Boreal Mammals Research Articles

A key to the identification of some small boreal mammals of central Canada from guard hairs

A key to the identification of some small boreal mammals of central Canada from guard hairs

Extinctions of montane mammals reconsidered: putting a global-warming scenario on ice

McDonald and Brown developed a model based on island biogeographic principles to predict the magnitude and composition of small mammal extinctions from isolated boreal habitats atop mountains of the Great Basin following global warming. The model predicts that three of 14 boreal mammals will go extinct regionally and that four of 19 mountain ranges will lose upwards of 50% of their present faunas. Here, we re-examine the model on the basis of its underlying assumptions, on the statistical and biogeographic protocols used, and on its predictive power. A key assumption, that populations of these small mammals are isolated by absolute barriers to dispersal, is challenged by published field observations and by extensive trapping records. Statistical procedures used to construct the model are questionable and the model itself yields imprecise estimates. The biogeographic principle used to identify extinction-prone species, nested subsets of species, makes predictions that are at odds with available autecological information. The demonstration of a nested pattern of species occurrences does not provide definitive evidence in resolving SLOSS- or whether a single large island or several small islands of equivalent total area will contain more species. We conclude that the model is not a reliable method for forecasting species extinctions following global warming. The final resolution of the biogeography of montane mammals (and predictive models of extinction) in the Great Basin must await a full and accurate accounting of past and present species distributions.

Holocene climate and vegetation in the Milford drainage basin, Maine, U.S.A., and their implications for human history

A 9200 14C year fossil pollen record from a small kettle lake in central Maine, northeast U.S.A., records the development of nearby upland vegetation throughout the Archaic, Ceramic, and Historic periods of human history. The Early Archaic period (9000 to 8000 B.P.) began as open woodland dominated by Picea, Populus, and Larix, which was replaced by Pinus forest. During the Middle Archaic (8000-6000 B.P.) Tsuga-dominated forest, which developed ca. 7400 B.P., was followed by Pinus forest (ca. 6400 B.P.). The Late Archaic (6000-3000 B.P.) was a period of great transition; Tsuga forest developed again ca. 5700 B.P., but was abruptly replaced by northern hardwood forest ca. 4700 B.P. That Late Archaic expansion of hardwoods would have provided better forage for beaver. Coincidentally, boreal wetland mammals such as beaver (Castor canadensis) and muskrat (Ondatra zibethicus) increase in faunal assemblages of local archaeological sites, while remains of anadromous fish decrease. We postulate that the apparent increase in human populations throughout the region during the Late Archaic may be attributed to an increase in the resource base within both upland and wetland areas resulting from the development of hardwood forest in response to climatic cooling.

Does Reproductive Synchrony Affect Juvenile Survival Rates of Northern Mammals?

Predator swamping is often cited as an adaptive function of reproductive synchrony. We measured juvenile survival rates of two boreal mammals, snowshoe hares (Lepus americanus) and red squirrels (Tamiasciurus hudsonicus), and evaluated the effect of timing of birth relative to the population mean on subsequent survival. Reproduction of hares was highly synchronous. Juvenile hares were born in three distinct litter groups per summer, and they suffered high early mortality due to predation. Juveniles born closest to the population mean had higher survival than those born later for two of the three litter groups. The timing of red squirrel litters was more variable, and squirrels only had one litter per summer. The juvenile survival rates of squirrels were high relative to those of hares. Degree of synchrony had no effect on survival rates of juvenile squirrels to emergence or from emergence to weaning. We suggest that predation selects for tighter reproductive synchrony of snowshoe hares, at least while they are at peak densities, but that it has little effect on the timing of red squirrel reproduction.

Missing Mammals on Great Basin Mountains: Holocene Extinctions and Inadequate Knowledge

The discontinuous distribution of boreal mammals across Great Basin mountains has provided a significant body of data for the analysis of biogeographic patterns in isolated populations of small mammals. Such use assumes that species unreported from particular ranges do not, in fact, occur there. Data from the Roberts and Diamond mountains (central Nevada) demonstrate that this assumption is incorrect. The new distributional records from these ranges further decrease the slope of the log species—log area relationship for Great Basin boreal mammals, but increase the nestedness of the montane faunas involved. These data underscore the need for more‐thorough assessments of the mammalian faunas of Great Basin mountains, but they also suggest that extinction of boreal mammals on these mountains is even more predictable than has appeared in the past.

