Changes In Species Occurrence Research Articles

Changes in waterbird occurrence and abundance at their northern range boundaries in response to climate warming: importance of site area and protection status

AbstractClimate warming is driving changes in species distribution, but habitat characteristics can interact with warming temperatures to affect populations in unexpected ways. We investigated wintering waterbird responses to climate warming depending on habitat characteristics, with a focus on the northern boundary of their non‐breeding distributions where winter climatic conditions are more extreme. At these Nordic latitudes, climate warming is expected to drive positive changes in species occurrence and abundance, with likely differences in species‐specific responses. We analyzed the occurrence and abundance of 18 species of waterbirds monitored over 2,982 surveys at 245 inland wetlands over a 25‐year period in Sweden. We used hierarchical modeling of species communities (HMSC) which enabled us to relate species‐specific changes to both functional traits and phylogenetic relatedness. We investigated occurrence and abundance changes in response to average temperature, temperature anomalies, site area, site protection status (Natura 2000), and land use in agricultural and urban surfaces. Unsurprisingly, both average temperatures and temperature anomalies were the most important variables influencing positively waterbird occurrence and abundance. For 60% of the species, the effect of temperature anomalies was even stronger in large or protected wetlands. Geese and mallard occurred more often at sites surrounded by agricultural and urban surfaces, respectively, but their occurrence in these habitats was not affected by interactive effects with climate warming. Species abundance was greater inside protected areas only for 11% of the species, but occurrence probability was higher inside protected areas for 44% of the species. Overall, we observed that species thermal affinity was a strong predictor for positive species response to temperature anomalies, and that species sharing similar phylogenetic history had similar relationships with environmental variables. Protection of large wetlands and restoration of the surrounding habitats are two targets for climate change adaptation strategies to facilitate future responses of waterbirds to climate warming.

Underprediction of extirpation and colonisation following climate and land‐use change using species distribution models

AbstractAimTo evaluate the performance of species distribution models in predicting observed colonisations, persistences and extirpations in response to changes in climate and land use over a multi‐decadal period.LocationSweden.MethodsWe use historical (early 20th century) land use and climate data to build species distribution models for 84 plant species across three provinces of Sweden. Model performance was then evaluated internally using a subset of the historical data for cross‐validation, as well as by using the models to project occurrences to the modern day and validating them with observed occurrences from 1990 to 2020. We then analysed predicted and observed occurrences in the modern period in terms of persistence, extirpation (local extinction) and colonisation in relation to species' habitat and climate associations.ResultsWe found overall high agreement between evaluation methods, although internal evaluation gave consistently higher values for model performance (using true skill statistic, TSS). Overall, extirpations were worst predicted, with on average fewer than one‐third of each species' extirpations being foreseen by the models. Colonisations were better predicted, while persistences were relatively well‐predicted. Predictive accuracy of colonisations was higher for species with relatively warmer temperature associations (climate‐driven expansion), while extirpations were better predicted in cool‐related species (retractions at cool edges). Colonisations of forest‐associated species were more common than predicted (underpredicted), despite widespread patterns of afforestation. Assessing grid‐cell level turnover, we found that in grid cells that experienced the largest changes in terms of climate and land use, predicted extirpations were less likely to have happened.Main ConclusionsWe found that commonly applied modelling approaches have limited ability to predict observed changes in species occurrences, especially extirpations. This suggests that we should take predictions of future biodiversity loss very seriously. However, the ability for species to (at least temporarily) persist in unsuitable conditions could be an opportunity for biodiversity conservation.

Effects of agriculture and nature reserves on avian behavior in northwestern Costa Rica.

Behavioral changes are often animals' first responses to environmental change and may act as a bellwether for population viability. Nonetheless, most studies of habitat conversion focus on changes in species occurrences or abundances. We analyzed >14,000 behavioral observations across 55 bird species in communities in northwestern Costa Rica to determine how land use affects reproductive, foraging, and other passive kinds of behaviors not associated with either foraging or reproduction. Specifically, we quantified differences in behaviors between farms, privately owned forests, and protected areas and implemented a novel modeling framework to account for variation in detection among behaviors. This framework entailed estimating abundances of birds performing different behaviors while allowing detection probabilities of individuals to vary by behavior. Birds were 1.2 times more likely to exhibit reproductive behaviors in forest than in agriculture and 1.5 times more likely to exhibit reproductive behaviors in protected areas than in private forests. Species were not always most abundant in the habitats where they were most likely to exhibit foraging or reproductive behaviors. Finally, species of higher conservation concern were less abundant in agriculture than in forest. Together, our results highlight the importance of behavioral analyses for elucidating the conservation value of different land uses.

