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]

ENHANCEMENTS, EASY SHORTCUTS, AND THE RICHNESS OF HUMAN ACTIVITIES

BIOETHICS, Issue 7 2008
MAARTJE SCHERMER
ABSTRACT One argument that is frequently invoked against the technological enhancement of human functioning is that it is morally suspect, or even wrong, to take an easy shortcut. Some things that usually take effort, endurance or struggle can come easily with the use of an enhancer. This paper analyses the various arguments that circle round the idea that enhancement of human functioning is problematic because of the ,easy shortcut' that it offers. It discusses the concern that quick fixes lead to corrosion of character and the idea that suffering, pain, hard work and effort are essential for real and worthy achievements, and argues that these views are largely mistaken. Next, the paper argues that the core worry about taking an easy shortcut is that it makes us lose sight of the complexities of our means and ends; in other words, the argument warns against reducing the richness of human activities. A vocabulary of ,practices', ,internal goods' and ,focal engagement' will be used to articulate this argument further. The conclusion is that the easy shortcut argument has no general validity as an argument against enhancement ,as such'. The paper urges us, however, to evaluate enhancement technologies not only in terms of their efficiency in reaching certain goals but also in terms of their contribution to intrinsically worthwhile human activities. It can point out some of the caveats, as well as the opportunities, of the use of enhancement technologies. [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]

On the importance of patch attributes, environmental factors and past human impacts as determinants of perennial plant species richness and diversity in Mediterranean semiarid steppes

DIVERSITY AND DISTRIBUTIONS, Issue 1 2004
Fernando T. Maestre
ABSTRACT Richness and diversity of perennial plant species were evaluated in 17 Stipa tenacissima steppes along a degradation gradient in semiarid SE Spain. The main objective of the study was to evaluate the relative importance of historical human impacts, small-scale patch attributes and environmental factors as determinants of perennial plant species richness and diversity in S. tenacissima steppes, where vegetation is arranged as discrete plant patches inserted on a bare ground matrix. Partial least squares regression was used to determine the amount of variation in species richness and diversity that could be significantly explained by historical human impacts, patch attributes, and environmental factors together and separately. They explained up to 89% and 69% of the variation in species richness and diversity, respectively. In both cases, the predictive power of patch attributes models was higher than that of models consisting of abiotic characteristics and variables related to human impact, suggesting that patch attributes are the major determinants of species richness and diversity in semiarid S. tenacissima steppes. However, patch attributes alone are not enough to explain the observed variation in species richness and diversity. The area covered by late-successional sprouting shrubs and the distance between consecutive patches were the most influencing individual variables on species richness and diversity, respectively. The implications of these results for the management of S. tenacissima steppes are discussed. [source]

Plant species richness and environmental heterogeneity in a mountain landscape: effects of variability and spatial configuration

ECOGRAPHY, Issue 4 2006
Alexia Dufour
The loss of biodiversity has become a matter of urgent concern and a better understanding of local drivers is crucial for conservation. Although environmental heterogeneity is recognized as an important determinant of biodiversity, this has rarely been tested using field data at management scale. We propose and provide evidence for the simple hypothesis that local species diversity is related to spatial environmental heterogeneity. Species partition the environment into habitats. Biodiversity is therefore expected to be influenced by two aspects of spatial heterogeneity: 1) the variability of environmental conditions, which will affect the number of types of habitat, and 2) the spatial configuration of habitats, which will affect the rates of ecological processes, such as dispersal or competition. Earlier, simulation experiments predicted that both aspects of heterogeneity will influence plant species richness at a particular site. For the first time, these predictions were tested for plant communities using field data, which we collected in a wooded pasture in the Swiss Jura mountains using a four-level hierarchical sampling design. Richness generally increased with increasing environmental variability and "roughness" (i.e. decreasing spatial aggregation). Effects occurred at all scales, but the nature of the effect changed with scale, suggesting a change in the underlying mechanisms, which will need to be taken into account if scaling up to larger landscapes. Although we found significant effects of environmental heterogeneity, other factors such as history could also be important determinants. If a relationship between environmental heterogeneity and species richness can be shown to be general, recently available high-resolution environmental data can be used to complement the assessment of patterns of local richness and improve the prediction of the effects of land use change based on mean site conditions or land use history. [source]

Species,energy relationships and habitat complexity in bird communities

ECOLOGY LETTERS, Issue 8 2004
Allen H. Hurlbert
Abstract Species,energy theory is a commonly invoked theory predicting a positive relationship between species richness and available energy. The More Individuals Hypothesis (MIH) attempts to explain this pattern, and assumes that areas with greater food resources support more individuals, and that communities with more individuals include more species. Using a large dataset for North American birds, I tested these predictions of the MIH, and also examined the effect of habitat complexity on community structure. I found qualitative support for the relationships predicted by the MIH, however, the MIH alone was inadequate for fully explaining richness patterns. Communities in more productive sites had more individuals, but they also had more even relative abundance distributions such that a given number of individuals yielded a greater number of species. Richness and evenness were also higher in structurally complex forests compared to structurally more simple grasslands when controlling for available energy. [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]

Can macroinvertebrate rapid bioassessment methods be used to assess river health during drought in south eastern Australian streams?

