Our knowledge on broad-scale patterns of biodiversity, as a basis for biogeographical models and conservation planning, largely rests upon studies on the spatial distribution of vertebrates and plants, neglecting large parts of the world's biodiversity. To reassess the generality of these patterns and better understand spatial diversity distributions of invertebrates, we analyzed patterns of species richness and endemism of a hyperdiverse insect taxon, carabid beetles (ca 11 000 Palaearctic species known), and its cross-taxon congruence with well-studied vertebrates (amphibians, reptiles) and plants across 107,units of the Palaearctic. Based on species accumulation curves, we accounted for completeness of the carabid data by separately examining the western (well-sampled) and eastern (partly less well-sampled) Palaearctic and China (deficient data). For the western Palaearctic, we highlight overall centers of invertebrate, vertebrate and plant diversity. Species richness and endemism of carabids were highly correlated with patterns of especially plant and amphibian diversity across large parts of the Palaearctic. For the well-sampled western Palaearctic, hotspots of diversity integrating invertebrates were located in Italy, Spain and Greece. Only analysis of Chinese provinces yielded low congruence between carabids and plants/vertebrates. However, Chinese carabid diversity is only insufficiently known and China features the highest numbers of annual new descriptions of carabids in the Palaearctic. Even based on the incomplete data, China harbors at least 25% of all Palaearctic carabid species. Our study shows that richness and endemism patterns of highly diverse insects can exhibit high congruence with general large scale patterns of diversity inferred from plants/vertebrates and that hotspots derived from the latter can also include a high diversity of invertebrates. In this regard, China qualifies as an outstanding multi-taxon hotspot of diversity, requiring intense biodiversity research and conservation effort. Our findings extend the limited knowledge on broad-scale invertebrate distributions and allow for a better understanding of diversity patterns across a larger range of the world's biodiversity than usually considered. [source]

Botanical richness and endemicity patterns of Borneo derived from species distribution models

ECOGRAPHY, Issue 1 2009
Niels Raes
This study provides a Borneo-wide, quantitative assessment of botanical richness and endemicity at a high spatial resolution, and based on actual collection data. To overcome the bias in collection effort, and to be able to predict the presence and absence of species, even for areas where no collections have been made, we constructed species distribution models (SDMs) for all species taxonomically revised in Flora Malesiana. Species richness and endemicity maps were based on 1439 significant SDMs. Mapping of the residuals of the richness-endemicity relationship identified areas with higher levels of endemicity than can be expected on the basis of species richness, the endemicity hotspots. We were able to identify one previously unknown region of high diversity, the high mountain peaks of East Kalimantan; and two additional endemicity hotspots, the Müller Mountains and the Sangkulirang peninsula. The areas of high diversity and endemicity were characterized by a relatively small range in annual temperature, but with seasonality in temperatures within that range. Furthermore, these areas were least affected by El Niño Southern Oscillation drought events. The endemicity hotspots were found in areas, which were ecologically distinct in altitude, edaphic conditions, annual precipitation, or a combination of these factors. These results can be used to guide conservation efforts of the highly threatened forests of Borneo. [source]

How can we preserve and restore species richness of pollinating insects on agricultural land?

ECOGRAPHY, Issue 6 2008
Markus Franzén
During recent decades, concern about the loss of biodiversity on agricultural land has increased, and semi-natural grasslands have been highlighted as critical habitats. Temperate European agricultural landscapes require distinct and appropriate management to prevent further impoverishment of the flora and fauna. This is especially urgent for pollinating insects that provide important ecosystem services. Our aim was to examine how species richness of three important groups of pollinating insects; solitary bees, butterflies and burnet moths are related to different farm characteristics, and if there are any differences between these three groups. A further aim was to test if red-listed species are related to any farm characteristics. Species richness of solitary bees, butterflies and burnets was measured on all semi-natural grasslands at 16 farms in a forest-dominated area of 50 km2 in southern Sweden, using systematic transect walks in April to September 2003 (only butterflies and burnets) and 2005. Species richness of solitary bees and butterflies was intercorrelated, both before and after controlling for the area of semi-natural grassland. Species richness of solitary bees increased with the area of semi-natural grassland. After controlling for the effect of the area of semi-natural grassland species richness was strongly positively related with the density of the plant Knautia arvensis and negatively related with the proportion of grazed grassland. The results were similar for solitary bees and butterflies. The number of red-listed solitary bees was positively related to the proportion of meadows with late harvest (after mid-July) and decreased with increased farm isolation. The number of burnet species (all red-listed) was positively related to vegetation height, flower density and the proportion of meadows with late harvest on a farm. Areas with a high density of K. arvensis and with traditional hay-meadow with late harvest present, harbour most species. Promoting traditional hay-meadows, late extensive grazing and the herb K. arvensis, people managing agricultural biodiversity can encompass high species richness of pollinating insects and support red-listed species. Further, we suggest that the density of K. arvensis at a farm can be used as a biodiversity indicator, at least for pollinating insects. [source]