Mammals of the Elm Creek Local Fauna, Late Pleistocene of Beaver County, Oklahoma

-Twelve mammalian taxa are identified (four to genus only) from the 1 1,410year-old Elm Creek local fauna. The water shrew Sorex palustris probably lived along margins of cold water streams of glacial meltwater. The chipmunk, Tamias striatus, probably inhabited broad-leafed woodlands marginal to the cold water streams. Other small mammals of the fauna are typical prairie or grassland forms. The ground squirrel, Spermophilus franklin ii, is now found to the north and west of Elm Creek. Remains of mammoth, horse and camel were recorded. The small mammals that lived at Elm Creek ca. 11,000 years ago principally were prairie forms. The boreal forest mammals recorded from northern Kansas and Nebraska at about this time did not extend as far south as the Oklahoma Panhandle in the terminal Pleistocene. A summary of eight late Pleistocene local faunas from Meade County, Kansas, and the panhandles of Oklahoma and Texas show cool-prairie environment, not cold climate or coniferous forest.

Nested Faunas and Extinction in Fragmented Habitats

Abstract: The faunas of habitat islands, such as those produced by fragmentation of formerly continuous habitats, are commonly made up of nonrandom subsets of the total available species pool. Faunas within an archipelago may form a nested series, with depauperate faunas made up of subsets of more species‐rich faunas. The pattern is seldom perfect: widespread species may be absent from otherwise rich faunas (holes), and uncommon species may occur in depauperate faunas (outliers). The “nestedness” of an assemblage of faunas (its fit to the “nested subset model”; Patterson & Atmar 1986) can be measured by summing the holes and outliers.The distributions of boreal mammals and birds among mountain ranges in the Great Basin of western North America were analyzed by this method Despite differences in their derivation (mammalian faunas are thought to be relicts, isolated since the Pleistocene; bird faunas have probably experienced recurrent colonization throughout their history] both groups show an approximately equal (and highly significant) fit to the nested subset model. They differ, however, in the relative numbers of holes and outliers in their patterns. The mammalian pattern is hole‐rich; the bird pattern is outlier‐rich.The present‐day composition of the mammalian faunas is the result of selective extinction of species of originally richer faunas. The existence of nested subsets in these faunas suggests that extinction is a highly deterministic process: extinctions occurred in approximately the same sequence throughout the region, despite wide variation in extinction rates Extinction sequence has, in fact, been less variable than extinction rates.

Use of track transects to measure the relative occurrence of some boreal mammals in uncut forest and regeneration stands

Tracks of marten (Martes americana), lynx (Felis lynx), red fox (Vulpes vulpes), ermine (Mustela erminea), snowshoe hare (Lepus americanus), and red squirrel (Tamiasciurus hudsonicus) were censused from 1980 to 1985 on 1-km transects in uncut stands and on eight sites that had been clear-cut between 1 and 33 years ago, in boreal mixedwood habitat near Manitouwadge, Ontario. Marten tracks were more common in uncut areas than in younger stands. Lynx tracks were most abundant on sites that were logged 20–30 years ago and were absent in uncut areas and stands less than 5 years old. Counts of red fox tracks were lowest in uncut stands and showed no consistent pattern among years of our survey with respect to stand age in second-growth forest. Hare tracks were most abundant in 20- and 30-year-old stands, and least abundant in stands less than 5 years old. Red squirrels were most common in uncut areas, but similar high values were also found in 20- and 30-year-old sites during 3 years when populations in the area were depressed. No selection of stands by age was seen for ermine. Numbers of tracks were significantly correlated with live captures of marten, hare, and red squirrels. Our results suggested that track abundance can be used as an index of habitat preferences and population trends. Highest counts were achieved in December for marten, red squirrel, and ermine, likely as a result of several types of over-winter mortality and inactivity in cold weather, which may have reduced counts in January and March. As a result of high and nonhomogeneous variance among transects and years, nonparametric statistical analysis was required. Transect length for fox and lynx should be substantially longer than 1 km (probably 3–5 km) to avoid numerous zero results.

The Biogeographic History of Small Mammals in the Great Basin: Observations on the Last 20,000 Years

Evidence from archaeological and paleontological sites meets key predictions drawn from J. H. Brown's argument that boreal mammals colonized the Great Basin during the Pleistocene, only to become isolated on, and differentially extinct across, Great Basin mountains during the Holocene. Sylvilagus idahoensis decreased in abundance here at about 7,000 years ago, apparently at about the same time that Ochotona princeps became extinct in the lowlands of the northern half of the Great Basin. These shifts seem correlated with a decrease in effective precipitation inferred from paleobotanical data. Hares ( Lepus sp.) appear to have been more abundant during the earlier Holocene than during later times in many more northerly parts of the Great Basin, while several sites suggest survival of the extinct noble marten ( Martes nobilis ) until a few thousand years ago. The fact that boreal mammals are isolated on Great Basin mountains has important implications for the management of high altitude habitats in this region.