FRESHWATER BIOLOGY, Issue 12 2008
PETER ROSE
Summary 1Despite significant concern about drought impacts in Australia, there have been no broad-scale studies of drought effects on river health. A severe and prolonged drought has been acting on many streams in south eastern Australia over the past decade. EPA Victoria has undertaken rapid bioassessment (RBA) of over 250 stream reference sites since 1990, providing an opportunity for a before-after-control-impact investigation of drought related changes to macroinvertebrate indices and water quality. This study uses data from 1990 to 2004 to critically evaluate the effectiveness of using RBA methods and indices, which were designed for assessment of human impacts, for monitoring streams during drought. 2Reference stream sites across Victoria (those with minimal anthropogenic disturbances and repeatedly sampled) were classified as being ,in drought' or ,not in drought' using the Bureau of Meteorology's rainfall deficiency definition. Four biological indices (SIGNAL, EPT, Family Richness and AUSRIVAS) were calculated for combined autumn and spring samples for edge and riffle habitats for the selected sites. 3General linear models and paired t -tests were used to detect drought related changes to index and water quality values at state-wide and bioregional scales. Changes in taxa constancy were examined to determine which taxa were sensitive to or benefited from drought conditions. Frequency of site failure against biological objectives specified in the State Environment Protection Policy (Waters of Victoria) (herein termed ,SEPP WoV') before and during drought was also examined to detect changes in a management context. 4Few significant changes in index values were detected for riffle habitat samples. Rates of failure against biological objectives were similar before and during drought for riffle samples. In contrast, edge habitat AUSRIVAS and SIGNAL scores were significantly reduced at the state-wide scale and most indices showed significant declines in the lower altitude forests, and foothills and coastal plains bioregions. 5Generally, more pollution tolerant, lentic taxa replaced sensitive and flow-requiring taxa in edge samples during drought. In contrast, there were few reductions in the taxa of riffle samples during drought. However, many pool preferring, but pollution sensitive taxa occurred more frequently in riffle areas. Hence, the riffle community began to resemble that of pools and edges. This was attributed to decreased flow and increased ,lentic' habitat opportunities in riffles. 6Detection of a drought effect was confined to the edge habitat and site failure could be assigned to drought and anthropogenic impacts, in conjunction or alone. The riffle sampling protocol was resistant to detection of drought effects as samples were only taken when sufficient water was present within this habitat. Therefore, biological changes at sites not meeting policy objectives for riffle habitats can be attributed to anthropogenic rather than drought impacts. [source]

Geomorphology and fish assemblages in a Piedmont river basin, U.S.A.

FRESHWATER BIOLOGY, Issue 11 2003
D. M. Walters
Summary 1.,We investigated linkages between fishes and fluvial geomorphology in 31 wadeable streams in the Etowah River basin in northern Georgia, U.S.A. Streams were stratified into three catchment sizes of approximately 15, 50 and 100 km2, and fishes and geomorphology were sampled at the reach scale (i.e. 20,40 times stream width). 2.,Non-metric multidimensional scaling (NMDS) identified 85% of the among-site variation in fish assemblage structure and identified strong patterns in species composition across sites. Assemblages shifted from domination by centrarchids, and other pool species that spawn in fine sediments and have generalised food preferences, to darter-cyprinid-redhorse sucker complexes that inhabit riffles and runs, feed primarily on invertebrates, and spawn on coarser stream beds. 3.,Richness and density were correlated with basin area, a measure of stream size, but species composition was best predicted (i.e. |r| between 0.60,0.82) by reach-level geomorphic variables (stream slope, bed texture, bed mobility and tractive force) that were unrelated to stream size. Stream slope was the dominant factor controlling stream habitat. Low slope streams had smaller bed particles, more fines in riffles, lower tractive force and greater bed mobility compared with high slope streams. 4.,Our results contrast with the ,River Continuum Concept' which argues that stream assemblages vary predictably along stream size gradients. Our findings support the ,Process Domains Concept', which argues that local-scale geomorphic processes determine the stream habitat and disturbance regimes that influence stream communities. [source]

Do arthropod assemblages display globally consistent responses to intensified agricultural land use and management?

