Species Richness Environment Relationships Research Articles

Deconstructing species richness–environment relationships in Neotropical lianas

AbstractAimStudying species richness patterns by considering all species as equivalent units may prevent a deeper understanding of the origin and maintenance of biodiversity. Here, we deconstructed the species richness of Neotropical lianas by specific attributes of species to study richness–environment relationships.LocationNeotropics.TaxonTribe Bignonieae (Bignoniaceae), the largest clade of Neotropical lianas.MethodsWe used five morphological, one geographical and two evolutionary attributes of species, each with 2–7 attribute states. We compared the environmental response of species richness of each attribute state to the response of overall Bignonieae species richness. For those groups of species that differed in their environmental response to three‐dimensional habitat structure, climate and soil we assessed: (a) the magnitude and direction of the environmental response; and (b) the variation in species richness explained by environmental variables and spatial filters using variation partitioning analysis.ResultsWe identified eight attribute states whose richness–environment relationship differed from the overall richness pattern: three morphological (species with shrubby habit, lacking tendrils and with seeds bearing ellipsoid wings), three geographical (species with small, small‐to‐medium and medium‐to‐large range sizes) and two evolutionary (species of the genera Amphilophium and Cuspidaria) attribute states. Areas with high species richness of these eight attribute states did not overlap with the centres of Neotropical diversity in the tribe Bignonieae. A high fraction of the variation in species richness of these eight attribute states was accounted for by spatial filters or remained unexplained.Main conclusionsThe richness deconstruction approach revealed that richness–environment relationships of species with specific attribute states differ from the overall species richness pattern. These morphological, geographical and evolutionary attribute states are mostly related to the survival and persistence in savanna habitats, and show that ecological strategies and evolutionary histories need to be taken into account to fully understand richness–environment relationships.

Principal factors controlling the species richness of European fens differ between habitat specialists and matrix‐derived species

AbstractAimWe present the first continental‐scale study of factors controlling the species richness of groundwater‐fed fens, comparing land snails, vascular plants and bryophytes. We separately analyse two ecologically distinct groups differing in conservation value and colonization/extinction dynamics, that is habitat specialists, and matrix‐derived species. Considering the island‐like nature of fen habitats, we hypothesize larger differences in the species richness–environment relationships between habitat specialists and matrix‐derived species than among the taxonomic entities.LocationSeven European regionsMethodsRichness was counted at 373 well‐preserved fens with undisturbed hydrology using the same protocols. Relationships between the species richness and water pH, waterlogging, climate and geography were explored by GLMs.ResultsLand snail richness responded mainly to water pH, regardless of habitat specialization. Richness of vascular plant and bryophyte specialists was strongly driven by geographical location of the sites, while that of matrix‐derived species was driven by waterlogging and water pH. The richness of matrix‐derived species of all taxa significantly increased with the decreasing waterlogging. Residual richness of specialists of all taxa decreased towards southern Europe.Main conclusionsIn island‐like terrestrial habitats, differences between specialists and matrix‐derived species may outweigh differences among taxa, unless there is one strong physiological determinant of species richness such as pH in land snails. The richness of specialists seems to be strongly related to difficult‐to‐measure regional factors such as historical frequency and connectivity of fen habitats. The richness of matrix‐derived species depends mainly on local conditions, such as pH and waterlogging, determining the degree of habitat contrast against the surrounding matrix. Sufficient waterlogging maintains a high representation of habitat specialists in fen communities, and disturbance of water regime may cause the increase in the number of matrix‐derived species and potentially trigger successional shifts towards non‐fen communities.

