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Detecting occupied sites of rare species, and estimating the probability that all occupied sites are known within a given area, are desired outcomes for many ecological or conservation projects. Examples include managing all occupied sites of a threatened species or eradicating an emerging invader. Occupied sites may remain undetected because (1) sites where the species potentially occurs had not been searched, and (2) the species could have been overlooked in the searched sites. For rare species, available data are typically scant, making it difficult to predict sites where the species probably occurs or to estimate detection probability in the searched sites. Using the critically endangered Rose's mountain toadlet (Capensibufo rosei), known from only two localities, we outline an iterative process aimed at estimating the probability that any unknown occupied sites remain and maximizing the chance of finding them. This includes fitting a species distribution model to guide sampling effort, testing model accuracy and sampling efficacy using the occurrence of more common proxy species, and estimating detection probability using sites of known presence. The final estimate of the probability that all occupied sites were found incorporates the uncertainties of uneven distribution, relative area searched, and detection probability. Our results show that very few occupied sites of C. rosei are likely to remain undetected. We also show that the probability of an undetected occupied site remaining will always be high for large unsearched areas of potential occurrence, but can be low for smaller areas intended for targeted management interventions. Our approach is especially useful for assessing uncertainty in species occurrences, planning the required search effort needed to reduce probability of unknown occurrence to desired levels, and identifying priority areas for further searches or management interventions., (© 2021 The Ecological Society of America.)

Many conservation actions are justified on the basis of managing biodiversity. Biodiversity, in terms of species richness, is largely the product of rare species. This is problematic because the intensity of sampling needed to characterize communities and patterns of rarity or to justify the use of surrogates has biased sampling in favor of space over time. However, environmental fluctuations interacting with community dynamics lead to temporal variations in where and when species occur, potentially affecting conservation planning by generating uncertainty about results of species distribution modeling (including range determinations), selection of surrogates for biodiversity, and the proportion of biodiversity composed of rare species. To have confidence in the evidence base for conservation actions, one must consider whether temporal replication is necessary to produce broad inferences. Using approximately 20 years of macrofaunal data from tidal flats in 2 harbors, we explored variation in the identity of rare, common, restricted range, and widespread species over time and space. Over time, rare taxa were more likely to increase in abundance or occurrence than to remain rare or disappear and to exhibit temporal patterns in their occurrence. Space-time congruency in ranges (i.e., spatially widespread taxa were also temporally widespread) was observed only where samples were collected across an environmental gradient. Fifteen percent of the taxa in both harbors changed over time from having spatially restricted ranges to having widespread ranges. Our findings suggest that rare species can provide stability against environmental change, because the majority of species were not random transients, but that selection of biodiversity surrogates requires temporal validation. Rarity needs to be considered both spatially and temporally, as species that occur randomly over time are likely to play a different role in ecosystem functioning than those exhibiting temporal structure (e.g., seasonality). Moreover, temporal structure offers the opportunity to place management and conservation activities within windows of maximum opportunity., (© 2016 Society for Conservation Biology.)

The identification of species at risk of extinction is a central goal of conservation. As the use of data compiled for IUCN Red List assessments expands, a number of misconceptions regarding the purpose, application and use of the IUCN Red List categories and criteria have arisen. We outline five such classes of misconception; the most consequential drive proposals for adapted versions of the criteria, rendering assessments among species incomparable. A key challenge for the future will be to recognize the point where understanding has developed so markedly that it is time for the next generation of the Red List criteria. We do not believe we are there yet but, recognizing the need for scrutiny and continued development of Red Listing, conclude by suggesting areas where additional research could be valuable in improving the understanding of extinction risk among species., (© 2016 The Author(s).)

Aim Location Time period Major taxa studied Methods Results Main conclusions Ecological and anthropogenic factors shift the abundances of dominant and rare tree species within local forest communities, thus affecting species composition and ecosystem functioning. To inform forest and conservation management it is important to understand the drivers of dominance and rarity in local tree communities. We answer the following research questions: (1) What are the patterns of dominance and rarity in tree communities? (2) Which ecological and anthropogenic factors predict these patterns? And (3) what is the extinction risk of locally dominant and rare tree species?Global.1990–2017.Trees.We used 1.2 million forest plots and quantified local tree dominance as the relative plot basal area of the single most dominant species and local rarity as the percentage of species that contribute together to the least 10% of plot basal area. We mapped global community dominance and rarity using machine learning models and evaluated the ecological and anthropogenic predictors with linear models. Extinction risk, for example threatened status, of geographically widespread dominant and rare species was evaluated.Community dominance and rarity show contrasting latitudinal trends, with boreal forests having high levels of dominance and tropical forests having high levels of rarity. Increasing annual precipitation reduces community dominance, probably because precipitation is related to an increase in tree density and richness. Additionally, stand age is positively related to community dominance, due to stem diameter increase of the most dominant species. Surprisingly, we find that locally dominant and rare species, which are geographically widespread in our data, have an equally high rate of elevated extinction due to declining populations through large‐scale land degradation.By linking patterns and predictors of community dominance and rarity to extinction risk, our results suggest that also widespread species should be considered in large‐scale management and conservation practices. [ABSTRACT FROM AUTHOR]

Species rarity is a common phenomenon across global ecosystems that is becoming increasingly more common under climate change. Although species rarity is often considered to be a stochastic response to environmental and ecological constraints, we examined the hypothesis that plant rarity is a consequence of natural selection acting on performance traits that affect a species range size, habitat specificity, and population aggregation; three primary descriptors of rarity. Using a common garden of 25 species of Tasmanian Eucalyptus, we find that the rarest species have 70% lower biomass than common species. Although rare species demonstrate lower biomass, rare species allocated proportionally more biomass aboveground than common species. There is also a negative phylogenetic autocorrelation underlying the biomass of rare and common species, indicating that traits associated with rarity have diverged within subgenera as a result of environmental factors to reach different associated optima. In support of our hypothesis, we found significant positive relationships between species biomass, range size and habitat specificity, but not population aggregation. These results demonstrate repeated convergent evolution of the trait‐based determinants of rarity across the phylogeny in Tasmanian eucalypts. Furthermore, the phylogenetically driven patterns in biomass and biomass allocation seen in rare species may be representative of a larger plant strategy, not yet considered, but offering a mechanism as to how rare species continue to persist despite inherent constraints of small, specialized ranges and populations. These results suggest that if rarity can evolve and is related to plant traits such as biomass, rather than a random outcome of environmental constraints, we may need to revise conservation efforts in these and other rare species to reconsider the abiotic and biotic factors that underlie the distributions of rare plant species. [ABSTRACT FROM AUTHOR]

Background: The northern Western Ghats (NWG) – a part of the Western Ghats and Sri Lanka biodiversity hotspot supports tropical forests of conservation priority, due to anthropogenic intensification. Woody species diversity and ecology in NWG is poorly studied, necessitating the knowledge of spatial variability in species and underlying environmental factors, for effective conservation. Aims: We described woody plant community composition and related it to climate data across a latitude of 1.4 degrees to obtain information about spatial and environmental variation to support protected area planning. Methods: To estimate abundance, importance value index, diversity indices and rank – abundance, we recorded woody species in 144 plots across 12 sites. Elevation, temperature, rainfall, humidity data were related to diversity descriptors in a canonical correspondence analysis. Results: We recorded 10,291 trees representing 187 species of 52 families. Divergent geo-climatic factors were related to distinct plant community structures, elevation and humidity being the most influential drivers of plant diversity and density. Numerous rare species were found restricted to environmentally distinct forests. Conclusion: The wide-ranging environment and corresponding variations in forest community composition across the narrow latitudinal range of the study area revealed the importance of including such gradients in planning future protected areas in the NWG. [ABSTRACT FROM AUTHOR]

