Species–area relationships explained by the joint effects of dispersal limitation and habitat heterogeneity (original) (raw)
Related papers
2012
Species abundance distributions (SADs) play an important role in the current dispute over mechanisms shaping community assembly. Niche theory assumes diff erential occurrence of species in diff erent habitats while neutral theory emphasizes stochastic events and dispersal. Th e previous tests of niche and neutral models shaping SADs lead to the claim that SADs are not informative for inferring underlying processes. Using spatial statistical models in a fully mapped 24-ha subtropical forest in China, we fi rst demonstrate that one can not distinguish between the eff ect of habitat heterogeneity and dispersal limitation on SADs by inspecting whether the observed SADs fall within 95% confi dence intervals of the simulated SADs. Subsequently, we demonstrate that SADs can be used to detect mechanisms shaping SADS by comparing alternative process-based models using model selection techniques. We found that dispersal limitation explain SADs at smaller spatial scales, while the combination of niche and dispersal limitation explain SADs at larger scales. Th ese processes are linked with the degree of conspecifi c aggregation, informing further attempts to refi ne and parameterize the statistical theory of sampling SADs.
Species Diversity Patterns Derived from Species–Area Models
Ecology, 2002
Although area, species abundances, spatial distribution, and species richness have been central components of community ecology, their interrelationships are not completely understood. To describe these interrelationships, we study and test three patterns regarding species richness using species-area models. The first one is the widely accepted generalization that states that the number of species monotonically increases with sampling area. The second pattern predicts the decrease in species richness with the increase of species dominance in a given area. The third one predicts that spatial aggregation of individuals within species results in lower species richness in communities. These three generalizations were investigated by modeling and simulations. First, a random-placement species-area model was used to evaluate the effects of relative species abundances on species richness in a sampling area. Then, a nonrandom species-area model was derived which explicitly encompasses the spatial distributions of species; it served to evaluate the effects of heterogeneity in spatial distributions on species richness. Species-area models were numerically evaluated using parameters estimated from a tropical rain forest community, and simulations were conducted to support the numerical solutions. The three patterns regarding species diversity were consistently supported by the results. A discussion ensues, describing how the three patterns can be used to interpret and predict species diversity, and how they are supported by other diversity hypotheses. The three generalizations suggest that, if we want to understand species diversity, we should go and look for mechanisms that influence the abundances and spatial distributions of species. If a mechanism can make the species abundances more even, or their spatial distributions more regular, this factor likely contributes to species coexistence.
Effects of community structure on the species-area relationship in China's forests
Ecography, 2012
The species-area relationship (SAR) is the oldest and most frequently documented law in ecology. In a community, the SAR is regulated by the abiotic environment and biotic interactions and depends on the individual-spatial distribution of species (ISD) and the species-abundance distribution (SAD). In this study, we explored the effects of aggregation of ISDs and unevenness of SADs on SARs in forests of China by comparing the empirical and simulated SARs of 32 nested plots distributed along an extensive latitudinal gradient. Both aggregation and unevenness affected the shape of SARs significantly: ISDs accounted for 12.6 4.0% of the incremental increase in species richness with area, and SADs accounted for 18.7 3.8 and 23.5 3.9% under the broken-stick model and even abundance model, respectively. Effects of both aggregation and unevenness decreased as temperature increased, suggesting that individuals of a species were spatially more aggregated than random, and the individuals among species were more discrepant from the null distribution (broken-stick model and even abundance model in this study), in the cold than in the warm areas. Taken together, our results demonstrate that ISDs and SADs within communities can shape SARs, but these effects vary along latitudinal gradients, and are likely mediated by temperature.
2004
A theory of spatial structure in ecological communities is presented and tested. At the core of the theory is a simple allocation rule for the assembly of species in space. The theory leads, with no adjustable parameters, to non-random statistical predictions for the spatial distribution of species at multiple spatial scales. The distributions are such that the abundance of a specie s at the largest measured scale uniquely determines the spatial-abundance distribution of the individuals of that species at smaller spatial scales. The shape of the species-area relationship, the endemics-area relationship, a scale-dependent community-level spatial-abundance distribution, the species-abundance distribution at small spatial scales, an index of intra-specific aggregation, the range-area relationship, and the dependence of species turnover on inter-patch distance and on patch size are also uniquely predicted as a function solely of the list of abundances of the species at the largest spatial scale. We show that the spatial structure of three spatially explicit vegetation census data sets, a 64-m 2 serpentine grassland plot, the 50-ha BCI tropical forest plot, and a 9.68-ha dry tropical forest plot are generally consistent with the theory's predictions, despite the very simple statistical assumption upon which the theory is based, and the absence of adjustable parameters. However, deviations between predicted and observed distributions do arise for the species with the highest abundances; the pattern of those deviations indicates that the theory, which currently contains no explicit description of interaction mechanisms amongst individuals within species, could be improved with the incorporation of intra-specific density dependence.