Environmental optimality, not heterogeneity, drives regional and local species richness in lichen epiphytes

AbstractAimWe evaluate the scale dependence of species richness–environment relationships with a continent‐wide analysis of lichen epiphyte communities. Specifically, our goals are to assess: (1) the dependence of local richness on regional processes, (2) whether species richness is primarily influenced by heterogeneity in environmental conditions or the central tendency of those conditions, and (3) whether the relative influence of these different aspects of the environment differs between local communities and regional species pools.LocationForests of the contiguous United States.MethodsWe used variation partitioning and model averaging of linear models to relate macrolichen richness at 1923 forest inventory plots (c. 4000 m2) to measures of environmental heterogeneity and mean conditions at local and regional scales. Data included 17 local environmental variables and 11 regional‐scale variables which were obtained from a national forest inventory, herbarium records and several climate data sources.ResultsRegional‐scale variables explained more unique variation in local species richness and generally had stronger effects than variables measured locally. However, most variation in local richness was explained jointly by local and regional variables. At both local and regional scales, variables measuring environmental heterogeneity explained little variation in species richness and had weaker effects than variables characterizing mean environmental conditions.Main conclusionsSpecies richness of epiphytic macrolichens is not regulated by environmental heterogeneity locally or regionally and instead tracks large‐scale climate gradients of water availability and temperature. Richness in local communities is influenced by processes operating at both regional and local scales, highlighting the importance of determining large‐scale drivers of lichen richness across the North American continent. This research demonstrates a general method for comparing the influence of different aspects of the environment on species richness across scales and should be applicable to many different taxonomic groups.

Urbanization altered latitudinal patterns of bird diversity-environment relationships in the southern Neotropics

Given the global expansion of urbanization, it is crucial for planning to understand how that process affects spatial patterns of diversity. At broad geographical scales, climatic conditions such as temperature or rainfall usually explain those patterns. Our objective was to analyze and compare the species richness-environment relationships and the distance decay in similarity of bird communities between urban centres and less intensively modified adjacent rural areas along a latitudinal gradient in the southern Neotropics. We surveyed birds in 15 urban centres and their adjacent rural areas from 26° to 38°S and compiled temperature and rainfall data. We performed regression analyses and Mantel tests to explore latitudinal changes in bird species richness and taxonomic composition as a response to those climatic variables in urban centres and in rural areas. Results showed that species richness decreased with latitude in rural areas, and temperature and rainfall accounted for that decline, but remained relatively constant in urban centres. The difference in species richness between urban centres and rural areas was larger at lower latitudes. Similarity in the composition of bird assemblages declined with distance at a similar rate in both urban centres and rural areas; however, similarity was higher between urban centres than in rural areas at any given distance. Environmental differences due to temperature and rainfall partially accounted for the distance decay in similarity for both urban and rural areas. The impact of urbanization on bird species richness seems to differ according to the climatic context in which urbanization develops, and it is expected to be higher in tropical than in more arid environments. Our study remarks the importance of considering urban systems as components of larger ecological systems.

Geographical sampling bias in a large distributional database and its effects on species richness–environment models

AbstractAimRecent advances in the availability of species distributional and high‐resolution environmental data have facilitated the investigation of species richness–environment relationships. However, even exhaustive distributional databases are prone to geographical sampling bias. We aim to quantify the inventory incompleteness of vascular plant data across 2377 Chinese counties and to test whether inventory incompleteness affects the analysis of richness–environment relationships and spatial predictions of species richness.LocationChina.MethodsWe used the most comprehensive database of Chinese vascular plants, which includes county‐level occurrences for 29,012 native species derived from 4,236,768 specimen and literature records. For each county, we computed smoothed species accumulation curves and used the mean slope of the last 10% of the curves as a proxy for inventory incompleteness. We created a series of data subsets with different levels of inventory incompleteness by excluding successively more under‐sampled counties from the full data set. We then applied spatial and non‐spatial regression models to each of these subsets to investigate relationships between the species richness of subsets and environmental factors, and to predict spatial patterns of vascular plant species richness in China.ResultsLog10‐transformed numbers of records and documented species were strongly correlated (r = 0.97). In total, 91% of Chinese counties were identified as under‐sampled. After controlling for inventory incompleteness, the overall explanatory power of environmental factors markedly increased, and the strongest predictor of species richness switched from elevational range to annual wet days. Environmental models calibrated with more complete inventories yielded better spatial predictions of species richness.Main conclusionsOur results indicate that inventory incompleteness strongly affects the explanatory power of environmental factors, the main determinants of species richness obtained from regression analyses, and the reliability of environment‐based spatial predictions of species richness. We conclude that even large distributional databases are prone to geographical sampling bias, with far‐reaching implications for the perception of and inferences about macroecological patterns.

