Patterns Of Taxonomic Richness Research Articles

Global meta-analysis reveals overall higher nocturnal than diurnal activity in insect communities

Insects sustain key ecosystem functions, but how their activity varies across the day–night cycle and the underlying drivers are poorly understood. Although entomologists generally expect that more insects are active at night, this notion has not been tested with empirical data at the global scale. Here, we assemble 331 quantitative comparisons of the abundances of insects between day and night periods from 78 studies worldwide and use multi-level meta-analytical models to show that insect activity is on average 31.4% (CI: −6.3%–84.3%) higher at night than in the day. We reveal diel preferences of major insect taxa, and observe higher nocturnal activity in aquatic taxa than in terrestrial ones, as well as in warmer environments. In a separate analysis of the small subset of studies quantifying diel patterns in taxonomic richness (31 comparisons from 13 studies), we detect preliminary evidence of higher nocturnal richness in tropical than temperate communities. The higher overall (but variable) nocturnal activity in insect communities underscores the need to address threats such as light pollution and climate warming that may disproportionately impact nocturnal insects.

A comparison of two widely used methods for estimating taxonomic and functional diversities of epigeal arthropods in some temperate grasslands

AbstractSuction sampling is increasingly being used to estimate abundance and diversity of epigeal arthropods, yet no study has quantified its efficiency to simultaneously assess diversity at different taxonomic and functional scales. Here, we evaluated the efficiency of this method (G‐Vac) relative to the pitfall (Barber) trap, which has been used for a long time, and their possible complementarity. To do that, we compared several diversity metrics of a wide range of arthropod taxa, with a particular focus on spiders (species level), and using functional traits such as trophic diet, hunting guild, and body size. Sampling took place in some coastal grasslands of Brittany (France) using a spatially paired design of vacuuming and unfenced pitfall trapping. In total, 21159 arthropods were identified to order or family levels, including 1018 adult spiders identified to species. Suction sampling was more efficient than pitfall trapping in collecting phytophagous arthropods, web‐builders, and small species living in the vegetation compared to detritivores, large‐bodied arthropods, and spiders living near the soil surface. We conclude that short‐term G‐Vac suction is more interesting than pitfall trapping to obtain a ‘snapshot’ of patterns in taxonomic richness. However, for assessing functional diversity, G‐Vac suction and pitfall trapping are complementary sampling methods.

Lizards (Reptilia: Squamata) from the Caatinga, northeastern Brazil: Detailed and updated overview

AbstractThe Caatinga is the largest seasonal dry tropical forest in South America and it has been historically neglected in terms of its biodiversity. Regarding lizards, different studies led to the current knowledge of diversity and endemism in Caatinga, but detailed syntheses are scarce in the literature. We present the most detailed and up-to-date synthesis of knowledge about Caatinga lizards by providing a detailed (i) list of species; (ii) taxonomic richness patterns; (iii) knowledge gaps and spatial biases; and (iv) detailed distribution maps of all species that contain at least one occurrence record within Caatinga limits. We created a distribution database using occurrences of lizards in Caatinga based on scientific collections, field collection, and literature. We produce up-to-date distribution maps, calculate the Extent of Occurrence and provide the environmental and bioclimatic profile for each species recorded. We draw taxonomic richness and sampling gap maps. Our database has 20,538 records of occurrence of lizards of the Caatinga. We recorded 93 lizard species (13 families), 52.7% of which are endemic. Forthy-four percent of the species present restricted distributions. We identified that 53% of the Caatinga area (or 70% of the municipalities) has no record of occurrence of lizards. The data presented are an important step towards synthesizing in detail the accumulated knowledge about Caatinga lizards and is crucial for accurate strategies for the conservation planning. It directs actions to advance our knowledge on Caatinga lizards: to concentrate inventories in sample void areas; continuous update of the species occurrence database, advance in the generation of autoecology data for species.

