Variation In Species Turnover Research Articles

Disentangling the effects of environmental and geographic distances on lizard assemblages in Amazonian forests

AbstractAimDistinguishing ecological and evolutionary processes that structure assemblages can provide a comprehensive vision of the variation in species turnover in heterogeneous regions. However, the causes of spatial variation in organism assemblies in most of the Amazon still require further studies. In view of this, our objective was to determine the relative roles of species interactions, categorical and continuous environmental filters and isolation by distance in the taxonomic and functional composition of lizard assemblages.LocationAmazonian rainforest.TaxonLacertilia.MethodsWe sampled 14 sites along 880 km in the Madeira‐Purus interfluvial region, central‐south‐western Amazonia. We used multiple linear models applied to distance matrices, spatial correlograms and partitioned variance to distinguish the effects of geographical distances from environmental distances on lizard assemblages. Additionally, to better understand the effects of environmental gradients and forest type on species traits, we used a combination of RLQ and fourth‐corner analysis.ResultsVariance in taxonomic distance was mainly explained by a continuous environmental gradient that selects different species. Although we found no evidence of overdispersion or clustering of traits, functional distance was mainly explained by forest type and precipitation. The weak effect of geographical distance on lizard assemblages suggests that different environmental conditions have selected distinct subsets of species and functional traits.Main ConclusionsWe showed that the structural heterogeneity along an environmental gradient in Amazonia has a significant impact on the taxonomic and functional composition of lizard assemblages. Environmental filtering along the interfluvial region has caused species turnover and determined differences in the functional characteristics found between assemblages in dense and open forests. These results are relevant for conservation since local species or trait subsets change across the landscape and are therefore irreplaceable in the case of local extinction.

Regional species richness determines local species turnover in ferns

The question of which factors determine the geographical change in species composition and abundance (turnover and β diversity) has typically been studied at a single scale, so that, e.g., regional-scale factors are used to explain regional turnover. But cross-scale effects are also important to understand species turnover and the spatial distribution of biodiversity in general. Here, we explored how regional richness, local forest-structure, and regional climatic factors interact to influence local species turnover. We analysed a dataset that includes the distribution of 916 fern species recorded in 1227 plots in the Bolivian Andes, forest-structure variables collected in the field, and climatic variables extracted from global databases. We used path analyses to: (i) select the best models explaining the variation in local species turnover and (ii) identify the factors that have a direct effect on species turnover and those with only indirect effects. We contrasted our results against those obtained from a null model analysis. The most important variable explaining variation in species turnover was regional species richness. We consider that this is the result of interspecific competition resulting in narrower realized ecological niches of species, although further studies are needed to confirm the mechanism. We also found that the relationship between climatic variables and local species turnover is best described by the indirect link between climatic factors and regional species richness. Our results might appear to be in conflict with previous studies finding that climatic and edaphic factors are direct predictors of local and regional variation in fern turnover. However, this is due to the different scales at which turnover was analysed. In contrast to previous studies, ours reflects the cross-scale effect of the variation in regional factors on local species turnover. Our study supports the idea that in regions with high species richness, biotic interactions strongly determine local community composition.

Historical legacies and contemporary processes shape beta diversity in Neotropical montane streams

AbstractAimContemporary dispersal constraints and environmental conditions are broadly recognized as significant drivers of beta diversity patterns. However, beta diversity patterns may also reflect the legacy of past climatic and geological events. In this study, we investigated the relative importance of historical and contemporary factors as drivers of taxonomic, functional and phylogenetic beta diversity in Neotropical stream communities.LocationThe Colombian Orinoco basin.TaxonDiatoms and insects.MethodsWe estimated taxonomic, phylogenetic and functional beta diversity using Baselga's (BAS) and Podani's (POD) frameworks. Following both frameworks, we further partitioned every biodiversity facet into turnover and nestedness or richness difference components. Then, we used generalized linear models (GLM) to relate each biodiversity facet with environmental, spatial and historical factors.ResultsWe found that both historical and contemporary factors affected current patterns of beta diversity. Historical factors and water pH and temperature had the strongest effect on beta diversity patterns, particularly for taxonomic and phylogenetic facets. GLM models performed better for insects than for diatoms in all three facets. Within communities, our analysis also revealed a partial congruence between BAS‐ and POD‐based results.Main conclusionsDue to their past geological history and contemporary environmental gradients, tropical montane streams are natural laboratories for disentangling the joint effects of ecological and biogeographical factors on biodiversity patterns. Our study reveals that present‐day distribution patterns cannot be fully explained without accounting for the effects of past geological and climatic events on mountain landscapes. In the Neotropics, montane geology sets the stage for speciation and landscape formation, with which ecological (e.g., dispersal limitation) and environmental factors interact to generate spatial variation in species turnover.

