Patterns Of Species Turnover Research Articles

Seasonal Change of Species Diversity Patterns of Non‐volant Small Mammals along Three Subtropical Elevational Gradients

AbstractOur understanding of geographic patterns of species diversity and the underlying mechanisms is increasing rapidly, whereas the temporal variation in these patterns remains poorly understood. We examined the seasonal species richness and species turnover patterns of non‐volant small mammals along three subtropical elevational gradients in southwest China. Small mammal diversity was surveyed in two seasons (early wet season and late wet season) using a standardized sampling protocol. The comparison of species richness patterns between two seasons indicated a temporal component in magnitude and shape, with species richness at high elevations clearly increased during the late wet season. Species richness demonstrated weak correlations with modelled temperature and precipitation. The elevational pattern of species turnover measured by Chao‐Sørenson similarity index also changed seasonally, even though the temporal pattern varied with scale. Species turnover between neighboring elevations at high elevations was slower in the late wet season. Meanwhile, there was an acceleration of species turnover along the whole range of the gradient. The seasonal change in species diversity patterns may be due to population‐level increases in abundance and elevational migration, whereas seasonal variation in factors other than temperature and precipitation may play a greater role in driving seasonal diversity patterns. Our study strongly supports the seasonality in elevational patterns of small mammal diversity in subtropical montane forests. Thus it is recommended that subsequent field surveys consider temporal sampling replicate for elevational diversity studies.

Contribution of environmental filtering and dispersal limitation to species turnover of temperate deciduous broad‐leaved forests in China

AbstractQuestionsHow and to what extent do environmental filtering and dispersal limitation affect species turnover among sites in the temperate deciduous broad‐leaved forests of China? Do different life forms respond to environmental filtering and dispersal limitation in the same way?LocationSeventeen mountains (31°8′–44°22′N, to 104°42′–128°8′E) in China.MethodsWe measured the plant species composition of 495 plots. We calculated the Jaccard's similarity (SJac) of species composition, geographic distance (Dg) and environmental divergence (De) for each plot pair for trees, shrubs and herbs. Three plot pair groups were distinguished: (1) plot pairs with both plots from the same mountain; (2) plot pairs with two plots from different mountains but with a similar environment; (3) plot pairs with two plots from different mountains and with a heterogeneous environment. We analysed the relationship between SJac, Dg and De for all three groups, and performed partial redundancy analysis. We also calculated beta‐diversity of mountains, and explored latitudinal and climatic patterns of beta‐diversity.ResultsSJac decreases significantly with both De and Dg for all three plot pair groups. Environmental and geographic variables together explain 13.8%, 11.6% and 11.1% of variance in species composition of trees, shrubs and herbs, respectively. For all life forms, environment explains more variance than geography, and environment and geography have strong co‐varying effects. The beta‐diversity for each mountain decreases with latitude, but increases with mean annual temperature (MAT).ConclusionEnvironmental filtering rather than dispersal limitation predominantly regulates patterns of species turnover in the temperate deciduous broad‐leaved forests of China. Furthermore, the increases of beta‐diversity along MAT also support the effects of environment on species turnover. These results indicate that environment might influence the distribution of most species in temperate forests of China. However, dispersal limitation still independently accounts for a small amount of variance in species turnover. We therefore conclude that environmental filtering and dispersal limitation have both combined and independent effects, but environmental filtering is more important in shaping the community assembly of temperate deciduous broad‐leaved forests of China.

Evaluation of Current Approaches to Stream Classification and a Heuristic Guide to Developing Classifications of Integrated Aquatic Networks

Conservation and management of fresh flowing waters involves evaluating and managing effects of cumulative impacts on the aquatic environment from disturbances such as: land use change, point and nonpoint source pollution, the creation of dams and reservoirs, mining, and fishing. To assess effects of these changes on associated biotic communities it is necessary to monitor and report on the status of lotic ecosystems. A variety of stream classification methods are available to assist with these tasks, and such methods attempt to provide a systematic approach to modeling and understanding complex aquatic systems at various spatial and temporal scales. Of the vast number of approaches that exist, it is useful to group them into three main types. The first involves modeling longitudinal species turnover patterns within large drainage basins and relating these patterns to environmental predictors collected at reach and upstream catchment scales; the second uses regionalized hierarchical classification to create multi-scale, spatially homogenous aquatic ecoregions by grouping adjacent catchments together based on environmental similarities; and the third approach groups sites together on the basis of similarities in their environmental conditions both within and between catchments, independent of their geographic location. We review the literature with a focus on more recent classifications to examine the strengths and weaknesses of the different approaches. We identify gaps or problems with the current approaches, and we propose an eight-step heuristic process that may assist with development of more flexible and integrated aquatic classifications based on the current understanding, network thinking, and theoretical underpinnings.

