Parasite species richness in carnivores: effects of host body mass, latitude, geographical range and population density

Aim  Comparative studies have revealed strong links between ecological factors and the number of parasite species harboured by different hosts, but studies of different taxonomic host groups have produced inconsistent results. As a step towards understanding the general patterns of parasite species richness, we present results from a new comprehensive data base of over 7000 host–parasite combinations representing 146 species of carnivores (Mammalia: Carnivora) and 980 species of parasites.
Methods  We used both phylogenetic and non-phylogenetic comparative methods while controlling for unequal sampling effort within a multivariate framework to ascertain the main determinants of parasite species richness in carnivores.
Results  We found that body mass, population density, geographical range size and distance from the equator are correlated with overall parasite species richness in fissiped carnivores. When parasites are classified by transmission mode, body mass and home range area are the main determinants of the richness of parasites spread by close contact between hosts, and population density, geographical range size and distance from the equator account for the diversity of parasites that are not dependent on close contact. For generalist parasites, population density, geographical range size and latitude are the primary predictors of parasite species richness. We found no significant ecological correlates for the richness of specialist or vector-borne parasites.
Main conclusions  Although we found that parasite species richness increases instead of decreases with distance from the equator, other comparative patterns in carnivores support previous findings in primates, suggesting that similar ecological factors operate in both these independent evolutionary lineages.     

Flea (Siphonaptera) species richness in the Great Basin Desert and island biogeography theory

Numbers of flea (Siphonaptera) species (flea species richness) on individual mammals should be higher on large mammals, mammals with dense populations, and mammals with large geographic ranges, if mammals are islands for fleas. I tested the first two predictions with regressions of H. J. Egoscue's trapping data on flea species richness collected from individual mammals against mammal size and population density from the literature. Mammal size and population density did not correlate with flea species richness. Mammal geographic range did, in earlier studies. The intermediate‐sized (31 g), moderately dense (0.004 individuals/m²) Peromyscus truei (Shufeldt) had the highest richness with eight flea species on one individual. Overall, island biogeography theory does not describe the distribution of flea species on mammals in the Great Basin Desert, based on H. J. Egoscue's collections. Alternatively, epidemiological or metapopulation theories may explain flea species richness.     

Density, body mass and parasite species richness of terrestrial mammals

We investigated the relationships between helminth species richness and body mass and density of terrestrial mammals. Cross-species analysis and the phylogenetically independent contrast method produced different results. A non-phylogenetic approach (cross-species comparisons) led to the conclusion that parasite richness is linked to host body size. However, an analysis using phylogenetically independent contrasts showed no relationship between host body size and parasite richness. Conversely, a non-phylogenetic approach generated a negative relationship between parasite richness and host density, whereas the independent contrast method showed the opposite trend – that is, parasite richness is positively correlated with host density. From an evolutionary perspective, our results suggest that opportunities for parasite colonization depend more closely on how many hosts are available in a given area than on how large the hosts are. From an epidemiological point of view, our results confirm theoretical models which assume that host density is linked to the opportunity of a parasite to invade a population of hosts. Our findings also suggest that parasitism may be a cost associated with host density. Finally, we provide some support for the non-linear allometry between density and mammal body mass (Silva and Downing, 1995), and explain why host density and host body mass do not relate equally to parasite species richness.     

Connecting species richness, abundance and body size in deep-sea gastropods

Aim This paper examines species richness, abundance, and body size in deep‐sea gastropods and how they vary over depth, which is a strong correlate of nutrient input. Previous studies have documented the empirical relationships among these properties in terrestrial and coastal ecosystems, but a full understanding of how these patterns arise has yet to be obtained. Examining the relationships among macroecological variables is a logical progression in deep‐sea ecology, where patterns of body size, diversity, and abundance have been quantified separately but not linked together. Location 196–5042 m depth in the western North Atlantic. Method Individuals analysed represent all Vetigastropoda and Caenogastropoda (Class Gastropoda) with intact shells, excluding Ptenoglossa, collected by the Woods Hole Benthic Sampling Program (3424 individuals representing 80 species). Biovolume was measured for every individual separately (i.e. allowing the same species to occupy multiple size classes) and divided into log₂ body size bins. Analyses were conducted for all gastropods together and separated into orders and depth regions (representing different nutrient inputs). A kernel smoothing technique, Kolmogorov‐Smirnov test of fit, and OLS and RMA were used to characterize the patterns. Results Overall, the relationship between the number of individuals and species is right skewed. There is also a positive linear relationship between the number of individuals and the number of species, which is independent of body size. Variation among these relationships is seen among the three depth regions. At depths inferred to correspond with intermediate nutrient input levels, species are accumulated faster given the number of individuals and shift from a right‐skewed to a log‐normal distribution. Conclusion A strong link between body size, abundance, and species richness appears to be ubiquitous over a variety of taxa and environments, including the deep sea. However, the nature of these relationships is affected by the productivity regime and scale at which they are examined.     