Regional forcing explains local species diversity and turnover on tropical islands

AbstractAimTo determine the role of regional forcing on plot‐level species diversity and composition, and to quantify the relative importance of biogeographical and climatic factors in explaining woody plant diversity and composition at the local‐, island‐ and archipelago‐scale.LocationForty‐one tropical islands of the Indo‐Pacific region from Madagascar to Hawai‘i Island.MethodsWe analysed the diversity and composition of tropical woody plant communities located across 113 plots, 41 islands and 19 archipelagos. We used generalized linear mixed‐effects models and generalized dissimilarity models to determine the role of regional forcing at the island and archipelago scale and to assess the relative importance of biogeographical (area and isolation of islands or archipelagos, geographical distance between plots) and climatic factors in explaining differences in local diversity and composition (species turnover). Analyses were conducted at different geographical scales (local, island and archipelago) and taxonomic levels (species, genus and family).ResultsVariation in local (plot‐level) diversity (as species density, the number of species per 100 woody plants) was primarily explained by island and archipelago identity. Maximum species density was positively correlated with the area of an island (or archipelago) and negatively correlated with the isolation of an archipelago. Local climatic variability was also a significant predictor of species density, but less important than regional forcing. Climate variables explained < 20% of the variation in species turnover across all plots. The importance of geographical distance between plots relative to climate in driving species turnover decreased from the species to family level, and from the regional to island level.Main conclusionsRegional forcing was the key driver of local diversity and composition on islands. Island area and archipelago isolation are likely driving local diversity through their effects on the pool of island species. Geographical distance between plots is the main factor explaining species turnover, while at higher taxonomic levels, climatic factors and niche conservatism are the main drivers.

Species turnover in Amazonian frogs: low predictability and large differences among forests

AbstractThe factors explaining species turnover at different spatial scales have been intensively studied, but most work in Amazonia has mainly focused on plants. For animals, it is not as obvious which environmental variables most affect differences in species composition among sites. We sought to identify what causes anuran turnover in Amazonian terra firme forests, and how the effectiveness of these factors varies among regions and across spatial scales. We sampled frogs in 56 plots along ponds and streams distributed over three terra firme forest areas in Eastern Amazonia. Using multiple regressions on distance matrices, we partitioned the variation in species turnover into components explained by variation in environmental and spatial distances. This was done in parallel for each area separately, and for all areas together, to assess the consistency of results between scales and across areas at the same scale. Each community seemed to respond to a set of factors specific to that area, and the identity of the variables that emerged as significant differed among areas and scales. Both geographical distances and environmental differences had larger explanatory power at the regional scale than at the local scale. The large differences among results from different areas caution against making broad generalizations about species turnover patterns from a single community, as real differences may exist among areas.

Do soil and climate properties drive biogeography of the Australian proteaceae?

The Proteaceae are a diverse family of approximately 80 genera and 1700 species with a mostly southern-hemisphere distribution. While distributional patterns of various subsets of the Proteaceae have been studied, no quantitative continental-scale study of species-level spatial biodiversity patterns of the Australian Proteaceae has been conducted. The aim of this study is to identify and examine patterns of distribution, diversity and endemism for the Proteaceae (at family, genera and species levels) of continental Australia and to investigate the environmental drivers for the observed patterns. Using 151,899 herbarium records for 1179 Australian Proteaceae species, we investigate taxon richness, endemism, and compositional turnover along with climatic and soil correlates. Species richness and endemism was highest in the Southwest phytogeographical region, as well as the Atherton and Southeastern subregions. Genus richness was highest in the Northeastern and Atherton subregions. Highest species turnover occured in the Southwestern region and the Southeastern subregion while lowest species turnover occured in the Northern, Northern Desert and Eremaean regions. Over the entire continent, soil geochemistry and climate explain 37% of the variation in species turnover; however, in areas of high species richness, they account for >75% of the variation in species turnover. These results suggest that the biogeographic patterns of the Proteaceae are impacted by climate and soils, where Proteaceae specialization has filled novel environmental niches associated with low nutrient and low water availability soils, particularly in southwestern Australia.

Spatial variation in the climatic predictors of species compositional turnover and endemism.

