Temporal turnover of common species in avian assemblages in North America

Aim We examine patterns of temporal turnover of common species in avian assemblages in North America to test the hypothesis that changes in avian diversity structure observed in these assemblages were associated with the colonization of common species. Location The contiguous United States and southern Canada. Methods We measured temporal turnover from 1968 to 2003 for 547 avian species at 1673 North American Breeding Bird Survey (BBS) routes. We used the Euclidian distance between expected and observed presence/absence vectors and randomization tests to place species into two categories, common and not‐common, and into three categories for common species: (1) always common, (2) common and colonizing, and (3) common and extirpated. We used these categories to identify species experiencing extreme colonization and extirpation events and to examine changes in species composition at BBS routes. We also determined how these patterns were associated with changes in species richness and changes in similarity in species composition. Results Nine of the 547 species represented outliers, where the number of BBS routes colonized greatly exceeded the number extirpated; no species showed extreme values for extirpation. The nine species colonized BBS routes primarily in the upper Midwest and north‐eastern United States. Presence of the nine species at BBS routes was correlated with increasing net gain in common species (difference between common colonized and common extirpated), higher levels of species richness and increasing species richness over time, more similar species compositions and increasing similarity over time, and a greater prevalence of common species over not‐common species. The literature indicates that all nine species experienced some form of geographical range expansion during the time of the survey involving four elements: (1) introduction and invasion; (2) the ability to use human‐altered environments, including habitats associated with agricultural, suburban, or urban areas; (3) intensive management activities, including habitat improvements and reintroductions and (4) the ability to use habitats formed through forest regeneration. These factors in combination point to anthropogenic activities and related land use histories as the primary drivers of change. One of the nine species colonized regions well outside its historic geographical range and the remaining eight species were native within the regions they colonized. Main conclusions Our results suggest that a combination of anthropogenic activities promoted, within certain regions of North America, the geographical expansion of a limited number of common species that were native to those regions. These colonization events were correlated with changes in diversity structure, implying that large‐scale diversity patterns were being influenced by anthropogenic activities. These changes can be characterized primarily by gains in species richness, an increased prevalence of common species, and more similar species compositions. Thus, using simple large‐scale measures of diversity could be problematic if recent biogeographical patterns of species diversity are not considered. Specifically, using species richness or an indicator species to assess diversity could bias assessments towards common species whose populations have recently benefited through anthropogenic activities.     

Climate change hastens the turnover of stream fish assemblages

Stream fish are expected to be significantly influenced by climate change, as they are ectothermic animals whose dispersal is limited within hydrographic networks. Nonetheless, they are also controlled by other physical factors that may prevent them moving to new thermally suitable sites. Using presence–absence records in 655 sites widespread throughout nine French river units, we predicted the potential future distribution of 30 common stream fish species facing temperature warming and change in precipitation regime. We also assessed the potential impacts on fish assemblages' structure and diversity. Only cold-water species, whose diversity is very low in French streams, were predicted to experience a strong reduction in the number of suitable sites. In contrast, most cool-water and warm-water fish species were projected to colonize many newly suitable sites. Considering that cold headwater streams are the most numerous on the Earth's surface, our results suggested that headwater species would undergo a deleterious effect of climate change, whereas downstream species would expand their range by migrating to sites located in intermediate streams or upstream. As a result, local species richness was forecasted to increase greatly and high turnover rates indicated future fundamental changes in assemblages' structure. Changes in assemblage composition were also positively related to the intensity of warming. Overall, these results (1) stressed the importance of accounting for both climatic and topographic factors when assessing the future distribution of riverine fish species and (2) may be viewed as a first estimation of climate change impacts on European freshwater fish assemblages.     