Shared patterns of species turnover between seaweeds and seed plants break down at increasing distances from the sea

We tested for correlations in the degree of spatial similarity between algal and terrestrial plants communities along 5500 km of temperate Australian coastline and whether the strength of correlation weakens with increasing distance from the coast. We identified strong correlations between macroalgal and terrestrial plant communities within the first 100 km from shore, where the strength of these marine–terrestrial correlations indeed weakens with increasing distance inland. As such, our results suggest that marine-driven community homogenization processes decompose with increasing distance from the shore toward inland. We speculate that the proximity to the marine environment produces lower levels of community turnover on land, and this effect decreases progressively farther inland. Our analysis suggests underlying ecological and evolutionary processes that give rise to continental-scale biogeographic influence from sea to land.

Biogeographical regions and phytogeography of the eucalypts

AbstractAimTo map spatial patterns of species richness, species endemism and species turnover of the eucalypts; to propose a biogeographical regionalization of eucalypts based on species turnover; and to identify the environmental correlates of these patterns.LocationAustralia andMalesia.MethodsWe analysed 798 eucalypt species (Angophora,CorymbiaandEucalyptus) with distributions acrossAustralia andMalesia using square cells with a resolution of 100 × 100 km. Species richness, endemism and species turnover were calculated. Phytogeographical regions were identified using an agglomerative cluster analysis derived from a matrix of pairwiseSimpson's beta (βsim) dissimilarity values. Eleven environmental variables were used to analyse the environmental correlates of species turnover. Non‐metric multidimensional scaling (NMDS) of the βsim,Getis‐OrdGi* hotspot spatial statistics and an ordination of the βsim‐NMDSwere used to investigate the environmental drivers at the continental level and for each of the phytogeographical regions.ResultsWe identified three centres of species richness and fourteen of endemism, of which several are newly identified. The main centres of species richness agree with previous studies. Six major eucalypt phytogeographical regions are proposed based on the species turnover: monsoon, tropical/subtropical, south‐east, south‐west,Eremaean north andEremaean south. These findings are supported by significant environmental differences of theNMDSvectors and theGi* statistics. The environmental drivers of species turnover are broadly consistent with the continental patterns of summer and winter rainfall below and above theTropic ofCapricorn.Main conclusionsThe proposed phytogeographical regions are similar to theAustralian biomes. Climate is the main driver of the phytogeographical regions, varying from region to region. Comprehensive bioregionalization frameworks and phytogeography updates, as proposed here, are fundamental for enhancing our understanding of the spatial distribution of biodiversity and therefore benefit global biogeography and help planners to identify regions of high conservation relevance.

Spatial and temporal variability in species richness in a temperate intertidal community

Understanding changes in estuarine benthic communities has important implications for conservation and yet it is a challenge due to the high natural variability of these systems. We addressed this challenge through the study of temporal and spatial patterns of species richness in an intertidal benthic community in New Zealand North Island. Five different locations within the estuary were monitored seasonally over 12 yr. This data set allowed the study of species–time–area relationships (STAR) and the delineation of patterns in species richness, heterogeneity and turnover in space and time. The site with the highest species richness also had the highest within‐site heterogeneity in species richness, a high number of species occurring infrequently in time, the lowest mud content and the most variable wave climate. Similarities and differences between sites were generally maintained over time, although seasonal and multi‐year patterns in species richness occurred at all sites. The STAR showed a significant negative interaction between space and time, with species accumulation rates in space and time being equivalent at 4 spatial replicates (250 m2) and 2 temporal replicates (6 months). The lowest source of variability in species turnover was within site, and the highest source was over years. This was reflected in the lack of an asymptotic relationship in the species accumulation curve despite the 12 yr of monitoring. These results contribute to the knowledge of the variability in diversity patterns in estuaries and have important implications for long‐term monitoring of natural communities and the estimation of diversity for conservation.