Species-area relationships are modulated by trophic rank, habitat affinity and dispersal ability
Ecology, 2014
In the face of ongoing habitat fragmentation, species-area relationships (SARs) have gained renewed interest and are increasingly used to set conservation priorities. An important question is how large habitat areas need to be to optimize biodiversity conservation. The relationship between area and species richness is explained by colonization-extinction dynamics, whereby smaller sites harbor smaller populations, which are more prone to extinction than the larger populations sustained by larger sites. These colonizationextinction dynamics are predicted to vary with trophic rank, habitat affinity, and dispersal ability of the species. However, empirical evidence for the effect of these species characteristics on SARs remains inconclusive.
Spatial distribution of tree species in a species-rich subtropical mountain forest in central China
Inferring the processes underlying the spatial distribution patterns of tree species is fundamental for understanding species coexistence. Here, we examined spatial distribution patterns of woody plants by using the univariate pair correlation function to quantify spatial patterns of species in a fullly mapped 25 ha subtropical plot in China. We analyzed the relationships between the species attributes and spatial distribution patterns of 137 tree species with at least one individual per hectare. The results showed that aggregated distributions were the dominant pattern for species in the Badagongshan subtropical forests, and that the percentage of significantly aggregated species decreased with increasing spatial scales. Rare species were more aggregated than intermediate and abundant species, but they were more easily influenced by habitat heterogeneity. Also, there was significantly negative relationship between species abundance and species aggregation intensity. The aggregation intensity showed negative relationships to species mean diameter at breast height (DBH) and maximum DBH, i.e., species became more regularly spaced as species stature increased. Species functional traits (e.g., growth form and phenological guild) also had obvious effects on the spatial patterns of species. However, spatial patterns of tree species were not related to the dispersal mode. Our results partially conformed to the prediction that species' attributes influenced species' spatial patterns following similar laws, even after controlling for the effects of habitat heterogeneity. Consequently, species attributes (species abundance, mean DBH, maximal DBH, growth form, phenological guild, etc.) and habitat heterogeneity may primarily contribute to spatial patterns and species coexistence in natural forests. Résumé : La déduction des processus à la base des patrons de distribution spatiale des espèces d'arbre est fondamentale pour comprendre la coexistence des espèces. Nous avons étudié les patrons de distribution spatiale de plantes ligneuses à l'aide d'une fonction univariée de corrélation de paire pour quantifier la répartition spatiale des espèces dans une parcelle complètement cartographiée de 25 ha établie dans la forêt subtropicale chinoise. Nous avons analysé les relations entre les caractéristiques des espèces et le patron de distribution spatiale de 137 espèces d'arbre ayant au moins un individu à l'hectare. Les résultats montrent que la distribution groupée était le patron de distribution spatiale dominant des espèces de la forêt subtropicale de Badagongshan et que le pourcentage d'espèces significativement groupées diminuait avec l'augmentation de l'échelle spatiale. Les espèces rares étaient davantage groupées que les espèces dont l'abondance était forte ou intermédiaire, mais elles étaient plus facilement influencées par l'hétérogénéité de l'habitat. Aussi, il y avait une relation inverse significative entre l'abondance et l'intensité de groupement des espèces. L'intensité de groupement était négativement liée au diamètre à hauteur de poitrine (DHP) moyen et maximal des espèces, c'est-à-dire que les espèces devenaient plus régulièrement espacées avec l'augmentation de leur taille. Les traits fonctionnels des espèces (c'est-à-dire leur forme de croissance et leur guilde phénologique) avaient aussi des effets manifestes sur la répartition spatiale des espèces. Toutefois, la répartition spatiale des espèces n'était pas reliée à leur mode de dispersion. Nos résultats sont partiellement conformes aux prévisions stipulant que les caractéristiques des espèces influencent leur répartition spatiale de façon similaire, même en tenant compte de l'hétérogénéité de l'habitat. Par conséquent, les caractéristiques des espèces (abondance, DHP moyen et maximal, forme de croissance, guilde phénologique, etc.) et l'hétérogénéité de l'habitat sont des facteurs importants pouvant contribuer à expliquer la répartition spatiale et la coexistence des espèces en forêt naturelle. [Traduit par la Rédaction]
A theory of spatial structure in ecological communities at multiple spatial scales
Ecological Monographs, 2005
A theory of spatial structure in ecological communities is presented and tested. At the core of the theory is a simple allocation rule for the assembly of species in space. The theory leads, with no adjustable parameters, to nonrandom statistical predictions for the spatial distribution of species at multiple spatial scales. The distributions are such that the abundance of a species at the largest measured scale uniquely determines the spatialabundance distribution of the individuals of that species at smaller spatial scales. The shape of the species-area relationship, the endemics-area relationship, a scale-dependent community-level spatial-abundance distribution, the species-abundance distribution at small spatial scales, an index of intraspecific aggregation, the range-area relationship, and the dependence of species turnover on interpatch distance and on patch size are also uniquely predicted as a function solely of the list of abundances of the species at the largest spatial scale. We show that the spatial structure of three spatially explicit vegetation census data sets (i.e., a 64-m 2 serpentine grassland plot, a 50-ha moist tropical forest plot, and a 9.68ha dry tropical forest plot) are generally consistent with the predictions of the theory, despite the very simple statistical assumption upon which the theory is based, and the absence of adjustable parameters. However, deviations between predicted and observed distributions do arise for the species with the highest abundances; the pattern of those deviations indicates that the theory, which currently contains no explicit description of interaction mechanisms among individuals within species, could be improved with the incorporation of intraspecific density dependence.