Previous research focusing on broad-scale or geographically invariant species-environment dependencies suggest that temperature-related variables explain more of the variation in reptile distributions than precipitation. However, species–environment relationships may exhibit considerable spatial variation contingent upon the geographic nuances that vary between locations. Broad-scale, geographically invariant analyses may mask this local variation and their findings may not generalize to different locations at local scales. We assess how reptile–climatic relationships change with varying spatial scale, location, and direction. Since the spatial distributions of diversity and endemism hotspots differ for other species groups, we also assess whether reptile species turnover and endemism hotspots are influenced differently by climatic predictors. Using New Zealand reptiles as an example, the variation in species turnover, endemism and turnover in climatic variables was measured using directional moving window analyses, rotated through 360°. Correlations between the species turnover, endemism and climatic turnover results generated by each rotation of the moving window were analysed using multivariate generalized linear models applied at national, regional, and local scales. At national-scale, temperature turnover consistently exhibited the greatest influence on species turnover and endemism, but model predictive capacity was low (typically r2 = 0.05, P < 0.001). At regional scales the relative influence of temperature and precipitation turnover varied between regions, although model predictive capacity was also generally low. Climatic turnover was considerably more predictive of species turnover and endemism at local scales (e.g., r2 = 0.65, P < 0.001). While temperature turnover had the greatest effect in one locale (the northern North Island), there was substantial variation in the relative influence of temperature and precipitation predictors in the remaining four locales. Species turnover and endemism hotspots often occurred in different locations. Climatic predictors had a smaller influence on endemism. Our results caution against assuming that variability in temperature will always be most predictive of reptile biodiversity across different spatial scales, locations and directions. The influence of climatic turnover on the species turnover and endemism of other taxa may exhibit similar patterns of spatial variation. Such intricate variation might be discerned more readily if studies at broad scales are complemented by geographically variant, local-scale analyses.

Acacia, climate, and geochemistry in Australia

In anticipation of global climate change, the question of whether shifts in plant community composition (beta-diversity) are predictable from environmental variation is receiving considerable interest. Species strongly associated with local soil environments may be more vulnerable to climate change than species with a broad tolerance of soil conditions. Here we investigate relationships between climate, geochemistry and the distribution of Acacia over Australia. We use geostatistics to estimate total Ca, Mg, Na, Al, P, pH, and electrical conductivity at sites where Acacia species have been recorded in the Australian Virtual Herbarium database. We compare the median predicted geochemistry and reported substrate for individual species that appear associated with extreme conditions; this provides a partial evaluation of the predictions. We generate a site-by-species matrix by aggregating observations to the centroids of grid cells 100 km on edge, calculate diversity indices, and use numerical ecology methods (ordination, variation partitioning) to investigate the ecology of Acacia and its response to climatic and geochemical gradients. Many species that tolerate extreme geochemical conditions are range restricted. Species in the genus Acacia are widely distributed across Australia but strong associations exist between species turnover and climate and geochemistry. Climate, pH, P, Na, and EC account for much of the variation in Acacia distribution over the continent, especially across southern Australia. Climate and geochemistry together account for half of the variation in species turnover of Acacia across Australia and for about 60–80 % in areas of high species richness. The unique contribution of geochemistry to variation in species turnover of Acacia is smaller than that of climate except in the most species rich areas. Climate is more important than geochemistry in explaining Acacia species distribution and turnover across northern Australia. Geochemical variables are important in explaining the occurrence of Acacia species where species richness is high in southern Australia—it is important to investigate this further with other genera. Aridification, which has driven some the observed extremes in geochemical concentrations, is a key process in landscape evolution as well as biogeography. This study of Acacia diversity and environmental conditions underscores Australia’s place as a natural laboratory for evolutionary ecology and biogeography.

Using maps of continuous variation in species compositional turnover to supplement uniform polygon species range maps