Species Richness-Environment Relationships of European Arthropods at Two Spatial Grains: Habitats and Countries

We study how species richness of arthropods relates to theories concerning net primary productivity, ambient energy, water-energy dynamics and spatial environmental heterogeneity. We use two datasets of arthropod richness with similar spatial extents (Scandinavia to Mediterranean), but contrasting spatial grain (local habitat and country). Samples of ground-dwelling spiders, beetles, bugs and ants were collected from 32 paired habitats at 16 locations across Europe. Species richness of these taxonomic groups was also determined for 25 European countries based on the Fauna Europaea database. We tested effects of net primary productivity (NPP), annual mean temperature (T), annual rainfall (R) and potential evapotranspiration of the coldest month (PETmin) on species richness and turnover. Spatial environmental heterogeneity within countries was considered by including the ranges of NPP, T, R and PETmin. At the local habitat grain, relationships between species richness and environmental variables differed strongly between taxa and trophic groups. However, species turnover across locations was strongly correlated with differences in T. At the country grain, species richness was significantly correlated with environmental variables from all four theories. In particular, species richness within countries increased strongly with spatial heterogeneity in T. The importance of spatial heterogeneity in T for both species turnover across locations and for species richness within countries suggests that the temperature niche is an important determinant of arthropod diversity. We suggest that, unless climatic heterogeneity is constant across sampling units, coarse-grained studies should always account for environmental heterogeneity as a predictor of arthropod species richness, just as studies with variable area of sampling units routinely consider area.

Ice age climate, evolutionary constraints and diversity patterns of European dung beetles

Current climate and Pleistocene climatic changes are both known to be associated with geographical patterns of diversity. We assess their associations with the European Scarabaeinae dung beetles, a group with high dispersal ability and well-known adaptations to warm environments. By assessing spatial stationarity in climate variability since the last glacial maximum (LGM), we find that current scarab richness is related to the location of their limits of thermal tolerance during the LGM. These limits mark a strong change in their current species richness-environment relationships. Furthermore, northern scarab assemblages are nested and composed of a phylogenetically clustered subset of large-range sized generalist species, whereas southern ones are diverse and variable in composition. Our results show that species responses to current climate are limited by the evolution of assemblages that occupied relatively climatically stable areas during the Pleistocene, and by post-glacial dispersal in those that were strongly affected by glaciations.

Plant species richness–environment relationships across the Subantarctic–Patagonian transition zone

AbstractAim To evaluate the relative importance of climate, productivity, environmental heterogeneity, biotic associations and habitat use by cattle to account for the species richness of trees, shrubs and herbs across the Subantarctic–Patagonian transition.Location An area of c. 150 × 150 km, within the transition zone between the Subantarctic and Patagonian subregions on the eastern slope of the Andes (c. 39–42° S, 70–72° W).Methods All vascular plants found at each one of 50 (10 × 10 m) sampling plots were counted to estimate the local tree, shrub and herb species richness. Path analysis was used to evaluate the relationship between the richness of the three life‐forms and plant cover, dried litter biomass, mean annual temperature, annual precipitation, daily temperature range, substrate heterogeneity and number of faecal pats. Principal coordinates of neighbour matrices was used to model the spatial autocorrelation of the data.Results Total plant species richness showed a unimodal pattern of spatial variation across the transition. Richness responded positively to indirect effects of precipitation mediated through plant cover, but there was a negative overall effect of precipitation on richness towards the west of the transition, most strongly for trees. An increase in substrate heterogeneity promoted a local increase in herb and shrub richness; the richness of trees increased in sites with steeper slopes. Canopy closure had a direct negative impact on herb richness; it also increased the local accumulation of litter, which negatively affected shrub and herb richness. The impact of habitat use by cattle negatively affected herb richness in areas to the east of the biogeographical transition.Main conclusions We suggest that the importance of indirect climatic effects mediated by vegetation cover can account for species richness patterns across this transition, most strongly for woody species, which supports the productivity hypothesis. The southern temperate forests towards the west may represent a deviation from the predictions of the water–energy dynamics hypothesis. Dissimilar spatial patterns of variation in the richness of woody and herbaceous species, and their different responses to climatic and heterogeneity variables across the transition, suggest that plant life‐form influences the plant species richness–environment relationships.

