Reduced Species Richness Research Articles

Rat eradication and the resistance and resilience of passerine bird assemblages in the Falkland Islands

Norway rats (Rattus norvegicus) were introduced to the Falkland Islands and are detrimental to native passerines. Rat eradication programmes are being used to help protect the avifauna. This study assesses the effectiveness of eradication programmes while using this conservation practice as a natural experiment to explore the ecological resistance, resilience and homeostasis of bird communities. We conducted bird surveys on 230 islands: 85 in the presence of rats, 108 that were historically free of rats and 37 from which rats had been eradicated. Bird detection data were used to build occupancy models for each species and estimate species-area relationships. Count data were used to estimate relative abundance and community structure. Islands with invasive rats had reduced species richness of passerines and a different community structure than islands on which rats were historically absent. Although the species richness of native passerines was remarkably similar on eradicated and historically rat-free islands, community structure on eradicated islands was more similar to that of rat-infested islands than to historically rat-free islands. The results suggest that in the Falkland Islands, species richness of passerines is not resistant to invasive rats, but seems to be resilient following their removal. In contrast, community structure seems to be neither resistant nor resilient. From a conservation perspective, rat eradication programmes in the Falkland Islands appear to be effective at restoring native species richness, but they are not necessarily beneficial for species of conservation concern. For species that do not recolonize, translocations following eradications may be necessary.

Selective‐logging and oil palm: multitaxon impacts, biodiversity indicators, and trade‐offs for conservation planning

Strong global demand for tropical timber and agricultural products has driven large-scale logging and subsequent conversion of tropical forests. Given that the majority of tropical landscapes have been or will likely be logged, the protection of biodiversity within tropical forests thus depends on whether species can persist in these economically exploited lands, and if species cannot persist, whether we can protect enough primary forest from logging and conversion. However, our knowledge of the impact of logging and conversion on biodiversity is limited to a few taxa, often sampled in different locations with complex land-use histories, hampering attempts to plan cost-effective conservation strategies and to draw conclusions across taxa. Spanning a land-use gradient of primary forest, once- and twice-logged forests, and oil palm plantations, we used traditional sampling and DNA metabarcoding to compile an extensive data set in Sabah, Malaysian Borneo for nine vertebrate and invertebrate taxa to quantify the biological impacts of logging and oil palm, develop cost-effective methods of protecting biodiversity, and examine whether there is congruence in response among taxa. Logged forests retained high species richness, including, on average, 70% of species found in primary forest. In contrast, conversion to oil palm dramatically reduces species richness, with significantly fewer primary-forest species than found on logged forest transects for seven taxa. Using a systematic conservation planning analysis, we show that efficient protection of primary-forest species is achieved with land portfolios that include a large proportion of logged-forest plots. Protecting logged forests is thus a cost-effective method of protecting an ecologically and taxonomically diverse range of species, particularly when conservation budgets are limited. Six indicator groups (birds, leaf-litter ants, beetles, aerial hymenopterans, flies, and true bugs) proved to be consistently good predictors of the response of the other taxa to logging and oil palm. Our results confidently establish the high conservation value of logged forests and the low value of oil palm. Cross-taxon congruence in responses to disturbance also suggests that the practice of focusing on key indicator taxa yields important information of general biodiversity in studies of logging and oil palm.

Forest fragmentation in an African biodiversity hotspot impacts mixed-species bird flocks