Phytoplankton guilds are commonly characterised by dominance effects, while the main contribution to biological diversity is given by rare species. Here, we analysed the influence of rare species on taxonomic and functional diversity, which is described by taxa richness and composition, cell size, and size–abundance relationships in phytoplankton guilds. We explore these relationships at global and regional scales by analysing phytoplankton guilds from five biogeographical regions: the Northern Atlantic Ocean (Scotland), the South-Western Atlantic Ocean (Brazil), the South-Western Pacific Ocean (Australia), the Indo-Pacific Ocean (Maldives), and the Mediterranean Sea (Greece and Turkey). We have comparatively analysed the phytoplankton taxonomic diversity of the whole dataset and with the datasets obtained by progressively subtracting taxa occurring in the last 1%, 5%, 10%, and 25% of both numerical abundance and overall biomass. Globally, 306 taxa were identified across five ecoregions with only 27 taxa accounting for 75% of overall numerical abundance and biomass; almost 50% of taxa were lost on every step. The removal of 1% of most rare taxa significantly affected the phytoplankton size–abundance relationships and body-size structure, strongly impacting on small taxa. The progressive removal of additional rare taxa did not further affect phytoplankton size–abundance relationships and size structure. [ABSTRACT FROM AUTHOR]

Using data from a wide range of natural communities including the human microbiome, plants, fish, mushrooms, rodents, beetles, and trees, we show that universally just a few percent of the species account for most of the biomass. This is in line with the classical observation that the vast bulk of biodiversity is very rare. Attempts to find traits allowing the tiny fraction of abundant species to escape rarity have remained unsuccessful. Here, we argue that this might be explained by the fact that hyper-dominance can emerge through stochastic processes. We demonstrate that in neutrally competing groups of species, rarity tends to become a trap if environmental fluctuations result in gains and losses proportional to abundances. This counter-intuitive phenomenon arises because absolute change tends to zero for very small abundances, causing rarity to become a “sticky state”, a pseudoattractor that can be revealed numerically in classical ball-in-cup landscapes. As a result, the vast majority of species spend most of their time in rarity leaving space for just a few others to dominate the neutral community. However, fates remain stochastic. Provided that there is some response diversity, roles occasionally shift as stochastic events or natural enemies bring an abundant species down allowing a rare species to rise to dominance. Microbial time series spanning thousands of generations support this prediction. Our results suggest that near-neutrality within niches may allow numerous rare species to persist in the wings of the dominant ones. Stand-ins may serve as insurance when former key species collapse. [ABSTRACT FROM AUTHOR]

Fires in northern Patagonia are very frequent events, especially in summer seasons, affecting a large percentage of the area each year. Its consequences on biodiversity are variable according to the intensity, permanence and environments that are affected. Fire in ecosystems appears with a dual behavior, as a catastrophic disturbance and as an agent capable of opening environments and allowing the colonization of new sites by rare species, that are considered poor competitors. Through the analysis of measurements in marked plants in the pre-fire season in the Lihué Calel National Park, it was possible to evaluate the response to this phenomenon of Gaillardia cabrerae Covas (Asteraceae), a rarity in the south-central of La Pampa province. The resprouting capacity allowed the recovery of the affected populations and the production of flower heads was recorded in a greater number than in the pre-fire season. These results suggest a positive response of the species to these particular events at the end of 2003. However, given the intrinsic vulnerability of species with such a limited distribution, fire continues to be a high-impact factor for populations and their effect remains uncertain. Considering its rare condition, it is necessary to take precautionary measures to ensure the survival of the species in a context of climate change that defines a near-future scenario characterized by a high degree of unpredictability. [ABSTRACT FROM AUTHOR]

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The establishment of protected areas to face global diversity declines has mainly prioritized taxonomic diversity, leaving aside phylogenetic and functional diversities, which determine ecosystem functioning and resilience. Furthermore, the assessment of protected areas' effectiveness is mainly done using short‐duration surveys (<2 h), which may undermine the detection of rare species.Through a long‐duration video approach, reef fish taxonomic, phylogenetic and functional facets of diversity were assessed for 3 days within a fully protected area and a nearby poorly protected area in Mayotte Island (Western Indian Ocean).We found that temporally rare species contributed to more than 60% of the taxonomic facet and 85% of the functional facet of biodiversity found on each site. Those rare species, which harbour the most distinct trait values, also make reef fish diversity particularly vulnerable to their loss. Taxonomic, phylogenetic and functional richness were similar between the fully protected area and the poorly protected area, while the species, lineage and trait compositions were markedly different.These results pinpoint the importance of considering taxonomic, functional and phylogenetic dissimilarities while assessing protected areas' effectiveness, instead of using only richness. In addition, benefits of the fully protected area were detected only using more than 15 h of video survey, which emphasizes the importance of long‐duration remote approaches to capture the within‐ and between‐day temporal variations. [ABSTRACT FROM AUTHOR]

Northern bog lemmings, Mictomys (Synaptomys) borealis, are currently being assessed for protections under the U.S. Endangered Species Act. A major impediment to comprehensive evaluation is a deficiency of data towards understanding the biology of these rodents. Inherent rarity and scarce specimen sampling, despite a continent-wide distribution, has precluded our ability to implement modern methods for resolving taxonomy, evolutionary history, and investigating multiple other species traits. Here we use a maternally inherited locus (mitochondrial cytochrome b) and between 5939 and 11 513 nuclear loci from reduced representation sequencing (ddRADseq) to investigate the evolutionary history of northern bog lemmings. We (1) qualify evidence based on morphological and early molecular studies for the genus assignment of Mictomys, (2) test the validity of multiple sub-species designations, (3) provide spatial and temporal historical biogeographic perspectives, and (4) discuss how incomplete sampling might influence conservation efforts. Both mitochondrial and nuclear datasets exhibit deep divergence and paraphyly between two recognized species, the northern (Mictomys borealis) and southern (Synaptomys cooperi) bog lemmings. Based on mtDNA, the geographically isolated subspecies (M. b. sphagnicola) was found to be divergent from all other specimens. The remainder of the species exhibited shallow intra-specific differentiation in mtDNA, however, nuclear data supports genetic distinction consistent with four geographic subspecies. Recent coalescence of all northern bog lemmings (except for M. b. sphagnicola) reflects divergence in multiple refugia through the last glacial cycle, including a well-known coastal center of endemism and multiple regions south of continental ice sheets. Regional lineages across North America suggest strong latitudinal displacement with global climate change, coupled with isolation-reconnection dynamics. This taxon suffers from a lack of modern samples through most of its distribution, severely limiting the interpretation of ongoing evolutionary processes, particularly in southern portions of the species' range. Limited voucher specimen sampling of vulnerable populations could aid in rigorous conservation decision-making. [ABSTRACT FROM AUTHOR]

Climate change is modifying plant communities and ecosystems around the world. Alpine ecosystems are of special concern on oceanic islands, due to their characteristic higher endemicity percentage, small area and undergoing severe climate change impact in the last few decades. During recent decades there has been increasing interest in the effects of climate change on biodiversity and a range of methods have been developed to assess species vulnerability. However, some new insights are necessary to obtain useful information for species management on oceanic islands. Here in the alpine area of two oceanic islands (Tenerife and La Palma) we evaluate the drivers that best explain the vulnerability of 63 endemic species along three scenarios, covering recent past to present and two future projections (2041–2060 and 2061–2080). The selected drivers were: loss of potential area, mismatch index between potential and occupied areas in different scenarios, and adaptive capacity constraints. We assess the influence of potential area size and whether the drivers of risk and the vulnerability for common, restricted and rare species are significantly different. Our results indicate that management must be widely distributed over the species, and not only focus on restricted species. Evidence for this was that drivers directly deriving from climate change showed no significant differences in their impact on the rarity groups identified. Vulnerability depends partially on the potential area size, showing a more complex picture where constraints on the adaptive capacity of the species have a strong enough influence to modify the effects of the characteristic drivers of climate change. [ABSTRACT FROM AUTHOR]