Robust metagenomic evidence that local assemblage richness increases with latitude in ground‐active invertebrates of North America

Biodiversity monitoring is imperative for understanding how changing climate may impact the distributions of taxa from single species to the spatial distribution of biological diversity. Large‐scale and cross‐taxa biodiversity monitoring also allows an empirical understanding of biogeographic patterns across taxa. One such pattern, where in taxonomic richness peaks at tropical latitudes are typically treated as a biogeographical rule with few notable exceptions. Here we leveraged the invertebrate pitfall collections of the National Ecological Observatory Network (NEON) across North America to describe patterns of local taxonomic richness across taxa and across taxonomic scale. We focused on Arthropoda, Annelida and Mollusca. Additionally, we estimated regional species richness using expert‐identified samples of three NEON sentinel taxa: Carabidae, Culicidae and Ixodida. To sample pitfall animals, we filtered storage ethanol and employed environmental DNA‐barcoding methodologies to amplify and sequence extracted DNA from the filtrate for two regions of a mitochondrial gene. We assigned taxonomic names to these sequences at 97% similarity to reference sequences and calculated local taxonomic richness at the levels of species, genus, family and order. We calculated local species richness for 12 common invertebrate taxa. We used generalized linear models to describe the relationships between taxonomic richness and spatial, climatic and abundance predictor variables. At four taxonomic scales, ranging from species to order, taxonomic richnessincreased significantly as a function of latitude. Of the twelve invertebrate taxa weexamined, seven mirrored this positive latitudinal gradient in species richness. At theregional scale, two of three NEON Sentinel Taxa showed positive latitudinal gradientsin species richness. Temperature, precipitation, abundance and sequence read numberplayed minor roles in explaining patterns of taxonomic richness. When considering these mostly temperate sites that span 46 degrees of latitude, we found no support for the expected negative latitudinal gradients across taxa and taxonomic scales. Instead, for many of these taxa and taxonomic scales, we observed significant, positive richness gradients with increasing latitude among ground‐dwelling invertebrate communities. Thus, one of the most ‘general' patterns in biogeography was not found for most invertebrate taxa across temperate latitudes.

Phytoplankton taxonomic and functional diversity patterns across a coastal tidal front

Oceanic physics at fine scale; e.g. eddies, fronts, filaments; are notoriously difficult to sample. However, an increasing number of theoretical approaches hypothesize that these processes affect phytoplankton diversity which have cascading effects on regional ecosystems. In 2015, we targeted the Iroise Sea (France) and evidenced the setting up of the Ushant tidal front from the beginning of spring to late summer. Seawater samples were taken during three sampling cruises and DNA-barcoding allowed us to investigate patterns of eukaryotic phytoplankton diversity across this front. First focusing on patterns of taxonomic richness, we evidenced that the front harbored a hotspot of eukaryotic phytoplankton diversity sustained throughout summer. We then detail the ecological processes leading to the formation of this hotspot by studying shifts in community composition across the Iroise Sea. Physical mixing mingled the communities surrounding the front, allowing the formation of a local ecotone, but it was cycles of disturbances and nutrient inputs over the front that allowed a decrease in competitive exclusion, which maintained a higher diversity of rare phytoplankton taxa. These processes did not select a specific ecological strategy as inferred by a trait approach coupled to our taxonomic approach. Instead the front favored higher richness within widespread strategies, resulting in functional redundancy. We detail how fine-scale ocean physics affect phytoplankton diversity and suppose that this interplay is a major control on regional ecosystems.

Accounting for multiple dimensions of biodiversity to assess surrogate performance in a freshwater conservation prioritization

Although freshwater ecosystems support a disproportionately large number of species, decision-support tools for prioritizing protected area efforts have mostly been implemented in marine and terrestrial environments. Systematic conservation planners rely on surrogate metrics to represent unsampled elements of biodiversity, yet few studies have considered the potential benefits associated with prioritizing multiple dimensions of freshwater biodiversity across multiple organism groups. In this study, we first evaluated relationships among patterns of taxonomic richness, functional diversity, functional redundancy, and biotic integrity for freshwater fish and benthic macroinvertebrate communities in the Congaree Biosphere Region, South Carolina, USA. We then used the decision-support tool Marxan to explore a potential trade-off between the number of organism groups sampled (i.e., taxonomic extent) and the multidimensional nature of biodiversity. Our central findings indicated that the processes driving patterns of taxonomic and functional diversity among organism groups were complementary, with direct implications for the evaluation of surrogate performance. Our results also suggest that within-taxa variation among measures of taxonomic and functional diversity may be more important to consider than the taxonomic representation of multiple organism groups. That is, we may be able to enhance the efficiency of conservation planning efforts by using available datasets in a more comprehensive way, as surrogate performance was largely mediated by the variation among metrics. Through the continued development of functional trait databases, we may be able to enhance the efficiency of data collection efforts and promote the timely and sustainable development of conservation strategies.