Species turnover and geographic distance in an urban river network

AbstractAimUnderstanding the relationships between species turnover, environmental features and the geographic distance between sites can provide important insights into the processes driving species diversity. This is particularly relevant where the effective distance between sites may be a function of the habitat or topographic features of the landscape and the means of dispersal of the organism. River networks, in particular in human‐modified landscapes, are a striking example of such a situation. Here, we use data for both aquatic and terrestrial organisms across an urban river network to examine patterns of species turnover and to determine whether these patterns differ between different taxonomic groups.LocationSheffield area, UK.MethodsAquatic (macroinvertebrates, diatoms) and terrestrial (birds, plants, butterflies) organisms were surveyed at 41 sites across an urban river network. We assessed the relationship between turnover and three alternative geographic distance measures (Euclidean, network and flow distance), whilst also taking into account the environmental distance between sites, using Mantel and partial Mantel tests.ResultsTurnover of all taxonomic groups apart from butterflies was significantly correlated with at least one measure of geographic distance. The aquatic taxonomic groups showed the strongest correlations with the geographic distance measures, and in particular with network distance. Terrestrial taxa were more closely associated with environmental than any of the geographic distance measures, although network distance remained significant for birds and some plant groups after removing the effect of environmental distance. Water‐dispersed and neophyte plant groups were significantly related to network and flow distance.Main conclusionsThe results suggest that aquatic communities are strongly influenced by spatial processes occurring within the river network. Terrestrial taxa have a more complex relationship with distance, with different components of these communities displaying different responses. Nevertheless, it is clear that connectivity along the river corridor is important for both aquatic and terrestrial communities.

A biogeographical regionalization of Australian Acacia species

AbstractAimTo develop a biogeographical regionalization of Australian Acacia species and to investigate their environmental correlates.LocationAustralia.MethodsWe used a previously published framework for delineating biogeographical regions. We calculated species turnover patterns of 1020 Australian Acacia species with distributions estimated from 171,758 georeferenced herbarium records aggregated to 100 km × 100 km cells (868 across Australia). An agglomerative cluster analysis using a matrix of pairwise Simpson's beta (βsim) dissimilarity values was applied. Eleven environmental variables at the same resolution as the aggregated herbarium records were used to explore the correlates of the βsim patterns using a non‐metric multidimensional scaling (NMDS) analysis. We also used an ANOVA to test the significance of the environmental changes between each pair of biogeographical regions.ResultsFive major Acacia biogeographical regions were proposed. These bioregions were broadly similar to the biomes of Australia. A new subdivision of the Eremaean biome was proposed for Acacia. The most influential environmental variables for the individual bioregions were: (1) temperature seasonality and topographic flatness for the south‐western temperate bioregion; (2) precipitation during the coldest quarter of the year for the south‐eastern temperate bioregion; (3) annual precipitation, annual mean temperature and precipitation seasonality for the monsoonal bioregion; and (4) percentage of sand in the top 30 cm of the soil, rock grain size, annual mean radiation and annual mean temperature for the Eremaean south and north regions. The NMDS analysis provided support for the observed biogeographical patterns. The statistical test showed a highly significant difference between the environments of the proposed bioregions. Climatic variables were consistent predictors across regions, whereas the influence of soils and topographic features varied among bioregions.Main conclusionsThe major Acacia biogeographical regions correspond well to historical bioregionalizations, suggesting that the environmental drivers of diversification in Acacia are broadly similar to those that act on the flora as a whole. Climate seasonality combined with annual values and non‐climatic factors provide support for the proposed biogeographical regionalization for Acacia.