The effect of the taxon and geographic range size of host eucalypt species on the species richness of gall-forming insects

Abstract This field study was designed to test whether the taxonomic group and geographic range size of a host plant species, usually found to influence insect species richness in other parts of the world, affected the number of gall species on Australian eucalypts. We assessed the local and regional species richness of gall-forming insects on five pairs of closely related eucalypt species. One pair belonged to the subgenus Corymbia, one to Monocalyptus, and three to different sections of Symphyomyrtus. Each eucalypt pair comprised a large and a small geographic range species. Species pairs were from coastal or inland regions of eastern Australia. The total number of gall species on eucalypt species with large geographic ranges was greater than on eucalypt species with small ranges, but only after the strong effect of eucalypt taxonomic grouping was taken into account. There was no relationship between the geographic range size of eucalypt species and the size of local assemblages of gall species, but the variation in insect species composition between local sites was higher on eucalypt species with large ranges than on those with small ranges. Thus the effect of host plant range size on insect species richness was due to greater differentiation between more widespread locations, rather than to greater local species richness. This study confirms the role of the geographic range size of a host plant in the determination of insect species richness and provides evidence for the importance of the taxon of a host plant.     

Generic species richness and body mass in North American mammals: Support for the inverse relationship of body size and speciation rate

Generic species richness, the number of species per genus, is examined as a function of mean generic body mass for extant North American mammals. Species richness decreases as an inverse power function with increased mass, and the Spearman rank correlation coefficient of the logio transformed data is significant (r_s= ‐0.37). When the data are partitioned by trophic level, the relationship is not statistically significant for carnivores but strengthens for herbivores (r_s= ‐0.46). This interesting but incidental effect is due to the negligible number of diminutive and excessively large carnivores, which is in turn determined by foraging strategies. Alternate hypotheses for the “right‐skewed”; size distribution of modern North American mammals, such as disproportionate extinction of large species, differential species longevity, and a geographical scaling function, are rejected in favor of the proposition that elevated levels of speciation are restricted to animals of small body mass, as originally proposed by Gould and Eldredge (1977). This phenomenon is explained as a function of habitat restriction and particularly in herbivores, limited home range size. Aquatic mammals, regardless of body size, speciate rarely. Cope's Rule, the tendency of many animal groups to evolve towards large size, is understood as a probabilistic statement reflecting the phylogenetic tendencies of a disproportionately high number of small species alive at any given point in time.     

Bat fly species richness in Neotropical bats: correlations with host ecology and host brain

Patterns of ectoparasite species richness in mammals have been investigated in various terrestrial mammalian taxa such as primates, ungulates and carnivores. Several ecological or life traits of hosts are expected to explain much of the variability in species richness of parasites. In the present comparative analysis we investigate some determinants of parasite richness in bats, a large and understudied group of flying mammals, and their obligate blood-sucking ectoparasite, streblid bat flies (Diptera). We investigate the effects of host body size, geographical range, group size and roosting ecology on the species richness of bat flies in tropical areas of Venezuela and Peru, where both host and parasite diversities are high. We use the data from a major sampling effort on 138 bat species from nine families. We also investigate potential correlation between bat fly species richness and brain size (corrected for body size) in these tropical bats. We expect a relationship if there is a potential energetic trade-off between costly large brains and parasite-mediated impacts. We show that body size and roosting in cavities are positively correlated with bat fly species richness. No effects of bat range size and group size were observed. Our results also suggest an association between body mass-independent brain size and bat fly species richness. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Rarity, commonness, and patterns of species richness: the mammals of Mexico