Conservation policies and environmental impact assessments commonly target threatened species and habitats. Nevertheless, macroecological research provides reasons why also common species should be considered. We investigate the consequences of focussing solely on legally protected species and habitats in a spatial conservation planning context using a comprehensive, benthic marine data set from the northern Baltic Sea. Using spatial prioritization and surrogacy analysis, we show that the common approach in conservation planning, where legally listed threatened species and habitats are the focus of conservation efforts, could lead to poor outcomes for common species (and therefore biodiversity as a whole), allowing them to decline in the future. If conservation efforts were aimed solely at threatened species, common species would experience a loss of 62% coverage. In contrast, if conservation plans were based only on common species, threatened species would suffer a loss of 1%. Threatened species are rare and their ecological niches distinct, making them poor surrogates for biodiversity. The best results are achieved by unified planning for all species and habitats. The minimal step towards acknowledging common species in conservation planning would be the inclusion of the richness of common species, complemented by information on indicator species or species of high importance for ecosystem functioning. The trade‐off between planning for rare and common species should be evaluated, to minimize losses to biodiversity. [ABSTRACT FROM AUTHOR]

Motivated by accelerating anthropogenic extinctions, decades of biodiversity–ecosystem function (BEF) experiments show that ecosystem function declines with species loss from local communities. Yet, at the local scale, changes in species' total and relative abundances are more common than species loss. The consensus best biodiversity measures are Hill numbers, which use a scaling parameter, ℓ, to emphasize rarer versus more common species. Shifting that emphasis captures distinct, function-relevant biodiversity gradients beyond species richness. Here, we hypothesized that Hill numbers that emphasize rare species more than richness does may distinguish large, complex and presumably higher-functioning assemblages from smaller and simpler ones. In this study, we tested which values of ℓ produce the strongest BEF relationships in community datasets of ecosystem functions provided by wild, free-living organisms. We found that ℓ values that emphasized rare species more than richness does most often correlated most strongly with ecosystem functions. As emphasis shifted to more common species, BEF correlations were often weak and/or negative. We argue that unconventional Hill diversities that shift emphasis towards rarer species may be useful for describing biodiversity change, and that employing a wide spectrum of Hill numbers can clarify mechanisms underlying BEF relationships. This article is part of the theme issue 'Detecting and attributing the causes of biodiversity change: needs, gaps and solutions'. [ABSTRACT FROM AUTHOR]

Aim: Support for different underlying mechanisms of species occupancy is inconsistent, yet this could be related to spatial scale. Since abiotic filtering typically acts at broader scales than biotic interactions, we hypothesise that occupancy could be more driven by species' abiotic niche (i.e. tolerance and preference of abiotic conditions) at broad scales, whereas species' traits affecting competitive ability could be more important at fine scales. Here, we test these hypotheses by assessing relationships of occupancy to niche and trait metrics across spatial scales. Location: Four study areas located north of Arctic Circle. Taxon: Vascular plants. Methods: We derived occupancy for 106 species at four spatial scales (micro‐scale with plot size of 0.04 m2 and extent of 2 km, local‐scale with plot size of 4 m2 and extent of 40 km, regional‐scale with plot size of 4 ha and extent of 800 km, and polar‐scale with plot size of 4 km2 and extent of 5200 km). We then assessed using generalized additive models whether the relationships between occupancy and species' niche breadth, niche marginality, intraspecific trait variability (ITV) and trait distinctiveness vary across the scales. Results: At the finer scales, ITV (especially of specific leaf area) had the highest contribution with positive relationship in explaining occupancy. At the broader scales, occupancy was better explained by niche metrics. Especially at the broadest scale, the occupancy had a positive relationship with species' climatic tolerance. Main Conclusions: Abiotic filtering, especially related to macro‐climate, drives species occupancy at broader spatial scales while biotic interactions are relatively more important at local scales. This scale‐dependency of factors behind species occupancy should be accounted for when, for example, planning conservation of rare species, forecasting invasions or anticipating the effects of changing climate on biota at local versus global scales. [ABSTRACT FROM AUTHOR]

The slender racer, Orientocoluber spinalis, is a monotypic species found in northeast Asia. We collected 67 O. spinalis samples from the Republic of Korea (hereafter, South Korea) and 7 from China and Mongolia and investigated their genetic diversity and population structure. In South Korea, O. spinalis populations were mainly found on Oeyeondo, Uido, and Udo islands and Woraksan Mountain and showed low genetic diversity in the analysis of concatenated mitochondrial sequences of the cytochrome b (Cytb) and NADH dehydrogenase subunit 4 (ND4) genes. Orientocoluber spinalis populations in South Korea showed low differentiation and likely diverged recently. Orientocoluber spinalis may have colonized the Korean Peninsula from China and Mongolia, but this route is not confirmed due to the lack of samples from the Democratic People's Republic of Korea and middle eastern China. Considering its extreme rarity, low population density, and low genetic diversity, O. spinalis should be designated an endangered species in South Korea, as it is in Russia, Mongolia, and Kazakhstan. [ABSTRACT FROM AUTHOR]

Questions: A variety of mechanisms sustain diversity in natural communities as a result of ecological interactions between organisms. Competition has been studied extensively in the context of species maintenance, but facilitation is often conceptualized as simply reducing competition between functionally different species, which tends to decline throughout the plants' life span. Here we explore how interspecific facilitation may sustain diversity throughout the species' life by avoiding the extinction of locally rare species at juvenile stages and reducing performance disparities between neighbors of differing species at mature stages. Methods: To do so, we measured whether rarer species relied more on facilitation than abundant ones in semiarid shrubland in southeast Spain. A mechanistic explanation of this relationship was subsequently tested by correlating rarity with the species' affinity to a particularly edaphic stressful environment. Finally, we assessed whether growing associated with neighbors in vegetation patches shaped by facilitation could balance performance disparities between species when they become adults. Results: We show that facilitation (i) favors the rare species, which, in addition, tend to be those with low affinity to the stressful environment, and (ii) reduces the performance dissimilarities among plants growing associated within multispecific vegetation patches compared to plants growing alone. Conclusions: These facilitative effects, beyond the reduction of competition between functionally similar species, might ensure positive and long‐lasting effects of biotic interactions, implying a more critical role for facilitation in preserving biodiversity than previously thought. [ABSTRACT FROM AUTHOR]

This study presents data on woody plant species richness and diversity of an inaccessible dry forest of Tula Mountains Woodland (TMW) located in the northeast of Nigeria. TMW supports a minimally disturbed mosaic of dry forest‐woodland. We sampled woody species in 190 plots of size 0.01‐ha, spaced 50 m apart on series of line transects. We found a total of 133 woody species belonging to 88 genera and 39 families in 1.9 ha area sampled in total. Out of 133 species, 120 were identified to species level, and 113 were recorded as trees, shrubs and lianas with diameter at breast height (dbh) ≥ 5 cm. Species accumulation curve was non‐asymptotic. Fisher's logseries model suggests that the plots sampled in the dry forest communities of TMW are represented by a high number of rare species. Of 120 identified species, 46 (38%) lacked evaluation on conservation status by IUCN. Out of 74 (62%) evaluated species, 2 were listed as critically endangered, 3 were vulnerable, and 69 were of least concern. In the TMW, 27% of woody species were restricted to Sudanian savannah biome, 61% occurred in Sudanian and Zambezian savannah biome. TMW serves as refugia for native plant species and plant communities in northeastern Nigeria. [ABSTRACT FROM AUTHOR]