Elevational patterns of frog species richness and endemic richness in the Hengduan Mountains, China: geometric constraints, area and climate effects

ECOGRAPHY, Issue 6 2006
Cuizhang Fu
We studied frog biodiversity along an elevational gradient in the Hengduan Mountains, China. Endemic and non-endemic elevational diversity patterns were examined individually. Competing hypotheses were also tested for these patterns. Species richness of total frogs, endemics and non-endemics peaked at mid-elevations. The peak in endemic species richness was at higher elevations than the maxima of total species richness. Endemic species richness followed the mid-domain model predictions, and showed a nonlinear relationship with temperature. Water and energy were the most important variables in explaining elevational patterns of non-endemic species richness. A suite of interacting climatic and geometric factors best explained total species richness patterns along the elevational gradient. We suggest that the mid-domain effect was an important factor to explain elevational richness patterns, especially in regions with high endemism. [source]

The effects of green tree retention and subsequent prescribed burning on ground beetles (Coleoptera: Carabidae) in boreal pine-dominated forests

ECOGRAPHY, Issue 5 2006
Petri Martikainen
We studied how two methods to promote biodiversity in managed forests, i.e. green tree retention and prescribed fire, affect the assemblages of carabid beetles. Our experiment consisted of 24 study sites, each 3,5 ha in size, which had been prepared according to factorial design. Each of the eight treatment combinations determined by the two factors explored , tree retention level (0, 10, 50 m3/ha,1 and uncut controls) and prescribed use of fire (yes/no) , was replicated three times. We sampled carabids using pitfall traps one year after the treatments. Significantly more individuals were caught in most of the burned sites, but this difference was partially reflective of the trap-catches of Pterostichus adstrictus. The fire did not increase no. of P. adstrictus in the uncut sites as much as in the other sites. Species richness was significantly affected by both factors, being higher in the burned than in the unburned sites and in the harvested than in the unharvested sites. Many species were concentrated in the groups of retention trees in the burned sites, but only a few were in the unburned sites. The species turnover was greater in the burned than in the unburned sites, as indicated by the NMDS ordinations. Greater numbers of smaller sized species and proportion of brachypterous species were present in the burned sites. Fire-favored species, and also the majority of other species that prefer open habitats were more abundantly caught in the burned sites than in the unburned sites. Dead wood or logging waste around the traps did not correlate with the occurrence of species. We conclude that carabids are well adapted to disturbances, and that frequent use of prescribed fire is essential for the maintenance of natural assemblages of carabid beetles in the boreal forest. Small retention tree groups can not maintain assemblages of uncut forest, but they can be important by providing food, shelter and breeding sites for many species, particularly in the burned sites. [source]

Relationships between spatial environmental heterogeneity and plant species diversity on a limestone pavement

ECOGRAPHY, Issue 6 2003
Jeremy T. Lundholm
No empirical studies have examined the relationship between diversity and spatial heterogeneity across unimodal species richness gradients. We determined the relationships between diversity and environmental factors for 144 0.18 m2 plots in a limestone pavement alvar in southern Ontario, Canada, including within-plot spatial heterogeneity in soil depth, microtopography and microsite composition. Species richness was unimodally related to mean soil depth and relative elevation. Microsite heterogeneity and soil depth heterogeneity were positively correlated with species richness, and the richness peaks of the unimodal gradients correspond to the maximally spatially heterogeneous plots. The best predictive models of species richness and evenness, however, showed that other factors, such as ramet density and flooding, are the major determinants of diversity in this system. The findings that soil depth heterogeneity had effects on diversity when the effects of mean soil depth were factored out, and that unimodal richness peaks were associated with high spatial heterogeneity in environmental factors represent significant contributions to our understanding of how spatial heterogeneity might contribute to diversity maintenance in plant communities. [source]

Impact of reindeer grazing on ground-dwelling Carabidae and Curculionidae assemblages in Lapland

