Two-phase species–time relationships in North American land birds

The species–time relationship (STR) is a macroecological pattern describing the increase in the observed species richness with the length of time censused. Understanding STRs is important for understanding the ecological processes underlying temporal turnover and species richness. However, accurate characterization of the STR has been hampered by the influence of sampling. I analysed STRs for 521 breeding bird survey communities. I used a model of sampling effects to demonstrate that the increase in richness was not due exclusively to sampling. I estimated the time scale at which ecological processes became dominant over sampling effects using a two‐phase model combining a sampling phase and either a power function or logarithmic ecological phase. These two‐phase models performed significantly better than sampling alone and better than simple power and logarithmic functions. Most community dynamics were dominated by ecological processes over scales <5 years. This technique provides an example of a rigorous, quantitative approach to separating sampling from ecological processes.     

Human impacts on the species-area relationship in reef fish assemblages

The relationship between species richness and area is one of the oldest, most recognized patterns in ecology. Here we provide empirical evidence for strong impacts of fisheries exploitation on the slope of the species–area relationship (SAR). Using comparative field surveys of fish on protected and exploited reefs in three oceans and the Mediterranean Sea, we show that exploitation consistently depresses the slope of the SAR for both power-law and exponential models. The magnitude of change appears to be proportional to fishing intensity. Results are independent of taxonomic resolution and robust across coral and rocky reefs, sampling protocols and statistical methods. Changes in species richness, relative abundance and patch occupancy all appear to contribute to this pattern. We conclude that exploitation pressure impacts the fundamental scaling of biodiversity as well as the species richness and spatial distribution patterns of reef fish. We propose that species–area curves can be sensitive indicators of community-level changes in biodiversity, and may be useful in quantifying the human imprint on reef biodiversity, and potentially elsewhere.     

Species–area relationship within benthic habitat patches of a tropical floodplain river: An experimental test

The curvilinear relationship between species richness and habitat area (species–area relationship (SAR)) is a fundamental ecological pattern. The relationship is often viewed from a long‐term perspective across relatively large spatial scales, reflecting a balance between immigration and extinction dynamics. We explored whether predictions of SAR also manifest over short time periods (days) in benthic habitat patches of a dynamic floodplain river where littoral faunal assemblages are continuously assembled and disassembled with changing water levels. We examined the relationship of patch size with faunal abundance (i.e. fish and aquatic invertebrates), taxonomic richness, trophic group richness and overall assemblage composition. Strong taxa–area relationships emerged despite the relatively short experimental time period (21 days); larger patches had more taxa and trophic groups. For the smallest patches, taxonomic richness was especially sensitive to abundance of individuals; abundance of individuals was a less important predictor of taxonomic and trophic group richness for the largest patches. Despite the relatively short time frame for study within this temporally dynamic ecosystem, our findings indicate a strong SAR for fishes and macroinvertebrates inhabiting patchy habitats in the littoral zone of this tropical river.     

Linking species-area and species-energy relationships in Drosophila microcosms

Resource availability is an important constraint on community structure. Some authors have suggested it conceptually links two of the most basic patterns in ecology, the species–area relationship and the latitudinal gradient in species richness. I present the first experimental test of this conjecture, by manipulating both the area and resource concentration of artificial larval drosophilid fly habitats and then allowing colonization from a natural species pool. Both the abundance and species richness of these habitats depended upon the total quantity of resources available, regardless of whether those resources were contained within smaller high-quality habitats or larger poor-quality habitats. While the intercepts of species–area relationships varied with resource concentration, they all collapsed onto the same species–energy curve. These results support the view that energetic constraints are of fundamental importance in structuring ecological communities, and that such constraints may even help explain ecological patterns such as the species–area relationship that do not explicitly address resource availability.     

Do generalized scaling laws exist for species abundance distribution in mountains?

