Spatial Variation In Richness Research Articles

Caves as wildlife refuges in degraded landscapes in the Brazilian Amazon

Cross-habitat spillover may be the outcome of a process of habitat loss or degradation where the receiving habitat serves as a refuge for organisms. Once surface habitats are lost or degraded, animals can find underground refuge in caves. This paper is focused on testing whether taxonomic order richness inside caves is positively affected by the loss of the native vegetation cover surrounding caves; whether degradation of native vegetation cover predicts cave community composition; and whether there is a pattern of cave community clusters delimited by similarity in the effects of habitat degradation on animal communities. We gathered a comprehensive speleological dataset consisting of occurrence data of thousands of invertebrates and vertebrates sampled in 864 iron caves in the Amazon, to test the effects of both variables measured inside caves and surrounding landscapes on spatial variation in richness and composition of animal communities. We show that caves can work as refuges for the fauna in landscapes where the native vegetation cover surrounding them was degraded, which was evidenced by landcover change increasing the richness of cave communities and clustering caves by similarity in community composition. Therefore, habitat degradation on the surface should be a key variable when characterizing cave ecosystems for conservation prioritization and offset planning. Habitat degradation causing a cross-habitat spillover effect highlights the importance of maintaining the connection between caves by the surface, especially large caves. Our study can help guide industry and stakeholders working on the complex conciliation between land use and biodiversity conservation.

Spatial distribution of bats richness in Mexico at different taxonomic levels: biogeographical and conservation implications

Due to the potential of bats to travel long distances, the great diversity of habitats in which they are found, and their biological peculiarities, bats typically have been excluded in biogeographic analyses. However, like other mammals, bats show common distributional patterns strongly influenced by their biotic and abiotic interactions, aspects that have been poorly analyzed mainly due to technical and methodological limitations. Such occurrence data are limited to a subset of a species’ range, the scale of occurrence records, characteristics of the life history ( e.g ., territory size, vagility) of the taxa being studied, and issues of environmental variable selection and, therefore, the modeling methods and the evaluation of them. In this work, the objectives were to: 1) Evaluate the spatial variation in bat richness in Mexico, both for the order as a whole and at the family taxonomic level. 2) Quantify overlapping species occurrences and corresponding richness values in order to statistically model and generate bat richness maps at different taxonomic levels. 3) Explore the relationship of bat richness with environmental factors and with the biogeographic regions proposed for Mexico. 4) Identify areas of interest with high richness. The information available on the Global Biodiversity Information Facility database for bat species with distribution in Mexico was downloaded, and clearly erroneous records deleted. Using the Kriging Ordinary utility (KO), inside the QGIS software, a geostatistical analysis interpolation data was used to determine patterns of richness. The relationship of bat richness to climate, vegetation, and the biotic provinces proposed for Mexico was also explored. Spatial variation in richness was evaluated at the taxonomic levels of order and family. Based on this determination, areas of interest were identified for their high richness. When considering all species of bats the highest diversity is in the central part of the West, the Northeast zone and on both sides of the Isthmus of Tehuantepec. However, there are differences present at the family level. Deciduous tropical forest vegetation type presents high bat richness, followed by pine-oak forest and evergreen tropical forest. Temperate sub-humid, warm sub-humid and warm-humid climate types correspond to the highest bat richness of both order and family. Collection localities are not uniformly distributed over the country, most of them being concentrated in the west, east and south of the country, while there are very few records in the north and central plateau, and this is reflected in the richness concentration per cell (values from 0 to 52 species per cell). Protection of the four areas with an overall high concentration of bat richness detected in this analysis should be a priority during the development of conservation strategies.