Effect of implementation of irrigation on raptor and corvid populations in a Mediterranean agrosystem

We analyzed changes in the composition of the community of birds of prey and corvids in a rainfed agrosystem after the transformation of 37.2 % of the sampled area into irrigated land between 2005 and 2020. We sampled 57 transects (372 km per year) and fitted generalized linear mixed models (GLMM) to study changes in species occurrence. Our results showed that specific richness and the Shannon index did not vary significantly between rainfed and irrigated transects, but there was a certain positive trend when comparing the years 2005 and 2020. Regarding the differences detected for each species, the occurrence of Montagu’s harrier Circus pygargus, hen harrier Circus cyaneus, Eurasian short-toed eagle Circaetus gallicus, griffon vulture Gyps fulvus and carrion crow Corvus corone was significantly lower in irrigated land than in rainfed land, while magpie Pica pica, Western marsh harrier Circus aeruginosus, common kestrel Falco tinnunculus and black kite Milvus migrans showed a significantly higher occurrence in the irrigated transects. In addition, our findings confirm a significant decrease in occurrence between 2005 and 2020 both in rainfed and irrigated areas for Montagu’s harrier, hen harrier and magpie, while Western marsh harrier, golden eagle Aquila chrysaetos, common buzzard Buteo buteo, red kite Milvus milvus, griffon vulture Gyps fulvus, red-billed chough Pyrrhocorax pyrrhocorax and Western jackdaw Coloeus monedula were detected significantly more frequently in 2020 than in 2005. These results suggest that assessment of the impact of a new irrigation system should focus on the most characteristic species of rainfed agrosystems because the apparently positive effect on other species, equally protected but more generalist, may mask the real effect on conservation.

Biotic homogenisation and differentiation as directional change in beta diversity: synthesising driver-response relationships to develop conceptual models across ecosystems.

Biotic homogenisation is defined as decreasing dissimilarity among ecological assemblages sampled within a given spatial area over time. Biotic differentiation, in turn, is defined as increasing dissimilarity over time. Overall, changes in the spatial dissimilarities among assemblages (termed 'beta diversity') is an increasingly recognised feature of broader biodiversity change in the Anthropocene. Empirical evidence of biotic homogenisation and biotic differentiation remains scattered across different ecosystems. Most meta-analyses quantify the prevalence and direction of change in beta diversity, rather than attempting to identify underlying ecological drivers of such changes. By conceptualising the mechanisms that contribute to decreasing or increasing dissimilarity in the composition of ecological assemblages across space, environmental managers and conservation practitioners can make informed decisions about what interventions may be required to sustain biodiversity and can predict potential biodiversity outcomes of future disturbances. We systematically reviewed and synthesised published empirical evidence for ecological drivers of biotic homogenisation and differentiation across terrestrial, marine, and freshwater realms to derive conceptual models that explain changes in spatial beta diversity. We pursued five key themes in our review: (i) temporal environmental change; (ii) disturbance regime; (iii) connectivity alteration and species redistribution; (iv) habitat change; and (v) biotic and trophic interactions. Our first conceptual model highlights how biotic homogenisation and differentiation can occur as a function of changes in local (alpha) diversity or regional (gamma) diversity, independently of species invasions and losses due to changes in species occurrence among assemblages. Second, the direction and magnitude of change in beta diversity depends on the interaction between spatial variation (patchiness) and temporal variation (synchronicity) of disturbance events. Third, in the context of connectivity and species redistribution, divergent beta diversity outcomes occur as different species have different dispersal characteristics, and the magnitude of beta diversity change associated with species invasions also depends strongly on alpha and gamma diversity prior to species invasion. Fourth, beta diversity is positively linked with spatial environmental variability, such that biotic homogenisation and differentiation occur when environmental heterogeneity decreases or increases, respectively. Fifth, species interactions can influence beta diversity via habitat modification, disease, consumption (trophic dynamics), competition, and by altering ecosystem productivity. Our synthesis highlights the multitude of mechanisms that cause assemblages to be more or less spatially similar in composition (taxonomically, functionally, phylogenetically) through time. We consider that future studies should aim to enhance our collective understanding of ecological systems by clarifying the underlying mechanisms driving homogenisation or differentiation, rather than focusing only on reporting the prevalence and direction of change in beta diversity, per se.