Aim To determine whether rare or common species contribute most to overall patterns of spatial variation in extant species richness. Location Mexico. Methods Using data on the distribution of mammal species across Mexico at a quarter degree resolution, we ranked species from the most widespread to the most restricted (common‐to‐rare) within the study area, and from the most restricted to the most widespread (rare‐to‐common), and generated a sequence of patterns of species richness for increasing numbers of species. At each stage along both series of richness patterns, we correlated the species richness pattern for the subassemblage with that of the full assemblage. This allows comparison of subassemblages of the n most common with the n most rare species, in terms of how well they match the full assemblage richness pattern. Further analyses examined the effects on these patterns of correlation of the amount of raw information contained in the distributions of given numbers of rare and common species. Results For the mammals of Mexico the more widely distributed species contribute disproportionately to patterns of species richness compared with more restricted species, particularly for non‐volant species and endemic species. This is not simply a consequence of differences in the volumes of information contained in the distributions of rare and common species, with the disproportionate contribution of common species if anything being sharpened when these differences are taken into account. The pattern is most clearly demonstrated by endemic species, suggesting that the contribution of common species is clearest when the causes of rarity and commonness are limited to those genuinely resulting in narrow and widespread geographical ranges, respectively, rather than artificial (e.g. geopolitical) boundaries to the extents of study regions. Conclusions Perhaps surprisingly, an understanding of the determinants of overall patterns of species richness may gain most from consideration of why common species occur in some areas and are absent from others, rather than consideration of the distributions of rare species.     

Energy flux, body size and density in relation to bird species richness along an elevational gradient in Taiwan

Aim To examine the species richness of breeding birds along a local elevational gradient and to test the following assumptions of the energy limitation hypothesis: (1) the energy flux through birds is positively correlated with above‐ground net primary productivity, (2) bird density is positively correlated with total energy flux, and (3) bird species richness is positively correlated with bird density. Location An elevational gradient from 1400 to 3700 m on Mt. Yushan, the highest mountain in Taiwan (23°28′30″ N, 120°54′00″ E), with a peak of 3952 m a.s.l. Methods We established 50 sampling stations along the elevational gradient. From March to July 1992, we estimated the density of each bird species using the variable circular‐plot method. Above‐ground net primary productivity was modelled using monthly averages from weather data for the years 1961–90. Results Bird species richness had a hump‐shaped relationship with elevation and with net primary productivity. Bird energy flux was positively correlated with net primary productivity and bird species richness was positively correlated with bird density. The relationship between bird density and energy flux was hump‐shaped, which does not support one assumption of the energy limitation hypothesis. Main conclusions The results supported two essential assumptions of the energy limitation hypothesis. However, when energy availability exceeded a certain level, it could decrease species richness by increasing individual energy consumption, which reduced bird density. Thus, energy availability is a primary factor influencing bird species richness at this scale, but other factors, such as body size, could also play important roles.     

Reconciling topographic and climatic effects on widespread and range-restricted species richness

Aim To identify the reasons behind differing geographical species richness patterns of range‐restricted and widespread species. Location The Western Hemisphere. Methods We used regression to determine the strongest environmental predictors of richness for widespread and range‐restricted mammal species in 10,000 km² quadrats in the continental Americas. We then used range‐placement models to predict the expected correlation between range‐restricted and widespread species richness were they to be determined by identical, random, or contrasting environmental factors. Finally, to determine the reasons underlying deviations from these predictions, we divided the Americas into 5% quantiles based on temperature and topographic heterogeneity and correlated richness of these two assemblages across quantiles – an approach that avoids constraints on statistical testing imposed by low potential for range overlap among range‐restricted species. Results Minimum annual temperature was the strongest predictor of widespread species richness while topographic heterogeneity was the best, although weak, predictor of range‐restricted species richness in conventional regression analysis. Our models revealed that the observed correlation between range‐restricted and widespread species richness was similar to what would be observed if both range‐restricted and widespread species richness were determined by temperature. Patterns of range‐restricted and widespread species richness were highly correlated across temperature quantiles, but range‐restricted species uniquely showed an increasing pattern across heterogeneity quantiles. Main conclusions Species richness gradients among range‐restricted species differ from those of widespread species, but not as extensively or for the reasons reported previously. Instead, these assemblages appear to share some but not all underlying environmental determinants of species richness. Our new approach to examining species richness patterns reveals that range‐restricted and widespread species richnesses share a common response to temperature that conventional analyses have not previously revealed. However, topographic heterogeneity has assemblage‐specific effects on range‐restricted species.     

The geography of body size – challenges of the interspecific approach

Recent compilations of large-scale data bases on the geographical distributions and body sizes of animals, coupled with developments in spatial statistics, have led to renewed interest in the geographical distribution of animal body sizes and the interspecific version of Bergmann's rule. Standard practice seems to be an examination of mean body sizes within higher taxa on gridded maps, with little regard to species richness or phylogeny. However, because the frequency distribution of body sizes is typically highly skewed, average size within grid cells may differ significantly between species-rich and species-poor cells even when the median and modal sizes remain constant. Species richness influences body size patterns because species are not added to communities at random in relation to their size: areas of low diversity are characterized by a higher range of body sizes than is expected by chance. Finally, a consideration of phylogenetic structure within taxa is necessary to elucidate whether patterns in the geography of size result from turnover between or within intermediate taxonomic levels. We suggest that the highest and lowest quantiles of body size distribution be mapped in order to expose possible physiological or ecological limitations on body size.     