GLOBAL ECOLOGY, Issue 5 2008
S. J. Attwood
ABSTRACT Aim, To determine whether arthropod richness and abundance for combined taxa, feeding guilds and broad taxonomic groups respond in a globally consistent manner to a range of agricultural land-use and management intensification scenarios. Location, Mixed land-use agricultural landscapes, globally. Methods, We performed a series of meta-analyses using arthropod richness and abundance data derived from the published literature. Richness and abundance were compared among land uses that commonly occur in agricultural landscapes and that represent a gradient of increasing intensification. These included land-use comparisons, such as wooded native vegetation compared with improved pasture, and a management comparison, reduced-input cropping compared with conventional cropping. Data were analysed using three different meta-analytical techniques, including a simple vote counting method and a formal fixed-effects/random-effects meta-analysis. Results, Arthropod richness was significantly higher in areas of less intensive land use. The decline in arthropod richness was greater between native vegetation and agricultural land uses than among different agricultural land uses. These patterns were evident for all taxa combined, predators and decomposers, but not herbivorous taxa. Overall, arthropod abundance was greater in native vegetation than in agricultural lands and under reduced-input cropping compared with conventional cropping. Again, this trend was largely mirrored by predators and decomposers, but not herbivores. Main conclusions, The greater arthropod richness found in native vegetation relative to agricultural land types indicates that in production landscapes still containing considerable native vegetation, retention of that vegetation may well be the most effective method of conserving arthropod biodiversity. Conversely, in highly intensified agricultural landscapes with little remaining native vegetation, the employment of reduced-input crop management and the provision of relatively low-intensity agricultural land uses, such as pasture, may prove effective in maintaining arthropod diversity, and potentially in promoting functionally important groups such as predators and decomposers. [source]

The coincidence of people and biodiversity in Europe

GLOBAL ECOLOGY, Issue 1 2003
Miguel B. Araújo
ABSTRACT A positive correlation between human population density and species richness has been recorded across the tropics. Here I investigate whether this correlation holds true for Europe. Analyses reveal a positive correlation between human population density and plant (rho = 0.505), mammal (rho = 0.471) and reptile and amphibian (rho = 0.556) species richness. The results are largely concordant with those obtained in similar studies for Africa. However, contrary to previous analyses, the correlation found between people and breeding bird species richness (rho = 0.186) was weak. Of three measures of endemism used, only combined European endemic species richness correlated with human density (rho = 0.437). Richness among combined restricted-range European endemics was not correlated (rho = 0.095) with human density, while richness among all combined restricted-range species was only weakly correlated with human density (rho = 0.167). The results partially support the idea of a correlation between people and biodiversity, although there are some important exceptions. Discussion of possible mechanisms underling the observed patterns is undertaken. [source]

Aquatic Coleoptera Distribution and Environmental Relationships in a Large Patagonian River

INTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 5 2006
María Laura Miserendino
Abstract The benthic coleopteran assemblages of the Chubut River basin were studied in order to assess the main factors affecting species composition and distribution along the upper, middle and lower catchments. A total of 13 sampling sites were selected and sampled seasonally. Eight taxa and 1,601 individuals were collected during the study. Richness was higher in the main channel of Chubut River at the upper basin than at the middle basin. Beetles were completely absent at the lower basin. Mean monthly density per sites varied from 0 to 85 ind m,2. Stethelmis kaszabi had a more restricted distribution whereas Hemiosus dejeanii, Austrelmis sp. and Austrolimnius spp. were more frequent and abundant. Austrelmis sp. appears as the most tolerant species, especially to higher TSS, ammonia, and conductivity values. Luchoelmis cekalovici was absent in stations associated with urban areas. A Canonical Correspondence Analysis shows that conductivity, total suspended solids, wet width, water temperature and pH were the most important variables structuring beetle assemblages. Land use related variables such as NH4, TP, and NO3 were less important but still significant. An increase in TSS affected negatively the coleopteran community; this could be related to both hydrogeological characteristics and agricultural activities (including overgrazing). This is the first approach to the knowledge of the ecological range of distribution of the coleopteran species in Patagonian rivers. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Factors Affecting Macroinvertebrate Richness and Diversity in Portuguese Streams: a Two-Scale Analysis

INTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 2 2004
Manuel A. S. Graça
Abstract We analysed the spatial patterns in macroinvertebrate taxon richness and abundance at two scales: sampling unit and basin. We sampled 12 stream sites in three zones of Portugal, differing in climate geomorphology and water chemistry. At a sampling unit scale, substratum organic matter content, depth and the dominant size of substratum particles were correlated with numbers of taxa and individuals. We propose that the number of taxa at a small scale depends on the number of individuals, which in turn is the result of organic matter accumulation, hydrologic and substratum characteristics. The environmental parameters better explaining the large-scale biological data were temperature, minimum size of substratum particles and pH. Regardless of the relative importance of variable types and mechanisms regulating stream invertebrates along the climatic gradient, rivers from the North and Centre appeared to be richer in taxa than the typically Mediterranean streams in the South. [source]