Fish Assemblage and In-Stream Habitat Variation in Relation to Dam Structures on the Withlacoochee River, Florida, with Notes on Historical Records

The Withlacoochee River in central Florida is a large blackwater river lacking substantive data on fish assemblage and has undergone extensive hydrological modification since the early 1900s. We compared fish assemblages in river segments above and below 2 major dams by conducting electrofishing surveys between April 2016 and June 2018. We also compiled historical records to assess temporal changes in species occurrence. We found that fish assemblages were significantly different in the lower segment than in the middle and upper segments. The lower segment had the lowest total catch-per-unit-distance and freshwater-fish species richness. Fish assemblage patterns were most highly correlated with Secchi depth, specific conductance, and percent of non-vegetative habitat cover. Much of the variation in fish assemblages among segments was consistent with that observed in undammed coastal rivers, but the lack of estuarine species in upper reaches of our study area suggests that the Inglis Dam may restrict upstream dispersal of these taxa. Comparison of species composition with historical records did not reveal any potential extirpations since 1931, but we recorded 8 marine species and 3 non-native species that were not present in historical records.

Road encroachment mediates species occupancy, trait filtering and dissimilarity of passerine communities

Assessing the road effects on biodiversity is challenging because impacts may depend on both wildlife responses to roads and on the spatial arrangement of roads. We questioned whether an increase in road encroachment leads to significant changes in species occurrence and community composition. Using a large citizen-science dataset of point-counts performed throughout Iberian Peninsula, we modelled the effect of road density on the occurrence of common birds (n = 78 species), while accounting for potential confounding effects of environment and survey effort. We then tested if species' occurrence patterns would be linked to specific traits related to the ability to cope with human presence. Finally, we assessed how road density affects the community compositional dissimilarity. We estimated 36 (46%) and 18 (23%) species to be negatively and positively affected by roads, respectively. Increased road encroachment was positively related with urban dwelling and fecundity, and negatively related with nesting on the ground. Furthermore, increasing road density translated into an increasing community compositional dissimilarity, mostly due to species turnover. Overall, we found that different species-specific responses to roads translate into changes at the community level. Landscape and road-network management should be conceived acknowledging that roads are contributing to biodiversity changes. As so, building upon the concepts of land sharing/land sparing, conservation actions should be tailored according to the different species responses e.g., road verge management targeting species having a positive relation with road density; and compensation actions targeting species showing a negative response toward roads.

Disentangling the impacts of environmental change and commercial fishing on demersal fish biodiversity in a northeast Pacific ecosystem

Conservation of marine biodiversity requires understanding the joint influence of ongoing environmental change and fishing pressure. Addressing this challenge requires robust biodiversity monitoring and analyses that jointly account for potential drivers of change. Here, we ask how demersal fish biodiversity in Canadian Pacific waters has changed since 2003 and assess the degree to which these changes can be explained by environmental change and commercial fishing. Using a spatiotemporal multispecies model based on fisheries independent data, we find that species density (number of species per area) and community biomass have increased during this period. Environmental changes during this period were associated with temporal fluctuations in the biomass of species and the community as a whole. However, environmental changes were less associated with changes in species occurrence. Thus, the estimated increases in species density are not likely to be due to environmental change. Instead, our results are consistent with an ongoing recovery of the demersal fish community from a reduction in commercial fishing intensity from historical levels. These findings provide key insight into the drivers of biodiversity change that can inform ecosystem-based management.

Growing grasses in unprofitable areas of US Midwest croplands could increase species richness

The US has large potential to grow perennial energy crops, but because these crops are rarely grown in current agricultural landscapes, it is unclear how biodiversity may be affected. Over time, as agriculture has increased, many grassland species have declined. In addition, not all agricultural land is profitable for growing annual crops. Unprofitable areas were responsible for a loss of approximately $110 million USD per year from 2013 to 2016. Based on this, we want to know how converting less-profitable portions of agricultural fields to switchgrass, a native prairie grass, would influence species occurrence. To address this question, we developed an alternative landscape in which clustered corn/soy acres with a low return on investment (ROI) were replaced with grassland. We also developed and validated species distribution models to predict changes in species occurrence for 28 avian species in Iowa in response to landscape management. We compared results for three different models: Random forest (RF), Stochastic gradient boosting (GBM), and Neural network (Nnet) and found that all models performed well and predicted similar species distribution. Predicted species richness increased by 3.66% (RF), 2.79% (GBM), and 7.51% (Nnet) when we simulated a change in management for ~3% of Iowa's low ROI corn/soybean areas to grassland. If harvested, these areas could generate approximately 7.6 million dry tons/year of switchgrass for bioenergy, thereby increasing farmers earnings. Unprofitable areas tended to occur along streams, which suggest that incorporating partially harvested riparian buffers can benefit avian biodiversity, while improving water quality and reducing unnecessary costs for farmers.