The effect of forest fragmentation on mixed-species foraging bird flocks has been poorly evaluated, particularly in African forests. We examined the consequences of forest fragmentation on such flocks in the East Usambara Mountains, Tanzania, by addressing ecological as well as behavioral components. We counted these flocks in five small (<31ha), isolated fragments and six widely spaced continuous forest sites. Given that flock cohesion and stability might be facilitated via positive interactions of leader or nuclear species, we focused on one putative nuclear species, the square-tailed drongo (Dicrurus ludwigii), and using playback of its vocalisations, we evaluated (i) if its vocalisations attracted flocking birds as expected by a nuclear species, and (ii) if loss of this species in fragments contributed to flock declines. We found that flocks in forest fragments had smaller sizes, reduced species richness, a reduced proportion of understorey specialists, a higher proportion of forest generalists and non-forest species, and were more variable in size and composition compared to flocks observed in continuous forest. Furthermore, flocks in fragments were composed of a higher proportion of omnivores than insectivores. Despite lower absolute abundance in fragments, D. ludwigii was observed in 86% of natural occurring flocks in both fragments and continuous forest, and flocks with D. ludwigii were significantly larger than those without it––especially in the continuous forest. Playback vocalisations of D. ludwigii attracted flocks of similar abundance and species richness in fragments and continuous forest, but a vastly different composition, confirming (i) its nuclear role and (ii) that, in fragments, flock assemblages had a distinct composition, with a high proportion of forest generalists and non-forest species. Loss or diminished abundance of nuclear species due to fragmentation may be an important factor that affects the presence and composition of mixed-species flocks. Given that 67% of flocking species forage in the understorey, and that insectivores were more negatively affected in fragments than omnivores, the implications of our findings are relevant for conservation in tropical forests.

Assessing impacts of unconventional natural gas extraction on microbial communities in headwater stream ecosystems in Northwestern Pennsylvania.

Hydraulic fracturing and horizontal drilling have increased dramatically in Pennsylvania Marcellus shale formations, however the potential for major environmental impacts are still incompletely understood. High-throughput sequencing of the 16S rRNA gene was performed to characterize the microbial community structure of water, sediment, bryophyte, and biofilm samples from 26 headwater stream sites in northwestern Pennsylvania with different histories of fracking activity within Marcellus shale formations. Further, we describe the relationship between microbial community structure and environmental parameters measured. Approximately 3.2 million 16S rRNA gene sequences were retrieved from a total of 58 samples. Microbial community analyses showed significant reductions in species richness as well as evenness in sites with Marcellus shale activity. Beta diversity analyses revealed distinct microbial community structure between sites with and without Marcellus shale activity. For example, operational taxonomic units (OTUs) within the Acetobacteracea, Methylocystaceae, Acidobacteriaceae, and Phenylobacterium were greater than three log-fold more abundant in MSA+ sites as compared to MSA− sites. Further, several of these OTUs were strongly negatively correlated with pH and positively correlated with the number of wellpads in a watershed. It should be noted that many of the OTUs enriched in MSA+ sites are putative acidophilic and/or methanotrophic populations. This study revealed apparent shifts in the autochthonous microbial communities and highlighted potential members that could be responding to changing stream conditions as a result of nascent industrial activity in these aquatic ecosystems.

Effects of ice and floods on vegetation in streams in cold regions: implications for climate change.

Riparian zones support some of the most dynamic and species-rich plant communities in cold regions. A common conception among plant ecologists is that flooding during the season when plants are dormant generally has little effect on the survival and production of riparian vegetation. We show that winter floods may also be of fundamental importance for the composition of riverine vegetation. We investigated the effects of ice formation on riparian and in-stream vegetation in northern Sweden using a combination of experiments and observations in 25 reaches, spanning a gradient from ice-free to ice-rich reaches. The ice-rich reaches were characterized by high production of frazil and anchor ice. In a couple of experiments, we exposed riparian vegetation to experimentally induced winter flooding, which reduced the dominant dwarf-shrub cover and led to colonization of a species-rich forb-dominated vegetation. In another experiment, natural winter floods caused by anchor-ice formation removed plant mimics both in the in-stream and in the riparian zone, further supporting the result that anchor ice maintains dynamic plant communities. With a warmer winter climate, ice-induced winter floods may first increase in frequency because of more frequent shifts between freezing and thawing during winter, but further warming and shortening of the winter might make them less common than today. If ice-induced winter floods become reduced in number because of a warming climate, an important disturbance agent for riparian and in-stream vegetation will be removed, leading to reduced species richness in streams and rivers in cold regions. Given that such regions are expected to have more plant species in the future because of immigration from the south, the distribution of species richness among habitats can be expected to show novel patterns.

Exotic grassland species have stronger priority effects than natives regardless of whether they are cultivated or wild genotypes.