Numerical abundance and biomass reveal different temporal trends of functional diversity change in tropical fish assemblages

Understanding how the biodiversity of freshwater fish assemblages changes over time is an important challenge. Until recently most emphasis has been on taxonomic diversity, but it is now clear that measures of functional diversity (FD) can shed new light on the mechanisms that underpin this temporal change. Fish biologists use different currencies, such as numerical abundance and biomass, to measure the abundance of fish species. Nonetheless, because they are not necessarily equivalent, these alternative currencies have the potential to reveal different insights into trends of FD in natural assemblages. In this study, the authors asked how conclusions about temporal trends in FD are influenced by the way in which the abundance of species has been quantified. To do this, the authors computed two informative metrics, for each currency, for 16 freshwater fish assemblages in Trinidad's Northern Range that had been surveyed repeatedly over 5 years. The authors found that numerical abundance and biomass uncover different directional trends in these assemblages for each facet of FD, and as such inform hypotheses about the ways in which these systems are being restructured. On the basis of these results, the authors concluded that a combined approach, in which both currencies are used, contributes to our understanding of the ecological processes that are involved in biodiversity change in freshwater fish assemblages.     

Predicting the structure and diversity of young-of-the-year fish assemblages in large rivers

1. Interactions between environmental variables and 0+ fish assemblages in the upper River Garonne (France) were quantified during late August 1995.
2. The abundance and diversity of the fish assemblages in floodplain channels were modelled using Artificial Neural Network (ANN) analysis and nine variables: the abundance of the six dominant species, fish specific richness, overall abundance of 0+ fish and the Shannon index of diversity. Multiple regression analysis was also used to assess ANN performance.
3. Using 596 samples, correlation coefficients ( r adjusted) between observed and estimated values of the nine dependent parameters were all highly significant ( P < 0.01). Expected values from the tested data were significantly related to the observed values. The correlation coefficient between observed and estimated values ( r ) varied from 0.70 to 0.85.
4. The ANN provided a high quality prediction, despite the complex nature of the relationship between microhabitat composition and fish abundance.
5. Garson's algorithm was used to provide the explanatory power needed in ecology when using black-box models. Parameters contained in the models (i.e. weighting) were used to determine the relative contributions of explanatory variables and thus to ascertain the structure of fish communities.     

Contrasting changes in the abundance and diversity of North American bird assemblages from 1971 to 2010

Although it is generally recognized that global biodiversity is declining, few studies have examined long‐term changes in multiple biodiversity dimensions simultaneously. In this study, we quantified and compared temporal changes in the abundance, taxonomic diversity, functional diversity, and phylogenetic diversity of bird assemblages, using roadside monitoring data of the North American Breeding Bird Survey from 1971 to 2010. We calculated 12 abundance and diversity metrics based on 5‐year average abundances of 519 species for each of 768 monitoring routes. We did this for all bird species together as well as for four subgroups based on breeding habitat affinity (grassland, woodland, wetland, and shrubland breeders). The majority of the biodiversity metrics increased or remained constant over the study period, whereas the overall abundance of birds showed a pronounced decrease, primarily driven by declines of the most abundant species. These results highlight how stable or even increasing metrics of taxonomic, functional, or phylogenetic diversity may occur in parallel with substantial losses of individuals. We further found that patterns of change differed among the species subgroups, with both abundance and diversity increasing for woodland birds and decreasing for grassland breeders. The contrasting changes between abundance and diversity and among the breeding habitat groups underscore the relevance of a multifaceted approach to measuring biodiversity change. Our findings further stress the importance of monitoring the overall abundance of individuals in addition to metrics of taxonomic, functional, or phylogenetic diversity, thus confirming the importance of population abundance as an essential biodiversity variable.     

Spatial and Temporal variations of mangrove fish assemblages in Martinique (French West Indies)

A study of the mangrove fish fauna in a bay of Martinique Island (French West Indies) was carried out at different seasons during two consecutive years. fishes were sampled with specific hoop-nets in the coastal areas at 8 stations.A total of 87 species was collected in the bay. Most individuals were represented by small-size specimens and juveniles. The overall species richness varied according to the stations and the sampling periods. The biomass and number of individuals were variable according to the location but remained stable in time. A factor correspondence analysis and a hierarchical clustering with median links were used to follow the evolution of the stations in space and time. Two types of stations were differentiated: the stations characterized by the mangrove and those under the influence of seagrass beds. A seasonal cycle, opposing the dry periods to the others, was observed.Thus, it seems that the use of the mangrove habitat by the fishes is optimized through a complete reorganization of communities in terms of species composition whereas the overall number and biomass remain stable. This model remains valid even for the most constraining biota of the mangrove ecosystem inhabited by a small number of well adapted species.     