Life‐history traits are promising tools to predict species commonness and rarity because they influence a population's fitness in a given environment. Yet, species with similar traits can have vastly different abundances, challenging the prospect of robust trait‐based predictions. Using long‐term demographic monitoring, we show that coral populations with similar morphological and life‐history traits show persistent (decade‐long) differences in abundance. Morphological groups predicted species positions along two, well known life‐history axes (the fast‐slow continuum and size‐specific fecundity). However, integral projection models revealed that density‐independent population growth (λ) was more variable within morphological groups, and was consistently higher in dominant species relative to rare species. Within‐group λ differences projected large abundance differences among similar species in short timeframes, and were generated by small but compounding variation in growth, survival, and reproduction. Our study shows that easily measured morphological traits predict demographic strategies, yet small life‐history differences can accumulate into large differences in λ and abundance among similar species. Quantifying the net effects of multiple traits on population dynamics is therefore essential to anticipate species commonness and rarity. [ABSTRACT FROM AUTHOR]

Cities are sometimes characterized as homogenous with species assemblages composed of abundant, generalist species having similar ecological functions. Under this assumption, rare species, or species observed infrequently, would have especially high conservation value in cities for their potential to increase functional diversity. Management to increase the number of rare species in cities could be an important conservation strategy in a rapidly urbanizing world. However, most studies of species rarity define rarity in relatively pristine environments where human management and disturbance is minimized. We know little about what species are rare, how many species are rare, and what management practices promote rare species in urban environments. Here, we identified which plants and species of birds and bees that control pests and pollinate crops are rare in urban gardens and assessed how social, biophysical factors, and cross‐taxonomic comparisons influence rare species richness. We found overwhelming numbers of rare species, with more than 50% of plants observed classified as rare. Our results highlight the importance of women, older individuals, and gardeners who live closer to garden sites in increasing the number of rare plants within urban areas. Fewer rare plants were found in older gardens and gardens with more bare soil. There were more rare bird species in larger gardens and more rare bee species for which canopy cover was higher. We also found that in some cases, rarity begets rarity, with positive correlations found between the number of rare plants and bee species and between bee and bird species. Overall, our results suggest that urban gardens include a high number of species existing at low frequency and that social and biophysical factors promoting rare, planned biodiversity can cascade down to promote rare, associated biodiversity. [ABSTRACT FROM AUTHOR]

Aim: Understanding ecological distributions of global biodiversity is stymied by incomplete knowledge of drivers of species rarity. These include trade‐offs among life‐history traits that impact dispersability, competition, reproductive output and speciation and extinction. In this study, we aim to understand potential drivers of rarity in North American lichens. Location and methods: With nearly 5500 species and a third of global species richness, North America is a hotspot for lichen biodiversity. Here, we employ a continental‐scale dataset on North American lichens to test potential drivers of species rarity. For all species, we determined coarse‐scale geographical distribution along with the mode of reproduction, substrate, growth form and photobiont type. Results: Our analyses found that most lichens are rare and known only from one or two ecoregions. Rare species are not equally distributed across ecoregions: the Eastern temperate hardwood forests and wet tropical forests of southern Florida harbour the vast majority of rare species. Wet to seasonally wet ecoregions of western North America are home to most remaining narrowly distributed lichen species. In contrast, northern ecoregions along with drier ecoregions including the Great Plains and deserts harbour primarily widespread species. Lichen rarity is significantly associated with species that live on bark or leaves, those with a Trentepohlia photobiont, those that are small, crustose and live closely appressed to their substrates, and those that reproduce sexually, dispersing only the mycobiont. North American lichens are represented unevenly across trait categories, with 65% of them having a crustose growth form, 73% bearing a Trebouxia or other green algal photobiont, 78% living on bark or rock and 77% reproducing sexually. Main conclusions: Our study, spanning an entire continental‐scale biota, helps to establish a generalized relationship among life‐history traits and rarity in lichens and highlights the significance of biotic interactions in structuring biogeographical distributions. [ABSTRACT FROM AUTHOR]

Until now, Gaillardia cabrerae Covas has been considered an exclusive endemic species of Lihué Calel, a mountain range system in the center-south of La Pampa and the only National Park in the province. In this work, two new presence sites are recorded outside the limits of the protected area. Through an active search in sites with similar geological characteristics to the known distribution site, a population was identified in the Sierras Chicas and another one in the Choique Mahuida Hills, the latter about 95 km southern Lihué Calel National Park. The condition of rarity and the criteria to be taken into account for the categorization of the species are discussed even when its spatial distribution is now resized. The sites in which G. cabrerae develops represent refuges in which many rare species find particularities of the microsite in order to survive. The vulnerability of the species deserves studies that account for its habitat requirements, emphasizing unprotected populations. [ABSTRACT FROM AUTHOR]

The slender racer, Orientocoluber spinalis, is a monotypic species found in northeast Asia. We collected 67 O. spinalis samples from the Republic of Korea (hereafter, South Korea) and 7 from China and Mongolia and investigated their genetic diversity and population structure. In South Korea, O. spinalis populations were mainly found on Oeyeondo, Uido, and Udo islands and Woraksan Mountain and showed low genetic diversity in the analysis of concatenated mitochondrial sequences of the cytochrome b (Cytb) and NADH dehydrogenase subunit 4 (ND4) genes. Orientocoluber spinalis populations in South Korea showed low differentiation and likely diverged recently. Orientocoluber spinalis may have colonized the Korean Peninsula from China and Mongolia, but this route is not confirmed due to the lack of samples from the Democratic People’s Republic of Korea and middle eastern China. Considering its extreme rarity, low population density, and low genetic diversity, O. spinalis should be designated an endangered species in South Korea, as it is in Russia, Mongolia, and Kazakhstan.

Among ectotherms, rare species are expected to have a narrower thermal niche breadth and reduced acclimation capacity and thus be more vulnerable to global warming than their common relatives. To assess these hypotheses, we experimentally quantified the thermal sensitivity of seven common, uncommon, and rare species of temperate marine annelids of the genus Ophryotrocha to assess their vulnerability to ocean warming. We measured the upper and lower limits of physiological thermal tolerance, survival, and reproductive performance of each species along a temperature gradient (18, 24, and 30 °C). We then combined this information to produce curves of each species' fundamental thermal niche by including trait plasticity. Each thermal curve was then expressed as a habitat suitability index (HSI) and projected for the Mediterranean Sea and temperate Atlantic Ocean under a present day (1970–2000), mid- (2050–2059) and late- (2090–2099) 21st Century scenario for two climate change scenarios (RCP2.6 and RCP8.5). Rare and uncommon species showed a reduced upper thermal tolerance compared to common species, and the niche breadth and acclimation capacity were comparable among groups. The simulations predicted an overall increase in the HSI for all species and identified potential hotspots of HSI decline for uncommon and rare species along the warm boundaries of their potential distribution, though they failed to project the higher sensitivity of these species into a greater vulnerability to ocean warming. In the discussion, we provide some caveats on the implications of our results for conservation efforts. [ABSTRACT FROM AUTHOR]

The Southwest Australian Floristic Region (SWAFR) supports an exceptional number of threatened and data-deficient flora. In this study, we: (i) collated statistics on the number, listing criteria and tenure of occurrence of threatened and data-deficient flora; (ii) conducted spatial and biogeographic analyses to address questions concerning patterns of diversity of threatened and data-deficient flora relative to the whole flora and evolutionary and threat drivers; and (iii) examined whether threatened and data-deficient flora richness is evenly distributed across plant lineages. We found that although threatened and data-deficient flora occurred across the breadth of the SWAFR, high richness was concentrated in a limited number of locations, which were not always strongly aligned with areas of higher land transformation. Data-deficient flora demonstrated different spatial patterns of occurrence to threatened flora. Approximately 70% of the populations of threatened and data-deficient flora occurred outside of lands managed primarily for conservation. Both evolutionary history and contemporary threats contribute to the current status and distribution of diversity of the threatened and data-deficient flora, with evolutionary history playing a significant role in predisposing a portion of the flora to having population traits that result in those flora meeting IUCN Red List criteria, along with ecological traits that predispose some to specific novel threats. An understanding of the distribution of species and threats, flora traits, and how these traits mediate susceptibility to threats, offers one potential way forward for an initial assessment of which of the 1819 data-deficient flora may be most at risk of extinction. [ABSTRACT FROM AUTHOR]