During community assembly, early arriving exotic species might suppress other species to a greater extent than do native species. Because most exotics were intentionally introduced, we hypothesize there was human selection on regeneration traits during introduction. This could have occurred at the across- or within-species level (e.g. during cultivar development). We tested these predictions by seeding a single species that was either native, exotic 'wild-type' (from their native range), or exotic 'cultivated' using 28 grassland species in a glasshouse experiment. Priority effects were assessed by measuring species' effect on establishment of species from a seed mix added 21 d later. Exotic species had higher germination and earlier emergence dates than native species, and differences were found in both 'wild' and 'cultivated' exotics. Exotic species reduced biomass and species diversity of later arriving species much more than native species, regardless of seed source. Results indicate that in situations in which priority effects are likely to be strong, effects will be greater when an exotic species arrives first than when a native species arrives first; and this difference is not merely a result of exotic species cultivation, but might be a general native-exotic difference that deserves further study.

Resource availability differentially drives community assemblages of plants and their root-associated arbuscular mycorrhizal fungi

Understanding the role of resource availability in structuring biotic communities is of importance in community ecology. This study investigates how light and soil nutrient availability drive assemblages of both plants and their root-associated arbuscular mycorrhizal fungi (AMF). We conducted a 4-year light [full light or shade] and soil fertility [unfertilized or fertilized with (NH4)(2)HPO4] interactive manipulations in an alpine meadow ecosystem. Species and phylogenetic compositions of plant and AMF communities were simultaneously measured, and the primary ecological processes structuring both communities were inferred from the community phylogenetic analysis. Reducing light and/or increasing soil fertility significantly reduced species richness and changed community compositions of both plant and AMF. Plant community phylogenetic structure shifted from random in untreated control to overdispersion in other treatments, whereas AMF communities were phylogenetically clustered and random in unfertilized and fertilized plots, respectively. These results suggest that plant communities in treated plots were mainly determined by competitive exclusion, and that AMF communities in unfertilized and fertilized plots were determined by environmental filtering and random process, respectively. We observed strong effects of light and soil nutrient availability on both plant and AMF communities, and our findings highlight that the primary ecological processes that drive plant and AMF assemblages should be highly dependent on the level of resource availability.

Invasiveness does not predict impact: response of native land snail communities to plant invasions in riparian habitats.

Studies of plant invasions rarely address impacts on molluscs. By comparing pairs of invaded and corresponding uninvaded plots in 96 sites in floodplain forests, we examined effects of four invasive alien plants (Impatiens glandulifera, Fallopia japonica, F. sachalinensis, and F.×bohemica) in the Czech Republic on communities of land snails. The richness and abundance of living land snail species were recorded separately for all species, rare species listed on the national Red List, and small species with shell size below 5 mm. The significant impacts ranged from 16–48% reduction in snail species numbers, and 29–90% reduction in abundance. Small species were especially prone to reduction in species richness by all four invasive plant taxa. Rare snails were also negatively impacted by all plant invaders, both in terms of species richness or abundance. Overall, the impacts on snails were invader-specific, differing among plant taxa. The strong effect of I. glandulifera could be related to the post-invasion decrease in abundance of tall nitrophilous native plant species that are a nutrient-rich food source for snails in riparian habitats. Fallopia sachalinensis had the strongest negative impact of the three knotweeds, which reflects differences in their canopy structure, microhabitat humidity and litter decomposition. The ranking of Fallopia taxa according to the strength of impacts on snail communities differs from ranking by their invasiveness, known from previous studies. This indicates that invasiveness does not simply translate to impacts of invasion and needs to be borne in mind by conservation and management authorities.

The Reduced Effectiveness of Protected Areas under Climate Change Threatens Atlantic Forest Tiger Moths