Knowing the global pattern of species diversity is a central goal of the science of ecology, and scaling laws can be useful for analysis of cross-scale biodiversity patterns. An elevational gradient in a warm temperate zone of the Donglingshan mountains (China) is used to test the scaling laws of species abundance distribution using multifractal analysis. We show that the power law scaling relationship holds for not just the classical SAR (species–area relationship for richness), but also for Shannon and Simpson diversity. In fact, we find power-laws in the generalized species abundance distribution at all stratal levels of the forest (trees, shrubs and herbs). The fact that these laws exist across a heterogeneous landscape representing a strong bioclimatic gradient suggests that biodiversity scaling laws may be more robust than previously thought.     

Ecological biogeography of Malagasy non‐volant mammals: community structure is correlated with habitat

Aim To examine the relationship between ecoregions, as a proxy for regional climate and habitat type, and mammalian community structure, defined by species composition and richness (e.g. taxonomic structure) and ecological diversity (e.g. ecological structure) of non‐volant species. Location Madagascar. Methods Faunal lists of non‐volant mammal species occurring in 35 communities from five World Wildlife Fund ecoregions were collected from published and unpublished sources. Species were assigned to ecological groups defined by trophic status, locomotor habits, activity cycle and body mass. We used Mantel tests, cluster analysis and principal coordinates analysis to evaluate geographic patterning in taxonomic composition and species richness. We used stepwise multiple discriminant analysis to characterize patterns in the ecological diversity of the mammalian communities from each ecoregion. Communities from transitional habitats (e.g. representing more than one ecoregion) were used to test the predictive power of the analyses. Results Non‐volant mammal communities divided into clusters that correspond to ecoregions. There was a strong distance effect in the taxonomic structure of communities across the island and within both humid and dry forest communities, but this effect was weak within humid forest communities. Mammalian species richness was significantly lower in dry forest than in humid forest communities. The ecological structure of communities was also correlated with ecoregions. Changes in the relative percentages of omnivory, arboreal quadrupedalism, terrestrial/arboreal quadrupedalism and two body mass classes accounted for 98.1% of the variation in ecological structure. Transitional communities were projected in intermediate positions by the discriminant model. Main conclusions Our analysis demonstrates that the broad‐scale habitat and climate variables captured by the ecoregion model have shaped the assembly of non‐volant mammal communities in Madagascar over evolutionary time. The spatial pattern is consistent with ecological sorting of species ranges along environmental gradients. Historical processes, such as recent extinction and migration, may have also affected the structure of mammal communities, although these factors have played a secondary role.     

Field theory for biogeography: a spatially explicit model for predicting patterns of biodiversity

Predicting the variation of biodiversity across the surface of the Earth is a fundamental issue in ecology, and in this article we focus on one of the most widely studied spatial biodiversity patterns: the species–area relationship (SAR). The SAR is a central tool in conservation, being used to predict species loss following global climate change, and is striking in its universality throughout different geographical regions and across the tree of life. In this article we draw upon the methods of quantum field theory and the foundation of neutral community ecology to derive the first spatially explicit neutral prediction for the SAR. We find that the SAR has three phases, with a power law increase at intermediate scales, consistent with decades of documented empirical patterns. Our model also provides a building block for incorporating non-neutral biological variation, with the potential to bridge the gap between neutral and niche-based approaches to community assembly.
Ecology Letters (2010) 13: 87–95     

The influence of species pools and local processes on the community structure: a test case with woody plant communities in China's mountains

