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ECOLOGÍA DE LA BIODIVERSIDAD
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Strategies are needed to recover the ocelot Leopardus pardalis from the endangered species list. Recently, a population viability analysis (PVA) was developed which concluded that combinations of different recovery strategies were needed to effectively reduce ocelot extinction probability in the United States (US), with habitat protection and restoration identified as the most effective recovery scenario. We expanded this PVA model by incorporating landscape data to develop a more realistic habitat-based PVA for ocelots in southern Texas. We used RAMAS/gis software to conduct a habitat-based PVA by linking landscape data with a demographic metapopulation model. The primary goal of this study was to provide a model for evaluating ocelot recovery strategies in the US. Each model scenario was simulated 1000 times over 50 years and we defined extinction as one individual remaining. Using the RAMAS/gis program we identified 11 possible ocelot habitat patches (i.e., subpopulations) occurring in southern Texas. In addition, based on the habitat-based PVA model we found that combinations of different recovery strategies were needed to effectively reduce ocelot extinction probability in the US, with reducing road mortality the single most effective strategy. Short-term recovery strategies should include reducing ocelot road mortality, and translocation of ocelots into the US from northern Mexico . Long-term recovery strategies should include the restoration of habitat between and around existing ocelot habitat patches and the establishment of a dispersal corridor between ocelot breeding populations. Biological Conservation, Vol. 132, No. 4, p424-436, 13p. |
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During Pleistocene, the Laurentide ice sheet rearranged and diversified biotic distributions in eastern North America, yet had minimal physical impact in western North America where lineage diversification is instead hypothesized to result from climatic changes. If Pleistocene climatic fluctuations impacted desert species, the latter would reflect patterns of restricted gene flow concomitant with indications of demographic bottlenecks. Accordingly, molecular evidence for refugia should be present within these distributions and for subsequent range expansions as conditions improved. We sought answers to these questions by evaluating mitochondrial DNA (mtDNA) sequences from four species of rattlesnakes [ Crotalus mitchellii (speckled rattlesnake), Crotalus cerastes (sidewinder), Crotalus tigris (tiger rattlesnake), Crotalus ruber (red diamond rattlesnake)] with distributions restricted to desert regions of southwestern North America. We inferred relationships using parsimony and maximum likelihood, tested intraspecific clades for population expansions, applied an isolation-with-migration model to determine bi-directional migration rates ( m) among regions, and inferred divergence times for species and clades by applying a semiparametric penalized likelihood approach to our molecular data. Evidence for significant range expansion was present in two of eight regions in two species ( Crotalus mitchellii pyrrhus, C. tigris region north). Two species ( C. cerastes, C. mitchellii) showed a distribution concomitant with northward displacement of Baja California from mainland México , followed by vicariant separation into subclades. Effects of Pleistocene climate fluctuations were found in the distributions of all four species. Three regional diversification patterns were identified: (i) shallow genetic diversity that resulted from Pleistocene climatic events ( C. tigris, C. ruber); (ii) deep Pleistocene divisions indicating allopatric segregation of subclades... Molecular Ecology, Vol. 15, No. 11, p3353-3374, 22p. |
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Many attempts to predict the potential range of species rely on environmental niche (or 'bioclimate envelope') modelling, yet the effects of using different niche-based methodologies require further investigation. Here we investigate the impact that the choice of model can have on predictions, identify key reasons why model output may differ and discuss the implications that model uncertainty has for policy-guiding applications. Location The Western Cape of South Africa. Methods We applied nine of the most widely used modelling techniques to model potential distributions under current and predicted future climate for four species (including two subspecies) of Proteaceae. Each model was built using an identical set of five input variables and distribution data for 3996 sampled sites. We compare model predictions by testing agreement between observed and simulated distributions for the present day (using the area under the receiver operating characteristic curve (AUC) and kappa statistics) and by assessing consistency in predictions of range size changes under future climate (using cluster analysis). Results Our analyses show significant differences between predictions from different models, with predicted changes in range size by 2030 differing in both magnitude and direction (e.g. from 92% loss to 322% gain). We explain differences with reference to two characteristics of the modelling techniques: data input requirements (presence/absence vs. presence-only approaches) and assumptions made by each algorithm when extrapolating beyond the range of data used to build the model. The effects of these factors should be carefully considered when using this modelling approach to predict species ranges. Main conclusions We highlight an important source of uncertainty in assessments of the impacts of climate change on biodiversity and emphasize that model predictions should be interpreted in policy-guiding applications along with a full appreciation of uncertainty. Journal of Biogeography, Vol. 33, No. 10, p1704-1711, 8p. |
