Papers in this Special Feature stem from a symposium on large-scale ecosystem change and the conservation of marine mammals convened at the 86th Annual Meeting of the American Society of Mammalogists in June 2006. Major changes are occurring in multiple aspects of the marine environment at unprecedented rates, within the life spans of some individual marine mammals. Drivers of change include shifts in climate, acoustic pollution, disturbances to trophic structure, fisheries interactions, harmful algal blooms, and environmental contaminants. This Special Feature provides an in-depth examination of 3 issues that are particularly troublesome. The 1st article notes the huge spatial and temporal scales of change to which marine mammals are showing ecological responses, and how these species can function as sentinels of such change. The 2nd paper describes the serious problems arising from conflicts with fisheries, and the 3rd contribution reviews the growing issues associated with underwater noise.

The earth's climate is changing, possibly at an unprecedented rate. Overall, the planet is warming, sea ice and glaciers are in retreat, sea level is rising, and pollutants are accumulating in the environment and within organisms. These clear physical changes undoubtedly affect marine ecosystems. Species dependent on sea ice, such as the polar bear (Ursus maritimus) and the ringed seal (Phoca hispida), provide the clearest examples of sensitivity to climate change. Responses of cetaceans to climate change are more difficult to discern, but in the eastern North Pacific evidence is emerging that gray whales (Eschrichtius robustus) are delaying their southbound migration, expanding their feeding range along the migration route and northward to Arctic waters, and even remaining in polar waters over winter—all indications that North Pacific and Arctic ecosystems are in transition. To use marine mammals as sentinels of ecosystem change, we must expand our existing research strategies to encompass the decadal and ocean-basin temporal and spatial scales consistent with their natural histories.

Direct fisheries interactions pose a serious threat to the conservation of many populations and some species of marine mammals. The most acute problem is bycatch, unintended mortality in fishing gear, although this can transition into unregulated harvest under some circumstances. A growing issue in some fisheries is depredation, in which marine mammals remove captured fish from nets or lines. Depredation reduces the value of catch and may lead to a greater risk of entanglement and the potential for retaliatory measures taken by fishermen. The conservation threat caused by direct fisheries interactions is most dire for small populations of cetaceans and dugongs. Immediate action is needed to assess the magnitude of bycatch, particularly in many areas of Africa and Asia where little work has been conducted. New and innovative solutions to this problem are required that take account of the socioeconomic conditions experienced by fishermen and allow for efficient transfer of mitigation technology to fisheries of the developing world.

The amount of underwater sound from ship traffic, commercial, research, and military sound sources has increased significantly over the past century. Marine mammals and many other marine animals rely on sound for short- and long-range communication, for orientation, and for locating prey. This reliance has raised concern that elevated sound levels from human sources may interfere with the behavior and physiology of marine animals. The dominant source of human sound in the sea stems from propulsion of ships. Shipping noise centers in the 20- to 200-Hz band. Frequencies this low propagate efficiently in the sea, and shipping has elevated the global deepwater ambient noise 10- to 100-fold in this frequency band. Baleen whales use the same frequency band for some of their communication signals, and concern has been raised that elevated ambient noise may reduce the range over which they can communicate. Marine mammals have a variety of mechanisms to compensate for increased noise, but little is known about the maximum range at which they may need to communicate. Some of the most intense human sources of sound include air guns used for seismic exploration and sonar for military and commercial use. Human sources of sound in the ocean can disturb marine mammals, evoking behavioral responses that can productively be viewed as similar to predation risk, and they can trigger allostatic physiological responses to adapt to the stressor. Marine mammals have been shown to avoid some human sound sources at ranges of kilometers, raising concern about displacement from important habitats. There are few studies to guide predictions of when such changes start to lower the fitness of individuals or have negative consequences for the population. Although acute responses to intense sounds have generated considerable interest, the more significant risk to populations of marine mammals is likely to stem from less visible effects of chronic exposure.

We identified specific areas where fin whales (Balaenoptera physalus) forage on daytime surface swarms of euphausiids in Ballenas Channel, Gulf of California. During 2003 and 2004, 4 field trips per year were carried out (winter–spring, spring, summer, and autumn). Systematic line transects and random surveys for whales were conducted in small boats (6 m) and euphausiid swarms were sampled with a zooplankton net. Fin whales foraged mostly in shallow waters (10–100 m) off the west and south coast of Coronado Island and were observed feeding on 18 of 19 swarms of Nyctiphanes simplex (5 in 2003 and 14 in 2004). Swarms occurred from March to early August and were almost absent from October to November. Although fin whales were sighted throughout the study area, there was a characteristic distribution pattern of feeding activity, mainly during spring and summer seasons. Examination of our data shows that the adjacent waters off Coronado Island constitute a unique seasonal foraging habitat for fin whales in the Gulf of California.