Models of alien species richness show moderate predictive accuracy and poor transferability

Robust predictions of alien species richness are useful to assess global biodiversity change. Nevertheless, the capacity to predict spatial patterns of alien species richness remains largely unassessed. Using 22 data sets of alien species richness from diverse taxonomic groups and covering various parts of the world, we evaluated whether different statistical models were able to provide useful predictions of absolute and relative alien species richness, as a function of explanatory variables representing geographical, environmental and socio-economic factors. Five state-of-the-art count data modelling techniques were used and compared: Poisson and negative binomial generalised linear models (GLMs), multivariate adaptive regression splines (MARS), random forests (RF) and boosted regression trees (BRT). We found that predictions of absolute alien species richness had a low to moderate accuracy in the region where the models were developed and a consistently poor accuracy in new regions. Predictions of relative richness performed in a superior manner in both geographical settings, but still were not good. Flexible tree ensembles-type techniques (RF and BRT) were shown to be significantly better in modelling alien species richness than parametric linear models (such as GLM), despite the latter being more commonly applied for this purpose. Importantly, the poor spatial transferability of models also warrants caution in assuming the generality of the relationships they identify, e.g. by applying projections under future scenario conditions. Ultimately, our results strongly suggest that predictability of spatial variation in richness of alien species richness is limited. The somewhat more robust ability to rank regions according to the number of aliens they have (i.e. relative richness), suggests that models of aliens species richness may be useful for prioritising and comparing regions, but not for predicting exact species numbers.

River ecosystems of the Central Highland ecoregion: Spatial distribution of benthic flora and fauna in the Plateau rivers (tributaries of the Yamuna and Ganga) in Central India

This study reveals the relationship of biotic assemblages to their environments in the Central Highland Ecoregion rivers (Ken, Paisuni and Tons). Such knowledge will enhance our predictive abilities in the ecological studies and resource management in the concerned region. Rivers of an ecoregion are expected to harbour similar flora, fauna, and communities. This hypothesis was examined by tracking the spatial variation in richness, density, and taxonomic composition of benthic diatom and macroinvertebrate assemblages in three Plateau rivers whose course lay within 3°N latitude. Taxonomic richness and density decreased with the reduction of substrate size from the headwaters to the lowlands. Cluster and ordination analyses indicate prevalence of intrabasin rather than interbasin gradients of abundance. In both assemblages, the most abundant taxon is rarely similar longitudinally or across the river sections in the ecoregion. Hence, proximate factors govern the assemblages rather than ecoregional properties (latitude, altitude). This, and the high richness of diatom flora, points to diverse assemblages from the headwater to the lowland section in each river and among the rivers of the ecoregion.

Influences of forest structure and landscape features on spatial variation in species composition in a palm community in central Amazonia

Abstract:The mechanisms that maintain palm species diversity in tropical rain forests are still debated. Spatial variation in forest structure produces small-scale environmental heterogeneity, which in turn can affect plant survival and reproductive performance. An understanding of how palms respond to variation in forest heterogeneity may help to explain the diversity and structure of their assemblages. We used multivariate ordination statistics and multiple linear models to analyse how palm assemblages are affected by forest structure and landscape features in central Amazonia. In 72 (250×4 m) forest plots distributed over an area of 64 km2, we recorded all seedling and adult palms, and measured topographic and soil variables, and components of forest structure and tree abundance. We found 16976 adults and 18935 seedlings of 46 palm species and five varieties including two morphological forms making a total of 50 botanical entities. Results show that landscape features (altitude, slope, proportions of soil sand and clay) and various components of forest structure (such as degree of forest openness, abundance of forest trees, logs and snags, and leaf litter mass), influence spatial variation in richness, abundance and species composition of palms, creating ecological gradients in palm community composition. Despite the statistically significant effects of environmental variables, most species occurred throughout the full range of the ecological gradients we studied, indicating that there is either relatively weak niche specialization in the palms, or that the competition between the species is mediated by diffuse demographic processes that cannot be evaluated only through studies of species distributions.

