Biogeography of body size in Pacific island birds

Many insular vertebrates have undergone rapid and dramatic changes in body size compared to their mainland counterparts. Here we explore the relationship between two well known patterns of island body size – the tendency for large‐bodied species to dwarf and small‐bodied species to get larger on islands, known as the “island rule”, and the scaling of maximum and minimum body size of island assemblages with island area. Drawing on both fossil and modern data, we examined the relationship between body size and island area in Pacific island birds, both within clades and at the island assemblage level. We found that the size of the smallest bird on each island decreased with island area while the maximum body size increased with island area. Similarly, within clades the body size of small‐bodied groups decreased and large‐bodied groups increased from small to large islands, consistent with the island rule. However, the magnitude of size change within clades was not sufficient to explain the overall scaling of maximum size with island area. Instead, the pattern was driven primarily by the evolution of very large, flightless birds on large islands. Human‐mediated extinctions on islands over the past few millennia severely impacted large, flightless birds, to the effect that this macroecological pattern has been virtually erased. After controlling for effects of biogeographic region and island area, we found island productivity to be the best predictor of maximum size in flightless birds. This result, and the striking similarities in maximum body size between flightless birds and island mammals, suggests a common energetic mechanism linking body size and landmass area in both the island rule and the scaling of island body size extremes.     

Self-similarity and the relationship between abundance and range size

Patterns in the relationships among the range, abundance, and distribution of species within a biome are of fundamental interest in ecology. A self-similarity condition, imposed at the community level and previously demonstrated to lead to the power-law form of the species-area relationship, is extended to the species level and shown to predict testable power-law relationships between range size and both species abundance and area of census cell across scales of spatial resolution. The predicted slopes of plots of log(range size) versus log(abundance) are shown to be in good agreement with data from British breeding bird and mammal censuses and with data on the distribution of fern species in old-growth forest. The predicted slopes of plots of log(range size) versus log (area of census cell) are consistent with the limited available data for British plant species. Self-similarity provides a testable theoretical framework for a unified understanding of patterns among the range, abundance, and distribution of species.     

Does the energy equivalence rule apply to intertidal macrobenthic communities?

Energy equivalence assumes equal contribution of large and small species to production and energy flow in communities. As in a double logarithmic plot, physiological rates decline with body weight by –0.25, log biomass should increase by 0.25 and log abundance decline by –0.75 with log species weight, when this concept is valid. This was tested with annual data sets of the macrobenthos of 4 intertidal sites in the German Wadden Sea (Königshafen) and 3 sites in a south Portuguese lagoon (Ria Formosa). Only abundance data from two of these sites displayed significantly negative slopes with mean body size of the species. Biomass and secondary production data were significantly positively correlated with mean body size for all Ria Formosa sites and also for the biomass of a mussel bed in Königshafen. However, high variation in body size of the individuals of a species limits interpretation of these plots.It is preferable to test this concept by body weight classes regardless of its species composition. At Königshafen, biomass and production displayed two distinct peaks. One peak at small body size was caused by browsing species. The other peak at larger body size was caused by animals which potentially extract their food from the water column. This bimodality was only vaguely reflected at one station in the Ria Formosa, possibly because of a dominance of detritus feeding species. In a normalized form (log biomass or production / width of size classvs. log size class), these spectra imply a dominance of small individuals in biomass and production at all sites (except for a mussel bank at Königshafen). This is interpreted as a consequence of permanent disturbances.     

Pattern and process in the geographical ranges of freshwater fishes

North American freshwater fishes were studied to determine whether they displayed the same relationships between log (geographical range size) and log (body size) and the same pattern of range shape as found among North American birds and mammals. The forces that produce these patterns were also investigated. The log (geographical range size) : log (body size) relationship was analysed for 121 North American freshwater fish species. Thirty‐two imperilled species were compared with 89 non‐imperilled species to determine if the overall relationship could result from differential extinction. Range geometries were analysed, within and among habitat guilds, to determine if general patterns could be detected. The log (geographical range size) : log (body size) pattern among freshwater fish species was triangular and qualitatively similar to that found for North American birds and mammals. The results suggest that below a minimum geographical range, the likelihood of extinction increases dramatically for freshwater fishes and that this minimum range size increases with body size. The pattern of fish species’ range shapes differs from that found for other North American vertebrate taxa because, on average, fish possess much smaller ranges than terrestrial species and most fish species’ geographical ranges extend further on a north–south axis than on an east–west axis. The log (geographical range size) : log (body size) pattern reveals that fish species’ geographical ranges are more constrained than those of terrestrial species. The triangular relationship may be caused by differential extinction of species with large bodies and small geographical ranges as well as higher speciation rates of small‐bodied fish. The restricted geographical ranges of freshwater fishes gives them much in common with terrestrial species on oceanic islands. Range shape patterns within habitat guilds reflect guild‐specific historical and current ecological forces. The overall pattern of range shapes emerges from the combination of ecologically different subunits.     

