North American Mammals Research Articles

Ecological biogeography of North American mammals: species density and ecological structure in relation to environmental gradients

AbstractAim To evaluate the relationship of climate and physiography to species density and ecological diversity of North American mammals.Location North America, including Mexico and Central America.Methods Species density, size structure and trophic structure of mammalian faunas and nine environmental variables were documented for quadrats covering the entire continent. Spatial autocorrelation of species density and the environmental variables illustrated differences in their spatial structure at the continental scale. We used principal component analysis to reduce the dimensionality of the climatic variables, linear multiple regression to determine which environmental variables best predict species density for the continent and several regions of the continent, and canonical ordination to evaluate how well the environmental variables predict ecological structure of mammalian faunas over North America.Results In the best regression model, five environmental variables, representing seasonal extremes of temperature, annual energy and moisture, and elevation, predicted 88% of the variation in species density for the whole continent. Among different regions of North America, the environmental variables that predicted species density vary.Changes in the size and trophic structure of mammalian faunas accompany changes in species density. Redundancy analysis demonstrated that environmental variables representing winter temperature, frostfree period, potential and actual evapotranspiration, and elevation account for 77% of the variation in ecological structure.Main conclusions The latitudinal gradient in mammalian species density is strong, but most of it is explained by variation in the environmental variables. Each ecological category peaks in species richness under particular environmental conditions. The changes of greatest magnitude involve the smallest size categories (< 10 g, 11–100 g), aerial insectivores and frugivores. Species in these categories, mostly bats, increase along a gradient of decreasing winter temperature and increasing annual moisture and frostfree period, trends correlated with latitude. At the opposite end of this gradient, species in the largest size category (101–1000 kg) increase in frequency. Species in size categories 3 (101–1000 g), 5 (11–100 kg) and 6 (101–1000 kg), herbivores, and granivores increase along a longitudinal gradient of increasing annual potential evapotranspiration and elevation.Much of the spatial pattern is consistent with ecological sorting of species ranges along environmental gradients, but differential rates of speciation and extinction also may have shaped the ecological diversity of extant North American mammals.

Review: The Smithsonian Book of North American Mammals, by Don E. Wilson and Sue Ruff

Review: <i>The Smithsonian Book of North American Mammals</i>, by Don E. Wilson and Sue Ruff

Climate, vegetation, and predictable gradients in mammal species richness in southern Africa

AbstractMany hypotheses have been proposed to account for geographic variations in species diversity. In general these relate to some aspect of climate, particularly climatic variables measuring available or potential energy, but while these relate directly to plant diversity they may only indirectly affect mammal species richness. We have examined these relationships by mapping and correlating mammal species richness in southern Africa (n= 285 species) with 15 climatic variables, two topographic variables, and woody plant species richness (n= 1359 species). The effect of area on richness was held a constant by using an equal‐area grid cell matrix superimposed on species range maps, with each grid cell equal to 25 000 km2. We found that variability in the plant species richness alone accounts for 75% of the variability in mammal species richness. Of the climatic variables, only thermal seasonality approaches this figure, accounting for 69% of the variability, while annual measures of temperature, precipitation or energy account for only 14–35% of variability. Differences from North American mammal diversity studies, where annual temperature, and hence annual potential evapotranspiration (PET), have been found to be more important, are attributed in part to southern Africa's climate and vegetation being largely temperate to tropical, as opposed to temperate to polar in North America. By distinguishing different types of mammal based on size, spatial and dietary guilds, other differences emerge. Strong correlations with annual temperature exist only for large mammals, accounting for 60–67% of the variability in species richness of large mammals compared with &lt;20% for small mammals. Small mammals are strongly correlated with other climatic or vegetation parameters, especially plant richness and thermal seasonality; frugivorous and insectivorous mammal richness is correlated with thermal seasonality and minimum monthly PET; and arboreal and aerial species richness is correlated with plant richness, thermal seasonality and minimum monthly PET. Up to 77% of the variability in richness of arboreal, frugivorous and insectivorous species can be explained by woody plant richness, compared with only 38–48% of the variability in terrestrial herbivores. It is clear from this that different kinds of mammals are differentially affected by climatic and environmental factors, and this explains some of the discrepancies found in earlier studies where no distinction was made between different sizes or guilds of mammal. This result has implications both for the conservation of mammalian communities at the present time and for understanding the evolution and structure of mammalian communities in the past.