A network of small protected areas favoured generalist but not specialized wetland birds in a 30-year period

Protected areas (PAs) have been established to promote the long-term conservation of biodiversity and ecosystems. Wetlands, which represent a key habitat worldwide, have been largely destroyed, particularly in more industrialized countries, and their remnants are now often preserved by PA networks, especially in the European Union. We tested the effectiveness of a PA network of 26 small wetlands in preserving wetland birds over a thirty-year period (1989–2019), by investigating changes in species occurrence and relating them to the species' ecological specialization. Out of 23 species, 10 showed an increase in occurrence, 7 remained stable and 6 declined. The number of occupied habitats (between 1 and 8) was significantly associated with the species' trend: specialized species decline, whereas generalists increased. Species with increasing occurrence mostly included common birds, whereas the declining ones were all species with an unfavourable conservation status at the national level. Generalist species increased their occurrence rates, whereas species with stricter, more specialized requirements, generally underwent contraction, suggesting that the conservation of isolated wetlands, managed according to criteria not strictly focused on birds, is not enough to preserve the more specialized species. The proper management of key habitats and the increase of ecological connectivity in the wetland system are crucial for the conservation of wetland-specialist birds.

Testing unidimensional species distribution models to forecast and hindcast changes in marsh vegetation over 40 years

• We test the performance of projecting over time of unidimensional SDMs. • We compare the performance of modelling methods and data types in prediction over time. • There is no significant difference between internal and external evaluation. • Cover is a little better than P/A model, and GAM is similar with eHOF model. • Our result provide guideline for SDMs in prediction under environmental change. Species distribution models (SDM) predicting changes in species occurrences and abundance are increasingly being used as a tool in biogeography and conservation biology. However, we have little information on their predictive performance. Here we used archive-recorded predictor and field-observational verifier data associated with water level to evaluate the performance of response curves over 40 years for marsh plant species in Northeast China. A consensus approach (AUC: area-under-curve) was used as the test measure for internal evaluation and external evaluation (forecast and hindcast). Our results demonstrated that there is no significant differences between internal and external evaluation, and they both showed reasonable accuracy (AUC = 0.73, respectively). There was considerable variation across species and projection direction in model accuracy, and accuracy of model fitting in internal evaluation and restricting the environmental range of data in different time periods may impact the performance of model projection over time. The performance of generalized additive models (GAM) is similar with that of extended Huisman-Olff-Fresco models (eHOF). Cover model is a little better than presence/absence models in prediction over time. Our findings provide some guidelines for the use of SDM for predictions under environmental change.

Using species records and ecological attributes of bryophytes to develop an ecosystem health indicator

• Bryological records and Ellenberg values were combined as Ecosystem Health Indicators. • We analysed change across Scotland (1960–2016) for each 10 km × 10 km grid square. • Ellenberg Nitrogen (N) showed a humped relationship indicating recent recovery. • Increasing trends were evident for January and July Temperature. • Bryological records can form the basis of an effective Ecosystem Health Indicator. Environmental policy decisions should be based on robust indicators of changes in the environment. In Scotland these have been formalised as Ecosystem Health Indicators. Indicators work best where there is a direct link between what is measured and environmental change; changes in indices of species diversity or abundance provide alerts to environmental change but do not in themselves provide evidence of mechanisms. An alternative approach is to replace species occurrence data with species habitat or attribute values to create an indicator that links changes in species occurrences to environmental drivers. A series of indicators based on biological recording data, Ellenberg habitat preference values and mean climate niche was created by taking all records for bryophytes in Scotland (522187 records, 1960–2016) and analysing changes in mean attribute values through time for each 10 km × 10 km grid square. The resulting mean attribute values were analysed at the country level and showed clear quadratic (humped) trends for Ellenberg Nitrogen (N) and Reaction (R), an index of environmental acidity. There are linear decreasing trends for Ellenberg Light (L) and Precipitation, and linear increasing trends for January and July Temperature. Ellenberg Moisture (F) showed a clear trend, but it was not interpretable and appeared influenced by recording effort. Disaggregating to region was partly successful, but reduced samples sizes meant that for many regions the national trend was not significant. Ellenberg N and the two Temperature indices appear to be useful indicators as they are interpretable and performed better in the downscaling. Changes in L were also interpretable, but it performed poorly in downscaling to regional values. Ellenberg R appeared to be driven by changes in N as the two values are highly correlated across species. The downward trend in Precipitation ran counter to increases in rainfall suggesting that temperature driven evaporation is more likely to be driving changes in bryophyte distribution and whilst the indicator performed well it is difficult to explain to non-experts. Opportunistically collected data, like plant records, have great potential to be employed as indicators, especially as citizen scientists are involved and state resources can be used for data archiving and analysis. Also, conversion to attribute values removes many of the biases brought by differences in recorder effort and it directly links changes in species occurrences to environmental drivers.