Spatial patterns of functional diversity are important in understanding community assembly as well as spatial variation in ecosystem functioning, yet the contribution of different species to these patterns remains unclear, making it difficult to generalise. Several studies have previously used a sequential addition approach to determine the subsets of species that contribute to the spatial distribution of species richness, frequently showing the importance of common species to richness patterns. This approach, however, has not been applied to functional diversity despite the central role of species traits in community ecology.Here we use a multiscale survey of plants from the Machair grassland system of the Western Isles of Scotland to ask the following questions: (i) Do functional diversity patterns correlate better with geographically common or geographically rare species?; (ii) Do their relative contributions vary with spatial scale?; and (iii) Do these patterns vary between functional diversity measures?We show that while species richness patterns correlate with geographically common species, common species contribute less than expected to spatial patterns of functional diversity at frequently used spatial monitoring scales. The relative contribution of species to overall biodiversity patterns, however, can vary with spatial scale.Synthesis. Surveying only common species may be inadequate for estimating spatial patterns of functional diversity, especially if using occurrence as opposed to percentage cover or abundance data, and spatial scale needs to be considered when designing surveys. Our approach highlights the species that may be adequate indicators of different dimensions of biodiversity and contributes to our understanding of the distribution of functional diversity in space. [ABSTRACT FROM AUTHOR]

Population genetic structure results from the interaction between historical events, current ecological conditions and life traits. The genetic structure and gene flow between populations are important to species dynamics, mainly for rare and endangered species that are more vulnerable to landscape changes and fragmentation. Here we evaluated the genetic diversity, population structure and gene exchange in Petunia bonjardinensis , P. reitzii and P. saxicola , three rare species endemic to subtropical highland grasslands in southern South America. We analysed the genetic diversity and structure considering historical events, such as founder effect and climate changes, and biological traits of each species. We also estimated the conservation status for these three species. We collected samples from all adult individuals and occurrence sites that could be found at the same flowering season and genotyped them for 13 nuclear microsatellite markers. Our results indicate that rarity is probably historical for these species, given that we found no genetic evidence for recent bottlenecks. Petunia bonjardinensis , with the largest occurrence area and population sizes, displayed the higher diversity indices. The other two showed lower genetic diversity and are geographically most restricted. Gene exchange among these species was low, although they share some ancestral genetic polymorphism. Historical migration, founder effects and Pleistocene climate cycles ae the main factors explaining genetic diversity, and this was also influenced by reproductive biology and recent habitat loss, whereas the landscape influences the structure. Based on IUCN criteria, the three species are endangered, and the main risk for their survival is probably anthropic activity in the occurrence area. We recommend an urgent programme for the preservation of these species in situ and ex situ. [ABSTRACT FROM AUTHOR]

Aim: Mountains shelter high biological diversity and constitute both important barriers and confluence areas for species. They often contain species whose populations occur at their range limit (peripheral species), which according to the "Centre‐Periphery" hypothesis (CPH) are expected to occur in marginal environments, exhibit low abundance and consequently high vulnerability. Our study investigates this hypothesis for the flora of the Pyrenees, a biogeographical crossroads containing a large proportion of the total European plant diversity. Location: Pyrenees. Methods: We determined whether more than 2600 native plant species were endemic to the Pyrenees or found at the centre or periphery of their whole distribution range within the mountain chain. We then compared the ecological preferences, local and regional abundance, and conservation status among central, peripheral and endemic species. Results: A quarter of the flora was found at its geographic range limit within the Pyrenees. Endemic and peripheral species were more likely to be soil specialists in alpine grasslands and rocks, and exhibited smaller regional ranges than central species, but their local abundance did not tend to differ. Peripheral species at their southern range edge were more widespread regionally than at their northern range edge. Peripheral taxa were more prevalent in the Pyrenean red list of threatened species (55%) compared to national and regional protection lists (40% and 31%, respectively). Main conclusions: Peripheral species contribute substantially to the diversity of the Pyrenean flora. They follow the predictions of the CPH given their occurrence in scarce habitats, their low regional abundance and their high vulnerability according to the Pyrenean red list, although they tend to show similar local abundances as other species and are infrequent in protection lists. Integrative and cross‐border assessments of the ecology and rarity of mountain floras provide better estimates of their vulnerability and ensure more efficient prioritization of their conservation. [ABSTRACT FROM AUTHOR]

Evolutionary processes on islands, and the attributes of rare plant species restricted to islands have received increasing attention in the last decade, but most of the evidence comes from oceanic archipelagos while continental islands have been much less studied. We test if narrow endemic species of Aegean islands (E Mediterranean region) have evolved particular trait values and ecological attributes. In 64 pairs of congeneric species i.e., an island endemic and a congeneric widespread species, we compared morphological traits (both vegetative and reproductive), and altitudinal range using a phylogenetically constrained multilevel model. Island endemics had larger propagules, larger petals, shorter stems, shorter flowering duration, and they occupied a narrower altitudinal range. The results are interpreted in terms of lower competitive ability and lower dispersal capacity in Aegean endemics. Larger corolla could be accounted for by competition for pollinators in insect-rich ecosystems. Field observations are needed to test if island endemics and their widespread congeners occupy distinct niches when in sympatry on the same island. [ABSTRACT FROM AUTHOR]

One of the most fundamental questions in ecology is how many species inhabit the Earth. However, due to massive logistical and financial challenges and taxonomic difficulties connected to the species concept definition, the global numbers of species, including those of important and well-studied life forms such as trees, still remain largely unknown. Here, based on global ground-sourced data, we estimate the total tree species richness at global, continental, and biome levels. Our results indicate that there are ~73,000 tree species globally, among which ~9,000 tree species are yet to be discovered. Roughly 40% of undiscovered tree species are in South America. Moreover, almost one-third of all tree species to be discovered may be rare, with very low populations and limited spatial distribution (likely in remote tropical lowlands and mountains). These findings highlight the vulnerability of global forest biodiversity to anthropogenic changes in land use and climate, which disproportionately threaten rare species and thus, global tree richness. [ABSTRACT FROM AUTHOR]

Ploidy and species range size or threat status have been linked to variation in phenotypic and phenological seed and seedling traits, including seed size, germination rate (speed) and seedling stature. There is surprisingly little known about the ecological outcomes of relationships between ploidy, key plant traits and the drivers of range size. Here we determined whether ploidy and range size in Pomaderris , a genus of shrubs that includes many threatened species, are associated with variation in seed and seedling traits that might limit the regeneration performance of obligate seeders in fire-prone systems. We experimentally quantified seed dormancy and germination processes using fire-related heat treatments and evaluated seedling performance under drought stress. We also examined the association of seed size with other seed and seedling traits. Polyploids had bigger seeds, a faster germination rate and larger and taller seedlings than diploids. There was a lack of any clear relationship between range size and seed or seedling traits. The ploidy effects observed for many traits are likely to be indirect and associated with the underlying seed size differences. These findings indicate that there is a higher potential competitive advantage in polyploid than diploid Pomaderris during regeneration, a critical stage in the post-fire environment. This insight to the regeneration phase may need to be considered when planning and prioritising management of threatened species. [ABSTRACT FROM AUTHOR]