Biodiversity of cephalopod early-life stages across the Southeastern Brazilian Bight: spatio-temporal patterns in taxonomic richness

The diversity patterns of cephalopod early-life stages on the continental shelf of Southeastern Brazilian Bight (SBB, 22–25°S) were investigated using a historical plankton archive of 22 oceanographic cruises carried out from 1974 to 2010. From 874 plankton samples, 438 were positive for cephalopod paralarvae (n = 2116), which were identified to the lowest taxonomic level possible, totaling 15 taxa belonging to 11 families. Richness and diversity indexes (Shannon-Wiener, Simpson, Pielou’s evenness) revealed a cross-shelf gradient, independent of season and latitude. Abundance k-dominance curves were consistent with this depth-related trend, resulting in high values of k-dominance for the inner shelf during both summer and winter. Two major assemblages were identified by cluster analyses: an inner shelf and a mid-outer shelf. During summer, the inner shelf assemblage was composed of neritic Loliginidae Lesueur, 1821 and epipelagic Argonautidae Tryon, 1879, while in winter, benthic Octopodidae Orbigny, 1840 replaced Argonautidae in importance. These data reveal a remarkable difference in Argonautidae and Octopodidae paralarvae abundance, suggesting a seasonal reproductive pattern for these cephalopods in the SBB. Mesopelagic Enoploteuthidae Pfeffer, 1900 and Ommastrephidae Steenstrup, 1857 characterized the mid-outer shelf assemblages both in summer and winter. Although based on a higher taxonomic level, the distribution of cephalopod paralarva families reflected not only oceanographic patterns of the SBB but also their adaptations and reproductive strategies. In particular, the cross-shelf gradient in cephalopod biodiversity reflects a more dynamic oceanographic conditions in inner shelf compared with mid-outer shelf ecosystems.

Gradients of mammalian biodiversity through space and time

Mammalian biodiversity exhibits strong geographic gradients that correspond to variation in the physical environment (habitat, area, climate, and landforms) and reflect biogeographic processes that have unfolded over millennia. Principal among these patterns are the species–area relationship, as well as latitudinal, elevational, and topographic gradients. We review these gradients for mammalian assemblages of today and over geologic time. Contemporary gradients are for the most part general. Nonetheless, variation across different phylogenetic and ecological subsets of continental mammalian faunas illuminates the multifactorial, historical nature of biodiversity gradients in terms of the diversification history of clades, variation in resources that support species with different ecological traits, and changes in landscapes over time. Accordingly, future work should integrate modern and historical patterns of taxonomic richness with phylogenetic and functional diversity of different clades and ecological subsets of continental faunas. Changes in global climate and land use are disrupting the integrity of biogeographic patterns. Insights from the study of gradients of mammalian biodiversity should address the challenges of conservation in a rapidly changing world.

Effects of land use on trophic states and multi-taxonomic diversity in Japanese farm ponds

Abstract Farm ponds are among the most biodiverse anthropogenic freshwater habitats because of their small size, shallow water depth, and aquatic vegetation. Land-use changes, such as converting riparian vegetation to human use or changing the management practices of farm ponds, are assumed to be major factors that change such ecosystems from a clear-water state to a turbid state, leading to deterioration of water quality and biodiversity in such ponds. Using the database of a large-scale pond survey, we evaluated the effects of surrounding land use (landscape factors and modern pond management practices), fish abundance, and other environmental variables on total phosphorus concentration and taxonomic richness patterns of six biological indicators associated with changes in the trophic state. Local- and landscape-level vegetation structure associated with land use and total fish abundance were among the factors influencing the total phosphorus concentration of farm ponds, a main driver of trophic state changes. In addition, a transition from a clear-water state to a turbid state was associated with lower taxonomic richness of aquatic plants, macroinvertebrates, and adult Odonata, and a higher taxonomic richness of phytoplankton and fish. Based on these results, we discuss potential land-use and pond management strategies for conserving and/or restoring the water quality and biodiversity of farm ponds through maintenance of a clear-water state.