Climate change leads to species' range shifts, which may end up reducing the effectiveness of protected areas. These deleterious changes in biodiversity may become amplified if they include functionally important species, such as herbivores or pollinators. We evaluated how effective protected areas in the Brazilian Atlantic Forest are in maintaining the diversity of tiger moths (Arctiinae) under climate change. Specifically, we assessed whether protected areas will gain or lose species under climate change and mapped their locations in the Atlantic Forest, in order to assess potential spatial patterns of protected areas that will gain or lose species richness. Comparisons were completed using modeled species occurrence data based on the current and projected climate in 2080. We also built a null model for random allocation of protected areas to identify where reductions in species richness will be more severe than expected. We employed several modern techniques for modeling species' distributions and summarized results using ensembles of models. Our models indicate areas of high species richness in the central and southern regions of the Atlantic Forest both for now and the future. However, we estimate that in 2080 these regions should become climatically unsuitable, decreasing the species' distribution area. Around 4% of species were predicted to become extinct, some of them being endemic to the biome. Estimates of species turnover from current to future climate tended to be high, but these findings are dependent on modeling methods. Our most important results show that only a few protected areas in the southern region of the biome would gain species. Protected areas in semideciduous forests in the western region of the biome would lose more species than expected by the null model employed. Hence, current protected areas are worse off, than just randomly selected areas, at protecting species in the future.

Effects of urbanization on avian community in southwestern China

Surveys at southwestern China were conducted from November 2004 to July 2005 in three habitat types. A total 3319 individual of 69 bird species were recorded. Although urbanization was presumed to be responsible for decreasing species richness and diversity, our results showed bird species richness, diversity and density in urban habitats were not different in rural habitats. Whereas, the wasteland with low human disturbances, was the lowest bird species richness, diversity and density than others habitats. We inferred habitats structural complexity, large forest patches, native trees and human litter sustain many bird species in campus and park. However, human disturbances, habitats substrate and predation from domestic animals may reduce species richness and diversity. Therefore, we suggested that high vegetative cover should be in urban areas, because it may increase the number of bird species, support larger populations of insectivores, and perhaps create suitable habitat for some ground nesters. Moreover, by recreating or preserving natural islands decreased human disturbance and predation from domestic animals.

Effect of varying Alternanthera philoxeroides (alligator weed) cover on the macrophyte species diversity of pond ecosystems: a quadrat–based study

This year-long study, covering three main seasons of India, focused on enumerating the effect of varying cover of Alternanthera philoxeroides (alligator weed) on the associated macrophyte species diversity of the littoral region of natural pond ecosystem. A total of 192 quadrats were randomly placed in the littoral region of 12 similar ponds containing varying degrees of A. philoxeroides infestation to estimate A. philoxeroides ‘cover (%)’ and number of associated macrophyte species in each quadrat. Overall, 20 associated macrophyte species, including 16 aquatic/ littoral-associated, 2 non-aquatic species, and grasses and sedges, were found to be present. A. philoxeroides infestation was categorized into 4 cover grades (Grade I-IV) from lowest (no/negligible: 60% cover). For each season, significant differences in the total number of associated macrophyte species across the 4 A. philoxeroides cover grades were found. A Poisson-regression model showed that for each season, even when the effect of other invasive species was adjusted, the number of associated native macrophyte species in a quadrat decreases significantly with increase in A. philoxeroides cover. A comparison of the quadrat communities between the lowest grade (Grade I) and highest grade (Grade IV) of A. philoxeroides infestation showed a significant reduction of species richness, diversity and evenness from the lowest to the highest infestation grades. Again, Mann-Whitney U tests further revealed that the number of native macrophyte species was significantly lower at highest (Grade IV) A. philoxeroides infestation than that at lowest infestation (Grade I). The presence of multiple invaders in A. philoxeroides infested aquatic ecosystems is also reported, indicating probable facilitative interactions between A. philoxeroides and other invasive species. The socio-economic valuation of some important native plants, which were found to be significantly reduced at high infestation levels of A. philoxeroides, has also been highlighted.

Stand structure and species co-occurrence in mixed and monodominant Central African tropical forests

Abstract:We compare forests dominated by Gilbertiodendron dewevrei at the Dja Biosphere Reserve (Cameroon) with adjacent high-diversity mixed forests in terms of tree-species composition and stand structure, in order to understand the co-occurrence of mixed forest tree species in the monodominant forest. A total of 18 1-ha permanent plots were established in the two forest types. In each plot, all trees with dbh ≥10 cm were identified as were those &lt;10 cm dbh within a subsample of 300 m2. Species richness was significantly different between the two forest types. Mixed forest had an average of 109 species ha−1 for trees ≥10 cm dbh and 137 species for trees &lt;10 cm dbh. By contrast, G. dewevrei-dominated forest had an average of 47 species ha−1 (≥10 cm dbh) and 92 species (&lt;10 cm dbh). There was no significant difference in terms of stem density of the trees with dbh &lt;10 cm between the two forests (mixed: 3.7 stems m−2; monodominant: 3.1 stems m−2). As G. dewevrei is a shade-tolerant species that can regenerate under its own shade, its higher stem density and basal area can reduce species richness of an area.