Areography of the genus Dendroctonus (Coleoptera: Curculionidae: Scolytinae) in Mexico

JOURNAL OF BIOGEOGRAPHY, Issue 7 2004
Yolanda Salinas-Moreno
Abstract Objective, To analyse whether the geographical ranges of Dendroctonus species are (1) associated with factors such as host species or elevation, and (2) in agreement with Halffter's Nearctic distribution pattern. (3) To identify and discuss the factors that are likely to act as barriers to the genus' geographical distribution. (4) To explore whether there is an association between the size of the geographical ranges of Dendroctonus species and the number of Pinus host species used by each of them, and (5) to assess if these host species are most common at the elevations preferred by the individual Dendroctonus species. Site, Mexico. Methods, Records of 12 species of Dendroctonus were gathered from entomological collections in Mexico. Distribution ranges were defined by using the propinquity method (Rapoport, 1975a). Analysed parameters were: (1) geographical distribution of single species, (2) overlapping of species ranges, (3) disjunction patterns and barriers by means of isoprobabilistic lines, based on the morphotectonic subdivision of Mexico (Ferrusquía-Villafranca, 1998), (4) spatial variation in species richness with respect to latitude and altitude, (5) size of geographical ranges, and (6) host species for each Dendroctonus species. A correlation was determined between area size and number of pine host species. Results, The species ranges varied in shape and size. Geographical ranges tend to be discontinuous in shape. Composite patterns showed that disjunctions among ranges do not closely follow Mexico's morphotectonic subdivision. There are repeated discontinuities among individual distributions, which define five areas: (1) Baja California Peninsula, (2) Sierra Madre Occidental (SMOC), (3) northern Sierra Madre Oriental (SMOR), (4) Sierra Madre de Chiapas, and (5) SMOR + Faja Volcanica Transmexicana (FVT) + Sierra Madre del Sur. The isoprobabilistic lines confirm that the inner part of SMOC provides an optimal environment for the genus, and the FVT province constitutes the broader corridor for it in the country. Richness does not directly decrease or increase with latitude. Richness behaviour of the insect is not associated with that of its host. Elevation distributions showed that most Dendroctonus species move within broad margins of tolerance and species richness is concentrated in the montane interval. Dendroctonus attack 24 of the 47 Pinus species distributed in Mexico. Preferred pine species belong predominantly to Leiophyllae, Ponderosae and Oocarpae subsections. The Spearman rank correlation between area size and number of pine host species was not significant. Dendroctonus clearly belongs to a Nearctic distribution pattern (sensuHalffter, 1987). Main conclusions,Dendroctonus is present in all montane systems of Mexico and its species coexist within a high geographical sympatry. Overlapping of species distribution appears to be the result of two elements , generalized polyphagy inside Pinus and a wide elevation tolerance within mountainous environments. This behaviour, linked to a high vagility, has allowed the genus Dendroctonus to expand its distribution across Mexico and to employ mountainous systems as corridors separated by barriers that exert a low selective filter effect. [source]

Plant diversity and endemism in sub-Saharan tropical Africa

JOURNAL OF BIOGEOGRAPHY, Issue 2 2001
Linder
Aim This paper has as its central aim the location of centres of species richness and endemism in the sub-Saharan African flora. Previous postulation of these centres has been based on an intuitive interpretation of distributional data; this paper provides a test of these centres. A second aim is to establish whether the two indices, richness and endemism, locate the same centres. Thirdly the relationship between species richness and endemism, and latitude and rainfall are explored. Location The study area includes much of sub-Saharan Africa, but excludes the species-poor southern margin of the Sahara and the Namib,Kalahari regions. Methods Analyses were based on 1818 species, scored on a 2.5 × 2.5 degree grid. Species richness was inferred from a simple grid-diversity count; endemism was determined by three measures: the number of species restricted to two grids, the sum of the inverse of the ranges of the component species of each grid, and the proportion of the species in each grid that have restricted ranges. Results The African flora shows a remarkably profound patterning, both in species richness and endemism. The two measures locate largely the same centres, although the rank order among them differs. These centres are: the Cape Floristic Region, East Coast, Congo-Zambezi watershed, Kivu, Upper and Lower Guinea. Richness is strongly related to maximum rainfall, but there are no obvious correlations between modern climate and endemism. Species richness and endemism north of the equator is much more concentrated into centres than south of the equator. Main conclusions There are strongly developed refugia in sub-Saharan Africa. North of the equator, these refugia are sharply delimited and rather small, separated by large areas of very low endemism. South of the equator endemism tends to be more generally distributed. Variation in species richness in sub-Saharan Africa can be explained largely by modern rainfall, while endemism may be related to palaeoclimatic fluctuations. Both species richness and endemism show a strong skewing towards the south, indicating that the fluctuations in the Sahara might have influenced the modern distribution of plants in Africa. [source]