Thesis abstract: Understanding the evolutionary radiation of the mega-diverse Monkey Beetle fauna (Scarabaeidae: Hopliini) of South Africa

news and update elling. Diversity and Distributions, 15, 59-69. Matthews, W.J. (1998). Patterns in Freshwater Fish Ecology. Chapman and Hall, London. McPherson, J.M. & Jetz, W. (2007) Effects of species' ecology on the accuracy of distribution models. Ecography, 30, 135-151. Mohseni, O., Stefan, H.G. & Eaton, J.G. (2003) Global warming and potential changes in fish habitat in US streams. Climatic Change, 59, 389-409. Pearson, R.G. & Dawson, T.P. (2003) Predicting the im- pacts of climate change on the distribution of species: are bioclimate envelope models useful? Global Ecology and Biogeography, 12, 361-371. Thuiller, W. (2003) BIOMOD - optimizing predictions of species distributions and projecting potential future shifts under global change. Global Change Biology, 9, 1353-1362. ISSN 1948-6596 Thuiller, W. (2004) Patterns and uncertainties of spe- cies' range shifts under climate change. Global Change Biology, 10, 2020-2027. Walther, G.R., Post, E., Convey, P., Menzel, A., Parme- san, C., Beebee, T.J.C., Fromentin, J.M., Hoegh- Guldberg, O. & Bairlein, F. (2002) Ecological re- sponses to recent climate change. Nature, 416, Edited by Nuria Roura-Pascual thesis abstract Understanding the evolutionary radiation of the mega-diverse Monkey Beetle fauna (Scarabaeidae: Hopliini) of South Africa Jonathan F. Colville PhD, Zoology Department, University Of Cape Town, South Africa Current address: Applied Biodiversity Research, South African National Biodiversity Institute, Private Bag X7 Claremont, Cape Town, South Africa E-mail: J.Colville@sanbi.org.za; http://www.sanbi.org/ South Africa is the global centre of diversification for monkey beetles (Scarabaeidae: Hopliini). 69 % of the world fauna occur here, with 98% of the 1040 South African species and 80% of the South African genera being national endemics. This the- sis was the first analysis of the regional distribu- tion patterns, and the processes underlying the generation of the mega-diverse monkey beetle fauna of South Africa. Specifically, the aims of the thesis were to: 1. Identify hotspots of richness and endemism, and to explore the relationship between area and richness. 2. Compare centres of endemism of monkey bee- tles with those of other faunal and floral taxa, and to investigate patterns of biogeographic congruence. 3. Explore the role of local environmental factors (rainfall, temperature, habitat heterogeneity, host plant diversity) as explanatory variables of regional richness patterns of monkey beetles. 4. Model spatial turnover (beta diversity) in bee- tle community composition as a function of environmental (rainfall, temperature, altitude, soil fertility) and plant (host species, vegetation types, and bioregions) variables. 5. Describe and quantify patterns of sexual dimor- phism and putative sexually selected traits and investigate the role of sexual selection in the generation of species richness. Methodological procedures followed cur- rent and newly-developed analytical techniques used in the fields of biogeography, spatial ecology, and evolutionary biology. A key first methodologi- cal step was the compilation of a geo-referenced presence-only dataset from field observations, museum collections, and taxonomic revisions. This comprised 6959 unique point locality records which were analysed within a geographical infor- mation system (GIS). This allowed portraying of the spatial variation in richness and endemism across local and regional habitats. © 2009 the authors; journal compilation © 2009 The International Biogeography Society — frontiers of biogeography 1.2, 2009