Plio‐Pleistocene climate change and geographic heterogeneity in plant diversity–environment relationships

Plio‐Pleistocene climate change may have induced geographic heterogeneity in plant species richness–environment relationships in Europe due to greater in situ species survival and speciation rates in southern Europe. We formulate distinct hypotheses on how Plio‐Pleistocene climate change may have affected richness–topographic heterogeneity and richness–water‐energy availability relationships, causing steeper relationships in southern Europe. We investigated these hypotheses using data from Atlas Florae Europaeae on the distribution of 3069 species and geographically weighted regression (GWR). Our analyses showed that plant species richness generally increased with topographic heterogeneity (ln‐transformed altitudinal range) and actual evapotranspiration (AET). We also found evidence for strong geographic heterogeneity in the species richness–environment relationship, with a greater increase in species richness with increasing topographic heterogeneity in southern Europe (mean standardized local slope 0.610±0.245 SD in southern Europe, but only 0.270±0.175 SD in northern Europe). However, the local AET slopes were, at most, weakly different between the two regions, and their pattern did not conform to predictions, as there was a band of high local slopes across southern‐central northern Europe. This band broadly matches the transition between the temperate and boreal zones and may simply reflect the fact that few species tolerate the boreal climate. We discuss the potential explanations for the contrasting findings for the two richness–environment relationships. In conclusion, we find support for the idea that Plio‐Pleistocene climate change may sometimes affect current species richness–environment relationships via its effects on regional species pools. However, further studies integrating information on species ages and clade differentiation rates will be needed to substantiate this interpretation. On a general level, our results indicate that although strong richness–environment relationships are often found in macroecological studies, these can be contingent upon the historical constraints on the species pool.

Predicting future shifts in species diversity

It is both an exciting and challenging time to be an ecologist. It is reasonable to say that our science has never before been confronted by such threats to biological diversity caused by global changes in land use and climate, nor advanced so fast to meet them. The pace of discovery has accelerated incredibly, and the recent ‘‘Danish Biodiversity Information Facility (DanBIF) International Conference on Biodiversity Informatics and Climate Change’’ was a remarkable landmark on the journey. The conference was jointly organized by DanBIF / , the Dept of Biological Sciences, Aarhus Univ., and the Dept of Biology, Copenhagen Univ., and held at Aarhus Univ. in Denmark 5 6 April, 2008. The aim of the conference was to bring world-leading scientists in the biodiversity informatics field together to provide a state-of-the-art overview of current and potential future climate change impacts on biodiversity. Biodiversity and ecosystems are already changing at unprecedented rates, and that pace could accelerate further in the 21st century due to global warming and other anthropogenic changes in the global environment (Sala et al. 2000, Fischlin et al. 2007). Thematically the conference focused hard on the roles of past and present climate as determinants of biodiversity as well as the potential biodiversity impacts of the anticipated climates of the near future, while acknowledging their possible lack of past analogs (Williams et al. 2007). These issues are the kind of complex broad-scale problems that are difficult to study by the traditional experimental approaches, motivating the macroecological research theme in common to all papers included here. We are pleased to present six papers from the DanBIF International Conference on Biodiversity Informatics and Climate Change in this issue of Ecography. Predicting how species diversity will respond to climate change is critical for conservation planning in the 21st century. Success in this area hinges on both conceptual and methodological advances in how we approach these problems. But success will not come easily and ignoring the past will not help predict the future: several papers provide evidence that past climate changes have left longlasting legacies in the geographic diversity patterns. Stropp et al. (2009) use an extensive data set of tree inventory plots spread across the Amazon Basin and Guiana Shield to elucidate the drivers of tropical tree diversity and find evidence that paleoclimatic stability is a key control of regional-scale diversity. Svenning et al. (2009) provide evidence for strong geographic heterogeneity in the species richness environment relationships in the European flora and discuss their linkage to Plio-Pleistocene climate change. Confidence in projections of the future distributions of species requires demonstration that recently-observed changes can be predicted adequately. Willis et al. (2009) use a dynamic spatially-explicit population modelling framework to demonstrate that recent changes at the expanding northern boundaries of three butterfly species can be predicted with good accuracy. In the line with the two previously mentioned studies, but at a smaller spatiotemporal scale Willis et al. (2009) find that each species’ distribution prior to expansion was critical in determining the exact spatial pattern of the current distribution. Willis et al. (2009) also show that realistic representation of dispersal is of key importance for modelling future range shifts. This issue is also a focus of the study by Engler et al. (2009): here, the authors carried out projections of future distribution over the 21st century for 287 mountain plant species in a study area of the western Swiss Alps using the often used unlimited and no dispersal scenarios and two more realistic scenarios, and conclude that the more realistic dispersal simulations produced results that were significantly closer to unlimited dispersal than to no dispersal. Baselga and Araujo (2009) investigate approaches to predicting biotic responses to changing environmental conditions, distinguising between community response models and species-based models. Algar et al. (2009) use global change as a pseudoexperiment, testing whether spatial relationships linking climate to butterfly species richness are able to predict how richness changed during the climate changes observed in the 20th century. Surprisingly, this approach proves at least as effective as species distribution models, suggesting both a new way to predict biodiversity responses to global change and that spatial macroecological relationships can truly be causative. These studies produce a strong consensus that accurate predictions of future shifts in species diversity will demand more sophistication than simple projections of species’ climatic niche space. Fortunately, these papers also advance the theoretical framework necessary to move the field beyond its correlative first principles and into a realm where both theory and empirical discovery can inform Ecography 32: 3 4, 2009 doi: 10.1111/j.1600-0587.2009.06024.x # 2009 The Authors. Journal compilation # 2009 Ecography