Patterns and drivers of long‐term changes in breeding bird communities in a global biodiversity hotspot in Mexico

AbstractAimTo evaluate changes in breeding bird communities and assess implications for conservation.LocationMadrean Sky Islands and northern Sierra Madre Occidental, Mexico.MethodsI compared observations from recent fieldwork (2009–2012) with an extensive historical data set (1887–1954) and used modelling and multivariate techniques to assess spatiotemporal changes in species occurrence, richness and assemblage composition, and associations with climate, land use and landscape factors.ResultsBreeding species richness peaked in larger ranges often in the south and east, and regional beta diversity was attributable much more to turnover (0.80) than nestedness (0.07). Although richness increased across time, spatial assemblage heterogeneity declined due only to changes in nestedness, with temporal shifts in beta diversity equally attributable to variation in nestedness and turnover. Community change was associated with variation in climate, land use and landscape factors in ways that depended on species’ traits. Major gains in Madrean and lowland Neotropical species from the south contrasted little change in Nearctic species, and there was some evidence lowland species expanded eastward into the higher‐elevation interior, suggesting poleward and up‐elevation shifts now occurring globally. Some such patterns were associated with increasing temperature and summer–fall precipitation typical of the south suggesting climate forcing. Despite regional gains in pine‐dependent species linked to post‐logging forest recovery, losses and turnover were greater in smaller more arid ranges due likely to climate‐mediated habitat loss. High regional losses of cavity‐nesting species in forest were greater in ranges subjected to past logging indicating effects of historical habitat degradation persist today.Main conclusionDespite ongoing forest recovery and potential for northward range expansion to offset climate‐mediated losses of montane species, further assemblage homogenization seems likely. Active forest restoration that promotes large old trees, snags and mature forest conditions combined with increasing the capacity of local communities to implement best management practices will enhance conservation.

Assessing temporal shifts in lotic fish community structure in the upper Red River basin, Oklahoma

ABSTRACTA long-term fish community monitoring program was established by the Oklahoma Department of Wildlife Conservation Streams Program in 2016. One of the primary goals of this program is to evaluate contemporary fish species distributions in Oklahoma and draw inferences regarding changes in those distributions over time. In 2016, fish community surveys took place from late June to early August at a total of 48 sites within the upper Red River basin. Compared to the most comprehensive historical sampling effort within the basin, contemporary surveys detected an additional eight species while three species historically present were not detected in 2016. Multivariate generalized linear model results indicated significant differences in community structure between historical and contemporary surveys. Univariate testing paired with Sum-of-LR analyses revealed differences in community structure were largely driven by increases in generalist fish species (e.g. Green Sunfish and Common Carp) and decreases in small-bodied specialist cyprinids (e.g. Chub Shiner). Although changes in species occurrences may be partially driven by differences in sampling methodology and effort, changes across multiple stream reaches likely reveal real trends.