Late Quaternary Environments and Biogeography in the Great Basin

AbstractPlant and animal remains found in packrat (Neotomaspp.) middens and cave fill from the eastern and southern Great Basin region reveal the presence of subalpine conifers and boreal mammals at relatively low elevations during the Late Wisconsin. Limber pine (Pinus flexilis) and bristlecone pine (P. longaeva) were important in the late Pleistocene plant communities throughout this region. Spruce (Piceacf.engelmannii) and common juniper (Juniperus communis) were present in some of the more northerly localities, and Douglas fir (Pseudotsuga menziesii) and white fir (Abies concolor) were present in southern and eastern localities. Single needle pinyon pine (Pinus monophylla), common across this region today, was apparently not present north of the Sheep Range of southern Nevada during the Late Wisconsin. Pikas (Ochotonacf.princeps), small boreal mammals present in only a few Great Basin mountain ranges today, were common throughout the region. Heather voles (Phenacomyscf.intermedius) have been found in two cave fill deposits in Nevada, though they are unknown in the Great Basin today. Limber and bristlecone pines are generally restricted to rocky substrates in modern subalpine habitats in the Great Basin, and this may also have been the case when these plants grew at lower elevations during the Late Wisconsin. Subalpine conifers were present on the rock outcrops sampled by the packrat middens, but shrub communities, perhaps dominated by sagebrush (Artemisiaspp.), may have been present on alluvial valley-bottom substrates. Forested habitats would thus have been isolated habitat islands, as they are today. Boreal small mammals, including pikas and heather voles, were able to colonize the Great Basin mountain ranges during the late Pleistocene. We suggest that these mammals were able to survive in the intervening valley-bottoms under a cool-summer climatic regime, and that continuous forest or woodland corridors were not necessary for migration.

A Mid-Holocene Record for the Heather Vole, Phenacomys cf. Intermedius, in the Central Great Basin and its Biogeographic Significance

Two specimens of Phenacomys cf. intermedius are reported from Gatecliff Shelter, in the Toquima Range of central Nevada. The presence of the heather vole in the central Great Basin at about 5,300 B.P. provides support for Brown's model of the biogeography of Great Basin boreal mammals and suggests that these voles were widespread in the Great Basin during late Pleistocene and early Holocene times.

Ecological Significance of Displaced Boreal Mammals in West Virginia Caves

Ecological Significance of Displaced Boreal Mammals in West Virginia Caves

Comparative Demography of Pikas (Ochotona): Effect of Spatial and Temporal Age‐Specific Mortality

The structure of 4 populations of a small boreal mammal, the pika (Ochotona princeps), is examined to explore the causal mechanisms of evolution of life—history features of the species. Litter size reflects potential and realized fecundity and is largest at Bodie (low latitude, low altitude), intermediate at Sierra and Colorado (low latitude, high altitude), and smallest at Alberta (high latitude). The age specificity of mortality largely determines the number of sites available for settlement by juveniles, which dictates the feedback to liter size. Populations are stable and habitats continuously saturated at Alberta; mortality of adults is predictable. The Sierra and Colorado sites possess unstable population. At these sites, snowmelt in spring (the harbinger of emergent vegetation and successful weaning) is relatively unpredictable compared to Alberta; adult mortality may be high in years of early or late snowmelt. The unpredictability also selects for asynchronous breeding such that more sites are available in any one year to offspring from certain successfully weaned litters. The habitat at Bodie is temporally and spatially unsaturated. Largely because of poor vagility of pikas, much of the habitat is vacant. Colonization is unable to completely offset extinction of populations on patches of habitat. Here, the selective factor determining litter size is juvenile production and not adult mortality.

On the Holocene History of Some Northern Great Basin Lagomorphs

Analysis of vertebrate faunas from archaeological sites in south-central Oregon's Fort Rock Basin supports the hypothesis that the common early Holocene jackrabbit in the northern Great Basin was Lepus townsendii , and that L. californicus did not become abundant in this area until middle Holocene times. The current range expansion of L. californicus at the expense of L. townsendii in the northern Great Basin and adjacent Plateau may, in part, represent the continuation of a process that began several thousand years ago. These faunas also document the presence of pikas ( Ochotona princeps ) in the Fort Rock Basin prior to, but not after, 7,000 years B.P. Pikas are absent from the area today; their disappearance here may have been due to the eruption of Mt. Mazama at, or just before, an episode of climatic change. These data support the argument that the distribution of boreal mammals on mountainous islands within the Great Basin can be accounted for by initial colonization followed by extinctions of geographically intermediate populations.

Beetles, Beach Drift, and Island Biogeography

Beetles, Beach Drift, and Island Biogeography

The Distribution and Dispersal of Pikas: Consequences of Insular Population Structure

The population structure of a small boreal mammal, the pika (Ochotona princeps), was analyzed from demographic data and the observed spacing of populations on discrete islands of habitat in the Sierra Nevada of California. These islands of habitat varied in size and distance from one another. Not all of the islands were occupied and most seemed to contain fewer individuals than they could hold. The populations apparently represent dynamic equilibria between extinction, which was directly related to island size, and recolonization, which was inversely related to interisland distance. Distances greater than 300 m appeared to pose difficult barriers to dispersing juveniles. The study site is near the distributional boundary of pikas in this area. The birth rate is higher, adult death rate lower, and juvenile death rate higher than for other pika populations found near the center of the altitudinal or geographic range of the species. It appears that the probability of successful colonization decreases with progressively lower elevations, until ultimately colonization is unable to offset extinction and the limit of the species range is determined.