Understanding how patterns of biodiversity vary among taxonomic levels can provide insights into the mechanisms that regulate the assembly of ecological communities. In this study, we examined the scale and environmental dependence of the relationship between number of species and number of genera/families in woody plant communities to investigate the influences of species pool and local ecological processes on the taxonomic structures of local communities. The data we used are based on a large number of forest plots collected across the eastern part of China and the globe. The results showed that the ratio of the number of genera/families:species and the taxonomic exponents, i.e. the exponents of the genus/family–species relationship, were generally lower than null expectations based on the regional species pool, suggesting that abiotic filtering (e.g. environmental filtering and dispersal limitation) is more important than interspecific competition in shaping local communities. The extent of species pool and the area sampled for local communities both influenced our ability to infer whether local ecological processes were important. In particular, the deviation of the taxonomic ratios and exponents between empirical and null patterns increased as the extent of species pool increased, and the taxonomic exponents declined as area of the local community increased, due partly to the reduced effect of interspecific competition. We conclude that regional species pools and local processes both influenced the taxonomic structure of local woody plant communities, but their effects vary substantially among spatial scales.     

Effect of community assembly and primary succession on the species-area relationship in disturbed ecosystems

The species-area relationship (SAR) provides a cornerstone for ecological theory. Implicit in SAR studies is the assumption that SAR properties, especially SAR slopes, remain constant through time, even though the ecosystem characteristics that they encompass–the spatial distribution and abundance of species–change on seasonal to evolutionary time scales. Focusing on disturbed subalpine systems, we evaluated whether SAR properties are a function of stage of succession at Mount St. Helens, WA, and at Gothic, CO. We found that the SAR flattens and shifts upward as these systems mature. The decrease in SAR curvature at Mount St. Helens suggests a transition toward power-law SAR behavior with assembly. Overall, the observed changes in SAR properties raise questions about the appropriateness of applying contemporary SARs to predict future levels of species richness in disturbed or successional systems.     

Spatio‐temporal scaling of biodiversity and the species–time relationship in a stream fish assemblage

1. The increase of species richness with the area of the habitat sampled, that is the species–area relationship, and its temporal analogue, the species–time relationship (STR), are among the few general laws in ecology with strong conservation implications. However, these two scale‐dependent phenomena have rarely been considered together in biodiversity assessment, especially in freshwater systems. 2. We examined how the spatial scale of sampling influences STRs for a Central‐European stream fish assemblage (second‐order Bernecei stream, Hungary) using field survey data in two simulation‐based experiments. 3. In experiment one, we examined how increasing the number of channel units, such as riffles and pools (13 altogether), and the number of field surveys involved in the analyses (12 sampling occasions during 3 years), influence species richness. Complete nested curves were constructed to quantify how many species one observes in the community on average for a given number of sampling occasions at a given spatial scale. 4. In experiment two, we examined STRs for the Bernecei fish assemblage from a landscape perspective. Here, we evaluated a 10‐year reach level data set (2000–09) for the Bernecei stream and its recipient watercourse (third‐order Kemence stream) to complement results on experiment one and to explore the mechanisms behind the observed patterns in more detail. 5. Experiment one indicated the strong influence of the spatial scale of sampling on the accumulation of species richness, although time clearly had an additional effect. The simulation methodology advocated here helped to estimate the number of species in a diverse combination of spatial and temporal scale and, therefore, to determine how different scale combinations influence sampling sufficiency. 6. Experiment two revealed differences in STRs between the upstream (Bernecei) and downstream (Kemence) sites, with steeper curves for the downstream site. Equations of STR curves were within the range observed in other studies, predominantly from terrestrial systems. Assemblage composition data suggested that extinction–colonisation dynamics of rare, non‐resident (i.e. satellite) species influenced patterns in STRs. 7. Our results highlight that the determination of species richness can benefit from the joint consideration of spatial and temporal scales in biodiversity inventory surveys. Additionally, we reveal how our randomisation‐based methodology may help to quantify the scale dependency of diversity components (α, β, γ) in both space and time, which have critical importance in the applied context.     