Species distribution,ecology, abundance,body size and phylogeny originate interrelated rarity patterns at regional scale

The most pervasive macroecological patterns concern (1) the frequency distribution of range size, (2) the relationship between range size and species abundance and (3) the effect of body size on range size. We investigated these patterns at a regional scale using the tenebrionid beetles of Latium (Central Italy). For this, we calculated geographical range size (no. of 10‐km square cells), ecological tolerance (no. of phytoclimatic units) and abundance (no. of sampled individuals) using a large database containing 3561 georeferenced records for 84 native species. For each species, we also calculated body mass and its ‘phylogenetic diversity’ on the basis of cladistic relationships. Frequency distribution of range size followed a log‐normal distribution as found in many other animal groups. However, a log‐normal distribution accommodated well the frequency distribution of ecological tolerance, a so far unexplored issue. Range size was correlated with abundance and ecological tolerance, thus supporting the hypothesis that a positive correlation between distribution and abundance is a reflection of interspecific differences in ecological specialization. Larger species tended to have larger ranges and broader ecological tolerance. However, contrary to what known in most vertebrates, not only small‐sized, but also many medium‐to‐large‐sized species exhibited great variability in their range size, probably because tenebrionids are not so strictly influenced by body size constraints (e.g. home ranges) as vertebrates. Moreover, in contrast to other animals, tenebrionid body size does not influence species abundances, probably because these detritivorous animals are not strongly regulated by competition. Finally, contrary to the assumption that rare species should be mainly found among lineages that split from basal nodes, rarity of a tenebrionid species was not influenced by the phylogenetic position of its tribe. However, lineages that split from more basal nodes had lower variability in terms of species geographical distribution, ecological tolerance and abundance, which suggests that lineages that split from more basal nodes are not only morphologically conservative but also tend to have an ecological ‘inertia’.     

The energetic equivalence rule rejected because of a potentially common sampling error: evidence from carabid beetles

Abundance data from pitfall traps are widely used to estimate the relationship between beetle body size and abundance. Such data probably overestimate densities of large bodied species and may overestimate slopes of size‐abundance relationships. Here, we test this idea by comparing size‐abundance patterns found using data from pitfall trapping with those found with data from a quantitative method of estimating abundance, quadrat sampling. We use data from a total of 47 communities. As expected, slopes of size‐abundance relationships are significantly more positive when estimated using data from pitfall traps compared to when using quadrat sampling data. This was seen when looking across different communities, within communities sampled by both methods and when focusing on the set of species found by both methods within a community. These results were also generally found regardless of method of analysis, which were done using regression with species values as independent data points and using the independent contrast method, and with slopes estimated using ordinary least square regression or the structural relation. Most important, slopes of size‐abundance relationships based on data from pitfall traps were on average significantly more positive than ?0.75 on log–log scales, and thus inconsistent with the energetic equivalence rule. Slopes based on quadrat sampling, on the other hand, were on average not significantly different from ?0.75. The rejection of the energetic equivalence rule based on data from pitfall traps here is therefore a sampling artefact. Similar problems may apply to abundance data from virtually all insect trapping methods, and should make us consider re‐examining many of the size‐abundance patterns documented so far. As a large proportion of all animal species are insects, and traps are widely used to estimate abundance, this is a potentially important problem for our general understanding of the relationship between species body size and abundance.     