Nonrandom community assembly and high temporal turnover promote regional coexistence in tropics but not temperate zone.

A persistent challenge for ecologists is understanding the ecological mechanisms that maintain global patterns of biodiversity, particularly the latitudinal diversity gradient of peak species richness in the tropics. Spatial and temporal variation in community composition contribute to these patterns of biodiversity, but how this variation and its underlying processes change across latitude remains unresolved. Using a model system of sessile marine invertebrates across 25 degrees of latitude, from the temperate zone to the tropics, we tested the prediction that spatial and temporal patterns of taxonomic richness and composition, and the community assembly processes underlying these patterns, will differ across latitude. Specifically, we predicted that high beta diversity (spatial variation in composition) and high temporal turnover contribute to the high species richness of the tropics. Using a standardized experimental approach that controls for several confounding factors that hinder interpretation of prior studies, we present results that support our predictions. In the temperate zone, communities were more similar across spatial scales from centimeters to tens of kilometers and temporal scales up to one year than at lower latitudes. Since the patterns at northern latitudes were congruent with a null model, stochastic assembly processes are implicated. In contrast, the communities in the tropics were a dynamic spatial and temporal mosaic, with low similarity even across small spatial scales and high temporal turnover at both local and regional scales. Unlike the temperate zone, deterministic community assembly processes such as predation likely contributed to the high beta diversity in the tropics. Our results suggest that community assembly processes and temporal dynamics vary across latitude and help structure and maintain latitudinal patterns of diversity.

The fossil record and macroevolutionary history of North American ungulate mammals: standardizing variation in intensity and geography of sampling

The record of the taxonomic evolution of North American ungulates is critical to our understanding of mammalian evolution and environmental change throughout the Cenozoic. The distribution of sampling in the ungulate fossil record over time and geographic space and the degree to which this biases the observed patterns of taxonomic evolution is poorly understood. To address these issues, I placed fossil collections and occurrences drawn from the Paleobiology Database into 2-Myr time intervals between 55 and 1 Ma. I determined the variation in numbers of fossil collections and occurrences, using three metrics to measure geographic variation: first, the area of the convex hull containing all collections in an interval, to determine the areal coverage of sampling; second, the mean pairwise geographic distance among collections as a measurement of the dispersion of collections within that area; and third, the interval-to-interval migration of the geographic centroid of all collections, to calculate changes in the geographic location of sampling. Each of these showed considerable variation over the Cenozoic, and both the area of the convex hull (ACH) encompassing all collections in an interval, and mean pairwise distance (MPWD) among them showed increasing trends over time.To minimize the effect of variation in numbers of fossil samples over time, I used standard sample-standardization procedures. To minimize the effect of geographic variation in sampling over time, I standardized the area of sampling among intervals. I also employed both standardizations sequentially. Each standardization procedure had surprisingly little effect on observed patterns of taxonomic richness and rates. This indicates that, for North American ungulates, neither variation in number nor geographic distribution of fossil samples exerts an overwhelming influence on perceived macroevolutionary patterns. These results confirm the ungulate fossil record as a critical and faithful record for our understanding of Cenozoic environmental change and the mammalian evolutionary response.