Decreased cryogenic disturbance: one of the potential mechanisms behind the vegetation change in the Arctic

During the last few decades, the Arctic has experienced large-scale vegetation changes. Understanding the mechanisms behind this vegetation change is crucial for our ability to predict future changes. This study tested the hypothesis that decreased cryogenic disturbances cause vegetation change in patterned ground study fields (non-sorted circles) in Abisko, Sweden during the last few decades. The hypothesis was tested by surveying the composition of plant communities across a gradient in cryogenic disturbance and by reinvestigating plant communities previously surveyed in the 1980s to scrutinise how these communities changed in response to reduced cryogenic disturbance. Whereas the historical changes in species occurrence associated with decreased cryogenic disturbances were relatively consistent with the changes along the contemporary gradient of cryogenic disturbances, the species abundance revealed important transient changes highly dependent on the initial plant community composition. Our results suggest that altered cryogenic disturbances cause temporal changes in vegetation dynamics, but the net effects on vegetation communities depend on the composition of initial plant species.

Detecting long-term occupancy changes in Californian odonates from natural history and citizen science records

In a world of rapid environmental change, effective biodiversity conservation and management relies on our ability to detect changes in species occurrence. While long-term, standardized monitoring is ideal for detecting change, such monitoring is costly and rare. An alternative approach is to use historical records from natural history collections as a baseline to compare with recent observations. Here, we combine natural history collection data with citizen science observations within a hierarchical Bayesian occupancy modeling framework to identify changes in the occupancy of Californian dragonflies and damselflies (Odonata) over the past century. We model changes in the probability of occupancy of 34 odonate species across years and as a function of climate, after correcting for likely variation in detection probability using proxies for recorder effort and seasonal variation. We then examine whether biological traits can help explain variation in temporal trends. Models built using only opportunistic records identify significant changes in occupancy across years for 14 species, with eight of those showing significant declines and six showing significant increases in occupancy in the period 1900–2013. These changes are consistent with estimates obtained using more standardized resurvey data, regardless of whether resurvey data are used individually or in conjunction with the opportunistic dataset. We find that species increasing in occupancy over time are also those whose occupancy tends to increase with higher minimum temperatures, which suggests that these species may be benefiting from increasing temperatures across California. Furthermore, these species are also mostly habitat generalists, whilst a number of habitat specialists display some of the largest declines in occupancy across years. Our approach enables more robust estimates of temporal trends from opportunistic specimen and observation data, thus facilitating the use of these data in biodiversity conservation and management.

Declining Occurrence and Low Colonization Probability in Freshwater Mussel Assemblages: A Dynamic Occurrence Modeling Approach

Mussel monitoring data are abundant, but methods for analyzing long-term trends in these data are often uninformative or have low power to detect changes. We used a dynamic occurrence model, which accounted for imperfect species detection in surveys, to assess changes in species occurrence in a long-term data set (1986–2011) for the Tar River basin of North Carolina, USA. Occurrence of all species decreased steadily over the time period studied. Occurrence in 1986 ranged from 0.19 for Utterbackiaimbecillis to 0.60 for Fusconaia masoni. Occurrence in 2010–2011 ranged from 0.10 for Lampsilisradiata to 0.40 for F. masoni. The maximum difference between occurrence in 1986 and 2011 was a decline of 0.30 for Alasmidonta undulata. Mean persistence for all species was high (0.97, 95% CI = 0.95–0.99); however, mean colonization probability was very low (<0.01, 95% CI = <0.01–0.01). These results indicate that mussels persisted at sites already occupied but that they have not colonized sites where they had not occurred previously. Our findings highlight the importance of modeling approaches that incorporate imperfect detection in estimating species occurrence and revealing temporal trends to inform conservation planning.

Persistence in the longitudinal distribution of lotic insects in a changing climate: a tale of two rivers

The longitudinal distribution of many taxa in rivers is influenced by temperature. Here we took advantage of two older datasets on net-spinning caddisflies (Hydropsychidae) from contrasting European rivers to assess changes in species occurrence and relative abundance along the river by resampling the same sites, postulating that an increase in river temperature over the intervening period should have resulted in cool-adapted species retreating into the headwaters and warm adapted species expanding upstream. Distributional changes in the Welsh Usk were slight between 1968/69 and 2010, one rare species appearing at a single headwater site and one warm-adapted species disappearing from the main river. Distributional changes in the French Loire, between 1989–93 and 2005, were similarly modest, with no consistent movement of species up- or downstream. We estimate that the decadal rate of increase in the mean summer daily maximum in the Usk was only 0.1°C at one ‘summer cool’ headwater site, while a neighbouring ‘summer warm’ tributary increased by 0.16°C per decade, and the main river by 0.22°C. The Loire is warmer than the Usk and the mean decadal rates of increase, over the period 1989–2005, at three sites along the lower reaches were 0.39, 0.48 and 0.77°C. Increases in stream and river temperature, therefore, were spatially variable and were not associated with consistent upstream movement of species in either of these (very different) rivers. We conclude that either the temperature increases have hitherto been insufficient to affect species distribution or, more speculatively, that it may not be possible for river organisms (that do not respond only to temperature) to move upstream because of a developing spatial mismatch between key habitat characteristics, some of them changing with the climate but others not.