Evolutionary relationships among the Schistosomatidae (Platyhelminthes:Digenea) and an Asian origin for Schistosoma.

Schistosome blood flukes parasitize birds, mammals, and crocodilians and are responsible for causing one of the great neglected diseases of humanity, schistosomiasis. A phylogenetic study of 10 schistosome genera using approximately 1,100 bases of the large subunit of the nuclear ribosomal gene complex revealed 2 major clades. One clade is entirely mammalian and includes the genera Schistosoma and Orientobilharzia. A close examination of relationships in this group suggests that the medically important Schistosoma arose in Asia and not in Africa as generally presumed and is paraphyletic. The second clade is primarily avian, consisting of 6 genera of exclusively avian parasites and 2 genera of North American mammal flukes. These results indicate a secondary host capture of mammals on the North American continent. This study provides little evidence concerning the ancestral molluscan or vertebrate schistosome host but does demonstrate that host switching has been an important feature of schistosome evolution. Evidence also indicates that the reduced sexual dimorphism characteristic of some avian schistosomes is derived evolutionarily.

The Smithsonian Book of North American Mammals, eds. Don E. Wilson and Sue Ruff [Review

The Smithsonian Book of North American Mammals, eds. Don E. Wilson and Sue Ruff [Review

Large Temporal and Spatial Scales in the Structure of Mammalian Assemblages in South America: A Macroecological Approach

We analyze the distribution of body masses for 701 species of South American terrestrial mammals at different spatial resolutions from continental to biome, to local habitat scales. Previous studies on North American mammals suggest that body size distributions are highly modal and right skewed at continental scales, but become more uniform as spatial scale decreases. We show, in general, that these patterns also hold for the body size distribution of South American terrestrial mammals. However, we also found some striking differences attributable to the history of this biota and related to the Great American Biotic Interchange (GABI). At continental scales the distribution of body masses for South American mammals is highly right skewed and possesses several modes. One mode corresponds to species derived from North American ancestors, while a second mode, towards larger size, is characteristic of the South American stock. The same pattern is apparent at biome and local habitat scales. We found support for the progressive flattening of the distributions as spatial scale decreases, but they do not become as flat (indistinguishable from log-uniform) as they do in North America. However, the pattern is stronger for species of South American origin. Our results indicate that there is a strong historical component affecting the macroecological structure of contemporary assemblages at different spatial scales. Body size distributions can provide valuable information on the ways biotas built up.

The fossil record of North American mammals: evidence for a Paleocene evolutionary radiation.

Paleontologists long have argued that the most important evolutionary radiation of mammals occurred during the early Cenozoic, if not that all eutherians originated from a single common post-Cretaceous ancestor. Nonetheless, several recent molecular analyses claim to show that because several interordinal splits occurred during the Cretaceous, a major therian radiation was then underway. This claim conflicts with statistical evidence from the well-sampled latest Cretaceous and Cenozoic North American fossil record. Paleofaunal data confirm that there were fewer mammalian species during the latest Cretaceous than during any interval of the Cenozoic, and that a massive diversification took place during the early Paleocene, immediately after a mass extinction. Measurement data show that Cretaceous mammals were on average small and occupied a narrow range of body sizes; after the Cretaceous-Tertiary mass extinction, there was a rapid and permanent shift in the mean. The fact that there was an early Cenozoic mammalian radiation is entirely compatible with the existence of a few Cretaceous splits among modern mammal lineages.

The historical assembly of continental biotas: Late Quaternary range‐shifting, areas of endemism, and bio‐geographic structure in the North American mammal fauna

A controversial question in biogeography and ecology involves the extent to which vicariance and dispersal interact to determine the structure of continental biotic assemblages, Accumulating evidence of” distributional changes during the past 40 000 yr (Late Quaternary) has suggested to ecologists that changes in geographic ranges during the Pleistocene were of sufficient magnitude to erode prior associations between earth and biotic evolution in continental biotas. This paper first argues that this question can only he addressed by examining the magnitude of Late Quaternary range‐shifting at the spatial scale established within the framework of historical historical geography (e.g., areas of endemism) rather than that of ecology (e.g., local community assemblages); and second reassesses patterns of range‐shifting in the FAUNMAP data base recording Late Quaternary distributions of North American mammals. At the scale of geo‐morphological provinces. North American rodents have exhibited highly stable distributions during this time frame, suggesting that previous inferences drawn from analyses of stability at a local community scale are not relevant to questions of congruence between earth and biotic history at regional or continental scales, A comprehensive understanding of processes underlying the assembly of continental biotas still requires incorporation of biogeographic patterns developed well before episodes of Late Quaternary climatic turbulence.