Aim: Habitat diversity has been linked to the diversity and structure of island communities, however, little is known about patterns and processes within habitats. Here we aim to determine the contributions of habitat type and inferred dispersal frequency to the differences in taxonomic structure between assemblages in the same island habitat. Location: The Macaronesian archipelagos (Azores, Madeira, the Canary Islands and Cabo Verde). Taxon: Spiders (Araneae). Methods: We established forest and dry habitat sites (each with five plots) on two islands per archipelago. We collected spiders using standardised sampling protocols. We tested the differences in beta diversity separately for each habitat and for each inferred category of ballooning (an aerial dispersal strategy) frequency across geographic scales through nested non-parametric permutational multivariate analyses of variance. We then tested whether ballooning and habitat influenced heterogeneity in species composition (dispersion in beta diversity) in the two habitat types. We analysed the effects of habitat and ballooning on species abundance distribution (SAD) and rarity by fitting Gambin models and evaluating the contribution of ballooning categories to SAD. Results: Communities of the same archipelago and habitat were taxonomically more similar, and beta diversity increased with geographic scale, being greater in dry habitats. There was greater species replacement among assemblages in dry habitats than in forests, with greater differences for rare ballooners. There were no differences in SAD between habitats although dry habitat sites seemed to harbour more species with low abundances (rare species) than forests. Main conclusions: Habitat type does not only condition the differences between spider assemblages of the same habitat but also the scale at which they occur. These differences may be determined by the heterogeneity in the physical structure of each habitat as well as how much this structure facilitates aerial dispersal (ballooning), and should be considered in theories/hypotheses on island community assembly as well as in conservation strategies. [ABSTRACT FROM AUTHOR]

Spatial rarity is often used to predict extinction risk, but rarity can also occur temporally. Perhaps more relevant in the context of global change is whether a species is core to a community (persistent) or transient (intermittently present), with transient species often susceptible to human activities that reduce niche space. Using 5–12 yr of data on 1,447 plant species from 49 grasslands on five continents, we show that local abundance and species persistence under ambient conditions are both effective predictors of local extinction risk following experimental exclusion of grazers or addition of nutrients; persistence was a more powerful predictor than local abundance. While perturbations increased the risk of exclusion for low persistence and abundance species, transient but abundant species were also highly likely to be excluded from a perturbed plot relative to ambient conditions. Moreover, low persistence and low abundance species that were not excluded from perturbed plots tended to have a modest increase in abundance following perturbance. Last, even core species with high abundances had large decreases in persistence and increased losses in perturbed plots, threatening the long‐term stability of these grasslands. Our results demonstrate that expanding the concept of rarity to include temporal dynamics, in addition to local abundance, more effectively predicts extinction risk in response to environmental change than either rarity axis predicts alone. [ABSTRACT FROM AUTHOR]

Measuring commonness and rarity is pivotal to ecology and conservation. Zeta diversity, the average number of species shared by multiple sets of assemblages, and Dark diversity, the number of species that could occur in an assemblage but are missing, have been recently proposed to capture two aspects of the commonness‐rarity spectrum. Despite a shared focus on commonness and rarity, thus far, Zeta and Dark diversities have been assessed separately. Here, we review these two frameworks and suggest their integration into a unified paradigm of the "rarity facets of biodiversity." This can be achieved by partitioning Alpha and Beta diversities into five components (the Zeta, Eta, Theta, Iota, and Kappa rarity facets) defined based on the commonness and rarity of species. Each facet is assessed in traditional and multiassemblage fashions to bridge conceptual differences between Dark diversity and Zeta diversity. We discuss applications of the rarity facets including comparing the taxonomic, functional, and phylogenetic diversity of rare and common species, or measuring species' prevalence in different facets as a metric of species rarity. The rarity facets integrate two emergent paradigms in biodiversity science to better understand the ecology of commonness and rarity, an important endeavor in a time of widespread changes in biodiversity across the Earth. [ABSTRACT FROM AUTHOR]

1. Anthropogenic land‐use change alters the ecological communities in a landscape's remaining natural habitat. These matrix effects are understudied in rare species, which comprise a majority of biodiversity, contribute to ecosystem services, and are particularly vulnerable to population declines. 2. This study used bee species survey data from New Jersey forest fragments, in conjunction with an independent museum data set, to identify rare bee species and developed regularised regularised regression models of matrix effects on their richness and abundance. 3. By using a regularised modelling approach, this study explains 44.43% of variation in rare bee species richness between forest fragments and 27.27% of variation in their abundance (average adjusted R2). 4. The present study's results identified specific subcategories of urban land use in the surrounding 1000 m of forest fragments that explained patterns in rare bee species richness and abundance, providing insights into how to select forest fragments to conserve rare bees. Low priority should be given to fragments in close proximity to high‐ and medium‐density housing, which likely harms rare bees by increasing impervious surface cover. Low priority should also be given to fragments near golf courses and athletic fields; this study speculates that these land uses harm rare bees through mowing and pesticide application. Finally, high priority should be given to fragments composed of a larger proportion of mature forest, which likely provides a greater diversity of native floral resources. Altogether, this study's model results reveal the importance of matrix habitats for the biodiversity of rare species in forest fragments. [ABSTRACT FROM AUTHOR]

Due to expanding global trade and movement of people, new plant species are establishing in exotic ranges at increasing rates while the number of native species facing extinction from multiple threats grows. Yet, how species losses and gains globally may, together, be linked to traits and macroevolutionary processes is poorly understood. Here, we show that, adjusting for diversification rate and clade age, the proportion of threatened species across flowering plant families is negatively related to the proportion of naturalised species per family. Moreover, naturalisation is positively associated with range size, short generation time, autonomous seed production and interspecific hybridisation, but negatively with age and diversification, whereas threat is negatively associated with range size and hybridisation, and positively with biotic pollination, age and diversification rate. That we find such a pronounced signature of naturalisation and threat across plant families suggests that both trait syndromes have coexisted over deep evolutionary time and counter to intuition, that neither strategy is necessarily superior to the other over long evolutionary timespans. [ABSTRACT FROM AUTHOR]

Aim: Detection of rare species is limited by their intrinsic nature and by the constraints associated with traditional field surveys. Remote sensing (RS) provides a powerful alternative to traditional detection methods through the increasing availability of RS products. Here, we assess the capacity of RS at high and medium resolution to detect rare plants with direct and indirect approaches, and how the performance of RS can be influenced by the characteristics of species. Methods: An extensive literature review was conducted to synthesize the use of RS to detect or predict rare plant occurrence at high and medium resolution (<30 m and 30–300 m, respectively). The concept of "rarity" was based on Rabinowitz's rare species classification. The literature review was performed in Scopus for the period 1990–2020. Results: While direct detection is often limited, it is possible with high and very high spatial resolution data for rare plants with distinctive traits. RS is also able to capture biophysical conditions driving rare plant distributions, which can indirectly provide accurate predictions for them. Both approaches have the potential to discover new populations of rare plants. RS can also feed SAMs of rare plants, which combined with SDMs can provide a valuable approach for rare plant detection. While direct detection is limited by the space occupied by a species within its habitat and its morphological, phenological and physiological characteristics, the predictive performance of RS‐based SDMs (indirect detection) can be influenced by habitat size, habitat specificity and phenological features of rare plants. Similarly, model predictive performance can be influenced by the rarity form of the target species according to the rarity classification criteria. Main conclusions. With this synthesis, the strong potential of RS for the purposes of detection and prediction of rare plant has been highlighted, with practical applications for conservation and management. [ABSTRACT FROM AUTHOR]

The generality and drivers of rarity, defined along the axes of geographic range, population size and habitat specificity, have received considerable scientific attention for well over a century. Yet, studies that examine rarity holistically among these three attributes are limited, especially among invertebrate and marine taxa. The perceived paradox of deep‐sea species, with often low population size but large geographic ranges, remains poorly resolved and understood. Here I assess seven forms of rarity and their drivers in deep‐sea bivalves across the Atlantic Ocean. Rarity appears to be a common trait among deep‐sea bivalves, with nearly 85% of the species exhibiting some form of rarity. Bivalves also showed a strong bimodal pattern of very common and very rare species. Geographic range, population size and habitat specificity were all heavily right skewed. Taxonomic superfamilies, body size, energy availability, temperature, depth and latitude, all significantly predicted geographic range, population size and habitat specificity. In a few cases, these patterns were counter to theoretical expectations. The drivers of rarity appear to be predictable from knowledge of the intrinsic biological and extrinsic environmental context of the species. These findings have major implications for deep‐sea conversation, especially as anthropogenic threats are increasing. [ABSTRACT FROM AUTHOR]