Does multi‐level environmental filtering determine the functional and phylogenetic composition of wild bee species assemblages?

A central goal in ecology is to develop theories that explain the diversity and distribution of species. The evolutionary history of species and their functional traits may provide mechanistic links between community assembly and the environment. Such links may be hierarchically structured such that the strength of environmental filtering decreases in a step‐wise manner from regional conditions through landscape heterogeneity to local habitat conditions. We sampled the wild bee species assemblages in power‐line strips transecting forests in south‐eastern Norway. We used altitude, landscape diversity surrounding sites and plant species composition, together with total plant cover as proxies for regional, landscape and local environmental filters, respectively. The species richness and abundance of wild bees decreased with altitude. The reduction in species richness and abundance was accompanied by a phylogenetic clustering of wild bee individuals. Furthermore, regional filters followed by local filters best explained the structure of the functional species composition. Sites at high altitudes and sites with Ericaceae‐dominated plant communities tended to have larger bees and a higher proportion of social and spring‐emerging bees. When Bombus species were excluded from the analysis, the proportion of pollen specialists increased with the dominance of Ericaceae. Furthermore, we also found that the taxonomic, phylogenetic and functional compositional turnover between sites was higher in the northern region than in the southern part of the study region. Altogether, these results suggest that regional filters drive the species richness and abundance in trait‐groups whereas local filters have more descrete sorting effects.We conclude that the model of multi‐level environmental filters provides a good conceptual model for community ecology. We suggest that future studies should focus on the relationship between the biogeographical history of species and their current distribution, and on the assumption that closely related species do indeed compete more intensely than distantly related species.

Seasonal and interannual variability of the calanoid copepod community structure in shelf waters of the Eastern Tropical Pacific

The response of the calanoid copepod community structure and diversity to the variability of the oceanographic conditions was analyzed from January 1996 to December 1998 in the central Mexican Pacific. Interannual variability in the water column was marked by the influence of the 1997-98 El Nino (EN). However, seasonal variability was principally linked to the periodicity of coastal upwelling processes. Two species, Subeucalanus subcrassus and Centro - pages furcatus, contributed 62% to the copepod abundance over the 3 yr period, with 16 species making up 95% of the copepod community. Most species were subtropical-tropical (88%), but equatorial (8%) and cosmopolitan (2%) species were also present. Up to 17 species were recorded in 50% or more of samples, of which 10 were coastal or neritic forms. The calanoid copepod com- munity structure varied seasonally, with increased abundance and reduced species richness dur- ing upwelling conditions. During upwelling relaxation, the abundance declined but the species richness increased. Additional community variations were related to the EN event, when copepod abundances were significantly lower than during non-El Nino (NEN) periods (F = 20.387, p < 0.05), but seasonal changes were still detectable. There was no increase of species richness in the area related to the influence of EN. These data suggest that the response of this tropical neritic copepod community diverges from that of other zooplankters and that the community is more stable than expected, keeping a seasonal pattern even during the influence of a strong EN.

Species contribute differently to the taxonomic, functional, and phylogenetic alpha and beta diversity of freshwater fish communities