Richness and diversity of helminth communities in tropical freshwater fishes: empirical evidence

JOURNAL OF BIOGEOGRAPHY, Issue 4 2000
Anindo Choudhury
Abstract Aim Published information on the richness and diversity of helminth parasite communities in tropical freshwater fishes is reviewed in response to expectations of species-rich parasite communities in tropical regions. Location Areas covered include the tropics and some subtropical areas. In addition, the north temperate area of the nearctic zone is included for comparison. Methods Data from 159 communities in 118 species of tropical freshwater fish, summarized from 46 published studies, were used for this review. Parasite community descriptors used in the analyses included component community richness and calculated mean species richness. Data from 130 communities in 47 species of nearctic north temperate freshwater fish were summarized from 31 studies and used for comparison. Results The component helminth communities of many tropical freshwater fish are species-poor, and considerable proportions of fish from certain parts of the tropics, e.g. West African drainages, are uninfected or lightly infected. Mean helminth species richness was low and equaled or exceeded 2.0 in only 22 of 114 communities. No single group of helminths was identified as a dominant component of the fauna and species composition was variable among and within broader geographical areas. The richest enteric helminth assemblages were found in mochokid and clariid catfish with a mixed carnivorous diet, whereas algal feeders, herbivores and detritivores generally had species-poor gut helminth communities. Comparisons indicated that certain areas in the north temperate region had higher helminth species richness in fishes than areas in the tropics. Main conclusions Expectations of high species richness in helminth communities of tropical freshwater fishes are not fulfilled by the data. Direct comparisons of infracommunities and component communities in host species across widely separated phylogenetic and geographical lines are inappropriate. Examination of latitudinal differences in richness of monophyletic parasite groups or of compound communities may uncover patterns different from those found in this study. Richness of helminth communities may be ultimately determined not by the number of host species present but by the degree of divergence of host lineages and by their diversification modes. A phylogenetic framework for hosts and parasites will reveal if increased host species richness within host clades, when host speciation is accompanied by habitat or diet specialization, or both, leads to lower helminth diversity in host species by fragmentation of a core helminth fauna characteristic or specific of the larger host clade. This pattern may be analysed in the context of cospeciation and acquisition from other unrelated hosts (host-sharing or host-switching). [source]

Observations on the histochemistry and ultrastructure of regenerating caudal epidermis of the tuatara Sphenodon punctatus (Sphenodontida, Lepidosauria, Reptilia)

JOURNAL OF MORPHOLOGY, Issue 2 2003
Lorenzo Alibardi
Abstract Study of the histology, histochemistry, and fine structure of caudal epidermal regeneration in Sphenodon punctatus through restoration of a scaled form reveals that the processes involved resemble those known in lizards. Following establishment of a wound epithelium (WE), subjacent scale neogenesis involves epidermal downgrowths into the dermis. Although the process is extremely slow, and most new scales do not overlap, their epidermal coverings reestablish epidermal generation (EG) formation. As in lizards, the flat, ,-keratogenic, WE cells contain lipids as revealed by their affinity for Sudan III. A few mucous cells that store large PAS-positive mucus-like granules also occur in WE. During differentiation of WE cells, among the bundles of 70-nm tonofilaments are many lamellar bodies (LBs) and mucous granules (MGs) that discharge their contents into the cytoplasm and extracellular spaces producing a strongly PAS-positive keratinized tissue. Richness of epidermal lipids coexistent with mucus is a primitive characteristic for amniote vertebrates, probably related to functions as a barrier to cutaneous water loss (CWL). As scale neogenesis begins, beneath the superficial WE appear 3,5 layers of irregularly shaped cells. These contain tonofilament bundles surrounded by small, round keratohyalin-like granules (KHLGs) and a keratinized matrix with ,-keratin packets and a 3,5-nm thick keratin granulation. This mixture of ,- and ,-keratogenic capacities resembles that seen in the innermost cells of a normal tuatara epidermal generation. As in the latter, but in contrast to both normal and regenerating lizard epidermis, no definable shedding complex with interdigitating clear layer and oberhautchen cells occurs (Alibardi and Maderson, 2003). The tortuous boundaries, and merging ,-keratin packets, identify subjacent keratinizing cells as precursors of the typical stratified, squamous ,-layer seen in long-term regenerated caudal skin wherein the entire vertical sequence of epidermal layers resembles that of normal scales. The sequence of events in caudal epidermal regeneration in S. punctatus resembles that documented for lizards. Observed differences between posttrauma scale neogenesis and scale embryogenesis are responses to functional problems involved in, respectively, restoring, or forming, a barrier to CWL while accommodating rapid somatic growth. J. Morphol. 256:134,145, 2003. © 2003 Wiley-Liss, Inc. [source]

Latitudinal gradient of taxonomic richness: combined outcome of temperature and geographic mid-domains effects?