ECOGRAPHY, Issue 4 2003
Otso Suominen
Reindeer Rangifer tarandus L. grazing shapes forest vegetation, microclimate, and soil respiration in Lapland, especially due to grazing on lichens (Cladina). We studied how these changes and their magnitude affect ground-dwelling species of beetle families Carabidae (predators) and Curculionidae (herbivores), by using pitfall traps to collect invertebrates from pairs of grazed and ungrazed study plots over a wide range of site types. Changes in abundance, composition, richness and diversity of beetle assemblage were tested in relation to magnitude of the impacts on vegetation. The species compositions of Carabidae and Curculionidae differed between grazed and ungrazed plots in all sites. The relative difference between grazed and ungrazed plots in the number of individuals increased linearly with the impact of reindeer on vegetation cover. Carabid beetles, as a family, were more common in grazed plots in all sites. Curculionid beetles were more common in ungrazed plots in the birch dominated sites. This difference was mainly due to the species that feeds on deciduous leaves. In the pine dominated sites with high Cladina cover and more changes in ground vegetation, the number of curculionids feeding on conifers was higher in grazed plots. Species richness and diversity (H') of both families were higher in grazed plots. Of the total 27 species, 11 were found only in grazed plots, while not a single species was found only in ungrazed plots. The relative difference between plots in diversity and evennes (H'/H'max) had humped response to the difference in Cladina cover. The diversity values were greater in grazed plots at the intermediate levels of grazing impact, and only in sites with very low or extremely high Cladina cover difference was the diversity higher in ungrazed plots. The response of beetle diversity resembled the hypotheses suggested for the relationship between grazing and vegetation diversity: greatest positive effect at intermediate grazing intensity and negative effects at unproductive sites. [source]

Effects of landscape structure and habitat type on a plant-herbivore-parasitoid community

ECOGRAPHY, Issue 3 2003
Andreas Kruess
The effects of local habitat and large-scale landscape factors on species diversity and species interactions were studied using the insect community in stems of the creeping thistle Cirsium arvense. Thistle abundance was higher in fallows than in crop fields and field margins, with fallows providing 67% of thistle abundance within 15 study areas on a landscape scale. Species richness of the herbivores was positively related with thistle abundance, parasitoid species richness was influenced by habitat type and was positively correlated with herbivore species richness. The abundance of herbivores and parasitoids was affected by local factors such as habitat type and host abundance, but also by landscape factors such as the percentage of non-crop area and the isolation of habitats. The infestation rate caused by the agromyzid Melanagromyza aeneoventris was positively related to percent non-crop area, whereas the parasitism rate of this fly increased with increasing habitat diversity on the landscape scale. For these two interactions and for total herbivore abundance, a scale-dependency of the landscape effects was found. The results emphasize that biological diversity and ecological functions within a plant-insect community are not only affected by local habitat factors but also by large-scale landscape characteristics. Hence, to improve future agri-environmental schemes for biodiversity conservation and biological control large-scale landscape effects and their scale-dependency should be considered. [source]

Trophic level modulates carabid beetle responses to habitat and landscape structure: a pan-European study

ECOLOGICAL ENTOMOLOGY, Issue 2 2010
ADAM J. VANBERGEN
1. Anthropogenic pressures have produced heterogeneous landscapes expected to influence diversity differently across trophic levels and spatial scales. 2. We tested how activity density and species richness of carabid trophic groups responded to local habitat and landscape structure (forest percentage cover and habitat richness) in 48 landscape parcels (1 km2) across eight European countries. 3. Local habitat affected activity density, but not species richness, of both trophic groups. Activity densities were greater in rotational cropping compared with other habitats; phytophage densities were also greater in grassland than forest habitats. 4. Controlling for country and habitat effects, we found general trophic group responses to landscape structure. Activity densities of phytophages were positively correlated, and zoophages uncorrelated, with increasing habitat richness. This differential functional group response to landscape structure was consistent across Europe, indicated by a lack of a country × habitat richness interaction. Species richness was unaffected by landscape structure. 5. Phytophage sensitivity to landscape structure may arise from relative dependency on seed from ruderal plants. This trophic adaptation, rare in Carabidae, leads to lower phytophage numbers, increasing vulnerability to demographic and stochastic processes that the greater abundance, species richness, and broader diet of the zoophage group may insure against. [source]

Patterns of abundance of fire ants and native ants in a native ecosystem

ECOLOGICAL ENTOMOLOGY, Issue 4 2009
KATHARINE L. STUBLE
Abstract 1.,This correlational study examines the relationship between the red imported fire ant (Solenopsis invicta) and native ants in a longleaf pine savanna. Fire ants are frequently associated with a decline in native ants throughout the invaded range, but fire ant invasion is often coupled with habitat disturbance. Invasion of fire ants into the longleaf pine savanna provides an opportunity to examine the structure of the ant community in the absence of habitat disturbance. 2.,Pitfall trapping was conducted within the longleaf pine savanna as well as across a naturally occurring soil moisture gradient, in plots that had been artificially watered. 3.,Species richness did not vary as a function of fire ant density. There was an inverse relationship between native ant density and fire ant density, but this abundance pattern does not necessarily imply a causal link between fire ant invasion and native ant decline. For individual species, fire ant densities were negatively correlated with the densities of only two native ant species, including Solenopsis carolinensis, a native species that potentially limits the invasion of fire ants. Additionally, fire ants and native ants respond differently to soil moisture, with native ants favouring drier conditions than fire ants. 4.,The possible exclusion of fire ants by some native ants, as well as differences in habitat preferences, provide alternative explanations for the frequently observed negative correlation between fire ants and native ants. [source]