AbstractAimWe examined the current biogeographical patterns of native fish communities throughout France, using a multifaceted taxonomic, functional and phylogenetic diversity approach. We then identified the contribution of individual species to each facet of watershed's native fish diversity.LocationContinental France.MethodsThe taxonomic, functional and phylogenetic diversity of the fish communities were quantified at the watershed‐scale (i.e. alpha diversity approach), and congruencies between diversity facets were assessed. Variation between watersheds was then quantified (i.e. beta diversity approach) using Jaccard's dissimilarity index for all three facets of diversity, and congruencies were assessed. We subsequently determined the relationship between alpha and beta diversity for each diversity facet. Lastly, the mean relative contribution of each species to watershed's alpha taxonomic, functional and phylogenetic diversity was quantified. The conservation status of each species was considered to determine if threatened and endangered species contributed more significantly to watershed alpha diversity than common species.ResultsAcross all watersheds, taxonomic, functional and phylogenetic diversity facets were found to be highly congruent using both the alpha and beta diversity approaches. In contrast, the relationship between the watersheds' alpha and beta diversity was primarily negative; watersheds with decreased beta diversity tended to have increased alpha diversity for all three facets. Individual species also rarely contributed prominently to more than one diversity facet, with conservation status insignificantly influencing species relative contributions.Main conclusionsWe found that native fish diversity ‘hotspots’ exist in France; exhibited in our results by areas of high, overlapping taxonomic, functional and phylogenetic diversity. Consequently, conservation planning approaches supported by species‐based metrics may concurrently target areas of increased ecological and evolutionary importance at the watershed‐scale. Interestingly, a diverse mosaic of species accounted for the different facets of diversity, suggesting that future reductions in species richness could have differential effects on each watershed's diversity facets.

Nitrogen and phosphorus additions impact arbuscular mycorrhizal abundance and molecular diversity in a tropical montane forest.

Increased nitrogen (N) depositions expected in the future endanger the diversity and stability of ecosystems primarily limited by N, but also often co-limited by other nutrients like phosphorus (P). In this context a nutrient manipulation experiment (NUMEX) was set up in a tropical montane rainforest in southern Ecuador, an area identified as biodiversity hotspot. We examined impacts of elevated N and P availability on arbuscular mycorrhizal fungi (AMF), a group of obligate biotrophic plant symbionts with an important role in soil nutrient cycles. We tested the hypothesis that increased nutrient availability will reduce AMF abundance, reduce species richness and shift the AMF community toward lineages previously shown to be favored by fertilized conditions. NUMEX was designed as a full factorial randomized block design. Soil cores were taken after 2years of nutrient additions in plots located at 2000m above sea level. Roots were extracted and intraradical AMF abundance determined microscopically; the AMF community was analyzed by 454-pyrosequencing targeting the large subunit rDNA. We identified 74 operational taxonomic units (OTUs) with a large proportion of Diversisporales. N additions provoked a significant decrease in intraradical abundance, whereas AMF richness was reduced significantly by N and P additions, with the strongest effect in the combined treatment (39% fewer OTUs), mainly influencing rare species. We identified a differential effect on phylogenetic groups, with Diversisporales richness mainly reduced by N additions in contrast to Glomerales highly significantly affected solely by P. Regarding AMF community structure, we observed a compositional shift when analyzing presence/absence data following P additions. In conclusion, N and P additions in this ecosystem affect AMF abundance, but especially AMF species richness; these changes might influence plant community composition and productivity and by that various ecosystem processes.

Non-linear responses of functional diversity and redundancy to agricultural intensification at the field scale in Mediterranean arable plant communities

Despite their key roles in agroecosystems, species diversity of arable plants is being severely reduced by agricultural intensification, although it remains unclear whether functional diversity is affected in a similar way. We analyzed the response of four functional traits of arable plants (specific leaf area, canopy height, seed mass and flowering onset) to agricultural intensification in Mediterranean arable plant communities. Two intensification gradients were obtained by PCA analysis on variables related either to management practices at the individual field scale or to the surrounding landscape structure and composition. Shifts in the community weighted mean (CWM) and the functional diversity (FD) of each trait along these intensification gradients were explored. The relationship between species richness and the FD of each trait (i.e. functional redundancy) along the same gradients was also analyzed. The responses of species richness and the considered functional traits were driven by intensification at the individual field scale, but not by intensification at the scale of the surrounding landscape. Species richness and FD of all the studied traits decreased with intensification, which favoured tall, heavy-seeded and early flowering species. The decrease of FD was non-linear for specific leaf area and seed mass, with maximum reductions at intermediate levels of intensification. Species richness and FD responses were decoupled, indicating that the functional redundancy in the studied communities responds to agricultural intensification in a non-linear fashion. Along the first stages of intensification, there was an important reduction in species richness that was not accompanied by changes in FD. Further levels of intensification resulted in substantial reductions in FD without changes in species richness. These findings provide new insights on how agricultural management interacts with plant communities through its non-linear effects on functional diversity and functional redundancy.