Multitaxonomic diversity patterns along a desert riparian-upland gradient

Riparian areas are noted for their high biodiversity, but this has rarely been tested across a wide range of taxonomic groups. We set out to describe species richness, species abundance, and community similarity patterns for 11 taxonomic groups (forbs & grasses, shrubs, trees, solpugids, spiders, scarab beetles, butterflies, lizards, birds, rodents, and mammalian carnivores) individually and for all groups combined along a riparian-upland gradient in semiarid southeastern Arizona, USA. Additionally, we assessed whether biological characteristics could explain variation in diversity along the gradient using five traits (trophic level, body size, life span, thermoregulatory mechanism, and taxonomic affiliation). At the level of individual groups diversity patterns varied along the gradient, with some having greater richness and/or abundance in riparian zones whereas others were more diverse and/or abundant in upland zones. Across all taxa combined, riparian zones contained significantly more species than the uplands. Community similarity between riparian and upland zones was low, and beta diversity was significantly greater than expected for most taxonomic groups, though biological traits explained little variance in diversity along the gradient. These results indicate heterogeneity amongst taxa in how they respond to the factors that structure ecological communities in riparian landscapes. Nevertheless, across taxonomic groups the overall pattern is one of greater species richness and abundance in riparian zones, coupled with a distinct suite of species.     

Concordance of species richness patterns among multiple freshwater taxa: a regional perspective

Geographical gradients in species richness and the degree to which different taxa show congruent patterns remain unknown for many taxonomic groups. Here, I examined broad-scale species richness patterns in five groups of freshwater organisms; macrophytes, dragonflies, stoneflies, aquatic beetles and fishes. The analyses were based on provincial distribution records in Denmark, Norway, Sweden and Finland. In general, variation in species richness across provinces was concordant among the groups, but stoneflies showed weaker negative relationships with the other taxonomic groups. Species richness in most groups decreased with increasing latitude and altitude, and a considerable part of the variation was explained by mean July temperature. However, stoneflies showed a reversed pattern, with species richness correlating positively, albeit more weakly, with mean provincial altitude. Nevertheless, combined species richness of all five taxa showed a strong relationship with mean July temperature, accounting for 74% of variation in provincial species richness alone. Such temperature-controlled patterns suggest that regional freshwater biodiversity will strongly respond to climate change, with repercussions for local community organization in freshwater ecosystems in Fennoscandia.     

How does habitat diversity affect the species–area relationship?

Aim   To examine the way in which 'area' and 'habitat diversity' interact in shaping species richness and to find a simple and valid way to express this interaction.
Location   The Natura 2000 network of terrestrial protected areas in Greece, covering approximately 16% of the national territory.
Methods   We used the Natura 2000 framework, which provides a classification scheme for natural habitat types, to quantify habitat heterogeneity. We analysed data for the plant species composition in 16,143 quadrats in which 5044 species and subspecies of higher plants were recorded. We built a simple mathematical model that incorporates the effect of habitat diversity on the species–area relationship (SAR).
Results   Our analysis showed that habitat diversity was correlated with area. However, keeping habitat diversity constant, species richness was related to area; while keeping area constant, species richness was related to habitat diversity. Comparing the SAR of the 237 sites we found that the slope of the species–area curve was related to habitat diversity.
Main conclusions   Discussion of the causes of the SAR has often focused on the primacy of area per se versus habitat heterogeneity, even though the two mechanisms are not mutually exclusive and should be considered jointly. We find that increasing habitat diversity affects the SAR in different ways, but the dominant effect is to increase the slope of the SAR. While a full model fit typically includes a variety of terms involving both area and habitat richness, we find that the effect of habitat diversity can be reduced to a linear perturbation of the slope of the species accumulation curve.     