1. A positive interspecific relationship between abundance and distribution is widely considered to be one of the most general patterns in ecology. However, the relationship appears to vary considerably across assemblages, from significant positive to significant negative correlations and all shades in between. 2. This variation has led to the suggestion that the abundance-distribution relationship has multiple forms, with the corollary that different patterns may inform about, or have different, causes. However, this variation has never been formally quantified, nor has it been determined whether the observed variation is indicative of sampling error in estimating a single effect or of real heterogeneity in such relationships. Here, we use the meta-analytical approach to assess variation in abundance-distribution relationships, and to test different hypotheses for it. 3. Analysis of 279 relationships found a mean effect size of 0·655, which was both highly significantly different from zero and indicative of a strong positive association between abundance and distribution. However, effect sizes were highly heterogeneous, supporting the contention that this relationship does indeed have multiple forms. 4. Most notably, relationships vary significantly in strength across realms, with the strongest in the marine and intertidal, intermediate relationships for terrestrial and parasitic assemblages, and the weakest relationships in freshwater systems. Effect sizes in all of the aquatic realms are homogeneous, suggesting that realm is an important source of the heterogeneity observed across all studies. We posit that this may be because the different spatial structure of the environment in each realm affects the opportunity for the dispersal of individuals between sites. 5. Some of the remaining heterogeneity in effect sizes for terrestrial assemblages could be explained by partitioning assemblages by habitat, scale, biogeographical region and... Journal of Animal Ecology, Vol. 75, No. 6, p1426-1439, 14p. |
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Macroecology sits at the junction of, and can contribute to, the fields of ecology, biogeography, palaeontology and macroevolution, using a broad range of approaches to tackle a diverse set of questions. Here, we argue that there is more to macroecology than mapping, and that while they are potentially useful, maps are insufficient to assess macroecological pattern and process. The true nature of pattern can only be assessed, and competing hypotheses about process can only be disentangled, by adopting a statistical approach, and it is this that has been key to the development of macroecology as a respected and rigorous scientific discipline. Global Ecology & Biogeography, Vol. 15, No. 6, p537-540, 4p. |
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We investigate processes through which organizations engaged in natural resource management pursue conservation innovations-that is, create capabilities that allow them to produce new goods and services or produce goods and services in ways that reduce environmental degradation. Through an accounting of organizational competencies, we conduct an exploratory analysis of investments Finnish forest management service providers-public agencies, private firms, and civil society actors-have made to address demand for biodiversity conservation. From the perspective of theory and method, our pilot study points to opportunities to test, and perhaps advance, hypothesized tendencies toward environmental improvement through assessment of material practices and organizational strategies. This materialist approach is applicable to analysis at the level of organizations, sectors and territories. From an empirical perspective, the research highlights the contemporary coevolution of incentives and patterns of organizational behavior in Finnish forestry in response to social demand for biodiversity conservation and multifunctional landscapes. anagement in Finland. Society & Natural Resources, Vol. 19, No. 9, p845-861, 17p, |
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Recent investigations suggest that marine biodiversity may be much higher than earlier estimates, and an important hidden source of diversity in marine systems is the phenomenon of cryptic species complexes. Such complexes are informative models for research into the evolutionary processes that govern species compositions of marine fauna. The snapping shrimp genera Alpheus and Synalpheus are known to harbour large numbers of cryptic species; here, I characterize the genetic structure of the Alpheus armillatus species complex in the northern Caribbean, west Atlantic, and Gulf of Mexico using mitochondrial and nuclear sequence data. Over this geographical region, the complex harbours at least three lineages that are probable reproductively isolated species; all major lineages diverged subsequent to the close of the Isthmus of Panama. Only one lineage was present in the Gulf of Mexico, whereas outside the Gulf of Mexico there was no clear tendency for lineage dominance by geographical region, as most sites were populated by shrimp from at least two lineages. However, within each lineage, there was strong evidence of population genetic differentiation between geographical regions. All lineages showed strong signals of demographic expansion, and one lineage showed sharply reduced genetic diversity, suggestive of past population bottlenecks or recently founded populations with low gene flow from other sites. These results show that evolutionary processes leading to divergence and speciation have been common and recent in the snapping shrimp, and suggest that connectivity among shrimp populations may be limited. Molecular Ecology, Vol. 15, No. 13, p4049-4063, 15p. |