JOURNAL OF ZOOLOGICAL SYSTEMATICS AND EVOLUTIONARY RESEARCH, Issue 3 2005
A. Brayard
Abstract For several decades, the origin and ecological consequences of large-scale continental and marine Latitudinal Gradients of Taxonomic Richness (LGTR) have been intensively debated. Among the various hypotheses, it has been proposed that a LGTR is the by-product of a geographic mid-domain effect, i.e. the result of a random distribution of ranges of taxa between physical hard boundaries such as the continent/ocean interface. In order to more realistically evaluate the role of the mid-domain effect on the origin and evolution of the LGTR of marine planktonic organisms, we present a 2D model based on a cellular-automaton approach in which sea surface temperatures (SST) and currents are forced in the biogeographic dispersal of a randomly generated clade (a 2D ,geophyletic' model). Sensitivity experiments allow to evaluate the effects of currents, SST and the geographical origin of a clade on the formation and shape of a LGTR for planktonic organisms when coupled with a geographic mid-domain effect. Results are discussed in the light of the empirical LGTR of extant planktonic Foraminifera in the Atlantic Ocean. Independently of any other biotic or abiotic parameter, inclusive of the surface currents and origination/extinction absolute and relative rates, our simulations show that the coupling of the mid-domain effect with two critical parameters, namely the shape and intensity of the SST gradient and the geographic origin of a clade, produces realistic patterns of diversity when compared with the observed LGTR of extant atlantic planktonic foraminifera. The results illustrate a non-linear relation between a unimodal latitudinal SST gradient and a resulting bimodal LGTR characterized by a drop in species richness near the equator. This relation indicates that the SST gradient exerts a mid-domain effect on the LGTR. The latitudinal positions of the modal values of the LGTR are also found to be influenced by the geographic origin of the simulated clade. Résumé Depuis plusieurs décennies, l'origine et l'interprétation écologique des Gradients Latitudinaux de Richesse Taxonomique (LGTR) marins ou continentaux, ont été intensivement débattues. Parmi de nombreuses hypothèses, il a été proposé qu'un LGTR puisse être le sous-produit d'un effet de milieu de domaine géographique, i.e. le résultat d'une distribution aléatoire des répartitions des taxa entre deux limites physiques telles que l'interface continent/océan. Afin d'évaluer plus efficacement le rôle de cet effet sur l'origine et l'évolution des LGTR des organismes planctoniques marins, nous proposons un modèle 2D basé sur une approche de type automate cellulaire dans laquelle les températures des eaux de surface (SST) et les courants régulent la dispersion biogéographique d'une phylogénie générée aléatoirement (un modèle «géophylétique»). Ce modèle permet d'évaluer les effets des courants, des SST et de la dépendance thermique des espèces sur la mise en place et la forme d'un LGTR impliquant des organismes planctoniques. Il permet aussi de discuter des influences respectives de ces paramètres quand ils sont superposés à l'effet de milieu de domaine géographique. Les résultats sont discutés à partir du LGTR empirique des foraminifères planctoniques atlantiques actuels. Indépendamment de tout autre paramètre biotique ou abiotique, y compris les courants ainsi que les taux relatifs et absolus d'apparition et d'extinction, les simulations font apparaître que le couplage de l'effet de milieu de domaine à deux contraintes principales, la forme et l'intensité du gradient de SST ainsi que la localisation géographique de l'origine du clade, produit des représentations réalistes de la diversité comparées au LGTR observé pour les foraminifères planctoniques actuels de l'océan atlantique. Nos résultats indiquent une relation non-linéaire entre la structure globale d'un gradient unimodal de SST et le LGTR bimodal correspondant, montrant une baisse de richesse spécifique au niveau de l'équateur. Cette relation suggère que le gradient de SST exerce un effet de milieu de domaine thermique sur le LGTR. Les positions latitudinales des modes du LGTR sont aussi influencées par le lieu d'origine du clade simulé. [source]

The Contribution of Secondary Space to Benthic Taxon Richness of a Coral Reef: Colonisation of Dendrostrea frons (Mollusca)

MARINE ECOLOGY, Issue 3 2001
David K. A. Barnes
Abstract. The reef-dwelling oyster Dendrostrea frons occupied only a small proportion of space in coral reefs of the Quirimba Archipelago, Mozambique, but supported a disproportionately high variety of taxa. Assemblages on primary (substratum), secondary (dead coral heads) and ephemeral secondary space (D. frons shells) of similar area were compared across 5 depths (5, 10, 15, 20 and 25 m) and at four taxonomic levels (species, genus, class and phylum). Differences between the taxonomic richness of each type of space differed with both taxonomic level considered and depth. Of the three categories of space considered, ephemeral secondary space had the most taxa at all levels with the maximum at 10,,,15 m. Despite being small in space and time, animal externa, such as shells of D. frons, may provide important niches for particular organisms at many taxonomic levels. [source]