Dynamic relationships between body size,species richness,abundance, and energy use in a shallow marine epibenthic faunal community

We study the temporal variation in the empirical relationships among body size (S), species richness (R), and abundance (A) in a shallow marine epibenthic faunal community in Coliumo Bay, Chile. We also extend previous analyses by calculating individual energy use (E) and test whether its bivariate and trivariate relationships with S and R are in agreement with expectations derived from the energetic equivalence rule. Carnivorous and scavenger species representing over 95% of sample abundance and biomass were studied. For each individual, body size (g) was measured and E was estimated following published allometric relationships. Data for each sample were tabulated into exponential body size bins, comparing species‐averaged values with individual‐based estimates which allow species to potentially occupy multiple size classes. For individual‐based data, both the number of individuals and species across body size classes are fit by a Weibull function rather than by a power law scaling. Species richness is also a power law of the number of individuals. Energy use shows a piecewise scaling relationship with body size, with energetic equivalence holding true only for size classes above the modal abundance class. Species‐based data showed either weak linear or no significant patterns, likely due to the decrease in the number of data points across body size classes. Hence, for individual‐based size spectra, the SRA relationship seems to be general despite seasonal forcing and strong disturbances in Coliumo Bay. The unimodal abundance distribution results in a piecewise energy scaling relationship, with small individuals showing a positive scaling and large individuals showing energetic equivalence. Hence, strict energetic equivalence should not be expected for unimodal abundance distributions. On the other hand, while species‐based data do not show unimodal SRA relationships, energy use across body size classes did not show significant trends, supporting energetic equivalence.     

Correlates of species richness in mammals: body size, life history, and ecology

We present the most extensive examination to date of proposed correlates of species richness. We use rigorous phylogenetic comparative techniques, data for 1,692 mammal species in four clades, and multivariate statistics to test four hypotheses about species richness and compare the evidence for each. Overall, we find strong support for the life-history model of diversification. Species richness is significantly correlated with shorter gestation period in the carnivores and large litter size in marsupials. These traits and short interbirth intervals are also associated with species richness in a pooled analysis of all four clades. Additionally, we find some support for the abundance hypotheses in different clades of mammals: abundance correlates positively with species richness in primates but negatively in microchiropterans. Our analyses provide no evidence that mammalian species richness is associated with body size or degree of sexual dimorphism.     

A comparative analysis of vigilance in birds

Individual variation in vigilance is known to vary with factors such as group size but the ecological determinants of vigilance among species have not been examined thus far in a systematic fashion. Earlier analyses suggested that vigilance should be lower in larger species and in species living in larger groups. These analyses were based on a small number of species and failed to take into account phylogenetic relationships among species. Here, I examined ecological determinants of vigilance in a large sample of bird species using a phylogenetic framework. I focused on vigilance in foraging groups of birds in the non-breeding season. Among species, vigilance by solitary foragers was not influenced by body mass. However, among species, asymptotic vigilance, the plateau reached by vigilance in larger groups, decreased with increasing group size in vegetarian clades but not in carnivorous clades. Asymptotic vigilance also increased with increasing body mass in vegetarian clades but not in carnivorous clades. Increasing group size may allow species to reduce vigilance in response to decreased predation risk. Increasing body mass may allow species to increase vigilance because more non-foraging time is available in larger species. Diet may modulate the effect of body mass and group size through factors such as within-group vigilance or foraging techniques.     

The evolution of body size in birds. I. Evidence for non-random diversification

The hypothesis that evolution of body size in birds was a random process coupled with an absolute lower boundary on body mass was tested using data on 6217 species of extant birds. The test was based on the fact that subclades within birds that have body masses much larger than this minimum should not have skewed log body mass distributions, while clades close to this boundary should. Bird species were classified into 23 orders suggested by Sibley and Monroe (1988). Thirteen orders that had average log body masses greater than the average for all birds had significantly skewed log body mass distributions. This is inconsistent with the hypothesis that evolution of body size in birds is random, but is constrained only at the smallest body masses. Most orders of birds cannot be considered random samples from the parental distribution of all birds. When the pattern of body mass evolution in birds is reconstructed using an estimate of the phylogenetic relationships among orders, there are many more instances where a large taxon putatively originated from a smaller one than vice versa. The non-random nature of body mass evolution in birds is consistent with models that postulate that evolution is constrained by the ability of individuals to turn resources into offspring.     

Body mass, habitat generality, and avian community composition in forest remnants