Species ranges are often represented using polygons, with the attendant issues that they show uniform ranges with abrupt boundaries and can overestimate species ranges. We demonstrate that such uniform species ranges can be supplemented by mapping the gradational variation in species turnover across a landscape. Directional variation in species turnover for 15 skink species (Reptilia: Scincidae) and topographic and climatic turnover in south-eastern Australia were measured using directional moving window analyses, rotated through 360°. The resultant species turnover maps were compared with published polygon range maps for two species within the group (Liopholis whitii and L. inornata). We also assessed how the relationships between species and environmental turnover varied in areas of low or high species turnover. Continuous transitions between distinct areas of low and high species turnover were mapped. Low turnover comprised only 19% of the L. whitii polygon species range within the study area extent. These low turnover areas were more densely populated by L. whitii (67% of observations), whereas areas of medium to high turnover contained substantially fewer observations (25%). Regions with the highest species turnover contained only 6% of observations. L. inornata observations were also clustered in low species turnover areas. Averaged climatic and elevation values were higher in low-turnover areas despite their close adjacency to high-turnover zones. The environmental turnover in low species turnover regions was also lower than in high-turnover areas. Correlations between environmental turnover and low species turnover areas were positive, whereas the opposite relationship applied in high species turnover areas. We identified both abrupt and gradual distributional breaks between separate reptile assemblages; an example of the latter is located in the Hunter Valley in the south-eastern coastal region. This break has been mapped using solid, uniform lines in species ranges and thus implicitly as an abrupt break. Environmental conditions may be more favourable to skinks in low-turnover areas. Since L. whitii and other skink species have very large populations in low-turnover areas, other squamate species may also be more likely to occur in these areas. This has potential implications for conservation prioritisation. The turnover maps used here can supplement the information provided about reptile distributions by the equivalent polygon ranges. This approach can be applied to point occurrence data for any taxonomic group or any similar georeferenced diversity data set.

Explaining the saproxylic beetle diversity of a protected Mediterranean area

Saproxylic beetle diversity is high at the Cabaneros National Park (central Spain), where woodland habitats exhibit remarkable heterogeneity. Our aim was to explain the diversity of saproxylic beetles, focusing on species turnover among mature woodland types. We surveyed five woodland types that represented the heterogeneity of the park’s woodland habitats. Beetles were collected using window traps over a period of 20 months. The Jaccard Similarity Index was used as indirect value of beta diversity among woodlands and to test the relation between species turnover and geographical distance. We also identified the contribution of species turnover to landscape diversity by using a partitioning model. Moreover, the presence of mixed woodlands (more than one tree species) allowed us to attempt to valorise the effect of tree species (coupled with their historical management) on species turnover among woodlands. Finally, we looked for different saproxylic beetle preferences for habitat and tree species using an indicator value method. We found that saproxylic beetle species composition varied significantly among the studied woodlands. The variation in species turnover was independent from the distance among woodlands, which suggested that beetle dispersal abilities could not explain this high turnover. Tree species within woodlands were a key factor that increased diversity turnover in woodlands and, consequently, the diversity of the park. Moreover, we found saproxylic beetle species that had different habitat and tree species preferences. We conclude that woodland heterogeneity (highly affected by woodland composition) seems to be the driving force for saproxylic beetle diversity in this protected area.

Disentangling the effects of geographic distance and environmental dissimilarity on global patterns of species turnover

ABSTRACTAim To distinguish the effects of geographic distance and environmental dissimilarity on global patterns of species turnover in four classes of terrestrial vertebrates (mammals, birds, reptiles and amphibians).Location Six hundred and sixty terrestrial ecoregions across the globe.Methods We calculated species turnover between each pair of ecoregions, using the Jaccard index (J). We selected seven variables to quantify environment in each ecoregion, and subjected the environmental values to a principal components analysis. For each realm, we applied multiple regression analysis relating the natural logarithm of the Jaccard index (lnJ) to geographic distance alone and in combination with differences in the environment variables measured as principal components (PC). We used partial correlations to partition variance in lnJ between unique contributions of distance and environmental PC scores, the covariation between distance and environment, and unexplained variance. To examine the latitude and species turnover relationship, we regressed lnJ on latitude with distance between ecoregions being included as a covariate.Results The natural logarithm of the Jaccard index (lnJ) decreased significantly with increasing geographic distance for all vertebrate classes in each zoogeographic realm, and the slopes of the relationships per 1000 km ranged from −0.251 to −1.043. With environmental differences included in the analysis, both geographic distance and environmental differences were substantial predictors of lnJ for every combination of taxon and realm. On average, the unique contribution of geographic distance to variation in species turnover between ecoregions was about 1.4 times that of the environmental differences between ecoregions. Species turnover generally decreased with increasing latitude when controlling for geographic distance. The value of lnJ for each vertebrate class was highly and positively correlated with those of the other vertebrate classes.Main conclusions Our analyses suggest that both dispersal‐based and niche‐based processes have played important roles in determining faunal similarities among vertebrate assemblages at the spatial scale examined. Furthermore, reptiles and amphibians exhibited greater distance‐independent faunal heterogeneity among ecoregions and greater turnover among ecoregions with respect to geographic and environmental distance than birds and mammals.