Random sampling, abundance–extinction dynamics and niche-filtering immigration constraints explain the generation of species richness gradients

Aim  The paradigm that species' patterns of distribution, abundance and coexistence are the result of adaptations of the species to their niches has recently been challenged by evidence that similar patterns may be generated by simple random processes. We argue here that a better understanding of macroecological patterns requires an integration of both ecological and neutral stochastic approaches. We demonstrate the utility of such an integrative approach by testing the sampling hypothesis in a species–energy relationship of forest bird species.
Location  A Mediterranean biome in Catalonia, Spain.
Methods  To test the sampling hypothesis we designed a metacommunity model that reproduces the stochastic sampling from a regional pool to predict local species richness variation. Four conceptually different sampling procedures were evaluated.
Results  We showed that stochastic sampling processes predicted a substantial part (over 40%) of the observed variation in species richness, but left considerable variation unexplained. This remaining variation in species richness may be better understood as the result of alternative ecological processes. First, the sampling model explained more variation in species richness when the probability that a species colonises a new locality was assumed to increase with its niche width, suggesting that ecological differences between species matter when it comes to explaining macroecological patterns. Second, extinction risk was significantly lower for species inhabiting high-energy regions, suggesting that abundance–extinction processes play a significant role in shaping species richness patterns.
Main conclusions  We conclude that species–energy relationships may not simply be understood as a result of either ecological or random sampling processes, but more likely as a combination of both.     

Bacterial communities in larger islands have reduced temporal turnover

Patterns of species diversity provide fundamental insights into the underlying mechanisms and processes that regulate biodiversity. The species–time relationship (STR) has the potential to be one such pattern; in a comparable manner to its more extensively studied spatial analogue, the species–area relationship (SAR), which has been pivotal in the development of ecological models and theories. We sought to determine the mechanisms and processes that underpin STR patterns of temporal turnover by sampling bacterial communities within ten water-filled tree-holes on the same European beech tree through the course of a year. We took this natural model system to represent an archipelago of islands of varying sizes and with shared common immigration sources. We observed an inverse relationship between STR-derived turnover rates and island size. Further, turnover was related to island size and not island isolation within the study system as indicated by a low frequency of dispersal limitation and high homogenizing dispersal. Compared to SARs, STRs are understudied, as such, the findings from the current study should provide a renewed interest in STR-based patterns and processes.Subject terms: Microbial ecology, Microbial ecology     

Non-randomness in the species–area relationship: testing the underlying mechanisms

The species–area relationship (SAR) is one of the best documented patterns in ecology. However, interrelations between the SAR and species distributions are largely unexplored. This research was aimed (1) to assess if the SAR for a group of sedentary insects is associated to a random or non-random distribution of species across islands in a land-bridge archipelago, and (2) to investigate possible factors responsible for the non-randomness. Communities of tenebrionid beetles on the Aegean Islands (Greece) were studied as a case of a relict fauna. Three aspects of non-randomness were analysed: (1) non-random variation of species richness in the SAR, (2) degree of nestedness and (3) presence of special patterns of co-occurrence. Species co-occurrence and nestedness analyses indicated that historical aspects, as opposed to interspecific competition or distance-mediated colonization events, have moulded these species distributions.     

The 29°N latitudinal line: an important division in the Hengduan Mountains, a biodiversity hotspot in southwest China

This paper aimed to explore the division of the southern and northern Hengduan Mountains based on gradients in species similarity and richness, and to analyze species richness in each sub-region. The Hengduan Mountain region was divided into nine latitudinal belts using one degree of latitude to define the belt after which distribution of seed plants within each latitudinal belt was recorded. Latitudinal patterns of species similarity were measured using the Jaccard similarity index for each pair of adjacent latitudinal belts. Non-metric multidimentional scaling (NMDS) was also used to analyze the similarity in species composition among the nine latitudinal belts. The latitudinal pattern of species similarity and the NMDS ordination both showed a great change in species composition across the 29°N latitudinal line, essentially dividing the Hengduan Mountain region into southern and northern sub-regions. Species richness, shown by the c-value of the species–area power function, and species–area ratio along a latitudinal gradient both showed a sharp decrease across the latitudinal belt from 29°0' to 29°59'N. The southern sub-region occupied 40% of the total area of the Hengduan Mountain region, but contained more than 80% of all the seed plants in the region. The higher species richness and endemism in the southern sub-region showed it to be the core of the Hengduan biodiversity hotspot, a result not unexpected because of the greater extremes of topography and wider diversity of habitats in the southern portion.     