The effect of range changes on the functional turnover,structure and diversity of bird assemblages under future climate scenarios

Animal assemblages fulfill a critical set of ecological functions for ecosystems that may be altered substantially as climate change‐induced distribution changes lead to community disaggregation and reassembly. We combine species and community perspectives to assess the consequences of projected geographic range changes for the diverse functional attributes of avian assemblages worldwide. Assemblage functional structure is projected to change highly unevenly across space. These differences arise from both changes in the number of species and changes in species’ relative local functional redundancy or distinctness. They sometimes result in substantial losses of functional diversity that could have severe consequences for ecosystem health. Range expansions may counter functional losses in high‐latitude regions, but offer little compensation in many tropical and subtropical biomes. Future management of local community function and ecosystem services thus relies on understanding the global dynamics of species distributions and multiscale approaches that include the biogeographic context of species traits.     

Ecological integrity assessment of the fish assemblages of the Matigulu/Nyoni and Umvoti estuaries,KwaZulu-Natal,South Africa

The estuarine fish community index (EFCI) and an estuarine fish guild assessment (EFGA) were used in 2004 and 2008 to determine the ecological state and effects of selected ecosystem variables on the Umvoti and Matigulu/Nyoni estuaries. The EFCI indicated that the Matigulu/Nyoni Estuary was in a moderate state and that the Umvoti Estuary was in a poor to very poor state. The EFGA revealed a clear spatial differentiation, based on the estuaries’ fish community structures, that was being driven primarily by the freshwater-dominated state of the Umvoti Estuary and the poor water quality of the Umvoti Estuary. The analysis of estuarine fish assemblage characteristics was shown to contribute towards the management and conservation of these systems.     

Resemblance in phylogenetic diversity among ecological assemblages

Questions: How can a resemblance (similarity or dissimilarity) measure be formulated to include information on both the evolutionary relationships and abundances of organisms, and how does it compare to measures lacking such information? Methods: We extend the family of Phylogenetic Diversity (PD) measures to include a generalized method for calculating pair‐wise resemblance of ecological assemblages. Building on previous work, we calculate the matching/mismatching components of the 2 × 2 contingency table so as to incorporate information on both phylogeny and abundance. We refer to the class of measures so defined as “PD resemblance” and use the term “SD resemblance” for the traditional class of measures based on species diversity alone. As an illustration, we employ data on the diversity and stem density of shrubs of Toohey Forest, Australia, to compare PD resemblance to its SD resemblance equivalent for both incidence and abundance data. Results: While highly correlated, PD resemblance consistently measures assemblages as more similar than does SD resemblance, and tends to “smooth out” the otherwise skewed and truncated distribution of pair‐wise resemblance indices of our high‐turnover data set, resulting in nMDS ordinations with lower stress. Randomization of species distributions across assemblages indicates that phylogeny has made a significant contribution to the ordination pattern. Conclusions: PD resemblance measures, in addition to providing an evolutionary perspective, have great potential to improve distance‐based analyses of community patterns, particularly if species responses to ecological gradients are unimodal and phylogenetically conserved.     

Temporal and spatial variability of pelagic wild fish assemblages around Atlantic bluefin tuna Thunnus thynnus farms in the eastern Adriatic Sea

The abundance and size structure of wild fishes aggregated around the sea‐cages of two commercial Thunnus thynnus farms, including control locations, were assessed and compared over a 1 year period. The T. thynnus farms were located in the eastern Adriatic Sea, offshore of the islands of Ugljan and Bra?. Fish assemblages were evaluated through visual census using scuba at 2 month intervals at two sites within each farm. The data suggest that wild fish assemblages at the study sites differed greatly; 20 species occurred at the Ugljan farm and 17 at the Bra? farm, while only seven species were observed at the control locations. The abundance and diversity of wild fish assemblages were greater at the farms in comparison to control locations. The most abundant families were Sparidae and Belonidae (>80% of aggregated fishes). At both farms, the abundance and diversity of wild fishes were highest during summer, while diversity was lowest in winter and was mainly characterized by schools of bogue Boops boops and garfish Belone belone. Variability was also detected in spatial assemblages between farms; B. boops and B. belone were the most abundant species for the overall study at the Bra? farm, while B. belone and saddled bream Oblada melanura were the most abundant at the Ugljan farm. The settlement also played a significant role in farm‐associated fish assemblages, as both juveniles and advanced juveniles were common residents at farms. The majority of species which settled at the farms belonged to the sparids. Results indicate that aggregations of wild fishes at T. thynnus farms are persistent year‐round, though the assemblage compositions and size structures of dominant species vary in respect to location and season.     