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Many attempts to predict the potential range of species rely on environmental niche (or 'bioclimate envelope') modelling, yet the effects of using different niche-based methodologies require further investigation. Here we investigate the impact that the choice of model can have on predictions, identify key reasons why model output may differ and discuss the implications that model uncertainty has for policy-guiding applications. Location The Western Cape of South Africa. Methods We applied nine of the most widely used modelling techniques to model potential distributions under current and predicted future climate for four species (including two subspecies) of Proteaceae. Each model was built using an identical set of five input variables and distribution data for 3996 sampled sites. We compare model predictions by testing agreement between observed and simulated distributions for the present day (using the area under the receiver operating characteristic curve (AUC) and kappa statistics) and by assessing consistency in predictions of range size changes under future climate (using cluster analysis). Results Our analyses show significant differences between predictions from different models, with predicted changes in range size by 2030 differing in both magnitude and direction (e.g. from 92% loss to 322% gain). We explain differences with reference to two characteristics of the modelling techniques: data input requirements (presence/absence vs. presence-only approaches) and assumptions made by each algorithm when extrapolating beyond the range of data used to build the model. The effects of these factors should be carefully considered when using this modelling approach to predict species ranges. Main conclusions We highlight an important source of uncertainty in assessments of the impacts of climate change on biodiversity and emphasize that model predictions should be interpreted in policy-guiding applications along with a full appreciation of uncertainty. Journal of Biogeography, Vol. 33, No. 10, p1704-1711, 8p. |
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Despite decades of research, the ecological determinants of microbial diversity remain poorly understood. Here, we test two alternative hypotheses concerning the factors regulating fungal diversity in soil. The first states that higher levels of plant detritus production increase the supply of limiting resources (i.e. organic substrates) thereby increasing fungal diversity. Alternatively, greater plant diversity increases the range of organic substrates entering soil, thereby increasing the number of niches to be filled by a greater array of heterotrophic fungi. These two hypotheses were simultaneously examined in experimental plant communities consisting of one to 16 species that have been maintained for a decade. We used ribosomal intergenic spacer analysis (RISA), in combination with cloning and sequencing, to quantify fungal community composition and diversity within the experimental plant communities. We used soil microbial biomass as a temporally integrated measure of resource supply. Plant diversity was unrelated to fungal diversity, but fungal diversity was a unimodal function of resource supply. Canonical correspondence analysis (CCA) indicated that plant diversity showed a relationship to fungal community composition, although the occurrence of RISA bands and operational taxonomic units (OTUs) did not differ among the treatments. The relationship between fungal diversity and resource availability parallels similar relationships reported for grasslands, tropical forests, coral reefs, and other biotic communities, strongly suggesting that the same underlying mechanisms determine the diversity of organisms at multiple scales. Ecology Letters, Vol. 9, No. 10, p1127-1135, 9p. |
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Recent research linking poverty alleviation and forest conservation has frequently focused on the potential contribution of the commercialization of Non-Timber Forest Products (NTFPs), and has consequently emphasized incomes from NTFPs rather than their consumption. This paper aims to understand the role played by the consumption of wild food plants in the livelihood of rural populations. Two methods of evaluation are used to estimate the value of the wild food plants consumed by Pwo Karen people living in the Thung Yai Naresuan Wildlife Sanctuary in western Thailand. The first calculates the time needed to gather the wild food plants (14.63 days/year per household), and the second uses the prices of commercial substitutes in the market to estimate the number of days household members would have to engage in paid work if they switched to commercial food crops (143 days/year). The paper concludes that consuming wild food plants is an efficient method of subsistence that should be encouraged. If it is not encouraged, economic growth could lead people to squander additional cash incomes on higher-status commercial food crops rather than spend it on productive investment. Progress in Development Studies, Vol. 6, No. 4, p275-286, 12p. |
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To provide a test of the conservatism of a species' niche over the last 20,000 years by tracking the distribution of eight pollen taxa relative to climate type as they migrated across eastern North America following the Last Glacial Maximum (LGM). Location North America. Methods We drew taxon occurrence data from the North American pollen records in the Global Pollen Database, representing eight pollen types - all taxa for which =5 distinct geographic occurrences were available in both the present day and at the LGM (21,000 years ago ± 3000 years). These data were incorporated into ecological niche models based on present-day and LGM climatological summaries available from the Palaeoclimate Modelling Intercomparison Project to produce predicted potential geographic distributions for each species at present and at the LGM. The output for each time