Universal species–area and endemics–area relationships at continental scales
Nature, 2012
Despite the broad conceptual and applied relevance of how the number of species or endemics changes with area (the species-area and endemics-area relationships (SAR and EAR)), our understanding of universality and pervasiveness of these patterns across taxa and regions has remained limited. The SAR has traditionally been approximated by a power law 1 , but recent theories predict a triphasic SAR in logarithmic space, characterized by steeper increases in species richness at both small and large spatial scales 2-6 . Here we uncover such universally upward accelerating SARs for amphibians, birds and mammals across the world's major landmasses. Although apparently taxon-specific and continent-specific, all curves collapse into one universal function after the area is rescaled by using the mean range sizes of taxa within continents. In addition, all EARs approximately follow a power law with a slope close to 1, indicating that for most spatial scales there is roughly proportional species extinction with area loss. These patterns can be predicted by a simulation model based on the random placement of contiguous ranges within a domain. The universality of SARs and EARs after rescaling implies that both total and endemic species richness within an area, and also their rate of change with area, can be estimated by using only the knowledge of mean geographic range size in the region and mean species richness at one spatial scale.
Effects of topography on structuring species assemblages in a subtropical forest
Aims Topography has long been recognized as an important factor in shaping species distributions. Many studies revealed that species may show species-habitat associations. However, few studies investigate how species assemblages are associated with local habitats, and it still remains unclear how the community-habitat associations vary with species abundance class and life stage. In this study, we analyzed the community-habitat associations in a subtropical montane forest. Methods The fully mapped 25-ha (500 × 500 m) forest plot is located in Badagongshan Nature Reserve in Hunan Province, Central China. It was divided into 625 (20 × 20 m) quadrats. Habitat types were classified by multivariate regression tree analyses that cluster areas with similar species composition according to the topographic characteristics. Indicator species analysis was used to identify the most important species for structuring species assemblages. We also compared the community-habitat associations for two levels of species abundances (i.e. abundant and rare) and three different life stages (i.e. saplings, juveniles and adults), while accounting for sample size effects. Important Findings The Badagongshan plot was divided into five distinct habitat types, which explained 34.7% of the variance in tree species composition. Even with sample size taken into account, community-habitat associations for rare species were much weaker than those for abundant species. Also when accounting for sample size, very small differences were found in the variance explained by topography for the three life stages. Indicator species of habitat types were mainly abundant species, and nearly all adult stage indicator species were also indicators in juvenile and sapling stages. Our study manifested that topographical habitat filtering was important in shaping overall local species compositions. However, habitat filtering was not important in shaping rare species' distributions in this forest. The community-habitat association patterns in this forest were mainly shaped by abundant species. In addition, during the transitions from saplings to juveniles, and from juveniles to adults, the relative importance of habitat filtering was very weak.
PLoS ONE, 2013
Quantifying the relative contributions of environmental conditions and spatial factors to species distribution can help improve our understanding of the processes that drive diversity patterns. In this study, based on tree inventory, topography and soil data from a 20-ha stem-mapped permanent forest plot in Guangdong Province, China, we evaluated the influence of different ecological processes at different spatial scales using canonical redundancy analysis (RDA) at the community level and multiple linear regression at the species level. At the community level, the proportion of explained variation in species distribution increased with grid-cell sizes, primarily due to a monotonic increase in the explanatory power of environmental variables. At the species level, neither environmental nor spatial factors were important determinants of overstory species' distributions at small cell sizes. However, purely spatial variables explained most of the variation in the distributions of understory species at fine and intermediate cell sizes. Midstory species showed patterns that were intermediate between those of overstory and understory species. At the 20-m cell size, the influence of spatial factors was stronger for more dispersal-limited species, suggesting that much of the spatial structuring in this community can be explained by dispersal limitation. Comparing environmental factors, soil variables had higher explanatory power than did topography for species distribution. However, both topographic and edaphic variables were highly spatial structured. Our results suggested that dispersal limitation has an important influence on fine-intermediate scale (from several to tens of meters) species distribution, while environmental variability facilitates species distribution at intermediate (from ten to tens of meters) and broad (from tens to hundreds of meters) scales.