Many large animal species have a high risk of extinction. This is usually thought to result simply from the way that species traits associated with vulnerability, such as low reproductive rates, ...scale with body size. In a broad-scale analysis of extinction risk in mammals, we find two additional patterns in the size selectivity of extinction risk. First, impacts of both intrinsic and environmental factors increase sharply above a threshold body mass around 3 kilograms. Second, whereas extinction risk in smaller species is driven by environmental factors, in larger species it is driven by a combination of environmental factors and intrinsic traits. Thus, the disadvantages of large size are greater than generally recognized, and future loss of large mammal biodiversity could be far more rapid than expected.
Understanding why some species are at high risk of extinction, while others remain relatively safe, is central to the development of a predictive conservation science. Recent studies have shown that ...a species' extinction risk may be determined by two types of factors: intrinsic biological traits and exposure to external anthropogenic threats. However, little is known about the relative and interacting effects of intrinsic and external variables on extinction risk. Using phylogenetic comparative methods, we show that extinction risk in the mammal order Carnivora is predicted more strongly by biology than exposure to high-density human populations. However, biology interacts with human population density to determine extinction risk: biological traits explain 80% of variation in risk for carnivore species with high levels of exposure to human populations, compared to 45% for carnivores generally. The results suggest that biology will become a more critical determinant of risk as human populations expand. We demonstrate how a model predicting extinction risk from biology can be combined with projected human population density to identify species likely to move most rapidly towards extinction by the year 2030. African viverrid species are particularly likely to become threatened, even though most are currently considered relatively safe. We suggest that a preemptive approach to species conservation is needed to identify and protect species that may not be threatened at present but may become so in the near future.
Beta-diversity, the change in species composition between places, is a critical but poorly understood component of biological diversity. Patterns of beta-diversity provide information central to many ...ecological and evolutionary questions, as well as to conservation planning. Yet beta-diversity is rarely studied across large extents, and the degree of similarity of patterns among taxa at such scales remains untested. To our knowledge, this is the first broad-scale analysis of cross-taxon congruence in beta-diversity, and introduces a new method to map beta-diversity continuously across regions. Congruence between amphibian, bird, and mammal beta-diversity in the Western Hemisphere varies with both geographic location and spatial extent. We demonstrate that areas of high beta-diversity for the three taxa largely coincide, but areas of low beta-diversity exhibit little overlap. These findings suggest that similar processes lead to high levels of differentiation in amphibian, bird, and mammal assemblages, while the ecological and biogeographic factors influencing homogeneity in vertebrate assemblages vary. Knowledge of beta-diversity congruence can help formulate hypotheses about the mechanisms governing regional diversity patterns and should inform conservation, especially as threat from global climate change increases.
Large mammals often play critical roles within ecosystems by affecting either prey populations or the structure and species composition of surrounding vegetation. However, large mammals are highly ...vulnerable to extirpation by humans and consequently, severe contractions of species ranges result in intact large mammal faunas becoming increasingly rare. We compared historical (AD 1500) range maps of large mammals with their current distributions to determine which areas today retain complete assemblages of large mammals. We estimate that less than 21% of the earth's terrestrial surface still contains all of the large (>20 kg) mammals it once held, with the proportion varying between 68% in Australasia to only 1% in Indomalaya. Although the presence of large mammals offers no guarantee of the presence of all smaller animals, their absence represents an ecologically based measurement of human impacts on biodiversity. Given the ecological importance of large mammals and their vulnerability to extinction, better protection and extension of sites containing complete assemblages of large mammals is urgently needed.
Some hosts harbor diverse parasite communities, whereas others are relatively parasite free. Many factors have been proposed to account for patterns of parasite species richness, but few studies have ...investigated competing hypotheses among multiple parasite communities in the same host clade. We used a comparative data set of 941 host‐parasite combinations, representing 101 anthropoid primate species and 231 parasite taxa, to test the relative importance of four sets of variables that have been proposed as determinants of parasite community diversity in primates: host body mass and life history, social contact and population density, diet, and habitat diversity. We defined parasites broadly to include not only parasitic helminths and arthropods but also viruses, bacteria, fungi, and protozoa, and we controlled for effects of uneven sampling effort on per‐host measures of parasite diversity. In nonphylogenetic tests, body mass was correlated with total parasite diversity and the diversity of helminths and viruses. When phylogeny was taken into account, however, body mass became nonsignificant. Host population density, a key determinant of parasite spread in many epidemiological models, was associated consistently with total parasite species richness and the diversity of helminths, protozoa, and viruses tested separately. Geographic range size and day range length explained significant variation in the diversity of viruses.