period was projected onto the 'other' time period, and tested using independent known occurrence information from that period. Results The result of our analyses was that all species tested showed general conservatism in ecological characteristics over the climate changes associated with the Pleistocene-to-Recent transition. Main conclusions This analysis constitutes a further demonstration of general and pervasive conservatism in ecological niche characteristics over moderate periods of time despite profound changes in climate and environmental conditions. As such, our results reinforce the application of ecological niche modelling techniques to the reconstruction of Pleistocene biodiversity distribution patterns, and to project the future potential distribution range of species in the face of global-scale climatic changes. Journal of Biogeography, Vol. 33, No. 10, p1779-1789, 11p. |
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Amazonia is famous for high biodiversity , and the highlands of the transition zone between the Andes and the lowlands of the Amazon basin show particularly high species diversity. Hypotheses proposed to explain the high levels of diversity in the highlands include repeated parapatric speciation across ecological gradients spanning the transition zone, repeated allopatric speciation across geographic barriers between the highlands and lowlands, divergence across geographic barriers within the transition zone, and simple lineage accumulation over long periods of time. In this study, we investigated patterns of divergence in frogs of the genus Epipedobates (family Dendrobatidae) using phylogenetic and biogeographic analyses of divergence in mitochondrial DNA (1778 aligned positions from genes encoding cyt b, 12S and 16S rRNA for 60 Epipedobates and 11 outgroup specimens) and coloration (measured for 18 specimens representing nine species in Epipedobates). The majority of phenotypic and species diversity in the poison frog genus Epipedobates occurs in the transition zone, although two morphologically conserved members of the genus are distributed across the lowlands of the Amazon basin. Phylogenetic analysis reveals that there is a single highland clade derived from an ancestral colonization event in northern Peru by a population of lowland ancestry. Epipedobates trivittatus, a widespread Amazonian species, is a member of the highland clade that reinvaded the lowlands. Comparative analyses of divergence in coloration and mtDNA reveals that divergence in coloration among populations and species in the highlands has been accelerated relative to the lowlands. This suggests a role for selection in the divergence of coloration among populations and species. Molecular Phylogenetics & Evolution, Vol. 41, No. 1, p149-164, 16p. |
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Our aim in this essay is to identify and analyze some of the difficulties with interdisciplinary integration of economic and ecological contributions to the study of biodiversity loss. We develop our analysis from a widely accepted definition of economics which is based on the concept of scarcity. Taking a closer look at this notion, we find that economics actually limits itself to a very particular aspect of scarcity, which we denote as relative scarcity. We describe in what respect the economic approach towards biodiversity is based on this notion, and also reflect on the specific understanding of the relation of humans and nature behind the economic approach. We then turn to absolute scarcity as another notion of scarcity, and show that this is not within the scope of economics, but has been a theme of ecology and ecological economics. We describe in which way ecological and ecological-economic approaches towards biodiversity are based on the idea of absolute scarcity, and also reflect on the specific understanding of the human-nature relationship behind this notion of scarcity. Against this background, we discuss the roles of economics and ecology for nature conservation. We conclude that the interdisciplinary integration of ecology and economics requires a philosophical underpinning, and suggest a framework for further research. Ecological Economics, Vol. 59, No. 4, p487-498, 12p. |
Although extensive areas of tropical forest are selectively logged each year, the responses of bat communities to this form of disturbance have rarely been examined. Our objectives were to (1) compare bat abundance, species composition, and feeding guild structure between unlogged and low-intensity selectively logged (1-4 logged stems/ha) sampling grids in the southeastern Amazon and (2) examine correlations between logging-induced changes in bat communities and forest structure. We captured bats in understory and canopy mist nets set in five 1-ha study grids in both logged and unlogged forest. We captured 996 individuals, representing 5 families, 32 genera, and 49 species. Abundances of nectarivorous and frugivorous taxa (Glossophaginae, Lonchophyllinae, Stenodermatinae, and Carolliinae) were higher at logged sites, where canopy openness and understory foliage density were greatest. In contrast, insectivorous and omnivorous species (Emballonuridae, Mormoopidae, Phyllostominae, and Vespertilionidae) were more abundant in unlogged sites, where canopy foliage density and variability in the understory stratum were greatest. Multivariate analyses indicated that understory bat species composition differed strongly between logged and unlogged sites but provided little evidence of logging effects for the canopy fauna. Different responses among feeding guilds and taxonomic groups appeared to be related to foraging and echolocation strategies and to changes in canopy cover and understory foliage densities. Our results suggest that even low-intensity logging modifies habitat structure, leading to changes in bat species composition. Conservation Biology, Vol. 20, No. 5, p1410-1421, 12p.