454 Pyrosequencing analyses of forest soils reveal an unexpectedly high fungal diversity

NEW PHYTOLOGIST, Issue 2 2009
M. Buée
Summary ,,Soil fungi play a major role in ecological and biogeochemical processes in forests. Little is known, however, about the structure and richness of different fungal communities and the distribution of functional ecological groups (pathogens, saprobes and symbionts). ,,Here, we assessed the fungal diversity in six different forest soils using tag-encoded 454 pyrosequencing of the nuclear ribosomal internal transcribed spacer-1 (ITS-1). No less than 166 350 ITS reads were obtained from all samples. In each forest soil sample (4 g), approximately 30 000 reads were recovered, corresponding to around 1000 molecular operational taxonomic units. ,,Most operational taxonomic units (81%) belonged to the Dikarya subkingdom (Ascomycota and Basidiomycota). Richness, abundance and taxonomic analyses identified the Agaricomycetes as the dominant fungal class. The ITS-1 sequences (73%) analysed corresponded to only 26 taxa. The most abundant operational taxonomic units showed the highest sequence similarity to Ceratobasidium sp., Cryptococcus podzolicus, Lactarius sp. and Scleroderma sp. ,,This study validates the effectiveness of high-throughput 454 sequencing technology for the survey of soil fungal diversity. The large proportion of unidentified sequences, however, calls for curated sequence databases. The use of pyrosequencing on soil samples will accelerate the study of the spatiotemporal dynamics of fungal communities in forest ecosystems. [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]

Does flooding of rice fields after cultivation contribute to wetland plant conservation in southern Brazil?

APPLIED VEGETATION SCIENCE, Issue 1 2010
Ana S. Rolon
Abstract Question: Does flooding of rice fields after cultivation contribute to wetland plant conservation in southern Brazil? Location: Rice fields in the coastal plain of southern Brazil. Methods: Six rice fields with different management practices were randomly selected (three dry rice fields and three flooded rice fields). Six collections were carried out over the rice cultivation cycle. Richness and biomass were measured using the quadrat method. Results: A total of 88 macrophyte species was recorded. There was no statistical interaction between management practices and rice cultivation phases for macrophyte richness and biomass. Macrophyte species richness and biomass changed over time, but were similar between flooded and dry rice fields. The first three axes generated by detrended correspondence analysis explained 29% of the variation in species composition and the multivariate analysis of variance showed that there was a statistical interaction between management practices and agricultural periods. Conclusions: Rice fields may help to conserve an important fraction of the aquatic macrophyte diversity of wetlands of southern Brazil by providing the setting up of a greater number of species within the agricultural landscape. However, rice fields must not be viewed as surrogate systems for natural wetlands. The difference in species composition between flooded and dry rice fields is interesting in terms of biodiversity conservation. If rice producers could keep part of their agricultural land flooded during the fallow phase, this management practice could be an important strategy for the conservation of biodiversity in areas where natural wetlands have been converted to rice fields. [source]

Understory vegetation response to thinning disturbance of varying complexity in coniferous stands

APPLIED VEGETATION SCIENCE, Issue 4 2009
Adrian Ares
Abstract Question: Can augmented forest stand complexity increase understory vegetation richness and cover and accelerate the development of late-successional features? Does within-stand understory vegetation variability increase after imposing treatments that increase stand structural complexity of the overstory? What is the relative contribution of individual stand structural components (i.e. forest matrix, gaps, and leave island reserves) to changes in understory vegetation richness? Location: Seven study sites in the Coastal Range and Cascades regions of Oregon, USA. Methods: We examined the effects of thinning six years after harvest on understory plant vascular richness and cover in 40- to 60-year-old forest stands dominated by Douglas-fir (Pseudotsuga menziesii). At each site, one unthinned control was preserved and three thinning treatments were implemented: low complexity (LC, 300 trees ha,1), moderate complexity (MC, 200 trees ha,1), and high complexity (HC, variable densities from 100 to 300 trees ha,1). Gaps openings and leave island reserves were established in MC and HC. Results: Richness of all herbs, forest herbs, early seral herbs and shrubs, and introduced species increased in all thinning treatments, although early seral herbs and introduced species remained a small component. Only cover of early seral herbs and shrubs increased in all thinning treatments whereas forest shrub cover increased in MC and HC. In the understory, we found 284 vascular plant species. After accounting for site-level differences, the richness of understory communities in thinned stands differed from those in control stands. Within-treatment variability of herb and shrub richness was reduced by thinning. Matrix areas and gap openings in thinned treatments appeared to contribute to the recruitment of early seral herbs and shrubs. Conclusions: Understory vegetation richness increased 6 years after imposing treatments, with increasing stand complexity mainly because of the recruitment of early seral and forest herbs, and both low and tall shrubs. Changes in stand density did not likely lead to competitive species exclusion. The abundance of potentially invasive introduced species was much lower compared to other plant groups. Post-thinning reductions in within-treatment variability was caused by greater abundance of early seral herbs and shrubs in thinned stands compared with the control. Gaps and low-density forest matrix areas created as part of spatially variably thinning had greater overall species richness. Increased overstory variability encouraged development of multiple layers of understory vegetation. [source]