Drying of a temperate, intermittent river has little effect on adjacent riparian arthropod communities

Summary Rivers and their adjacent riparian zones are intimately linked by fluxes of water, air masses, nutrients and organisms. Intermittent rivers constitute ideal systems to examine these linkages because they are characterised by alternating wet and dry phases, and hence, natural and contrasting variations occur in aquatic resources and environmental conditions. We addressed the effects of river drying on riparian communities by collecting ground‐dwelling arthropods at three perennial sites and at four intermittent sites during a wet and a dry phase in the Albarine River (France). We first predicted that during dry phases, declines in aquatic resources and loss of water would create harsh environmental conditions and alter community structure and composition, due to decreases in predators and hygrophilous taxa. Second, we predicted that alternating wet and dry phases would enhance cumulative taxonomic richness over time owing to an increase in species turnover. We found similar decreasing temporal patterns in taxonomic richness and abundance at intermittent and perennial sites, indicating that river drying had no effect on the structure of riparian arthropod communities. Community composition at intermittent and perennial sites differed only during the dry phase, indicating that intermittent and perennial sites gained and lost different sets of taxa as the river dried. Nevertheless, species turnover did not differ between sites, while taxonomic richness was always higher at intermittent sites. Although some taxa were sensitive to river drying, the Albarine River supports rich and abundant riparian arthropod communities. While several studies have reported a strong dependence of riparian populations on aquatic resources, our results indicate that the effects of river drying on riparian arthropods at the community level are weak and discrete in time in the Albarine River.

Ammonoid recovery after the Permian–Triassic mass extinction: a re-exploration of morphological and phylogenetic diversity patterns

The explosive ammonoid rediversification after the Permian–Triassic mass extinction is now well understood in terms of taxonomic richness and biogeography. Using an updated dataset of Early Triassic ammonoids, we compare morphological disparity and taxonomic richness patterns at the regional and global scales. Disparity evolved similarly at both scales, suggesting a global influence of abiotic factors. Morphological diversification occurred early in the Smithian and a marked contraction of the morphospace took place during the end-Smithian extinction. We confirm that trends in disparity and richness were decoupled during the Griesbachian and Dienerian. Three macroevolutionary processes may be involved: (1) a nonselective extinction at the Permian–Triassic boundary; (2) a Dienerian constrained radiation with several homeomorphic genera; (3) a potential deterministic extinction during the end-Smithian crisis. We also demonstrate a superfamily imprint upon disparity for the Spathian when most superfamilies occupied a restricted part of the morphospace. Sphaerocones were the most affected by the Dienerian and end-Smithian extinction, but explanations remain elusive. On the one hand, this may be linked to widespread harsh conditions at those times. On the other hand, as the sphaerocones occurred episodically during the Early Triassic, this might be explained by a relaxing of ecological constraints or simply by convergent evolution. Supplementary materials: The database, including measurements of specimens illustrated in previously published plates and of unpublished specimens from Utah, South China and Spiti, as well as the number of genera present in each studied substage of the Early Triassic, are available at www.geolsoc.org.uk/SUP18571.

Turnover patterns in fish versus macroinvertebrates — implications for conservation planning

Spatial patterns in taxonomic richness and turnover for fish and aquatic macroinvertebrates are compared to assess the relative usefulness of each taxonomic group in mapping biodiversity patterns. Fish and aquatic macroinvertebrate species data for sites down the longitudinal axes of nine rivers in four provinces along the eastern side of South Africa were analysed. Fish and aquatic macroinvertebrate data from previous studies and recent river surveys were used in analyses of species richness and turnover. Fish proved to be not useful for mapping biodiversity patterns, as measured by turnover, whereas aquatic macroinvertebrate species patterns exhibited predictable patterns of turnover with downstream distance. Average turnover rates could be decomposed into turnover of common (‘core’) species, which were accelerated by presence of rare and narrow-range species. Disruptions to the river continuum impacted on the rate of turnover. Consistent with other research on South African rivers, aquatic macroinvertebrate communities could be grouped into upland versus lowland assemblages, and also be defined by longitudinal zones. Fish biodiversity patterns should be viewed at a riverscape scale, whereas macroinvertebrate patterns are more easily discerned at a segment-reach scale, and applied to reflect connectivity and environmental gradients respectively.