Mammals on Mountaintops: Nonequilibrium Insular Biogeography

An analysis of the distribution of the small boreal mammals (excluding bats) on isolated mountaintops in the Great Basin led to the following conclusions: 1. The species-area curve is considerably steeper (z = .43) than the curves usually obtained for insular biotas. 2. There is no correlation between number of species of boreal mammals and variables which are likely to affect the probability of colonization, such as distance between island and mainland, distance between islands, and elevation of intervening passes. Apparently the present rate of immigration of boreal mammals to isolated mountains is effectively zero. 3. Paleontological evidence suggests that the mountains were colonized by a group of species during the Pleistocene when the climatic barriers that currently isolate them were abolished. 4. Subsequent to isolation of the mountains, extinctions have reduced the faunal diversity to present levels. Probability of extinction is inversely related to population size and, therefore, is influenced by body size, diet, and habitat. The rate of extinction has been low, and all of the islands still have one or more species of boreal mammals. 5. The mammalian faunas of the mountaintops are true relicts and do not represent equilibria between rates of colonization and extinction.

Adaptive Responses to Cold in Arterial Smooth Muscle from Heterothermic Tissues of Marine Mammals

PERIPHERAL heterothermy is essential for temperature regulation in many boreal, aquatic or subarctic mammals and birds. Dissipation of heat to the environment is controlled by changes in blood flow to peripheral tissues. Seal flippers are a typical example in which both the skin and deep tissues are normally maintained at temperatures near those of the surrounding water (1°–5° C)1 but which may serve as heat dissipators when the seal bears a positive heat load. The tissues of a seal flipper are thus able to function normally through a temperature range as large as 35° C while the central or core body temperature is regulated within the narrow range typical of mammals. The present investigation was designed to determine if vascular smooth muscle in several species of seals is functional at temperatures near freezing and whether differences exist between central and peripheral vascular smooth muscle.

Mathematical Formulas Expressing Faunal Resemblance

Two populations, isolated from one another, evolve independently and given sufficient time usually become different from one another. Close relationship of two kinds of animals-for example, one in Eurasia and one in North Ameirca-indicates that a barrier was recently enterposed between them. Many boreal mammals of North America do have morphologically similar Eurasian counterparts. The circumboreal distributions of these related kinds indicate a land bridge connecting Eurasia and North America in the not too distant past (see Simpson, 1940). Two or more faunas that have many wide-ranging kinds in common closely resemble each other, but it is a different sort of resemblance from that of two other faunas made up of many kinds in common that have small geographic ranges (Hershkovitz, 1958:593). Also, the number of kinds in common may vary according to this person's or that person's classification of the kinds (Burt, 1959:137). For instance, the North American grizzly bear is thought by some workers [for example, Erdbrink (1953)1] to be of the same species as the Eurasian brown bear, whereas other (in this case, earlier) workers [for example, Merriam (1918)] thought that they were different species. Nevertheless, it is useful to analyze animal distributions in order to determine relative degrees of resemblance between or among them, and it is convenient to communicate these resemblances in mathematical terms if the terms have

Zoogeography of the Montane Mammals of Colorado

In Colorado the distribution of montane or boreal habitats is at present closely-associated with the local climate produced by the mountains. Peculiarities of this habitat are high precipitation, both in winter and summer, cool temperatures, a continuous water supply and a coniferous forest. Certain mammals are more or less restricted in geographic range, in this part of the continent, to the mountains. In Pleistocene time the distribution of boreal habitat and hence of boreal mammals has undoubtedly fluctuated widely with the advances and retreats of continental and alpine glaciers. The contemporary pattern of distribution is, at least in part, a result of the most recent major glacial advance and retreat which took place in the Wisconsinan Age. It seems probable to us that most contemporary subspecies have differentiated in late Pleistocene time; otherwise the frequent correspondence of their ranges with current topographical and ecological features, which stem from late Pleistocene events in many cases, seems inexplicable. In the western United States the Boreal Zone is found at higher and higher elevations as one proceeds southward until it is scattered on isolated mountain peaks. The presence of isolated populations of boreal mammals on some of these mountains is evidence of a former displacement southward and downward in altitude of the Boreal Zone in a glacial age, presumably the Wisconsin, and subsequent elevation of the Boreal Zone in altitude and latitude in an ensuing interglacial interval, presumably the Recent. These southern, marginal populations …