Species richness, rarity and endemicity of European mammals: a biogeographical approach

This paper investigates the distribution of species richness, rarity and endemicity of European land mammals (bats and introduced species excluded). The highest level of species richness was in Central Europe, while Southern areas had the highest rarity and endemicity scores. The distribution of richness was affected by the location of sampling points in islands and peninsulas. After excluding these sampling points, richness continued to decrease Westward suggesting the existence of a large-scale peninsular effect on mammal distribution. These patterns of continental distribution of richness, rarity and endemicity could be the result of the distribution of refuge areas in the southern Mediterranean peninsulas, and the Pleistocene advances and retreats of mammals throughout the Western Palearctic. Thus, European mammal distribution can be interpreted on the basis of two different patterns of abundance distribution in which Palearctic species reduce their abundance from central-Europe outwards, while endemic, rare species show a similar depletion in the North. It should be useful to evaluate the role of the different regions in Europe in conserving the demographic interactions between central and peripheral populations of mammal species. Given the restricted distribution and potential small size of population, these endemic species are most likely to be susceptible to anthropogenic environmental degradation.     

Patterns and causes of species richness: a general simulation model for macroecology

Understanding the causes of spatial variation in species richness is a major research focus of biogeography and macroecology. Gridded environmental data and species richness maps have been used in increasingly sophisticated curve‐fitting analyses, but these methods have not brought us much closer to a mechanistic understanding of the patterns. During the past two decades, macroecologists have successfully addressed technical problems posed by spatial autocorrelation, intercorrelation of predictor variables and non‐linearity. However, curve‐fitting approaches are problematic because most theoretical models in macroecology do not make quantitative predictions, and they do not incorporate interactions among multiple forces. As an alternative, we propose a mechanistic modelling approach. We describe computer simulation models of the stochastic origin, spread, and extinction of species’ geographical ranges in an environmentally heterogeneous, gridded domain and describe progress to date regarding their implementation. The output from such a general simulation model (GSM) would, at a minimum, consist of the simulated distribution of species ranges on a map, yielding the predicted number of species in each grid cell of the domain. In contrast to curve‐fitting analysis, simulation modelling explicitly incorporates the processes believed to be affecting the geographical ranges of species and generates a number of quantitative predictions that can be compared to empirical patterns. We describe three of the ‘control knobs’ for a GSM that specify simple rules for dispersal, evolutionary origins and environmental gradients. Binary combinations of different knob settings correspond to eight distinct simulation models, five of which are already represented in the literature of macroecology. The output from such a GSM will include the predicted species richness per grid cell, the range size frequency distribution, the simulated phylogeny and simulated geographical ranges of the component species, all of which can be compared to empirical patterns. Challenges to the development of the GSM include the measurement of goodness of fit (GOF) between observed data and model predictions, as well as the estimation, optimization and interpretation of the model parameters. The simulation approach offers new insights into the origin and maintenance of species richness patterns, and may provide a common framework for investigating the effects of contemporary climate, evolutionary history and geometric constraints on global biodiversity gradients. With further development, the GSM has the potential to provide a conceptual bridge between macroecology and historical biogeography.     

Latitudinal patterns in European ant assemblages: variation in species richness and body size

Using published distributions of 65 species from the British Isles and northern Europe, we show that ant assemblages change with latitude in two ways. First, as commonly found for many types of organisms, the number of ant species decreased significantly with increasing latitude. For Ireland and Great Britain, species richness also increased significantly with region area. Second, although rarely demonstrated for ectotherms, the body size of ant species, as measured by worker length, increased significantly with increasing latitude. We found that this body-size pattern existed in the subfamily Formicinae and, to a lesser extent, in the Myrmicinae, which together comprised 95% of the ant species in our study area. There was a trend for formicines to increase in size with latitude faster than myrmicines. We also show that the pattern of increasing body size was due primarily to the ranges of ant species shifting to higher latitudes as their body sizes increased, with larger formicines becoming less represented at southerly latitudes and larger myrmicines becoming more represented at northerly latitudes. We conclude by discussing five potential mechanisms for generating the observed body-size patterns: the heat-conservation hypothesis, two hypotheses concerning phylogenetic history, the migration-ability hypothesis, and the starvation-resistance hypothesis.     