Species richness-environment relationships within coastal sclerophyll and mesophyll vegetation in Ku-ring-gai Chase National Park, New South Wales, Australia

Abstract Patterns in species richness from a wide range of plant communities in Ku-ring-gai Chase National Park, New South Wales, Australia, were examined in relation to a number of environmental variables, including soil physical and chemical characteristics. Total species richness and richness of three growth-form types (trees, shrubs and ground cover) were determined in duplicate 500-m2 quadrats from 50 sites on two geological substrata: Hawkesbury Sandstone and Narrabeen shales and sandstones. Generalized linear models (GLM) were used to determine the amount of variation in species richness that could be significantly explained by the measured environmental variables. Seventy-three per cent of the variation in total species richness was explained by a combination of soil physical and chemical variables and site attributes. The environmental variables explained 24% of the variation in tree species richness, 67% of the variation in shrub species richness and 62% of the variation in ground cover species richness. These results generally support the hypothesis of an environmental influence on patterns in total species richness and richness of shrubs and ground cover species. However, tree species richness was not adequately predicted by any of the measured environmental variables; the present environment exerts little influence on the richness of this growth-form type. Historical factors, such as fire or climatic/environmental conditions at time of germination or seedling establishment, may be important in determining patterns in tree species richness at the local scale.

Species richness–environment relationships within coastal sclerophyll and mesophyll vegetation in Ku‐ring‐gai Chase National Park, New South Wales, Australia

Abstract Patterns in species richness from a wide range of plant communities in Ku‐ring‐gai Chase National Park, New South Wales, Australia, were examined in relation to a number of environmental variables, including soil physical and chemical characteristics. Total species richness and richness of three growth‐form types (trees, shrubs and ground cover) were determined in duplicate 500‐m2 quadrats from 50 sites on two geological substrata: Hawkesbury Sandstone and Narrabeen shales and sandstones. Generalized linear models (GLM) were used to determine the amount of variation in species richness that could be significantly explained by the measured environmental variables. Seventy‐three per cent of the variation in total species richness was explained by a combination of soil physical and chemical variables and site attributes. The environmental variables explained 24% of the variation in tree species richness, 67% of the variation in shrub species richness and 62% of the variation in ground cover species richness. These results generally support the hypothesis of an environmental influence on patterns in total species richness and richness of shrubs and ground cover species. However, tree species richness was not adequately predicted by any of the measured environmental variables; the present environment exerts little influence on the richness of this growth‐form type. Historical factors, such as fire or climatic/environmental conditions at time of germination or seedling establishment, may be important in determining patterns in tree species richness at the local scale.