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.
The spatial scale of conservation necessary to avoid species extinctions is one of the most vigorous debates in conservation biology. One approach holds that protecting sites should be the primary ...level for action on the ground, the other that conservation action targeting broader seascapes and landscapes is more important. We address this debate systematically by assessing the appropriate spatial scales of conservation for all 4,239 threatened mammals, birds, tortoises and turtles, and amphibians. We find that, in the short‐ to medium term, 20% of these species are dependent on conservation at single sites, 62% on multiple sites, 18% on both sites and sea‐ or landscape‐scale efforts, and <1% on broad‐scale actions alone (where sites are variably sized units that are actually or could potentially be managed for conservation, and “broad scale” refers to sea‐ or landscape‐scale and is determined by the needs of the species in question). Calls for broad‐scale conservation action have generally focused on terrestrial birds and mammals, and we confirm that a fifth and a tenth of these, respectively, require conservation action at the landscape scale. However, we also find that two‐fifths of threatened freshwater turtles and one‐fifth of threatened amphibians depend on broad‐scale conservation action to address changes in freshwater processes. Furthermore, the overwhelming majority of threatened marine mammals, birds, and turtles require urgent conservation action at the seascape scale. Our key conclusion is that neither site‐scale nor broad‐scale approaches alone can prevent mass extinction. Although site protection should remain the cornerstone for almost all threatened species, we demonstrate that a substantial proportion and unexpected diversity of threatened species will be lost in the absence of urgent conservation interventions at the sea‐ or landscape scale.
Infectious disease risk is thought to increase in the tropics, but little is known about latitudinal gradients of parasite diversity. We used a comparative data set encompassing 330 parasite species ...reported from 119 primate hosts to examine latitudinal gradients in the diversity of micro and macroparasites per primate host species. Analyses conducted with and without controlling for host phylogeny showed that parasite species richness increased closer to the equator for protozoan parasites, but not for viruses or helminths. Relative to other major parasite groups, protozoa reported from wild primates were transmitted disproportionately by arthropod vectors. Within the protozoa, our results revealed that vector-borne parasites showed a highly significant latitudinal gradient in species richness. This higher diversity of vector-borne protozoa near the tropics could be influenced by a greater abundance or diversity of biting arthropods in the tropics, or by climatic effects on vector behaviour and parasite development. Many vector-borne diseases, such as leishmaniasis, trypanosomiasis, and malaria pose risks to both humans and wildlife, and nearly one-third of the protozoan parasites from free-living primates in our data set have been reported to infect humans. Because the geographical distribution and prevalence of many vector-borne parasites are expected to increase because of global warming, these results are important for predicting future parasite-mediated threats to biodiversity and human health.
Efficient planning for biodiversity conservation requires a consideration of complementarity when assessing the value of adding new areas for management. Unfortunately, complementarity in ...biodiversity across all groups cannot usually be measured directly, so methods are needed to choose good surrogates (or ‘indicators’) for predicting this overall complementarity. Previous attempts at assessment of biological surrogates have measured dissimilarity among biotas, or congruence between sets of selected areas, or species representation within a set of selected areas, all of which can seriously misrepresent the strength of a surrogate relationship across all areas. Therefore, we propose a new approach to complementarity analysis. We show that the pattern of complementarity among all biotas can be assessed in terms of the frequency of false high and false low predictions by the surrogates. We also show how the spatial pattern in these false predictions can be mapped and discuss their usefulness. On the one hand, areas on these maps associated with many false high predictions are overvalued and would be an inefficient investment for scarce conservation resources. On the other hand, areas associated with many false low predictions are undervalued and unlikely to attract conservation action, so we need to know whether they are particularly likely to be highly threatened. These geographical patterns can be used to identify habitat-associated biases in the performance of surrogate groups.
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