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Assessing the effects of logging on different aspects of biodiversity and general ecosystem properties is of prime importance if the few remaining areas of intact tropical forest are to be efficiently protected. Commonly used measures of biodiversity may only inadequately reflect actual disturbance after logging and studies restricted to only one specific eco-region do not allow for generalizations of results. We hence measured the impact of selective logging on different levels of diversity of two tropical anuran communities in two geographically distinct eco-regions. Species-diversity patterns were incoherent both, within and between studies. In West Africa, species richness did not differ between primary and exploited forest sites, whereas South American anuran communities exhibited higher species richness in primary sites. Yet, in both eco-regions, functional diversity (FD) was higher in primary forest communities. Absolute values of FD were higher in South American anuran communities, despite higher species richness in West African communities. FD was higher in older recovery, as compared to younger recovery states, even though species-diversity did not differ significantly. Three major conclusions can be drawn from our results. 1. Scale matters: it is important to monitor different levels of biodiversity in order to reveal its actual loss after anthropogenic disturbance. 2. Time matters: the disturbance history of a site is important in order to detect patterns that otherwise remain unnoticed. 3. Geographic history matters at the local scale: whereas general patterns at higher diversity levels were identical in both eco-regions, species richness, species diversity and turnover patterns differed. Biological Conservation, Vol. 133, No. 2, p143-155, 13p. |
1 Small and isolated populations of species are susceptible to loss of genetic diversity, owing to random genetic drift and inbreeding. This loss of diversity may reduce the evolutionary potential to adapt to changing environments, and may cause immediate loss of fitness (cf. inbreeding depression). Together with other population size-dependent stochastic processes, this may lead to increased probabilities of population extinction. 2 This set of processes and theories forms the core of conservation genetics and has developed into the conservation genetics paradigm. Many empirical studies have concentrated on the relationship between population size and genetic diversity, and in many cases evidence was found that small populations of plants do indeed have lower levels of genetic diversity and increased homozygosity. Although less empirical attention has been given to the relationship between low genetic diversity, fitness and, in particular, evolutionary potential, the paradigm is now widely accepted. 3 Here we present five areas of the paradigm which could be refined, i.e. the 'rough' edges of the conservation genetics paradigm. 4 Treating population size and isolation not as interchangeable parameters but as separate parameters affecting population genetics in different ways could allow more accurate predictions of the effects of landscape fragmentation on the genetic diversity and viability of populations. 5 There is evidence that inbreeding depression may be a genotype-specific phenomenon, rather than a population parameter. This sheds new light on the link between population inbreeding depression and the expected increased probability of extinction. 6 Modern eco-genomics offers the opportunity to study the population genetics of functional genes, to the extent that the role of selection can be distinguished from the effects of drift, and allowing improved insights into the effects of loss of genetic diversity on evolutionary potential. 7 ... Journal of Ecology, Vol. 94, No. 6, p1233-1248, 16p. |
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Understanding the interactive effects of multiple keystone species where they co-occur may have important consequences for regional biodiversity . Additionally, understanding how the impacts of keystone species vary across different ecosystems is important for effectively guiding conservation and management. We conducted a large-scale field study in northern Mexico where the geographic distributions of black-tailed prairie dogs Cynomys ludovicianus and banner-tailed kangaroo rats Dipodomys spectabilis overlap. These species are considered both keystones and ecosystem engineers of grassland environments, but little is known about their separate and interacting roles in desertified systems where they co-occur. Our research evaluated 1) the independent impacts of black-tailed prairie dogs and banner-tailed kangaroo rats in a desertified annual grassland, and 2) their interactive effects on grassland community structure and biodiversity . Prairie dogs and kangaroo rats differentially affected vegetation structure, plant cover, species composition, and species richness across multiple spatial and temporal scales. The interactive effects of these keystone species resulted in enhanced landscape heterogeneity and biodiversity . Our results demonstrate the importance of prairie dogs and kangaroo rats in desertified grasslands, and have important implications for understanding the interactive effects and context-dependency of keystone species. Ecography, Vol. 29, No, 5, p755-765, 11p. |