Premise: Rarity is a complex and central concept in ecology and conservation biology. Yet, it is still poorly understood why some species are rare and others common. Here, we aimed to understand the drivers of species rarity patterns in woody plant communities. Methods: We analyzed the local abundance and landscape frequency of 121 woody plant species across 238 plots on American Samoa and Hawaiian islands. We first assessed whether taxonomy, life form (shrub, small tree, large tree), and dispersal syndrome (dispersed by animals or by other means) are associated with the rarity of species. We then analyzed phylogenetic patterns in plant rarity and tested whether rarity patterns are associated with species evolutionary distinctiveness and the number of species within genera and families. Results: Large trees were less abundant but more frequent than shrub species. Animal‐dispersed species tended to be less abundant than species dispersed by other means, while species frequency was not associated with dispersal syndromes. Relative frequency in Hawai′i exhibited a more robust phylogenetic signal than did abundance. Both evolutionary distinctiveness and taxa species richness were significantly associated with the frequency of shrub species in Hawai′i. Conclusions: Life form appears consistently associated with the rarity of species. High diversification rate is probably a key factor explaining landscape‐scale rarity of native species on isolated archipelagos like Hawai′i. At the landscape scale, rarity appears to be inversely associated with evolutionary distinctiveness, but at the local scale, species abundance may be not associated with evolutionary distinctiveness. [ABSTRACT FROM AUTHOR]

Most species in ecological communities are rare, whereas only a few are common. This distributional paradox has intrigued ecologists for decades but the interpretation of species abundance distributions remains elusive.We present Fuzzy Quantification of Common and Rare Species in Ecological Communities (FuzzyQ) as an R package. FuzzyQ shifts the focus from the prevailing species‐categorization approach to develop a quantitative framework that seeks to place each species along a rarity‐commonness gradient. Given a community surveyed over a number of sites, quadrats, or any other convenient sampling unit, FuzzyQ uses a fuzzy clustering algorithm that estimates a probability for each species to be common or rare based on abundance–occupancy information. Such a probability can be interpreted as a commonness index ranging from 0 to 1. FuzzyQ also provides community‐level metrics about the coherence of the allocation of species into the common and rare clusters that are informative of the nature of the community under study.The functionality of FuzzyQ is shown with two real datasets. We demonstrate how FuzzyQ can effectively be used to monitor and model spatiotemporal changes in species commonness, and assess the impact of species introductions on ecological communities. We also show that the approach works satisfactorily with a wide range of communities varying in species richness, dispersion and abundance currencies.FuzzyQ produces ecological indicators easy to measure and interpret that can give both clear, actionable insights into the nature of ecological communities and provides a powerful way to monitor environmental change on ecosystems. Comparison among communities is greatly facilitated by the fact that the method is relatively independent of the number of sites or sampling units considered. Thus, we consider FuzzyQ as a potentially valuable analytical tool in community ecology and conservation biology. [ABSTRACT FROM AUTHOR]

Quantifying the abundance of species is essential to ecology, evolution, and conservation. The distribution of species abundances is fundamental to numerous longstanding questions in ecology, yet the empirical pattern at the global scale remains unresolved, with a few species' abundance well known but most poorly characterized. In large part because of heterogeneous data, few methods exist that can scale up to all species across the globe. Here, we integrate data from a suite of well-studied species with a global dataset of bird occurrences throughout the world--for 9,700 species (~92% of all extant species)--and use missing data theory to estimate speciesspecific abundances with associated uncertainty. We find strong evidence that the distribution of species abundances is log left skewed: there are many rare species and comparatively few common species. By aggregating the species-level estimates, we find that there are ~50 billion individual birds in the world at present. The global-scale abundance estimates that we provide will allow for a line of inquiry into the structure of abundance across biogeographic realms and feeding guilds as well as the consequences of life history (e.g., body size, range size) on population dynamics. Importantly, our method is repeatable and scalable: as data quantity and quality increase, our accuracy in tracking temporal changes in global biodiversity will increase. Moreover, we provide the methodological blueprint for quantifying species-specific abundance, along with uncertainty, for any organism in the world. [ABSTRACT FROM AUTHOR]

The distribution of the rare Karst Snowfly, Allocapnia cunninghami Ross & Ricker, 1971, was assessed during winters of 2019 and 2020. This species has been assigned a NatureServe ranking of G1 (= Critically Imperiled) and was recently included in a Center for Biological Diversity petition to the U.S. Fish and Wildlife Service as potentially threatened or endangered. Sampling for adult A. cunninghami occurred in 45 unique localities in central Kentucky and middle Tennessee, USA, mainly within the known historical range of this species. This species was found in winters of 2019 and 2020 in very low numbers compared to regional Allocapnia and the winter-emergent fauna in general. Allocapnia cunninghami was collected at only five unique localities and comprised only 1.1% and 1.0% of all Allocapnia and the total winter-emergent fauna individuals collected, respectively. By comparison, the widespread species A. rickeri Frison, 1942 was collected from 41 of 45 unique localities and comprised 70% of all individual adults collected. Despite the difficulties of interpreting historical locality data from 1964 to 1966, A. cunninghami appears to now be present in fewer stream sites and distributed more patchily compared to ca. 55 years ago. A confounding biological factor for A. cunninghami is that Allocapnia adults in general have poor dispersal capacity, making natural colonization and potential recolonization events substantially more problematic for what appears to be a rare species in slow decline within an already small native geographic range. Implications for insect conservation: By including positive collection data from 1999–2012, increasing the number of known contemporaneous sites to nine, predictive distributional models can now be generated to allow for more focused searching for previously undetected populations and potentially expand the known geographic range of this rare species. [ABSTRACT FROM AUTHOR]

Three metrics of species diversity – species richness, the Shannon index and the Simpson index – are still widely used in ecology, despite decades of valid critiques leveled against them. Developing a robust diversity metric has been challenging because, unlike many variables ecologists measure, the diversity of a community often cannot be estimated in an unbiased way based on a random sample from that community. Over the past decade, ecologists have begun to incorporate two important tools for estimating diversity: coverage and Hill diversity. Coverage is a method for equalizing samples that is, on theoretical grounds, preferable to other commonly used methods such as equal‐effort sampling, or rarefying datasets to equal sample size. Hill diversity comprises a spectrum of diversity metrics and is based on three key insights. First, species richness and variants of the Shannon and Simpson indices are all special cases of one general equation. Second, richness, Shannon and Simpson can be expressed on the same scale and in units of species. Third, there is no way to eliminate the effect of relative abundance from estimates of any of these diversity metrics, including species richness. Rather, a researcher must choose the relative sensitivity of the metric towards rare and common species, a concept which we describe as 'leverage.' In this paper we explain coverage and Hill diversity, provide guidelines for how to use them together to measure species diversity, and demonstrate their use with examples from our own data. We show why researchers will obtain more robust results when they estimate the Hill diversity of equal‐coverage samples, rather than using other methods such as equal‐effort sampling or traditional sample rarefaction. [ABSTRACT FROM AUTHOR]