Tenebrionid beetle distributional patterns in Italy: multiple colonisation trajectories in a biogeographical crossroad

Abstract Placed in the centre of the Mediterranean Basin, Italy is a complex biogeographical crossroad between North Western Europe, Central Europe, Eastern Europe and North Africa. The distribution of 280 species and subspecies of tenebrionid beetles in 17 Italian natural regions was used to study the influence of climatic, spatial and historical (palaeogeographical and palaeoecological) factors on current patterns of species richness, endemism and turnover (i.e. inter‐regional biogeographical differences). In accordance with the general latitudinal pattern of biodiversity in Europe, both tenebrionid richness and endemism increase southwards, in response to variations in rainfall and temperatures, as expected for thermo‐xerophilic animals. Turnover was correlated with both inter‐regional climatic dissimilarities and geographical distances. The importance of spatial relationships independent from climate, but consistent with palaeogeographical and palaeoecological history, was also confirmed by inter‐regional relationships based on all species and endemics only. Biogeographical similarities between Italian regions and adjacent European and North African source areas showed distinct geographical patterns which reflect various dispersal trajectories. During the Pleistocene glacials, cold adapted species coming from northern areas via the Alps used the Apennines as a filter to disperse into central and southern Italy, thereafter remaining confined to high altitude areas after deglaciation. Xero‐thermophilic species coming from North Africa or east Mediterranean countries colonised southern Italian regions probably in more ancient times. Islands and southern areas acted as centres of both speciation and post‐glacial recolonisation.

RECAMBIO TEMPORAL DE ESPECIES DE LEPIDÓPTEROS NOCTURNOS EN FUNCIÓN DE LA TEMPERATURA Y LA HUMEDAD EN UNA ZONA DE SELVA CADUCIFOLIA EN YUCATÁN, MÉXICO

El principal objetivo de este trabajo es cuantificar el recambio temporal de mariposas nocturnas y su relación con dos gradientes ambientales: temperatura (° C) y humedad relativa (%). Utilizando una trampa de luz se realizó un muestreo por un periodo de 12 meses de una comunidad de mariposas nocturnas en la Reserva Biocultural Kaxil Kiuic (RBKK), ubicada enYucatán, México. Se observó que el recambio de especies exhibe un marcado patrón temporal en relación con la variación de la temperatura y humedad relativa entre periodos climáticos. El periodo cálido y seco (marzo a julio) presentó la mayor disimilitud en la composición de especies, determinada principalmente por las familias: Noctuidae, Crambidae y Geometridae. Los resultados obtenidos tienen implicaciones para la conservación de la biodiversidad de mariposas nocturnas, ya que permiten establecer una línea base enfocada a detectar la influencia de las variaciones climáticas sobre la composición de especies.

Comparing the Response of Birds and Butterflies to Vegetation-Based Mountain Ecotones Using Boundary Detection Approaches

Mountains provide an opportunity to examine changes in biodiversity across environmental gradients and areas of transition (ecotones). Mountain ecotones separate vegetation belts. Here, we aimed to examine whether transition areas for birds and butterflies spatially correspond with ecotones between three previously described altitudinal vegetation belts on Mt. Hermon, northern Israel. These include the Mediterranean Maquis, xero-montane open forest and Tragacanthic mountain steppe vegetation belts. We sampled the abundance of bird and butterfly species in 34 sampling locations along an elevational gradient between 500 and 2200 m. We applied wombling, a boundary-detection technique, which detects rapid changes in a continuous variable, in order to locate the transition areas for bird and butterfly communities and compare the location of these areas with the location of vegetation belts as described in earlier studies of Mt. Hermon. We found some correspondence between the areas of transition of both bird and butterfly communities and the ecotones between vegetation belts. For birds and butterflies, important transitions occurred at the lower vegetation ecotone between Mediterranean maquis and the xero-montane open forest vegetation belts, and between the xero-montane open forest and the mountain steppe Tragacanthic belts. While patterns of species turnover with elevation were similar for birds and butterflies, the change in species richness and diversity with elevation differed substantially between the two taxa. Birds and butterflies responded quite similarly to the elevational gradient and to the shift between vegetation belts in terms of species turnover rates. While the mechanisms generating these patterns may differ, the resulting areas of peak turnover in species show correspondence among three different taxa (plants, birds and butterflies).