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1. Widespread and rapid losses of tropical rain forests have made understanding the responses of species to rain forest fragmentation an area of major concern. In this study we examined the impacts of habitat fragmentation on the species richness and faunal composition of butterflies in tropical rain forests in Sabah, Borneo. We analysed patterns of both alfa- and beta-diversity to assess the relative importance of differences in patch size, isolation and vegetation structure on the diversity and similarity of species assemblages. We used additive partitioning to assess the relative contributions of intact forest and forest remnants to overall species richness at a landscape scale and we examined which traits of species best predicted their responses to fragmentation. 2. Species richness and diversity in rain forest remnants was significantly positively related to remnant size and significantly negatively related to isolation, in keeping with theories of island biogeography. Species assemblages at different sites were significantly nested, with those species most adversely affected by forest fragmentation having a narrow range of larval host-plants and, to a lesser extent, being large-bodied. No species endemic to Borneo was recorded in forest remnants smaller than 4000 ha, but even the smallest remnant (120 ha) supported species with geographical distributions confined within Sundaland (West Malaysia and the islands of the Sunda Shelf). 3. Although assemblages were significantly nested, they departed substantially from perfect nestedness, with some species recorded only or predominantly in small, relatively depauperate remnants. As a result there was substantial beta-diversity among sites, which was related to variation in both fragment size and vegetation structure. At the landscape scale, diversity within sites was less than that between sites, and the majority of the diversity between sites was related to variation in fragment size. 4.... Journal of Applied Ecology, Vol. 43, No. 5, p967-977, 11p. |
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Human-dominated marine ecosystems are experiencing accelerating loss of populations and species, with largely unknown consequences. We analyzed local experiments, long-term regional time series, and global fisheries data to test how biodiversity loss affects marine ecosystem services across temporal and spatial scales. Overall, rates of resource collapse increased and recovery potential, stability, and water quality decreased exponentially with declining diversity. Restoration of biodiversity, in contrast, increased productivity fourfold and decreased variability by 21%, on average. We conclude that marine biodiversity loss is increasingly impairing the ocean's capacity to provide food, maintain water quality, and recover from perturbations. Yet available data suggest that at this point, these trends are still reversible. Science,
Vol. 314, No. 5800, p787 - 790. |
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Phylogeography is concerned with the observation, description and analysis of the spatial distribution of genotypes and the inference of historical scenarios. In the past, the discipline has concentrated on the historical 'phylo-' component through the utilization of phylogenetic analyses. In contrast, the spatial ' -geographic' component is not a prominent feature of many existing phylogenetic approaches and has often been dealt with in a relatively naive fashion. Recently, there has been a resurgence of interest in the importance of geography in evolutionary biology. Thus, we believe that it is time to assess how geographic information is currently handled and incorporated into phylogeographical analysis. Geographical information systems (GISs) are computer systems that facilitate the integration and interrelation of different geographically referenced data sets; however, so far they have been little utilized by the phylogeographical community to manage, analyse and disseminate phylogeographical data. However, the growth in individual studies and the resurgence of interest in the geographical components of genetic pattern and biodiversity should stimulate further uptake. Some advantages of GIS are the integration of disparate data sets via georeferencing, dynamic data base design and update, visualization tools and data mining. An important step in linking GIS to existing phylogeographical and historical biogeographical analysis software and the dissemination of spatial phylogenies will be the establishment of 'GeoPhylo' data standards. We hope that this paper will further stimulate the resurgence of geography as an equal partner in the symbiosis that is phylogeography as well as advertise some benefits that can be obtained from the application of GIS practices and technologies. Journal of Biogeography, Vol. 33, No. 11, p1851-1865, 15p.