Habitat use and deconstruction of richness patterns in Cerrado birds

At lower spatial scales, richness spatial patterns probably lead to more complex ecological–evolutionary interactions. In this paper, we used a “deconstruction” approach to evaluate the Cerrado breeding bird's richness, according to their habitat use categories (independent, semi-dependent and dependent on forest habitats). Six environmental variables and current human population size were used as predictors of species richness. Moran's I coefficients revealed strong spatial autocorrelation in ordinary least squares multiple regression residuals, and thus a Principal Coordinate of Neighbour Matrices (PCNM) was used to evaluate the influence of richness predictors, minimizing the problems caused by spatial autocorrelation. Models generated for total richness and for species richness by habitat categories were compared. We showed that, despite the total richness being more concentrated in south and southeast regions of Cerrado, these patterns changed when analysing semi-dependent and dependent forest habitat species, demonstrating a spatial variation in richness for these categories. The PCNM analyses demonstrated that, for total species richness, only partial coefficients of AET and temperature were significant. For independent forest richness, significant partial regression coefficients were found for AET, PET, TEMP and PREC, whereas for semi-dependent forest habitats richness, only AET was significant. On the other hand, for dependent of forest richness, a significant positive coefficient was found for precipitation and for human population. Most spatial variation in richness can be explained by joined effects of geographic structure and environmental predictors. These analyses reveal that deconstruction can be a step to a more effective understanding of richness patterns and their environmental drivers.

Latitudinal gradient in species richness

What is the gradient? Amongst the earliest remarked, and best documented, of broad-scale spatial patterns of life on Earth is a trend for more species to be found towards lower latitudes. The latitudinal gradient in species richness is such that most extant eukaryote, perhaps also prokaryote, species are found in the tropics. Even when counted over quite small areas in which it is present, the species richness of a taxonomic group might commonly vary by orders of magnitude between high and low latitudes.How general is the gradient? The latitudinal gradient in species richness occurs in terrestrial, freshwater and marine realms, is repeated for local and regional assemblages, and has been documented for a wide range of taxonomic groups, including viruses, bacteria, plants, arthropods and vertebrates. There are some exceptions, but these tend foremost to concern relatively species-poor taxonomic groups. This said, for any group typically only at rather coarse spatial resolutions is the gradient one of relatively continuous increase in richness towards lower latitudes. More usually, it is quite variable, with substantial regions in which richness can be notably high or low in comparison with the broad trend, and the peak often being displaced from the equator. In particular, the gradient can be influenced by the shape of continents or ocean basins, marked discontinuities in environmental conditions, and major historical events (such as periods of glaciation). It is helpful to consider the gradient in the context of the wider patterns of spatial variation in richness of which it is a part, rather than in isolation.How long has the gradient persisted? It is strongly suspected that the latitudinal gradient in species richness has been a persistent feature of life on Earth for much of its history, although obviously the positions of land and water masses have shifted, and the geographic pattern of environmental conditions has altered dramatically. There is evidence, however, that for some particular groups of organisms that remain quite speciose the latitudinal gradient has become steeper through evolutionary time.Why does the gradient occur? Ultimately, the latitudinal gradient in species richness must be a consequence of a greater period of net diversification in the tropics, likely following the origins of life there, or higher speciation rates and/or lower extinction rates at low latitudes compared with other regions. There is evidence that many temperate clades had their origins in the tropics. The prevailing view is that the tropics seem also to have been a ‘cradle of diversity’ (with high speciation rates), and that they have served as a ‘museum of diversity’ (with low extinction rates). The balance between the two rates is not well understood, and is a topic of much research interest. Some empirical evidence suggests that rates of speciation may have been lower at low latitudes but, accompanied by sufficiently low extinction rates, have nonetheless led to higher richness in the tropics.The proximate reasons for any latitudinal differences in speciation and extinction rates continue to be much debated. It is difficult to disentangle the potential influences of the many abiotic and biotic variables that show systematic patterns of variation with latitude. In the absence of substantial constraints on water supply, high speciation rates in the tropics may have resulted from higher and more stable temperatures leading to high biological rates, and hence shorter generation times and higher mutation rates. Extinction rates may be lower in the tropics because of environmental conditions that support a greater and more stable biomass, enabling more species to persist at low abundances. Speciation rates may also have been heightened and extinction rates reduced by the greater extent of the tropics in the past, and the accumulation of species at higher latitudes may have been reduced by the historical adaptation of most clades to tropical environments.What are the consequences of the gradient for conservation? Perhaps the most obvious consequence of the latitudinal gradient in species richness is that maintenance of the absolute numbers of species on Earth, or at least reduction of their current rates of loss, requires disproportionate attention to be paid to conservation activities in the tropics. Indeed, global schemes for identifying priority areas for conservation almost invariably place the majority of these in the tropics. A high proportion of tropical species tend also to have rather limited geographic distributions, which means that conservation efforts need to be dispersed throughout much of the tropics.Are there other significant implications of the gradient? The vast majority of studies in biology have been conducted on organisms from mid- to high northern latitudes. This means that they have usually concerned species that exist under conditions, and perhaps face challenges, that are very different from those relevant to most extant species. The consequences for understanding of many facets of biology could be profound.