The Vampyressa melissa species complex comprises three rare bat species poorly represented in museum collections. Vampyressa melissa and V. sinchi are restricted to the eastern slope of the Andes, while V. elisabethae only is known from Panama, in Central America. The species complex has received recent attention in terms of systematic reviews, which concluded in the description of two species: one from Panama (V. elisabethae) and one from Colombia (V. sinchi). Vampyressa melissa recently was reported from the eastern slopes of the Cordillera Oriental of Colombia, in the department of Casanare. However, morphological and genetic (Cytochrome b) comparisons showed that these specimens belong to an undescribed species of the genus. The new species is the smallest member of the V. melissa complex and has a unique set of morphological characters compared to other Vampyressa species. Molecular evidence shows that the new species is sister to V. melissa (sensu stricto) from Colombia and Peru, albeit with high genetic divergence (7.9%). Nevertheless, Cytochrome b sequences of V. elisabethae and V. sinchi still are unknown. This new species increases to six the number of species in the genus. Vampyressa melissa , V. sinchi , and the new species, exhibit restricted distributions in the eastern slopes of the Andean Cordillera, in specific altitudinal ranges. Because of geographic constraints, their biological rarity, and the high deforestation rates in their distributional area, we suggest that these three species must be considered as taxa threatened with extinction. [ABSTRACT FROM AUTHOR]

Inland sand areas scattered across the North American eastern deciduous forest and western tallgrass prairie ecotone are known for supporting pyrogenic early-successional vegetation and specially adapted terrestrial faunas. Many of these globally and regionally rare systems contain functionally connected wetland networks ("wetscapes") potentially important for aquatic insects. Sampling adults, nymphs, and exuviae in a remnant sand prairie-savanna wetscape in Illinois, USA, I assessed odonate species diversity (alpha, gamma, beta), distributions (spatial, temporal, abundance), and rarity status. In one field season (12 sites, 12 visits) I found more than a third of Illinois odonate species and close to half of the state's lentic breeding odonates, including a new state record (Erythemis vesiculosa). Richness averaged 25.8 species per site, reducing to 12.4 species with removal of nonbreeding occurrences. Three sites including a shrub swamp, beaver pond, and forested vernal depressions complex made significant contributions to beta diversity, dependent on general versus breeding occurrences. Majorities of Anisoptera species (70%) and Zygoptera species (53%) bred at three or fewer sites. Eight species flew during all or most of the study period (late May to early Oc-tober) whereas 14 species were detected on a single survey. Status classification derived from the observed spatial, temporal, and abundance distributions resulted in 24 common or very common species, 20 uncommon or rare species, and 10 vagrants across the wetscape. These context-specific classifications may be combined with diversity and breeding patterns and other information in wetscape prioritization schemes. [ABSTRACT FROM AUTHOR]

Despite increasing awareness of global biodiversity loss, we lack quantitative data on local extinctions for many species. This is especially true for rare species, which are typically assessed on the basis of expert judgment rather than data. Revisiting previously assessed populations enables estimation of local extinction rates and the identification of species characteristics and habitats with high local extinction risk. Between 2010 and 2016, in a nationwide revisitation study, 420 volunteer botanists revisited 8,024 populations of the 713 rarest and most threatened plant species in Switzerland recorded between 1960 and 2001. Of the revisited 8,024 populations, 27% had gone locally extinct. Among critically endangered species, the local extinctions increased to 40%. Species from ruderal and freshwater habitat types showed the highest proportion of local extinctions. Our results provide compelling evidence for rapid and widespread local extinctions and suggest that current conservation measures are insufficient. Local extinctions precede and provide early warnings for global extinctions. The ongoing loss of populations suggests that we will lose species diversity unless we scale up species‐targeted conservation and restoration measures, especially in anthropogenic landscapes. [ABSTRACT FROM AUTHOR]

Various factors influence patterns of genetic diversity within and between populations that are important considerations for plant conservation. Both clonality and population genetic differentiation are key factors informing conservation actions, especially for rare species. Banksia mimica is a rare species that occurs in three disjunct locations in the biodiversity hotspot of the southwest Australian Floristic Region of Western Australia. Extant populations are suspected to have varying levels of clonality and high levels of genetic differentiation due to geographic disjunction. A genetic analysis was undertaken in order to confirm clonal reproduction and obtain initial estimates of genotypic diversity, and to assess genetic diversity within, and genetic structure among, populations. Genotypic richness ranged from 0.210 to 1.00 supporting observations in the field of variable degrees of clonal growth. The most clonal populations showed genetic signals of greater levels of observed heterozygosity than expected heterozygosity and negative FIS values that were not present in other populations of B. mimica or populations of the nonclonal sister taxon B. vestita. There was strong genetic structure with high genetic divergence among geographically disjunct population groups (global FST = 0.392, DST = 0.475), as is often found within the Australian flora. Genetic differentiation among disjunct populations located on the Whicher Scarp and more northern populations approached, or was greater than, that between Whicher populations and populations of the sister taxa B. vestita. This result is consistent with several other species that show genetic differentiation in disjunct populations located on the Whicher Scarp geomorphological formation. Results suggest a reassessment of the taxonomy and identification of evolutionary significant units for populations of B. mimica would support effective conservation management of this species. [ABSTRACT FROM AUTHOR]

When can small, isolated populations overcome the negative consequences of rarity? Despite considerable effort to understand threats to rare species, few studies consider how community context alters these threats. Plant–pollinator interactions offer the opportunity to test the effect of community context on rare species success, as plant–pollinator dynamics are thought to be influenced by neighbouring plants, both through competition for pollinators (reducing success in small populations) and attraction of potential pollinators (increasing success in small populations). Here, we test these predictions by experimentally decoupling community‐level rarity (relative abundance) from population‐level rarity (population size) in experimental two‐species fragments.We created experimental plant communities varying independently in population rarity (population size) and community rarity (relative abundance) of two annual plant species. We isolated plant roots to eliminate resource competition. We then compared the effects of population size versus relative abundance on pollinator visitation rates and an estimate of seed production.Both species had greatest pollinator visitation in large populations, but the negative effects of population rarity on visitation were partially offset when the neighbouring species was more abundant—community rarity offset the impacts of population rarity for the most common group of pollinators, solitary bees. These visitation trends impacted seed production for one species. When at low relative abundance, Polanisia dodecandra had higher seed set, matching increased visitation by solitary bees. Chamaecrista fasciculata showed no change in seed production with population‐ or community‐level rarity.Synthesis. Our results suggest that the surrounding community can offset the negative effects of low absolute abundance on fitness when neighbouring species are more abundant, and may ultimately maintain diversity even in fragmented ecological communities. [ABSTRACT FROM AUTHOR]

Aim: Ecological niches shape species commonness and rarity, yet, the relative importance of different niche mechanisms within and across ecosystems remains unresolved. We tested the influence of niche breadth (range of environmental conditions where species occur) and niche position (marginality of a species' environmental distribution relative to the mean environmental conditions of a region) on tree‐species abundance and occupancy across three biogeographic regions. Location: Argentinian Andes; Bolivian Amazon; Missouri Ozarks. Time period: 2002–2010. Major taxa studied: Trees. Methods: We calculated abiotic‐niche breadths and abiotic‐niche positions using 16 climate, soil and topographic variables. For each region, we used model selection to test the relative influence of niche breadth and niche position on local abundance and occupancy in regional‐scale networks of 0.1‐ha forest plots. To account for species–environment associations caused by other mechanisms (e.g., dispersal), we used null models that randomized associations between species occurrences and environmental variables. Results: We found strong support for the niche‐position hypothesis. In all regions, species with higher local abundance and occupancy occurred in non‐marginal environments. Observed relationships between occupancy and niche position also differed from random species–environment associations in all regions. Surprisingly, we found little support for the niche‐breadth hypothesis. Observed relationships between both local abundance and niche breadth, and occupancy and niche breadth, did not differ from random species–environment associations. Main conclusion: Niche position was more important than niche breadth in shaping species commonness and rarity across temperate, sub‐tropical and tropical forests. In all forests, tree species with widespread geographic distributions were associated with environmental conditions commonly found throughout the region, suggesting that niche position has similar effects on species occupancy across contrasting biogeographic regions. Our findings imply that conservation efforts aimed at protecting populations of common and rare tree species should prioritize conservation of both common and rare habitats. [ABSTRACT FROM AUTHOR]