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There is an urgent need for conservation in threatened tropical forest regions. We explain and predict the spatial variation of alfa (i.e. within plot) and beta (i.e. between plot) tree diversity in a tropical montane landscape subjected to a high deforestation rate. A major aim is to demonstrate the potential of a method that combines data from multiple sources (field data, remote sensing imagery and GIS) to evaluate and monitor forest diversity on a broad scale over large unexplored areas. Location The study covered an area of c. 3500 km<sup>2</sup> in the Highlands of Chiapas, southern Mexico. Methods We identified all of the tree species within 204 field plots (1000 m<sup>2</sup> each) and measured different environmental, human disturbance-related, and spatial variables using remote sensing and GIS data. To obtain a predictive model of a tree diversity (Fisher's alpha) based on selected explanatory variables, we used a generalized linear model with a gamma error distribution. Mantel tests of matrix correspondence were used to determine whether similarities in floristic composition were correlated with similarities in the explanatory variables. Finally, we used a method that combines a and beta tree diversity to define priority areas for conservation. Results The model for a tree diversity explained 44% of the overall variability, of which most was mainly related to precipitation, temperature, NDVI, and canopy (all relationships were positive, and quadratic for temperature and NDVI). There were no spatially structured regional factors that were ignored. Similarity in tree composition was correlated positively with climate and NDVI. Main conclusions The results were used to: (1) identify and assign conservation priority of unexplored areas that have high tree diversity, and (2) demonstrate the importance of several vegetation formations in the region's biodiversity . The method we present can be particularly... Global Ecology & Biogeography, Vol. 15, No. 6, p602-613, 12p. |
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We explored the relative contributions of climatic and land-cover factors in explaining the distribution patterns of butterflies in a boreal region. Location Finland, northern Europe. Methods Data from a national butterfly atlas survey carried out during 1991-2003, with a 10-km grain grid system, were used in these analyses. We used generalized additive models (GAM) and hierarchical partitioning (HP) to explore the main environmental correlates (climate and land-cover) of the realized niches of 98 butterfly species. The accuracy of the distribution models (GAMs) was validated by resubstitution and cross-validation approaches, using the area under the curve (AUC) derived from the receiver operating characteristic (ROC) plots. Results Predictive accuracies of the 98 individual environment-butterfly models varied from low to very high (cross-validated AUC values 0.48-0.99), with a mean of 0.79. The results of both the GAM and HP analyses were broadly concordant. Most of the variation in butterfly distributions is associated with growing degree-days, mean temperature of the coldest month and cover of built-up area in all six phylogenetic groups (butterfly families). There were no statistically significant differences in predictive accuracy among the different butterfly families. Main conclusions About three-quarters of the distributions of butterfly species in Finland appear to be governed principally by climatic, predominantly temperature-related, factors. This indicates that many butterfly species may respond rapidly to the projected climate change in boreal regions. By determining the ecological niches of multiple species, we can project their range shifts in response to changes in climate and land-cover, and identify species that are particularly sensitive to forecasted global changes. Journal of Biogeography, Vol. 33, No. 10, p1764-1778, 15p. |
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The role of inbreeding depression in the extinction of wild populations is controversial, largely because there are no quantitative estimates of its impact using realistic levels of inbreeding depression. To address this deficiency, this study (1) provides a comprehensive estimate of the impact of inbreeding depression on wild, mammalian and avian species via a meta-analysis, and (2) determines the impact of this level of inbreeding depression on extinction risk over a broad taxonomic range via stochastic computer projections with and without inbreeding depression for populations with carrying capacities of 100, 500 and 2000 individuals. An average overall effect of 12 diploid lethal equivalents was found across the life-history of the species in the meta-analysis. In the stochastic computer projections, 12 diploid lethal equivalents of inbreeding depression (with purging) decreased median times to extinction by an average of 37%. These decreases were significant and of very similar magnitude, regardless of the carrying capacity modelled. Disregarding the influence of inbreeding depression on extinction risk will lead to serious overestimates of the survival prospects of threatened mammalian and avian taxa. Further, inappropriate recovery plans may be instituted if the causes of extinction risk and their relative contributions are not recognized. Biological Conservation, Vol. 133, No. 1, p42-51, 10p. |