Raptorial birds and environmental gradients in the southern Neotropics: A test of species‐richness hypotheses

Abstract We investigated the spatial patterns of raptor species richness in the southern Neotropics and tested three hypotheses that were most likely to explain spatial variations: ambient energy, productivity and habitat heterogeneity. We used non‐linear regression analysis and eliminated alternative hypotheses by finding the best single environmental predictor of raptor species richness among potential evapotranspiration (PET), actual evapotranspiration (AET), mean annual temperature and precipitation and vegetation structure coefficient. As expected, the number of raptor species decreases monotonically as latitude increases. Raptor species richness was significantly correlated with each of the environmental factors considered in this study, reflecting covariation of climatic and habitat descriptors. Correlation coefficients showed positive associations between species richness and each single environmental variable. Mean annual temperature was the strongest environmental predictor of raptor species richness (explaining 82% of the variance), consistent with the ambient energy hypothesis. Another descriptor of ambient energy (PET) explained 75% of the spatial variation. Both the AET and the vegetation structure coefficient explained 77% of the spatial variation in richness. The spatial clusters of extreme residuals identified the subtropical rainforests and the arid heights and low plateaux of the study area as regions where local environmental conditions appear to interfere with the general trend identified by the model at the regional scale.

Fine-scale spatial variation in plant species richness and its relationship to environmental conditions in coastal marshlands

Previous studies have shown that variations in environmental conditions play a major role in explaining variations in plant species richness at community and landscape scales. In this study, we considered the degree to which fine-scale spatial variations in richness could be related to fine-scale variations in abiotic and biotic factors. To examine spatial variation in richness, grids of 1 m2 plots were laid out at five sites within a coastal riverine wetland landscape. At each site, a 5 × 7 array of plots was established adjacent to the river’s edge with plots one meter apart. In addition to the estimation of species richness, environmental measurements included sediment salinity, plot microelevation, percent of plot recently disturbed, and estimated community biomass. Our analysis strategy was to combine the use of structural equation modeling (path modeling) with an assessment of spatial association. Mantel’s tests revealed significant spatial autocorrelation in species richness at four of the five sites sampled, indicating that richness in a plot correlated with the richness of nearby plots. We subsequently considered the degree to which spatial autocorrelations in richness could be explained by spatial autocorrelations in environmental conditions. Once data were corrected for environmental correlations, spatial autocorrelation in residual species richness could not be detected at any site. Based on these results, we conclude that in this coastal wetland, there appears to be a fine-scale mapping of diversity to microgradients in environmental conditions.

Does climate determine broad‐scale patterns of species richness? A test of the causal link by natural experiment

ABSTRACTAim Broad‐scale spatial patterns of species richness are very strongly correlated with climatic variables. If there is a causal link, i.e. if climate directly or indirectly determines patterns of richness, then when the climatic variables change, richness should change in the manner that spatial correlations between richness and climate would predict. The present study tests this prediction using seasonal changes in climatic variables and bird richness.Location We used a grid of equal area quadrats (37 000 km2) covering North and Central America as far south as Nicaragua.Methods Summer and winter bird distribution data were drawn from monographs and field guides. Climatic data came from published sources. We also used remotely sensed NDVI (normalized difference vegetation index — a measure of greenness).Results Bird species richness changes temporally (between summer and winter) in a manner that is close to, but statistically distinguishable from, the change one would predict from models relating the spatial variation in richness at a single time to climatic variables. If one further takes into account the seasonal changes in NDVI and within‐season variability of temperature and precipitation, then winter and summer richness follow congruent, statistically indistinguishable patterns.Main conclusions Our results are consistent with the hypothesis that climatic variables (temperature and precipitation) and vegetation cover directly or indirectly influence patterns of bird species richness.