Ever since Clements: from succession to vegetation dynamics and understanding to intervention

APPLIED VEGETATION SCIENCE, Issue 1 2009
S.T.A. Pickett
Abstract Introduction: This paper surveys a framework for vegetation dynamics to provide conceptual background for a series of papers addressing the role of vegetation dynamics in restoration. Richness of the foundation: Classical succession theory provides key ingredients for contemporary process studies of vegetation dynamics. The contemporary framework incorporates processes identified by Gleason and other critics of Clements' theory. Multiple causality: The Clementsian causes, when expanded to include interaction and to clarify net effects, accommodate those now recognized in vegetation dynamics. A mature successional framework: A hierarchical framework has emerged to evaluate the causes of vegetation dynamics. The framework identifies the general causes as site availability, species availability, and species performance. Differentials as drivers: Differentials in any of the three general causes can drive change in plant communities. Each general cause consists of specific mechanisms. A model template: To predict vegetation dynamics trajectories, models are required. A model template is presented to operationalize the hierarchical framework. Outcomes are contingent on species pools and environmental contexts and may be progressive or retrogressive. Relationships of frameworks: Other contemporary frameworks in biology relate to vegetation dynamics. Application to restoration: The vegetation dynamics framework is relevant to restoration through linkages with landscape ecology, disturbance ecology, competition, invasion ecology, and community assembly. The differentials of site availability, species availability, and species performance suggest the processes and strategies available for restoration. Conclusions: A synthetic framework of vegetation brings together the mechanisms required for successful restoration. [source]

Tree age is a key factor for the conservation of epiphytic lichens and bryophytes in beech forests

APPLIED VEGETATION SCIENCE, Issue 1 2009
Örjan Fritz
Abstract Questions: What factors limit the distribution of epiphytic lichens and bryophytes at plot and tree level in beech forests? At what ages do epiphytic species, and species of conservation concern in particular, occur along a chronosequence of beech? Location: South-west Sweden. Method: Five hundred and seventy-one age-determined trees from 37 plots distributed among 29 beech-dominated stands were surveyed along with a number of environmental (16) and substrate (seven) variables in a landscape of ca. 550 ha. Non-metric multidimensional scaling (NMS) and indicator species analysis (ISA) were used for data analysis. Results: Plots containing old trees, confined to the base of slopes and with low impacts of recent forestry (thinning), generally had a high richness of species of conservation concern. Richness of common species and red-listed bryophytes were mostly related to the surveyed bark area. At tree level, primary factors explaining both species richness and composition were age, diameter at breast height and moss cover. There was a gradual replacement of tree age ranges for 58 lichens and 37 bryophytes along the chronosequence of beech. Red-listed lichens favoured damaged beech trees (,180 years), whereas red-listed bryophytes were found on old and young stems in dense stands. Conclusions: Tree age exerts a profound influence on epiphytic lichens and bryophytes growing on beech. Many of the habitat specialists were found mainly on old beech because they inhabit specific substrates that occur on older trees. The association to high tree age commonly excludes red-listed lichens from conventionally managed beech forests with a 100- to 140-year rotation period. [source]

Pattern and process in the distribution of North American freshwater fish

BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2010
DAVID GRIFFITHS
Published species lists were analysed to determine the contributions of dispersal, habitat preference, river channel size, body size, and glacial history to large-scale patterns in freshwater fish species richness in North America, north of central Mexico. Total species richness declines to the north and west but the pattern for endemics differs from that of widespread species. Mississippi Basin regions are more species rich than more isolated, coastal, regions. Richness declines more rapidly with increasing latitude in riverine specialist than in habitat generalist species. Levels of endemism are greatest in species found in small- to medium-sized river channels. The strong Rapoport effect, more marked in migratory than resident species, is correlated with habitat preference, channel size, and glacial history. Body size increases with latitude, largely as a result of a trend from small resident to large migrant species. In unglaciated regions, ancestral species survived in large habitats because these are longer-lived, more extensive, less isolated and more stable than headwaters, permitting larger populations and lower extinction levels. Reduced levels of gene flow in small, peripheral, channels isolated by larger downstream habitats have resulted in the production of many, small range, small-bodied species. The latitudinal richness gradient is a consequence of speciation and extinction events in unglaciated faunas and an increasing domination of faunas by generalist, large bodied, large channel, recolonizing species in more northern regions. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 46,61. [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]