A meta‐analysis of nestedness and turnover components of beta diversity across organisms and ecosystems

Aim

The number of studies investigating the nestedness and turnover components of beta diversity has increased substantially, but our general understanding of the drivers of turnover and nestedness remains elusive. Here, we examined the effects of species traits, spatial extent, latitude and ecosystem type on the nestedness and turnover components of beta diversity.

Location

Global.

Time period

1968–2017.

Major taxa studied

From bacteria to mammals.

Methods

From the 99 studies that partition total beta diversity into its turnover and nestedness components, we assembled 269 and 259 data points for the pairwise and multiple site beta‐diversity metrics, respectively. Our data covered a broad variation in species dispersal type, body size and trophic position. The data were from freshwater, marine and terrestrial realms, and encompassed geographical areas from the tropics to near polar regions. We used linear modelling as a meta‐regression tool to analyse the data.

Results

Pairwise turnover, multiple site turnover and total beta diversity all decreased significantly with latitude. In contrast, multiple site nestedness showed a positive relationship with latitude. Beta‐diversity components did not generally differ among the realms. The turnover component and total beta diversity increased with spatial extent, whereas nestedness was scale invariant for pairwise metrics. Multiple site beta‐diversity components did not vary with spatial extent. Surprisingly, passively dispersed organisms had lower turnover and total beta diversity than flying organisms. Body size showed a relatively weak relationship with beta diversity but had important interactions with trophic position, thus also affecting beta diversity via interactive effects. Producers had significantly higher average pairwise turnover and total beta diversity than carnivores.

Main conclusions

The present results provide evidence that species turnover, being consistently the larger component of total beta diversity, and nestedness are related to the latitude of the study area and intrinsic organismal features. We showed that two beta‐diversity components had generally opposing patterns with regard to latitude. We highlight that beta‐diversity partition may give additional insights into the underlying causes of spatial variability in biotic communities compared with total beta diversity alone.     

牛山湖两种不同生境小型鱼类的种类组成、多样性和密度

研究了2003年春季浅水草型湖泊牛山湖小型鱼类空间分布（种类组成、多样性和密度等）与生境异质性之间的关系.根据水生植被状况、离岸距离和水深,选择了两种差异较大且有代表性的生境类型,即近岸沉水植物茂密的生境A和远岸沉水植物稀疏的生境B.使用围网（180 m²）在这两种生境中进行小型鱼类的采样,采用多次标志回捕法和Zippin去除法估算了围网内小型鱼类的密度.结果表明,两种不同生境中小型鱼类的种类组成、多样性度量值和密度估算值均存在一定程度的差异：1）生境A中的渔获物由5科14种小型鱼类组成,优势种类为生活在中、下水层的高体鳑鲏、彩副鱊和麦穗鱼;生境B中的渔获物由3科9种小型鱼类组成,优势种类为生活在湖底的子陵吻鰕虎鱼和小黄黝鱼.2）生境A和生境B小型鱼类群落间的Bray-Curtis指数为0.222,结构相似性较低;但二者的物种等级丰度分布则无显著差异,均属于对数级数分布.3）生境A中高体鳑鲏、彩副鱊、麦穗鱼等9种小型鱼类的总密度值为8.71 ind·m^-2,生境B中子陵吻鰕虎鱼、小黄黝鱼等5种小型鱼类的总密度值只有3.54 ind·m^-2.小型鱼类在这两种不同生境中的空间分布差异可能与其逃避捕食、觅食和繁殖等生态习性的生境需求有关,因此,水生植被生境对小型鱼类资源合理开发和多样性保护具有重要意义.     