Functional beta-diversity patterns reveal deterministic community assembly processes in eastern North American trees

Aim Determining the relative influence of niche-based and neutral processes in driving the spatial turnover of community composition is a central challenge in community ecology. Spatial patterns of functional turnover, or functional beta diversity, may capture important signals of niche-based assembly processes, but these patterns have not been quantified for communities across broad geographic and environmental gradients. Here, we analyse continental-scale patterns of species and functional beta diversity in relation to space and the environment to assess the relative importance of niche-based and neutral community assembly mechanisms. Location Eastern North America. Methods We use a continental-scale forest plot dataset and functional trait data to quantify spatial patterns of species and functional beta diversity. We use redundancy analysis-based variance partitioning to evaluate the influence of space, soil and climate on beta-diversity metrics. We use a null model approach to test for non-random functional beta diversity given the observed patterns of species turnover across spatial scales. Results Species and functional beta diversity increased with increasing geographic distance (i.e. distance decay of community similarity). Results of variance partitioning analysis show that species and functional beta diversity were spatially structured and significantly related to environmental, particularly climatic, variation. Results of null model analysis show that functional beta diversity was lower than expected based on species turnover at fine scales (< 600 km) and higher than expected at broad scales (> 1800 km). Main conclusions The observed patterns of functional beta diversity support a niche-based model of community assembly, driven by the deterministic filtering of species across environmental gradients based on their functional traits.

The relationship of tropical bird communities to tree species composition and vegetation structure along an Andean elevational gradient

AbstractAimUnderstanding patterns of species turnover along environmental gradients and their consistency across taxonomic groups is central to the study of biodiversity. We may expect congruence in diversity patterns across groups whose ranges could be influenced by species interactions. We explore associations between bird and vegetation communities in the tropical Andes to determine whether patterns of species richness and turnover in birds and trees are congruent with elevation, and whether tree species composition, vegetation structure, elevation, or a combination of these best predicts bird species composition.LocationA forested 2600‐m elevational gradient on the eastern slope of the Peruvian Andes.MethodsBird surveys and vegetation measurements were conducted at 172 points, and a subset of these were spatially matched with fourteen 1‐ha tree inventory plots. Diversity patterns were described for trees, birds, and avian foraging guilds. We used dissimilarity matrices to examine patterns of turnover and nestedness. Turnover of birds and trees was examined by comparing compositional change of adjacent plots along the gradient. Multiple regression on distance matrices was employed to determine contributions of tree species composition, vegetation structure and elevation to explaining variation in bird species composition.ResultsSpecies richness was higher for trees than for birds, and whereas diversity in both taxa decreased with elevation, tree richness showed a low‐elevation plateau before declining at higher elevations. Tree species had narrower distributions compared to birds, but patterns of turnover were largely congruent between taxa. Nestedness contributed much less to dissimilarity than turnover, although birds showed higher nestedness, particularly at high elevations. Tree species composition, elevation and vegetation structure were all important predictors of bird species composition; the best model explained 78% of bird dissimilarity across plots. Tree species composition was always included in the best models, for all birds and foraging guilds.Main conclusionsOur assessment of Andean bird and vegetation communities suggests strong correspondence, perhaps due to direct interactions or similar underlying drivers. We hypothesize that with climate change, range shifts in these groups may not occur independently. Rather, birds may have delayed upslope shifts or may be limited to high‐elevation patches where appropriate vegetation communities exist.

Geography, environment, and spatial turnover of species in China's grasslands

Environment and spatial processes are key factors in shaping species composition in a community. These two factors make competing predictions concerning the decay of species composition similarity with environmental divergence and geographic distance. Unfortunately, these can be difficult to test independently because changes in environment are commonly well correlated with geographic distance. However, an opportunity is provided by exploiting marked regional differences in the spatial structure of the environment. In this study, we test the predictions of environment filtering and dispersal in explaining species turnover using &gt; 300 study sites spanning ˜4000 km, across three major grasslands in China in which the environment is spatially structured to different degrees. We find that species composition similarity decayed with environmental divergence in the same way in all three regions, and even across biogeographic regions between which dispersal barriers are evident; in contrast, the decay of species composition similarity with geographic distance depended largely on the spatial structure of the environment. We conclude that, at the scale of study, environmental filtering rather than spatial processes best explains patterns of species turnover in China's grasslands.