Diachrony of mammalian appearance events: Implications for biochronology

A multivariate biochronological analysis of the North American mammal fossil record has established an independent ordering of appearance events for all described genera and species. This geochronologically confirmed hypothesis shows that first and last appearances in different parts of the continent are highly diachronous. Additional results show that (1) despite this diachrony, the new event sequence is compatible with a previously hypothesized sequence of immigrant first appearances; (2) immigrant genera are not particularly widespread, abundant, or synchronous in their appearances; (3) last appearances, large-mammal appearances, and species-level appearances are the most reliable; and (4) most of the observed diachrony appears to result from undersampling. Because diachrony has little effect on the overall multivariate analysis, and because the differences among classes of events are not extreme, joint analyses of all known appearance events are preferable to the a priori selection of particular appearance events as time indicators.

Habitat heterogeneity as a determinant of mammal species richness in high-energy regions

A fundamental problem in ecological research is to explain large-scale gradients in species richness1,2. Although many causative agents for this phenomenon have been suggested, the species richness–energy hypothesis has received the strongest empirical support3–6: this hypothesis states that higher energy availability provides a broader resource base, permitting more species to coexist. Here we show that the species richness–energy hypothesis applies to North American mammals only over a limited geographical area in which climatic energy levels are low (Alaska and most of Canada), rather than on a continental scale as had previously been accepted6. In relatively high-energy regions of North America, corresponding to most of the continental United States and southern Canada, we find that mammal species richness is best predicted by topographic heterogeneity and local variation in energy availability. Our results contradict previous studies of large-scale richness patterns that dismissed the importance of habitat heterogeneity2,7–9, and have implications for climate change research.

Constant extinction, constrained diversification, and uncoordinated stasis in North American mammals

Abstract The coordinated stasis model has far-reaching implications. Among them are three important predictions concerning diversity dynamics that I test here against the Cenozoic fossil record of terrestrial North American mammals. First, origination and extinction rates should be correlated; second, turnover should be a composite function of very low background rates and occasional, dramatic turnover pulses; and finally, stasis should result from ecological (niche) incumbency, with the domains of incumbent species being defined by ecological similarity, which in the case of mammals corresponds closely with taxonomic affinity. The data used to test these hypotheses are standing diversity levels and counts of originations and extinctions for 1193 genera and 3161 species. Instead of relying on a traditional time scale comprised of “ages” having uneven and unpredictable durations, the diversity curve is computed directly from a multivariate ordination of 3870 faunal lists, and then sectioned into 1.0 m.y. intervals. The lists span the late Cretaceous through late Pleistocene interval, exclusive of the Wisconsinan, and are taxonomically standardized to remove junior synonyms, out-dated combinations, and nomina dubia. Because Cretaceous and Paleocene diversity dynamics are idiosyncratic, only the last 55 intervals (Eocene-Pleistocene: 55-0.01 Ma) are analyzed. The test of origination and extinction rates shows that an apparent correlation between them is a statistical artifact related to the necessary coincidence of first and last appearances for taxa known from just one interval. The test of variation in turnover shows that most of the observed extinction rates could be generated by a single, invariant underlying rate, wheras origination rates show many well-defined pulses. Furthermore, origination pulses within particular orders are not fully coincident. The very largest pulses of origination therefore seem to be mediated by key adaptations within particular groups, not by the general opportunity to fill niches opened up by extinction. Both of these tests argue against the idea of sweeping “reorganization” intervals bounding placid “stasis” intervals, and against Vrba's turnover pulse hypothesis. Finally, tests for niche incumbency, based on plots of per-taxon turnover rates against standing diversity, show that incumbency is widespread and mediated by the suppression of origination at high diversity levels in all groups. Extinction is a far less important controlling factor. Because orders are ecologically distinct, but random subsamples of the entire data set actually show stronger controls than groupings based on ordinal affinity, it appears that niche space has little or no important ecological substructuring. Therefore, mammalian diversity seems to be integrated at the highest possible taxonomic level, in opposition to the coordinated stasis concept of static guilds. On balance, the results indicate that although the data are robust and provide strong support for the niche incumbency model and the idea of diversity equilibrium, they generally disconfirm the unique predictions of coordinated stasis.