Mid-domain models of species richness gradients: assumptions, methods and evidence.

Patterns of species richness along latitudinal, elevational and depth gradients often exhibit a mid-gradient peak. Similar patterns with a mid-domain peak in richness are produced, as a result of geometric constraints on species distributions, by models that randomize species range size and placement over a bounded gradient. Proponents of these so-called mid-domain models argue that they provide an appropriate null hypothesis for examining species richness patterns along spatial gradients. Furthermore, some claim that because these models seem to explain a large proportion of the large-scale spatial variation in richness, geometric constraints on species distribution are in fact the cause of these patterns. A critical examination of model assumptions reveals that some are unrealistic, conceptually flawed or internally inconsistent. Additionally, tests of mid-domain models have suffered from methodological deficiencies derived from arbitrariness and circularity in the definition of domain boundaries, collapsing two-dimensional (2-D) patterns into a single dimension (1-D), and the use of interpolated ranges, all of which can bias test results in favour of the models. Tests have also been statistically naive by using fairly insensitive measures of deviation between observed and predicted patterns and ignoring the increased probability of Type I error that can result in analyses of spatially autocorrelated data. In spite of this, a review of the empirical evidence indicates that most studies do not show a high degree of concordance between observed and predicted species richness patterns, particularly in 2-D. Additionally, spatial patterns of variation in range size and species turnover do not unequivocally support mid-domain models. Thus, the models do not adequately describe observed species richness gradients and thus fail to explain them. Although mid-domain models have served a useful purpose in drawing attention to the need to clarify the null expectation in the study of species richness gradients, their use appears to be severely limited by difficulties associated with the treatment of ranges, boundary definitions and a lack of clarity regarding the extent to which the observed data should be used to generate the null patterns.

THE DIVERSITY–DISTURBANCE RELATIONSHIP: IS IT GENERALLY STRONG AND PEAKED?

The contemporary literature accepts that disturbance strongly influences pat- terns of species diversity, and that the relationship is peaked, with a maximum at inter- mediate levels of disturbance. We tested this hypothesis using a compilation of published species diversity-disturbance relationships that were gleaned from a literature search of papers published from 1985 through 1996 and from references therein. We identified 116 species richness-, 53 diversity-, and 28 evenness-disturbance relationships in the literature, which we grouped according to shape of relationship (nonsignificant, peaked, negative monotonic, positive monotonic, or U-shaped). We tested the relationships between the strength and shapes of these relationships and attributes of the community, disturbance, and sampling and study design. Nonsignificant relationships were the most common, com- prising 35% of richness, 28% of diversity, and 50% of evenness studies. Peaked responses were reported in only 16% of richness, 19% of diversity, and 11% of evenness cases. Explained variation in the three measures of diversity was variable among studies but averaged -50%. It was higher when few samples and few disturbance levels were examined and when organisms within the samples were not exhaustively censused, suggesting that procedural artifact contributes to these relationships. Explained variation was also higher in studies in which disturbance was measured as a gradient of time passed since the last disturbance (mean r2 = 61%), vs. studies of spatial variation in richness (mean r2 = 42%). Peaked richness relationships had the greatest odds of being observed when sampled area and actual evapotranspiration were small, when disturbances were natural rather than an- thropogenic in origin, and when few disturbance levels were examined. Thus, on average, diversity-disturbance relationships do not have consistently high r2 and are not as consis- tently peaked as the contemporary consensus would suggest.