Niche conservatism and species richness patterns of squamate reptiles in eastern and southern Africa

Niche conservatism has been proposed as a mechanism influencing large-scale patterns of taxonomic richness. We document the species richness patterns of five monophyletic squamate reptile groups (gekkonids, cordylids-scincids, lacertids, chameleons and alethinophidian snakes) in eastern and southern Africa, and explore if observed patterns reflect niche conservatism processes. We quantified richness and its relationships with current climatic conditions by gridding species' range maps at 110 × 110 km. Also, dated phylogenies and palaeoclimatic reconstructions, coupled with evidence from the fossil record, were used to approximate the areas and climate characteristics in which each group originated and/or radiated. Mean species richness and geographically corrected confidence intervals in current climate types were calculated for each group in order to establish their climatic preferences. On average, the species richness of older groups (gekkonids, cordylids-scincids and lacertids) was lower in equatorial climates and higher in arid and temperate conditions, whereas more recent groups (chameleons and alethinophidian snakes) were richer in equatorial and temperate climates and less rich in arid conditions. Across all groups, higher richness was associated with climatic characteristics similar to those prevailing at the time in which each group originated/radiated. The congruence of the current climates where reptile groups are richer and the past climates amidst which those groups originated is consistent with an explanation for their diversity gradients based on niche conservatism.

Lateral organization of aquatic invertebrates along the corridor of a braided floodplain river

Although spatial scale, upstream–downstream gradients, environmental variability, and floodplain connectivity and complexity have been recognized as integral components of our understanding of riverine pattern and process, aquatic invertebrate community structure across lateral gradients from headwaters to the lowland of a river has received little empirical documentation. Aquatic invertebrate density, distribution, and richness were investigated at 29 study sites distributed laterally (main channel–floodplain) among 6 geomorphologically distinct river reaches from the headwaters to near the mouth of one of the last seminatural river corridors draining the European Alps, the Tagliamento River in northeastern Italy. Community relationships were examined using multivariate and diversity analyses to investigate patterns of taxonomic richness. Diversity parameters were scaled at the site, reach, and catchment levels to better understand local and regional patterns. Mean invertebrate density increased from 7484 ± 2480 (±1 SE) individuals/m2 in the headwaters to 98,811 ± 18,037 individuals/m2 on the lowland floodplain. Crustacea, Coleoptera, and Ephemeroptera richness increased and nonchironomid Diptera and Plecoptera richness declined along the corridor. Richness (α diversity) and turnover (β diversity) showed no consistent increase or decrease along connectivity gradients within geomorphic reaches along the river corridor, possibly because each reach had unique characteristics. α diversity was similar among geomorphic reaches along the corridor, whereas β diversity between reaches increased as a function of distance between them. Direct gradient analysis indicated high taxa-to-environment concordance along lateral (i.e., floodplain water bodies) and longitudinal (upstream–downstream) dimensions and indicated distinct floodplain communities. These results demonstrate how lateral gradients (floodplain dimension) structure zoobenthic communities and how this structure can change along the longitudinal dimension (upstream–downstream). Our results highlight the importance of off-channel environments to macroinvertebrate community structure and diversity. Conservation, restoration, and preservation measures must consider the lateral dimension along river corridors as integral to maintaining diversity and community structure.

The role of coastal ecotones: a case study of the salt marsh/upland transition zone in California

Summary Ecotones, the transition zones between adjacent ecological systems, may intensify or concentrate the flow and processing of materials and organisms between systems. To determine whether the salt marsh/upland transition zone is an ecotone, both in functioning as a habitat, as well as concentrating materials and organisms, I conducted an extensive survey of 12 marsh/upland transition zones in the Pt Reyes area of California. The high saltmarsh was identified as an ecotone, with biological and physical conditions distinct from the adjacent marsh plain and upland. It supports a unique plant assemblage and greater total soil nitrogen than the adjacent upland. Taxonomic richness patterns did not reflect changes in habitat spatial characteristics (e.g. ecotone area, ecotone area/perimeter), instead showing a quadratic correlation along the gradient, with increased diversity of both plants and spiders in the ecotone. Spider richness was enhanced with increased vegetation complexity, which was greatest in the ecotone. This study presents empirical evidence that suggests coastal marsh/upland ecotones harbour increased diversity and may concentrate nitrogen pools, thereby highlighting the need for further research investigating the relationship between landscape connections and the coupling of species and biogeochemical processes.