Conservation Implications of Georaphic Range Size—Body Size Relationships

The oft-cited statement that 'big fierce animals are rare' (Colinvaux 1978) is, like most such generalizations in ecology, only partially correct. Animals with large bodies, fierce or otherwise, do have lower densities than smaller species, at least in studies based on compendia of data drawn from the literature (for example, Damuth 1981, 1987, 1993; Peters & Wassenberg 1983; Currie 1993; Silva & Downing 1994); conclusions may be rather different when based on sampling whole assemblages of taxonomically similar animals e.g. Brown & Maurer 1987; Morse et al. 1988; Cotgreave 1993; Blackburn & Lawton 1994). However, a growing body of work has documented positive relationships between the geographic range size and the body size of animal species (Table 1). In terms of geographic range size, within taxonomic assemblages (such as North American mammals) big animals are often rather common; geographic range size is a dimension of the rare-common axis equally as valid, and perhaps as widely applied, as density or population size (Rabinowitz 1981; Rabinowitz et al. 1986; Reed 1992; McCoy & Mushinsky 1992; Fiedler & Ahouse 1992; Gaston 1994). Moreover, at least amongst terrestrial mammals, the big fierce species may tend to have particularly large geographic range sizes; carnivores have larger geographic ranges on average than species in other terrestrial mammalian orders (Brown 1981; Rapoport 1982; Pagel et al. 1991; Letcher & Harvey 1994). The relationship between interspecific geographic range size and body size has attracted attention primarily in the context of macroecology and may explain how species partition space and resources (Brown & Maurer 1987, 1989; Gaston & Lawton 1988b; Gaston 1994; Lawton et al. 1994; Taylor & Gotelli 1994). It also has some potentially important consequences for conservation (as do various other macroecological patterns) (Lawton 1993; Gaston 1994; Gaston & Blackburn 1995a,b). We limit ourselves here to consideration of interspecific range size to body size relationships from studies on assemblages at large geographic scales, such that all or most of the geographic ranges of the species in the assemblage are considered. It is on global, rather than local, scales that the conservation status of species is most important. At more restricted scales the form of the range size to body size relationship is less clear (see for example Gaston 1988; Gaston & Lawton 1988a,b).

Cenozoic Migration Rates, Exinction Rates, and Diversity Patterns in North American Mammals: Stability in the Face of Stochastic Migration

Cenozoic Migration Rates, Exinction Rates, and Diversity Patterns in North American Mammals: Stability in the Face of Stochastic Migration

A latitudinal gradient in the density of human languages in North America

The number of different species found in a given area of the Earth increases from the poles towards the equator for a wide range of terrestrial and marine organisms. A similar but opposite latitudinal gradient is also generally found in the size of the geographic range over which a species is found: range sizes are larger in more northern latitudes becoming smaller in the south, a phenomenon known as Rapaport9s rule. Here we show that the density of human language-cultural groups in North America, at the time of contact by colonizing Europeans, also followed a strong latitudinal gradient qualitatively similar to that found in North American mammals. Six times, or more, different languages were spoken in a given area in southern latitudes, compared to the density of language groups nearer to the poles. In addition, the amount of territory over which the speakers of a given language were found increases with latitude: linguistic-cultural groups conform to Rapaport9s rule. Finally, based upon a categorization of North America into 23 distinct major habitat types, we find greater linguistic diversity in areas of greater habitat diversity, independently of latitude. `Linguistic ecology9, or the examination of ecological factors associated with diversity in the number of linguistic groups, may shed new light on some features of cultural and linguistic evolution.

Defining the role of pollutants in the disruption of reproduction in wildlife.

Although chemical exposure has been associated with reduced reproduction in certain North American fish, reptiles, and mammals, definitive cause-and-effect data are lacking in many instances. Because the increasing use and global transport of industrial chemicals pose significant risk to successful reproduction, methods should be developed that can define the geographic extent and magnitude of injury and risk to wildlife. Because industrial chemicals are articles of commerce, information about injury to wildlife has been contentious and too often ineffective in changing societal behavior. The following strategies are advocated for inferring causal relationships. First, a balanced and comprehensive assessment of the data is necessary to determine the geographic extent of exposure and reproductive effects associated with environmental pollution. Initial efforts to document reproductive injury should focus on specific ecosystems in which detrimental effects have been observed, but lack sufficient causal data. Model systems (including experimental mesocosms or field ecosystems) should be identified or designed that can adequately test multigenerational reproductive effects. Mechanistic data from supportive laboratory studies on reproductive toxicity, quantitative structure-activity relationships, and bioaccumulation can be used to predict effects of related pollutants and to determine risk. Such information is essential to prevent future injury to wildlife and to prioritize the numerous remediation decisions facing our society.