面积、温度及分布区限制对物种丰富度海拔格局的影响: 以秦岭太白山为例

 物种丰富度的分布格局及其形成机制是生态学研究的热点。以往的研究主要描述丰富度的格局, 而对其形成机制研究较少, 且主要集中于探讨单个因子或过程的影响。物种丰富度同时受到多个因子和过程的综合作用, 面积、温度及物种分布区限制被认为是控制山地物种丰富度海拔格局的主要因素, 三者同时沿海拔梯度而变化, 同时作用于丰富度的海拔格局。幂函数种-面积关系(SAR)、生态学代谢理论(MTE)及中域效应假说(MDE)分别基于以上3个因素, 从机制上解释了物种丰富度 的海拔格局。探讨这些假说的相对影响对研究物种丰富度的大尺度格局及其形成机制具有重要意义。方差分离方法有利于分解不同因素的影响, 为此, 该文以秦岭太白山的植物物种丰富度为例, 采用方差分离和逐步回归方法, 分析了SAR、MTE及MDE对物种丰富度海拔格局的影响。结果表明, 太白山的植物物种丰富度沿海拔梯度呈单峰分布格局, 但丰富度峰值存在类群差异; 对太白山所有植物物种丰富度的垂直格局而言, SAR、MTE及MDE分别解释了其物种丰富度随海拔变化的66.4%、19.8%和37.9%, 共同解释了84.6%, 在消除其他因素的影响后, SAR和MTE的独立影响较高(分别为25.5%和17.7%), 而MDE的独立影响不显著; 分类群研究则发现, 苔藓植物丰富度的海拔格局主要受MDE的影响, 蕨类植物丰富度的海拔格局同时受到SAR、MTE以及MDE的影响, 而种子植物物种丰富度的海拔格局主要受SAR和MTE影响。     

Decomposing the process of species accumulation into area dependent and time dependent parts

In 1960, Preston predicted that the process of species accumulation in time (species–time relationship, STR) should be similar to the species–area relationship (SAR) and follow a power function with a slope of about 0.26. Here these two conjectures are tested using data of the spatiotemporal species accumulation in a local community of beech forest Hymenoptera. A power function species–area–time model of the form S = S₀ A^z t gave better fits to observed species numbers than a simple power function SAR model, and was able to predict similar species turnover rates (about 9% per year) to those inferred by other methods. The STR was well fitted by a power function, although due the limited time span (8 years) a logarithmic STR pattern cannot be ruled out. STR slopes ranged between 0.01 and 0.23 and were lower than predicted by Preston. Temporal species turnover appeared to be negatively correlated to species densities and positively correlated to species body weights. Ecological guild and taxon membership did not significantly influence temporal species turnover.     

Diversity-stability relationship varies with latitude in zooplankton

Analyses of temporal patterns of diversity across a wide range of taxa have found that more diverse communities often show smaller compositional changes over time. This generality indicates that high diversity is associated with greater temporal stability in species composition. We examined patterns of diversity and community stability in zooplankton time series data from 36 lakes sampled over a combined 483 years. The species–time relationship was flatter in more species-rich lakes in the temperate zone. However, high-latitude lakes had both low richness and low turnover. These patterns were consistent for turnover both within and among years. Daily, annual and long-term richness were all higher in large lakes while turnover was unaffected by the surface area. Richness on all time scales, as well as turnover within and among years, all declined at high latitude. Species–area relations and latitudinal gradients in richness therefore reflect different temporal components of diversity. Our results suggest that diversity shows strong associations with compositional stability that vary qualitatively across biogeographical provinces. Community stability increases with diversity among lakes in the temperate zone; however, the two are negatively correlated across latitudinal gradients. These patterns indicate that either the direct effects of diversity on stability or their covariance with environmental fluctuations vary with latitude.