Grazing‐induced shifts in community functional composition and soil nutrient availability in Tibetan alpine meadows

SummaryThe functional structure of plant communities can be altered by grazing through two main mechanisms: species turnover (i.e. changes in species occurrence and relative abundance) and intraspecific trait variability (ITV), which is driven by phenotypic responses of individual plants and shifts in the relative abundance of genotypic variants within species. Studies of grassland ecosystem function under grazing often focus on community changes induced by species turnover, which ignores the effects ofITVon biomass productivity, soil carbon or nutrient availability. By quantifying the relative contribution of both effects on shifts in community‐wide traits, we highlight the role ofITVin community functional response to grazing and its implications for ecosystem function in Tibetan alpine meadows.We measured three chemical traits (LC: leaf carbon,LN: leaf nitrogen andLP: leaf phosphorus concentrations) and two morphological traits (SLA: specific leaf area,LDMC: leaf dry matter content) that are critical components of plant production and forage quality in grazed and ungrazed plots. Using variance decomposition of community‐weighted means (CWM) for these foliar traits, we distinguished the relative importance ofITVvs. change in species occurrence and abundance in response to grazing and the associated changes in soil carbon and nutrient availability.TheCWMfor foliar nutrients andSLACWMincreased in response to grazing together with decreases in soil carbon and nutrient stores, especiallyLPCWMenrichment and loss of available soil P. TheLPCWMwas strongly negatively correlated withLDMCCWM, which was significantly higher in ungrazed plots. These community‐wide trait responses to grazing were generally best captured byITVand not changes in species occurrence and abundance, althoughITVwas consistently correlated with species turnover for all traits.Synthesis and applications. In response to continuous grazing, plants in Tibetan alpine meadows increase specific leaf area and foliar nutrients but tend to have lower leaf dry matter content, a response consistent with faster growth and regrowth under grazing. This intraspecific trait variability response drives a shift in community function from conservative, slow‐growing resource use in ungrazed meadows to exploitative resource use under grazing. This community‐wide functional response enhances forage quality, in turn favouring the secondary productivity of small herbivorous mammal communities, but also contributes to accelerated depletion of soil available phosphorus. We discuss the implications of these results for biodiversity conservation, ecosystem function and rangeland sustainability in the Qinghai–Tibetan Plateau, especially with regard to managing grazing rotation to strike a balance between favouring secondary productivity of domesticated stock vs. small herbivorous mammals.

Disentangling the relative importance of species occurrence, abundance and intraspecific variability in community assembly: a trait‐based approach at the whole‐plant level in Mediterranean forests

Understanding which factors and rules govern the process of assembly in communities constitutes one of the main challenges of plant community ecology. The presence of certain functional strategies along broad environmental gradients can help to understand the patterns observed in community assembly and the filtering mechanisms that take place. We used a trait‐based approach, quantifying variations in aboveground (leaf and stem) and belowground (root) functional traits along environmental gradients in Mediterranean forest communities (south Spain). We proposed a new practical method to quantify the relative importance of species turnover (distinguishing between species occurrence and abundance) versus intraspecific variation, which allowed us to better understand the assemblage rules of these plant communities along environmental gradients. Our results showed that the functional structure of the studied plant communities was highly determined by soil environment. Results from our modelling approach based on maximum likelihood estimators showed a predominant influence of soil water storage on most of the community functional traits. We found that changes in community functional structure along environmental gradients were mainly promoted by species turnover rather than by intraspecific variability. Specifically, our new method of variance decomposition demonstrated that between‐site trait variation was the result of changes in species occurrence rather than in the abundance of certain dominant species. In conclusion, this study showed that water availability promoted the predominance of specific trait values (both in above and belowground fractions) associated to a resource acquisition or conservation strategy. In addition, we provided evidence that changes on community functional structure along the environmental gradient were mainly promoted by a process of species replacement, which represent a crucial step towards a more general understanding of the relative importance of intraspecific versus interspecific trait variation in these woody Mediterranean communities.