Long-Term Observations of Epibenthic Fish Zonation in the Deep Northern Gulf of Mexico

A total of 172 bottom trawl/skimmer samples (183 to 3655-m depth) from three deep-sea studies, R/V Alaminos cruises (1964–1973), Northern Gulf of Mexico Continental Slope (NGoMCS) study (1983–1985) and Deep Gulf of Mexico Benthos (DGoMB) program (2000 to 2002), were compiled to examine temporal and large-scale changes in epibenthic fish species composition. Based on percent species shared among samples, faunal groups (≥10% species shared) consistently reoccurred over time on the shelf-break (ca. 200 m), upper-slope (ca. 300 to 500 m) and upper-to-mid slope (ca. 500 to 1500 m) depths. These similar depth groups also merged when the three studies were pooled together, suggesting that there has been no large-scale temporal change in depth zonation on the upper section of the continental margin. Permutational multivariate analysis of variance (PERMANOVA) also detected no significant species changes on the limited sites and areas that have been revisited across the studies (P>0.05). Based on the ordination of the species shared among samples, species replacement was a continuum along a depth or macrobenthos biomass gradient. Despite the well-known, close, negative relationship between water depth and macrofaunal biomass, the fish species changed more rapidly at depth shallower than 1,000 m, but the rate of change was surprisingly slow at the highest macrofaunal biomass (>100 mg C m−2), suggesting that the composition of epibenthic fishes was not altered in response to the extremely high macrofaunal biomass in the upper Mississippi and De Soto Submarine Canyons. An alternative is that the pattern of fish species turnover is related to the decline in macrofaunal biomass, the presumptive prey of the fish, along the depth gradient.

Severe loss of suitable climatic conditions for marsupial species in Brazil: challenges and opportunities for conservation.

A wide range of evidences indicate climate change as one the greatest threats to biodiversity in the 21st century. The impacts of these changes, which may have already resulted in several recent species extinction, are species-specific and produce shifts in species phenology, ecological interactions, and geographical distributions. Here we used cutting-edge methods of species distribution models combining thousands of model projections to generate a complete and comprehensive ensemble of forecasts that shows the likely impacts of climate change in the distribution of all 55 marsupial species that occur in Brazil. Consensus projections forecasted range shifts that culminate with high species richness in the southeast of Brazil, both for the current time and for 2050. Most species had a significant range contraction and lost climate space. Turnover rates were relatively high, but vary across the country. We also mapped sites retaining climatic suitability. They can be found in all Brazilian biomes, especially in the pampas region, in the southern part of the Brazilian Atlantic Forest, in the north of the Cerrado and Caatinga, and in the northwest of the Amazon. Our results provide a general overview on the likely effects of global climate change on the distribution of marsupials in the country as well as in the patterns of species richness and turnover found in regional marsupial assemblages.

Geographical patterns and partition of turnover and richness components of beta-diversity in faunas from Tocantins river valley

There has been a resurging interest in patterns of β-diversity, especially by the mechanisms driving broad-scale, continental and global patterns, and how partitioning β-diversity into richness (or nestedness) and turnover components can be linked with such mechanisms. Here we compared two recent methodologies to find richness and turnover components of β-diversity, using a large regional scale dataset of mammal, bird, reptiles and amphibian species found in seven regions of Central, North and Northeastern Brazil. As well as a simple comparison of the metrics available, we analyzed spatial patterns (i.e., distance-decay similarity) and the effects of biome type in these components using raw and partial Mantel tests. Our analyses revealed that turnover estimated using Baselga's (2010) approach is slightly higher than the estimate using Carvalho's et al. (2012) approach, but all analyses show consistent spatial patterns in species turnover using both methods. Spatial patterns in β-diversity revealed by Mantel tests are also consistent with expectations based on differential dispersal abilities. Our results also reinforce that spatial patterns in β-diversity, mainly in the turnover components expressing faunal differentiation, are determined by a mix or broad scale environmental effects and short distance spatially-structured dispersal.

Effects of water and nitrogen addition on species turnover in temperate grasslands in northern China.