Chronostratigraphy and “Land-Mammal Ages” in the Cenozoic of southern South America: principles, practices, and the “Uquian” problem

The concept of “land-mammal age” as developed in South America is examined. The “Uquian Land-mammal age” is used as a study case. “Land-mammal age” parataxonomy is here considered methodologically but not conceptually different from chronostratigraphic taxonomy. “Land-mammal ages” in South America are based on stages. However, we consider that accurate biostratigraphic studies must be done in South America for establishing the biostratigraphy and precise boundary stratotypes of most stages-ages. The Uquia outcrops are here considered inadequate as a stratotype. A new South American continental stage-age is proposed. This stage is based on a biostratigraphic scheme. The stratotypes of the stage and biozones are located in the fossiliferous southeastern Buenos Aires Province marine cliffs. The lower boundary stratotype is proposed. The stage-age is probably correlated with the Gauss Chron and the lower Matuyama Chron. Additionally, some major units of Ameghino are validated and a different timing for the arrival of North American mammals to southern South America is presented.

Mammals as Seed-Dispersal Mutualists in North America

A number of North American mammals are regular frugivores and seed dispersal vectors; the «carnivores» (particularly bears, procyonids, some mustelids and canids) are among the most important mammalian dispersal agents. Most genera of fleshy fruits are eaten by terrestrial mammals in North America, but few species are consumed only by mammals. The largely unstudied mutualism between fleshy-fruited plants and mammals in North America has important implications for the biology and conservation of both participants

Magnetic polarity stratigraphy of Inchasi: a Pliocene mammal-bearing locality from the Bolivian Andes deposited just before the Great American Interchange

The newly discovered section at Inchasi, located about 50 km southeast of Potosi, Bolivia, in the eastern Cordillera, consists of about 120 m of undeformed terrestrial sediments containing fossil mammals. Paleomagnetic analysis of 54 sites indicates a polarity pattern with an estimated duration of about 0.64 Ma. The rich Inchasi local fauna indicates a Montehermosan and/or Chapadmalalan land mammal age (Pliocene). Given these constraints, Inchasi correlates from the interval between the late Gilbert (within the Cochiti subchron) to the early Gauss (within the Mammoth subchron) chrons; that is, between about 4.0 and 3.3 Ma. The distinct lack of North American mammals in the Inchasi local fauna provides some of the first well-calibrated evidence that the Great American Interchange occurred after about 3.0 Ma, as has been previously stated based on other calibrations of the earliest immigrant (Uquian) faunas.

The 'individualization' of large North American mammals.

The enforcement of wildlife laws and the captive breeding of threatened/endangered species requires the ability to identify individual animals. DNA profiles of a variety of large North American mammals, birds, and fish were generated using ten different oligonucleotide probes. The probes tested were four multilocus probes [33.6, 33.15, JE46, and (TGTC)5] and six 'human unilocus' probes [MS1 (D1S7), CMM101 (D14S13), YNH24 (D2S44), EFD52 (D17S26), TBQ7 (D10S28), and MS43 (D12S11). Each of the probes was chemically synthesized, and labeled by the attachment of alkaline phosphatase; after hybridization, the probes were detected by chemiluminescence catalyzed by the enzyme. Initial screening against zoo blots including samples of bear, wolf, large cat, wild sheep, deer, birds, marine mammals, and fish indicated that three multilocus probes [33.15, 33.6, (TGTC)5] gave informative patterns containing 15-40 bands for most or all of the animals tested, as did two of the 'human unilocus' probes (MS1 and CMM101). The other five probes appeared informative only in some species (for example, YNH24 against canids). Subsequent screenings of populations within species were used to determine genetic diversity by analysis of observed bandsharing (S). Large heterologous populations, such as white-tailed deer, exhibited highly diverse band patterns (S < or = 0.2). Geographically isolated and/or genetically constricted animals, such as endangered Mexican wolves, Tule elk, and Columbian white-tailed deer, exhibited much higher frequencies of bandsharing (0.6 < or = S < or = 0.95).(ABSTRACT TRUNCATED AT 250 WORDS)

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 func...