Estimating and conserving patterns of invertebrate diversity: a test case of New Zealand land snails

AbstractAim Using New Zealand land snails as a case study, we evaluated recent spatial modelling approaches for the analysis of diversity in species‐rich invertebrate groups. Applications and prospects for improved conservation assessment were investigated.Location New Zealand.Methods The study used a spatially extensive and taxonomically comprehensive, plot‐based dataset on community structure in New Zealand land snails. Generalized regression analysis and spatial prediction (GRASP) was used to model and predict species richness as a function of environmental variables (including aspects of climate, soils and vegetation). Generalized dissimilarity modelling (GDM) was used to model turnover in species composition in relation to environmental and geographical distances, and to assess community similarity and the representativeness of the reserve network.Results Observed land snail richness in 20 × 20 m plots ranged from 1 to 74 (mean 17.5). The GRASP model explained a modest 27% of the variation in richness. The GDM model explained 57% of the variation in species turnover and indicated approximately equal amounts related to environmental (Cody’s beta diversity) and geographical distance (Cody’s gamma diversity). Temperature and moisture were the most important environmental variables. Results indicate that snail distributions are not only sorted by environment but are also strongly influenced by historical effects consistent with those expected of poorly dispersing taxa that have persisted in refugia during past climatic change. The GDM model enabled spatial classifications of snail communities, highlighting diverse communities in heterogeneous regions, such as the South Island mountains, and also enabled continuous depictions of community similarity and adequacy of New Zealand’s protected natural areas network.Main conclusions The GRASP and GDM analyses allowed us to model and depict spatial patterns of diversity in land snail communities involving 845 species, and produce community classifications and estimates of community similarity. These tools advance conservation assessment in species‐rich groups, but require further conceptual and methodological development.

Plant extinction dynamics in an insular metacommunity

Changes in the composition of local communities through time (i.e. species turnover) is a common phenomenon in insular biology. However, the mechanisms promoting variation in species turnover, both among islands and among species, are poorly understood. In an effort to better understand the causes of variation in species turnover, we evaluated the colonization and extinction dynamics of plant populations on 18 small islands off the west coast of Canada. In 1997, we quantified total population sizes of 10 woody angiosperm species. A decade later, we resampled islands to test whether: 1) species turnover occurred, 2) colonization events were offset by extinction events, 2) variation in extinction rates among islands was associated with population sizes, average plant heights, island area, island isolation or each island's exposure to ocean‐born disturbances, and 3) variation in extinction rates among species was associated with plant life history traits. Results showed that extinction events outnumbered colonization events, suggesting that the metacommunity is in ‘disequilibrium’. Variation in extinction rates among islands was unrelated to island area and isolation. However, extinction rates increased with exposure to ocean‐born disturbances and decreased with both initial population sizes and average plant heights. Species with thicker, tougher leaves (i.e. high leaf mass per area) were less prone to extinction than species with thinner, more papery leaves. Overall results indicate that species turnover is common and that it is generated primarily by extinction. Variation in extinction rates appears to result from an interaction between among‐island effects (exposure, population size and plant stature) and among‐species effects (leaf toughness), suggesting that ocean‐born disturbances play a key role in determining metacommunity structure.

Drought impacts and recovery are driven by local variation in species turnover

In forest systems, drought acts as a disturbance that can generate impacts on community structure and composition at multiple scales. This study focused on a 2-month drought event within an early successional forest system to determine the mechanism(s) of community response to, and recovery from, drought. Drought induced a 28% decline in neighborhood species richness and cover as a result of decreased colonization and increased extinction rates. Following drought, neighborhood richness quickly recovered via increased colonization rates while extinction rates were unaltered. Drought had little long-term effect on neighborhood structure (species richness and cover) and generated only subtle changes in neighborhood composition. Ruderal (annual and biennial) species were more likely to change (increase or decrease) in cover and frequency than the more stress tolerant perennial and woody species. However, population dynamics appeared to be generally driven by stochastic species turnover among fields and not by uniform shifts in species performance across the site. Although drought impacts and recovery appeared predictable at the neighborhood scale, population responses to drought within the site were rather unpredictable. Our findings suggest that stochastic fine-scale processes can generate predictable course-scale dynamics within a disturbed system. The scale-specific mechanisms of community change presented here should be explored in other systems to determine the extent of their generality in driving disturbance impacts on communities.