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Statistical methods for modelling plant species distributions are difficult to evaluate using field data because "truth" is unknown. Artificial data based on explicit theory can be used as "truth". Statistical models should be capable of recovering "truth" if they are to be useful when applied to field data. Use of artificial data in plant community ecology to evaluate statistical methods is reviewed. Two plant community theoretical models based on the continuum concept are identified for describing species responses, the Swan/ter Braak model (Gaussian symmetric unimodal responses) and the Ellenberg/Minchin model (skewed unimodal responses). Theory regarding both indirect and direct environmental gradients is used to simulate a realistic species/environment data set. The software package COMPAS with a restricted set of options is used to generate two types of data set: (1) direct, where species show typical responses to variables such as radiation and (2) indirect, where variables like aspect and slope which are related to radiation by complex environmental processes. An example of generalised linear models (GLM) and generalised additive models (GAM) applied to the artificial data sets by analysts unaware of truth is presented. The results are evaluated on the following criteria: correct selection of predictors; accurate description of response curves; prediction of abundance; and ecologically rational relationships. The potential impacts of differences in the skills of the analysts are discussed. Both GLM and GAM performed well with Gaussian responses and direct gradient predictors. GAM performed marginally better with the skewed response model and direct predictors. GAM performed consistently better than GLM with the indirect predictors. The main conclusion was that the ecological knowledge and statistical skills of the analysts were more important than the method used. Ecological Modelling, Vol. 19, No. 9, No. 2, p197-216, 20p. |
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Using new tools (boosted regression trees) in predictive biogeography, with extensive spatial 23 distribution data for >19 000 species, we developed predictive models for South African plant species richness patterns. Further, biome level analysis explored possible functional determinants of country-wide regional species richness. Finally, to test model reliability independently, we predicted potential alien invasive plant species richness with an independent dataset. Amongst the different hypotheses generally invoked to explain species 30 diversity (energy, favorableness, topographic heterogeneity, irregularity and seasonality), results revealed topographic heterogeneity as the most powerful single explanatory variable for indigenous South African plant species richness. Some biome-specific responses were observed, i.e. two of the five analyzed biomes (Fynbos and Grassland) had richness best explained by the “species-favorableness” hypothesis, but even in this case, topographic heterogeneity was also a primary predictor. This analysis, the largest conducted on an almost exhaustive species sample in a species-rich region, demonstrates the preeminence of topographic heterogeneity in shaping the spatial pattern of regional plant species richness. Model reliability was confirmed by the considerable predictive power for alien invasive species richness. It thus appears that topographic heterogeneity controls species richness in two main ways: firstly, by providing an abundance of ecological niches in contemporary space (revealed by alien invasive species richness relationships) and secondly, by facilitating the persistence of ecological niches through time. The extraordinary richness of the South African Fynbos biome, a world-renowned hotspot of biodiversity with the steepest environmental gradients in South Africa, may thus have arisen through both mechanisms. Comparisons with similar regions of the world outside South Africa are needed to confirm the... Ecography, Vol. 29, No. 5, p733-744, 12p. |
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Phylogeographic analyses using mitochondrial DNA (mtDNA) have revealed many examples of apparently deep historical subdivisions (‘phylogroups') within many vertebrates. It remains unclear whether these phylogroups represent independently evolving, adaptively differentiated lineages or groups that show little functional differentiation and, hence, will merge on contact. Here, we use mtDNA sequence data to evaluate the phylogeographic relationships between two of the northernmost populations of black ratsnakes ( Pantherophis obsoletus complex) in Ontario, Canada and previously analysed populations in the United States. We then use population-level analyses to evaluate the level of adaptive divergence between previously established mtDNA phylogroups. Phylogenetic analyses show that southern Ontario snakes have mtDNA haplotypes that fall within the Central mtDNA phylogroup, as designated by Burbrink et al. (2000 ). In contrast, snakes in eastern Ontario carry either Central or Eastern-specific haplotypes. Within the hybrid region, we found highly variable frequencies of mtDNA haplotypes among isolated sub-populations, no association between variation in cytonuclear (mtDNA) and nuclear (microsatellite DNA) markers, no difference in survival or reproductive success among snakes with different mtDNA haplotypes, and no effect of mate similarity in mtDNA on female clutch size. These results argue that the Eastern and Central phylogroups have merged in this region, likely due to a lack of adaptive differentiation between individuals in each lineage. Hence, in these snakes, phylogeographic structure in mtDNA is more a reflection of historical isolation rather than adaptive divergence. The observed reticulation between lineages and lack of evidence for hybrid disgenesis also bears on the classification of these lineages as distinct species. Molecular Ecology, Vol. 15, No. 12, p3755-3767, 13p. |
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