Disparity between range map- and survey-based analyses of species richness: patterns, processes and implications

Species richness patterns are characterized either by overlaying species range maps or by compiling geographically extensive survey data for multiple local communities. Although, these two approaches are clearly related, they need not produce identical richness patterns because species do not occur everywhere in their geographical range. Using North American breeding birds, we present the first continent‐wide comparison of survey and range map data. On average, bird species were detected on 40.5% of the surveys within their range. As a result of this range porosity, the geographical richness patterns differed markedly, with the greatest disparity in arid regions and at higher elevations. Environmental productivity was a stronger predictor of survey richness, while elevational heterogeneity was more important in determining range map richness. In addition, range map richness exhibited greater spatial autocorrelation and lower estimates of spatial turnover in species composition. Our results highlight the fact that range map richness represents species coexistence at a much coarser scale than survey data, and demonstrate that the conclusions drawn from species richness studies may depend on the data type used for analyses.     

Size-dependent species richness: trends within plant communities and across latitude

We examine how species richness and species‐specific plant density (number of species and number of individuals per species, respectively) vary within community size frequency distributions and across latitude. Communities from Asia, Africa, Europe, and North, Central and South America were studied (60°4′N–41°4′S latitude) using the Gentry data base. Log–log linear stem size (diameter) frequency distributions were constructed for each community and the species richness and species‐specific plant density within each size class were determined for each frequency distribution. Species richness in the smallest stem size class correlated with the Y‐intercepts (β‐values) of the regression curves describing each log–log linear size distributions. Two extreme community types were identified (designated as type A and type B). Type A communities had steep size distributions (i.e. large β‐values), log–log linear species‐richness size distributions, low species‐specific plant density distributions, and a small size class (2–4 cm) containing the majority of all species but rarely conspecifics of the dominant tree species. Type B communities had shallow size distributions (i.e. small β‐values), more or less uniform (and low) size class species‐ richness and species‐specific density distributions and size‐dominant species resident in the smallest size class. Type A communities were absent in the higher latitudes but increased in number towards the equator, i.e. in the smallest size class, species richness increased (and species‐specific density decreased) towards the tropics. Based on our survey of type A and type B communities (and their intermediates), species richness evinces size‐dependent and latitudinal trends, i.e. species richness increased with decreasing body size and most species increasingly reside in the smallest plant size class towards the tropics. Across all latitudes, a trade‐off exists between the number of species and the number of individuals per species residing in the smaller size classes.     

中国陆栖哺乳动物物种丰富度的地理格局及其与环境因子的关系

物种丰富度的大尺度地理格局及其成因是宏观生态学和生物地理学的中心议题之一。本文利用中国陆栖哺乳动物分布数据, 结合高分辨率的气候、地形、植被等环境信息, 探讨了中国陆栖哺乳动物及主要类群的物种丰富度格局及其影响因素。结果显示, 中国陆栖哺乳动物物种丰富度具有显著的纬度梯度格局, 总体上呈现出由低纬度向高纬度逐渐减少的趋势, 并与宏观地形具有良好的对应关系; 其中, 亚热带、热带西部山区的物种丰富度最高, 而东部平原地区、西北干旱区和青藏高原腹地则是丰富度的低值区。各主要类群的物种丰富度格局既有相似性, 又存在差异。最优线性模型的分析结果显示, 由归一化植被指数(NDVI)、生态系统类型数和气温年较差构成的回归模型对哺乳动物物种丰富度格局的解释率最高, 其中NDVI对模型解释率的贡献最大, 这表明中国陆栖哺乳动物物种丰富度的地理分异受多种环境因素的共同影响, 其中植被生产力起主导作用。各主要类群的最优线性模型显示, 影响物种丰富度格局的主要环境因子因类群而异, 这可能反映了各类群进化历史及生理适应的差异。     

Species richness, species range size and ecological specialisation among African primates: geographical patterns and conservation implications

The geographical distribution of species richness and species range size of African anthropoid primates (catarrhines) is investigated and related to patterns of habitat and dietary niche breadth. Catarrhine species richness is concentrated in the equatorial regions of central and west Africa; areas that are also characterised by low average species range sizes and increased ecological specificity. Species richness declines with increasing latitude north and south of the equator, while average species range size, habitat and dietary breadth increase. Relationships between species richness, species range size and niche breadth remain once latitudinal and longitudinal effects have been removed. Among areas of lowest species richness, however, there is increased variation in terms of average species range size and niche breadth, and two trends are identified. While most such areas are occupied by a few wide-ranging generalists, others are occupied by range-restricted specialist species. That conservation efforts increasingly focus on regions of high species richness may be appropriate if these regions are also characterised by species that are more restricted in both their range size and their ecological versatility, although special consideration may be required for some areas of low species richness.