Regional patterns of plant species richness in southern New Zealand

We examine the proposition that spatial heterogeneity, as modelled by land area, productivity‐influencing climatic variables, and elevation, is a usefd predictor of regional patterns of species richness in 56 regions of southern New Zealand stretching from mid Canterbury to Campbell Island. We also examine whether regional patterns of taxonomic richness support the concept of a Late Cenozoic radiation of upland floras and that this was sourced from just a few genera in a few widespread to cosmopolitan families. We found several contrasting geographical patterns in taxonomic richness. Several mainly mountain regions just east of the main divide in western Canterbury, Otago, and Southland are unusually species‐rich, but not genus‐ or family‐rich. Conversely, several coastal regions of eastern South Island are unusually genus‐ and family‐rich, but not species‐rich. Four geographically distinct groups of regions share relatively species‐, genus‐, and family‐depauperate floras: maritime‐influenced regions of Fiordland, the Chatham and subantarctic islands, inland and lowland basins of Otago and Southland, and eastern Otago's block mountains. Various combinations of elevation range, climatic variability, and land area explain 54% to 61% of the variability in richness of species, genera, families, and life‐form groups. Mean daily temperature of the coldest month appears the strongest climatic variable at depressing floristic richness, although moderate degrees of continentality of climate increase it. We conclude that both propositions are supported by the present study. Databases of regional‐scale patterns of plant species richness should be useful for selecting mainland islands for ecosystem restoration, estimating ecosystem or guild diversity, and testing the ecological distinctiveness of ecological regions and districts.

Concordance of taxonomic richness patterns across multiple assemblages in lakes of the northeastern United States

We investigated the concordance of taxonomic richness patterns and their environmental correlates for assemblages of benthic macroinvertebrates, riparian birds, sedimentary diatoms, fish, planktonic crustaceans, and planktonic rotifers in 186 northeastern U.S. lakes. Taxon counts were standardized with respect to sampling effort using rarefaction. The degree of concordance among assemblage richness measures was low, but this was at least partly attributable to measurement precision. Aspects of lake morphology (area, depth) superseded other environmental features (climate, human development, water chemistry, nearshore physical habitat) as correlates of assemblage richness and were the strongest source of concordance. The benthic macroinvertebrates, birds, fish, and zooplankton all showed positive associations between richness and lake area. The diatoms showed negligible associations between richness and area and negative associations between richness and depth. Associations with human development were much weaker than with lake morphology and varied from positive (fish, planktonic crustaceans) to negative (diatoms). We conclude that taxonomic richness alone may be of ambiguous value as an indicator of biological integrity in lakes and that its natural drivers must be controlled for prior to assessing anthropogenic effects.

Spatial Pattern of Vascular Plant Diversity in North America North of Mexico and its Floristic Relationship with Eurasia

This paper reports: (1) patterns of taxonomic richness of vascular plants in North America (north of Mexico), an area accounting for 16.6% of the total world land, in relation to latitudinal and longitudinal gradients; (2) floristic relationships between different latitudinal zones, longitudinal zones, and geographic regions of North America; and (3) floristic relationships between North America and Eurasia at various geographic scales. North America was geographically divided into twelve regions, which were latitudinally grouped into four zones, each with three regions, and longitudinally grouped into three zones, each with four regions. The native vascular flora of North America consists of 162 orders, 280 families, 1904 genera and 15352 species. Along the latitudinal gradient, species richness shows a striking increase with decreasing latitude (e.g. the northernmost latitudinal zone has only 11.7% of the number of species in the southernmost latitudinal zone). However, about 63% of the species of the northernmost latitudinal zone are also present in the southernmost latitudinal zone of North America. Among the three longitudinal zones, the zone on the Pacific coast has 1.48 and 1.64-times as many species as the zones in the interior and on the Atlantic coast, respectively. About 36% of the species in the zone of the Atlantic coast also occur in the Pacific coast zone. However, each of over 40% of the species in North America occupies less than 10% of the total land area of North America. Some 48% of the genera and 6.5% of the species of North America are also native to Eurasia. In general, the number of genera common to North America and Eurasia increased from the north to the south and from the west to the east of North America, whereas the number of species common to the two continents decreased along the same two geographic gradients.