Aim Many theories of biodiversity and biogeography assume that species respond equally to variability in habitat area and isolation. This assumption does not allow for differential responses due to interspecific competition or other mechanisms, and therefore does not allow community composition to be predicted. As body size is relevant to area requirements and interspecific dominance, a natural experiment was conducted to quantify the differential responses of avian species abundance to variability in remnant area, isolation and forest cover based on average species body mass. Location Deciduous forest remnants of varying area and isolation throughout the State of Delaware, USA. Methods Forest remnants within stratified area and isolation classes were randomly selected for breeding bird surveys; total forest cover (ha) within 2 km of each survey point was subsequently determined as a covariate. Surveys were conducted within 100–150 m from the edge of each remnant and detected bird species were divided into five classes based on a log₂‐transformation of body mass (very small, small, medium, large and very large). Assuming a negative binomial distribution, the abundance of detected individuals in each mass class was analysed using generalized linear models with remnant area, isolation, local forest cover and two‐way interactions specified as independent variables. The same analyses were conducted for individual species where sample size allowed. Results Very small, small and very large bodied species decreased in abundance with decreasing local forest cover and remnant area and with increasing remnant isolation, while large species increased in abundance. Medium‐sized species decreased in abundance with increasing forest cover, did not respond to remnant isolation and showed a concave, curvilinear response to increasing remnant area. Large and medium‐sized species were the most abundant birds in small, isolated remnants despite occurring in the largest remnants with the more abundant very small and small species, suggesting that communities are not randomly organized. Main conclusions Regardless of presumed habitat associations, large and medium‐sized species are of the appropriate size to be dominant competitors when forest resources are limiting, and thus may be considered ‘generalists’. The smallest species may be excluded entirely from small, isolated remnants even though such remnants meet their ecological needs; the needs of very large species are not met in small remnants. The applicability of biodiversity theories to community composition, species abundance and, by extension, to conservation, can be improved by incorporating differential responses based on body mass into their assumptions.     

Shotgun mitogenomics across body size classes in a local assemblage of tropical Diptera: Phylogeny,species diversity and mitochondrial abundance spectrum

Mitochondrial genomes can be assembled readily from shotgun‐sequenced DNA mixtures of mass‐trapped arthropods (“mitochondrial metagenomics”), speeding up the taxonomic characterization. Bulk sequencing was conducted on some 800 individuals of Diptera obtained by canopy fogging of a single tree in Borneo dominated by small (<1.5 mm) individuals. Specimens were split into five body size classes for DNA extraction, to equalize read numbers across specimens and to study how body size, a key ecological trait, interacts with species and phylogenetic diversity. Genome assembly produced 304 orthologous mitochondrial contigs presumed to each represent a different species. The small‐bodied fraction was the by far most species‐rich (187 contigs). Identification of contigs was through phylogenetic analysis together with 56 reference mitogenomes, which placed most of the Bornean community into seven clades of small‐bodied species, indicating phylogenetic conservation of body size. Mapping of shotgun reads against the mitogenomes showed wide ranges of read abundances within each size class. Ranked read abundance plots were largely log‐linear, indicating a uniformly filled abundance spectrum, especially for small‐bodied species. Small‐bodied species differed greatly from other size classes in neutral metacommunity parameters, exhibiting greater levels of immigration, besides greater total community size. We suggest that the established uses of mitochondrial metagenomics for analysis of species and phylogenetic diversity can be extended to parameterize recent theories of community ecology and biodiversity, and by focusing on the number mitochondria, rather than individuals, a new theoretical framework for analysis of mitochondrial abundance spectra can be developed that incorporates metabolic activity approximated by the count of mitochondria.     

Relating species abundance distributions to species-area curves in two Mediterranean-type shrublands

Abstract. Based on both theoretical and empirical studies there is evidence that different species abundance distributions underlie different species‐area relationships. Here I show that Australian and Californian shrubland communities (at the scale from 1 to 1000 m²) exhibit different species‐area relationships and different species abundance patterns. The species‐area relationship in Australian heathlands best fits an exponential model and species abundance (based on both density and cover) follows a narrow log normal distribution. In contrast, the species‐area relationship in Californian shrublands is best fit with the power model and, although species abundance appears to fit a log normal distribution, the distribution is much broader than in Australian heathlands. I hypothesize that the primary driver of these differences is the abundance of small‐stature annual species in California and the lack of annuals in Australian heathlands. Species‐area is best fit by an exponential model in Australian heathlands because the bulk of the species are common and thus the species‐area curves initially rise rapidly between 1 and 100 m². Annuals in Californian shrublands generate very broad species abundance distributions with many uncommon or rare species. The power function is a better model in these communities because richness increases slowly from 1 to 100 m² but more rapidly between 100 and 1000 m² due to the abundance of rare or uncommon species that are more likely to be encountered at coarser spatial scales. The implications of this study are that both the exponential and power function models are legitimate representations of species‐area relationships in different plant communities. Also, structural differences in community organization, arising from different species abundance distributions, may lead to different species‐area curves, and this may be tied to patterns of life form distribution.     