Partitioning the turnover and nestedness components of beta diversity

Aim  Beta diversity (variation of the species composition of assemblages) may reflect two different phenomena, spatial species turnover and nestedness of assemblages, which result from two antithetic processes, namely species replacement and species loss, respectively. The aim of this paper is to provide a unified framework for the assessment of beta diversity, disentangling the contribution of spatial turnover and nestedness to beta-diversity patterns.
Innovation  I derive an additive partitioning of beta diversity that provides the two separate components of spatial turnover and nestedness underlying the total amount of beta diversity. I propose two families of measures of beta diversity for pairwise and multiple-site situations. Each family comprises one measure accounting for all aspects of beta diversity, which is additively decomposed into two measures accounting for the pure spatial turnover and nestedness components, respectively. Finally, I provide a case study using European longhorn beetles to exemplify the relevance of disentangling spatial turnover and nestedness patterns.
Main conclusion  Assigning the different beta-diversity patterns to their respective biological phenomena is essential for analysing the causality of the processes underlying biodiversity. Thus, the differentiation of the spatial turnover and nestedness components of beta diversity is crucial for our understanding of central biogeographic, ecological and conservation issues.     

Changes in the composition of British butterfly assemblages over two decades

Changes in the abundance and distribution of individual species have been widely documented in Britain and other countries in recent decades, but little has been done to determine changes in community composition over broad geographic areas. Here, we studied species turnover in 51 butterfly assemblages in Britain since 1976, examining extinction and colonisation events together with variation in the abundances of the species. We showed that the species turnover that occurred over 20 years in Britain was associated with colonisation and extinction events and also with variability in the abundance of the species. These changes in community composition differed according to the habitat requirements of the species and their previous distributions, being more evident for habitat specialists and for southerly distributed species. Colonising species often became abundant components of the communities they joined, although this was more evident for generalist than for specialist species. The abundance of species following their arrival, increased with time since colonisation. Species turnover associated with southerly species expanding northwards is consistent with being a response to climate change. The results suggest that climate- and habitat-driven changes in the identity and abundance of species within communities are widespread, and probably ubiquitous. Similar changes are likely to be occurring in other groups of organisms that are similarly undertaking major range shifts associated with climate change.     

Woodland area,species turnover and the conservation of bird assemblages in lowland England

A study over 4 years into the number of breeding bird species and species turnover (extinctions and colonisations) in relation to area was conducted in 35 woodlands, set in an intensively farmed landscape, in north-east Essex, UK. A total of 46 species was recorded. The number of species breeding increased with woodland area; the slope of the species–area relationship did not differ between years. Habitat diversity was the only other measured variable to influence species richness. Absolute species turnover was independent of woodland area but relative turnover declined with increase in woodland area. The numbers of territories of nine species were determined. For four summer visitors the number of woods occupied increased as the overall populations increased but, for the other species, changes in overall population size led to changes in numbers in occupied woods. Chaffinch Fringilla coelebs and Song Thrush Turdus philomelos were more associated with woodland edges, Nightingale Luscinia megarhynchos, Garden Warbler Sylvia borin, Chiffchaff Phylloscopus collybita and Willow Warbler P. trochilus with interiors. Several species showed an inverse relationship between population density and woodland area. Collections of small woods hold similar species richness to single large woods. While the acquisition of large woods for conservation purposes should be a priority, the extension of smaller woods to a size of about 10 ha would be highly beneficial to both the species richness and population stability of regional woodland bird assemblages.     

Change in the dominance structure of two marine-fish assemblages over three decades

Marine fish are an irreplaceable resource, but are currently under threat through overfishing and climate change. To date, most of the emphasis has been on single stocks or populations of economic importance. However, commercially valuable species are embedded in assemblages of many species and there is only limited understanding of the extent to which the structure of whole communities has altered in recent years. Most assemblages are dominated by one or a few species, with these highly abundant species underpinning ecosystem services and harvesting decisions. This paper shows that there have been marked temporal changes in the dominance structure of Scottish marine-fish assemblages over the past three decades, where dominance is measured as the proportional numerical abundance of the most dominant species. We report contrasting patterns in both the identity of the dominant species and shifts in the relative abundance of the dominant in assemblages to the east and west of Scotland, UK. This result highlights the importance of multi-species analyses of harvested stocks and has implications not only for fisheries management but also for consumer choices.