Global nitrogen (N) deposition and climate change have been identified as two of the most important causes of current plant diversity loss. However, temporal patterns of species turnover underlying diversity changes in response to changing precipitation regimes and atmospheric N deposition have received inadequate attention. We carried out a manipulation experiment in a steppe and an old-field in North China from 2005 to 2009, to test the hypothesis that water addition enhances plant species richness through increase in the rate of species gain and decrease in the rate of species loss, while N addition has opposite effects on species changes. Our results showed that water addition increased the rate of species gain in both the steppe and the old field but decreased the rates of species loss and turnover in the old field. In contrast, N addition increased the rates of species loss and turnover in the steppe but decreased the rate of species gain in the old field. The rate of species change was greater in the old field than in the steppe. Water interacted with N to affect species richness and species turnover, indicating that the impacts of N on semi-arid grasslands were largely mediated by water availability. The temporal stability of communities was negatively correlated with rates of species loss and turnover, suggesting that water addition might enhance, but N addition would reduce the compositional stability of grasslands. Experimental results support our initial hypothesis and demonstrate that water and N availabilities differed in the effects on rate of species change in the temperate grasslands, and these effects also depend on grassland types and/or land-use history. Species gain and loss together contribute to the dynamic change of species richness in semi-arid grasslands under future climate change.

Pattern detection in null model analysis

SynthesisThe identification of distinctive patterns in species x site presence‐absence matrices is important for understanding meta‐community organisation. We compared the performance of a suite of null models and metrics that have been proposed to measure patterns of segregation, aggregation, nestedness, coherence, and species turnover. We found that any matrix with segregated species pairs can be re‐ordered to highlight aggregated pairs, indicating that these seemingly opposite patterns are closely related. Recently proposed classification schemes failed to correctly classify realistic matrices that included multiple co‐occurrence structures. We propose using a combination of metrics and decomposing matrix‐wide patterns into those of individual pairs of species and sites to pinpoint sources of non‐randomness.Null model analysis has been a popular tool for detecting pattern in binary presence–absence matrices, and previous tests have identified algorithms and metrics that have good statistical properties. However, the behavior of different metrics is often correlated, making it difficult to distinguish different patterns. We compared the performance of a suite of null models and metrics that have been proposed to measure patterns of segregation, aggregation, nestedness, coherence, and species turnover. We found that any matrix with segregated species pairs can be re‐ordered to highlight aggregated pairs. As a consequence, the same null model can identify a single matrix as being simultaneously aggregated, segregated or nested. These results cast doubt on previous conclusions of matrix‐wide species segregation based on the C‐score and the fixed‐fixed algorithm. Similarly, we found that recently proposed classification schemes based on patterns of coherence, nestedness, and segregation and aggregation cannot be uniquely distinguished using proposed metrics and null model algorithms. It may be necessary to use a combination of different metrics and to decompose matrix‐wide patterns into those of individual pairs of species or pairs of sites to pinpoint the sources of non‐randomness.

How does plant species composition change from year to year? A case study from the herbaceous layer of a submediterranean oak woodland

Over millions of years there is a long-term increase in species richness, accompanied by substantial turnover in species composition. However, little is known about species temporal turnover over shorter, ecologically relevant time periods, such as years. In the present study, we examine the inter-annual temporal turnover in species composition in 100 m2 plots of the herbaceous layer in a submediterranean oak woodland over six years. We found that approximately half of the accumulated number of species over the six years is accommodated as temporal turnover. We also found that species temporal turnover in undisturbed control plots was not significantly different from that in plots where vegetation was recovering naturally without assistance, i.e., plots undergoing ecological succession. Only in the most disturbed (continuously overgrazed) plots temporal turnover was low to non-existent. We therefore suggest that diversity estimates based on a single year of observations may seriously underestimate species richness or the detrimental effects of disturbance, at least at the 100 m2 scale. Furthermore, we found that, with the exception of the heavily grazed plots, short-lived species (annuals and biennials) did not display significantly greater temporal turnover than long-lived (perennial) species. Our analysis also supports that the space for time substitution applies in the patterns of species turnover. Spatial species turnover was comparable to temporal turnover. Species that are observed in many plots are also present in many years, and vice versa. Also, the similarity in species composition decreased as the time period between observations increased, as is the case with distance decay. Overall we conclude that the patterns of species turnover in time resemble those in space, and thus temporal turnover makes an important contribution to total biodiversity that should not be ignored.