Patterns in the abundance and distribution of ichneumonid parasitoids within and across habitat patches

Abstract 1. Knowing how species are distributed across a landscape can considerably aid the management of populations and species richness. Insect parasitoids constitute a large fraction of terrestrial biodiversity and help regulate other insect populations, but their ecology is poorly known at a landscape scale. 2. Using Malaise traps distributed first extensively and then intensively across woodland patches in an agricultural landscape, we tested whether four ichneumonid subfamilies display (i) a positive relationship between abundance and occupancy, (ii) a positive relationship between abundance in the extensive sample and abundance in the intensive sample, and (iii) aggregation across traps. 3. A positive relationship between abundance and occupancy was found across species in both samples, and was relatively strong. Abundance in the extensive samples was positively correlated with abundance in the intensive samples. On average, species were aggregated in both samples, although aggregation was not necessary for a positive abundance–occupancy relationship. 4. These results suggest that ichneumonid species can largely be classified on a continuum from widespread and locally abundant to localised and locally scarce. The former species allow the potential for pervasive natural control of host populations. The latter species, which constitute a substantial majority of the species list, will be vulnerable to extinction through both stochastic forces and widespread adverse forces such as climate change and habitat modification. However, the assessment of species’ status is likely to be facilitated by the positive abundance–occupancy relationship. 5. Species inventories for ichneumonids will be taxing because of the need to sample both intensively and extensively to detect rare species, which constitute the majority of species. However, it is possible to generalise species abundances across spatial scales and years, facilitating monitoring.     

Species–area relationship within benthic habitat patches of a tropical floodplain river: An experimental test

The curvilinear relationship between species richness and habitat area (species–area relationship (SAR)) is a fundamental ecological pattern. The relationship is often viewed from a long‐term perspective across relatively large spatial scales, reflecting a balance between immigration and extinction dynamics. We explored whether predictions of SAR also manifest over short time periods (days) in benthic habitat patches of a dynamic floodplain river where littoral faunal assemblages are continuously assembled and disassembled with changing water levels. We examined the relationship of patch size with faunal abundance (i.e. fish and aquatic invertebrates), taxonomic richness, trophic group richness and overall assemblage composition. Strong taxa–area relationships emerged despite the relatively short experimental time period (21 days); larger patches had more taxa and trophic groups. For the smallest patches, taxonomic richness was especially sensitive to abundance of individuals; abundance of individuals was a less important predictor of taxonomic and trophic group richness for the largest patches. Despite the relatively short time frame for study within this temporally dynamic ecosystem, our findings indicate a strong SAR for fishes and macroinvertebrates inhabiting patchy habitats in the littoral zone of this tropical river.     

Mass extinctions do not explain skew in interspecific body size distributions

In several higher animal taxa, such as mammals and birds, the distribution of species body sizes is heavily skewed towards small size. Previous studies have suggested that small‐bodied organisms are less prone to extinction than large‐bodied species. If small body size is favourable during mass extinction events, a post mass extinction excess of small‐bodied species may proliferate and maintain skewed body size distributions sometime after. Here, we modelled mass extinctions and found that even unrealistically strong body mass selection has little effect on the skew of interspecific body size distributions. Moreover, selection against large body size may, counter intuitively, skew size distributions towards large body size. In any case, subsequent evolutionary diversification rapidly erases these rather small effects mass extinctions may have on size distributions. Next, we used body masses of extant species and phylogenetic methods to investigate possible changes in body size distributions across the Cretaceous–Paleogene (K‐Pg) mass extinction. Body size distributions of extant clades that originated during the Cretaceous are on average more skewed than their subclades that originated during the Paleogene, but the difference is only minor in mammals, and in birds, it can be explained by a positive relationship between species richness and skewness that is also present in clades that originated after the transition. Hence, we cannot infer from extant species whether the K‐Pg mass extinctions were size‐selective, but they are not the reason why most extant bird and mammal species are small‐bodied.     