Marine benthic ecological functioning over decreasing taxonomic richness

Alterations to ecosystem function due to reductions in species richness are predicted to increase as humans continue to affect the marine environment, especially in coastal areas, which serve as the interface between land and sea. The potential functional consequences due to reductions in species diversity have attracted considerable attention recently but little is known about the consequence of such loss in natural communities. We examined how the potential for function is affected by natural reductions in taxon richness using empirical (non-simulated) coastal marine benthic macrofaunal data from the Skagerrak-Baltic Sea region (N. Europe), where taxon richness decreases 25-fold, from 151 to 6 taxa. To estimate functional changes we defined multiple traits (10 traits and 51 categories) on which trait category richness, functional diversity (FD) and number of taxa per trait category were calculated. Our results show that decrease in taxon richness leads to an overall reduction in function but functional richness remains comparatively high even at the lowest level of taxon richness. Although the taxonomic reduction was sharp, up to 96% of total taxon richness, we identified both potential thresholds in functioning and subtler changes where function was maintained along the gradient. The functional changes were not only caused by reductions in taxa per trait category, some categories were maintained or even increased. Primarily, the reduction in species richness altered trait categories related to feeding, living and movement and thus potentially could have an effect on various ecosystem processes. This highlights the importance of recognising ecosystem multifunctionality, especially at low taxonomic richness. We also found that in this system rare species (singletons) did not stand for the functional complexities and changes. Our findings were consistent with theoretical and experimental predictions and suggest that a large proportion of the information about alterations of function is found in measures such as functional diversity and number of taxa per trait category.

Birds at the urban fringe: avian community shifts in different peri‐urban ecotones of a megacity

AbstractCities can be regionalized in intra‐urban and peri‐urban areas. The space between urban areas and adjacent systems represents an ecological transition that often acts as a semi‐permeable biological filter. In this study, we assessed changes in avian community species richness, density, and composition at different peri‐urban ecotones (i.e., urban‐croplands, urban‐grasslands, urban‐shrublands) of northeastern Mexico City. Species richness was lower in the urban component of urban‐grassland and urban‐shrubland ecotones, while bird densities were higher in the urban components of the urban‐grassland and urban‐shrubland peri‐urban ecotones, mainly due to the high number of urban exploiter species. However, the urban‐cropland peri‐urban ecotone exhibited a different pattern, with similar low bird species richness and density values between both components (urban and non‐urban). A species composition analysis revealed that urban bird communities were not influenced by adjacent non‐urban habitats, since the urban components of peri‐urban ecotones were more similar among them than in relation to the rest of non‐urban components. In summary, results of this study show that urbanization can represent an important biological filter for birds, often reducing species richness and homogenizing avian communities at local scales. As the environmental variables determining ecological processes related to the semi‐permeable filter effect that urban areas pose to biodiversity might depend on urban habitats, regions, and spatial scales, further studies are needed to fully understand this phenomenon.

The Role of Nitrogen Deposition in Widespread Plant Community Change Across Semi-natural Habitats

Experimental studies have shown that deposition of reactive nitrogen is an important driver of plant community change, however, most of these experiments are of short duration with unrealistic treatments, and conducted in regions with elevated ambient deposition. Studies of spatial gradients of pollution can complement experimental data and indicate whether the potential impacts demonstrated by experiments are actually occurring in the ‘real world’. However, targeted surveys exist for only a very few habitats and are not readily comparable. In a coordinated campaign, we determined the species richness and plant community composition of five widespread, semi-natural habitats across Great Britain in sites stratified along gradients of climate and pollution, and related these ecological parameters to major drivers of biodiversity, including climate, pollution deposition, and local edaphic factors. In every habitat, we found reduced species richness and changed species composition associated with higher nitrogen deposition, with remarkable consistency in relative species loss across ecosystem types. Whereas the diversity of mosses, lichens, forbs, and graminoids declines with N deposition in different habitats, the cover of graminoids generally increases. Considered alongside previous experimental studies and survey work, our results provide a compelling argument that nitrogen deposition is a widespread and pervasive threat to terrestrial ecosystems.