Body size in (mostly) mammals: mass,speciation rates and the translation of gamma to alpha diversity on evolutionary timescales

This study tests the hypothesis that high species richness in small-bodied mammals results from higher speciation rates than in clades composed of large-bodied individuals. A right-skewed pattern is evident in size distributions of all mammal groups tested. Gaps between 100 g bins expand smoothly for the global mammal database. Less diverse mammal clades composed of large-sized individuals originated at relatively large size. Mechanisms promoting isolation and higher speciation rates in small mammals include the environmental mosaic, low absolute energy needs, small home range size, stenotopy, and intraspecific competition. A decline in diversity for the smallest size category in some clades suggests there is a lower limit in homoiotherms of about 1.5–2 g, possibly related to high metabolic rate and high surface area to volume ratio. Mammal size diversity from young Canadian ecosystems (≤19,000 years BP) is right-skewed, and diversity of species per unit area is approximately the same as for North America. Diversity and size distributions for mammals and select animal groups from southern Minnesota follow expected right-skewed patterns, suggesting the inverse relationship of body size and speciation rate is universal for complex metazoans. A logistic model is presented integrating γ and α diversity over evolutionary timescales.     

Does size really matter? Species–area relationships in human settlements

Aim To describe species–area relationships in human settlements and compare them with those from a non‐urban habitat. Location West‐central Mexico. Methods We surveyed breeding birds in 13 human settlements and five shrubland patches. We estimated bird species richness using an abundance‐based coverage estimator with equal sample sizes to eliminate biases related to sampling effort differences. To assess species–area relationships, we performed log–log linear regressions between the size of the studied patches and their estimated bird richness. We also used a logarithmic approach to determine how the species–area relationship asymptoted and made use of the Michaelis–Menten model to identify the size at which the studied patches reached their maximum species richness. We also investigated (1) possible relationships among the estimated bird richness and other variables known to affect urban‐dwelling birds (built cover, plant species richness, tree cover or human population density) and (2) changes in bird community composition related to the size of the studied human settlements. Results Species–area relationships exhibited different patterns among the studied habitats. The log–log regression slope was steeper in human settlements, while the intercept was higher in shrublands. The maximum number of species was more than twofold higher in shrublands. Human settlement patch size was the only variable significantly related to bird richness. Our community composition results show that two main bird groups are related to human settlement size, and that as the size of human settlements increases, bird community similarity in relation to the largest city increases. Main conclusions Human settlements act as ecological islands, with pronounced species–area relationships. Our results suggest that an important threshold for bird species richness and community composition is reached in human settlements > 10.2 km². This threshold is unlikely to be generalizable among bio‐regions, and thus should be quantified and considered when studying, managing and/or planning urban systems.     

One size does not fit all: no evidence for an optimal body size on islands

Aim Optimal body size theories predict that large clades have a single, optimal, body size that serves as an evolutionary attractor, with the full body size spectrum of a clade resulting from interspecific competition. Because interspecific competition is believed to be reduced on islands, such theories predict that insular animals should be closer to the optimal size than mainland animals. We test the resulting prediction that insular clade members should therefore have narrower body size ranges than their mainland relatives. Location World‐wide. Methods We used body sizes and a phylogenetic tree of 4004 mammal species, including more than 200 species that went extinct since the last ice age. We tested, in a phylogenetically explicit framework, whether insular taxa converge on an optimal size and whether insular clades have narrow size ranges. Results We found no support for any of the predictions of the optimal size theory. No specific size serves as an evolutionary attractor. We did find consistent evidence that large (> 10 kg) mammals grow smaller on islands. Smaller species, however, show no consistent tendency to either dwarf or grow larger on islands. Size ranges of insular taxa are not narrower than expected by chance given the number of species in their clades, nor are they narrower than the size ranges of their mainland sister clades – despite insular clade members showing strong phylogenetic clustering. Main conclusions The concept of a single optimal body size is not supported by the data that were thought most likely to show it. We reject the notion that inclusive clades evolve towards a body‐plan‐specific optimum.     

Relationships between geographical range size, body size, local abundance, and habitat breadth in North American suckers and sunfishes

Aim I examine the relationship between geographical range size and three variables (body size, an index of habitat breadth, and an index of local abundance) within a phylogenetic framework in North American species of suckers and sunfishes. Location North America Methods Regressions after independent contrasts of geographical range size, body size, habitat breadth, and local abundance. Results Species with large range sizes tend to be larger-bodied, be more locally abundant, and have higher habitat breadths. Character reconstructions support the prediction that variables associated with rarity (small geographical range size, low local abundance, low niche breadth, and large body size) evolve in unison, although large body size was associated with the opposite traits in these taxa. Gaston & Blackburn (1996a) suggested using visual identification of the lower boundary of the geographical range-body size relationship to identify extinction-prone species; this resulted in thirteen species that are potentially extinction-prone. Main conclusions Similar evolutionary mechanisms appear to operate on body size and other variables related to rarity, even in distantly related taxa.