The annual cycle of adult female southern elephant seals (Mirounga leonina) can be divided into 2 pelagic phases, separated by relatively short terrestrial phases: breeding and molting. We used resighting data collected from tagged female southern elephant seals at Marion Island during 1986–1999 to investigate seasonal survival during the 2 pelagic phases in relation to reproductive experience. Mean postbreeding (pelagic phase between breeding and molting, about 62 days) survival of primiparous females was 0.830 compared to 0.912 for more-experienced females. Postmolting (pelagic phase between molting and breeding, about 255 days) survival was 0.847 (0.960 when rescaled to 62 days for comparative purposes) and was not dependent on reproductive experience. Postbreeding survival of experienced females was higher than postmolting survival, but per unit time the opposite applied. A 2-stage survival model, in which survival was constrained to be constant before 1994 (when the population was declining) and from 1994 onward (during the stable phase), had overwhelming support from the data. Postbreeding survival of primiparous females increased from 0.799 before 1994 to 0.880 from 1994 onward. Postmolting survival of all females also increased from 0.817 to 0.872 over the same period. Postbreeding and postmolting mortality risk varied independently over time, demonstrating the importance of an intra-annual approach in population studies of southern elephant seals.

Monogamy is rare among mammals and molecular investigations have revealed that many socially monogamous species participate in extrapair mating. The North American beaver (Castor canadensis) is a socially monogamous species that exhibits classic monogamous behavior, generally living in discrete colonies composed of a mated pair and their offspring. We examined genetic relationships within and among beaver colonies for 2 populations in Illinois to investigate average relatedness within colonies, occurrences of extrapair mating within or between colonies, and the influence of geographic distance on intercolony relatedness. Seven microsatellite loci developed for the beaver were used to estimate relatedness and parentage for 55 beavers in central Illinois and 72 beavers in southern Illinois. Average within-colony relatedness varied widely in both populations, ranging from 0.04 to 0.64 in central Illinois and from 0.16 to 0.41 in southern Illinois. Colonies were composed primarily of 1st- and 2nd-order relatives, but included unrelated individuals. Paternity analysis revealed that 5 (56%) of 9 litters had been sired by ≥2 males. Extrapair mating frequently occurred between members of neighboring colonies in southern Illinois. In contrast to long-held views that beavers are genetically monogamous and colonies are typically 1st-order relatives, we documented a wide range of relationships among colony members and multiple paternity in >50% of litters.

The distinctive features of reproduction in squirrels are the lack of allometric influences on the duration of reproductive investment; the strong allometric influences on offspring mass; and a trade-off between number and size of young, suggesting an important developmental component to reproduction. Lengths of gestation and lactation do not vary with body size but neonatal and weaning mass do. Apparently, the major constraint on reproduction in squirrels is not resources per se (food, calories, minerals, or water) but rather the length of time such resources are available. Squirrels adjust growth rate to fit the timing of resource abundance. Within the familial reproductive pattern, arboreal squirrels invest more into reproduction than do ground squirrels. Flying squirrels (Pteromyini) have a larger temporal investment into reproduction but a smaller energetic investment compared with other squirrels. Ground squirrels do not have a distinct reproductive profile, because marmotine and nonmarmotine ground squirrels differ. Marmotine ground squirrels have a small temporal investment and a large energetic investment on a per litter but not on an annual basis. Nonmarmotine ground squirrels have a reproductive pattern similar to that of tree squirrels, a pattern intermediate between marmotines and flying squirrels. Within this locomotor–ecological framework, reproductive patterns differ among subfamilies. Tribes differ in having few (2–4) versus many (4–8) young, and in the relative allocation of investment into gestation versus lactation. Specific environmental influences on reproduction in squirrels occur at lower taxonomic levels within the framework of a broad reproductive pattern set by earlier radiations into particular locomotor and nest-site niches.

The sciurid tribe Marmotini has a distinctive, highly specialized reproductive profile characterized by annually produced litters of many offspring, each of small mass and fast growth rate. However, not all genera of marmotines follow the reproductive profile of the tribe. In fact, included in the tribe are squirrels with the highest and lowest energetic investment into reproduction of the entire family. Because of its large litter size, Ammospermophilus has the largest energetic investment into reproduction of nearly all squirrels. Also, Ammospermophilus is not limited to 1 litter per year. At the opposite extreme, Marmota has the smallest energetic investment into reproduction of all squirrels. Of the other 4 marmotine genera, reproduction in Cynomys is similar to that of Marmota, whereas that of Tamias is similar to that of Ammospermophilus; reproduction in Sciurotamias and Spermophilus may reflect their phylogenetic positions. Litter size in the basal Sciurotamias (2.5) is the lowest for all marmotines and is closest to that of other squirrel taxa. Consistent with the probable paraphyly of the genus, spermophiline data are the most variable and many reproductive characters sort along the probable clades within Spermophilus. For spermophilines, a litter size of 4 is probably basal and the larger litter sizes of 6–8 in some clades are derived. Two other derived features are the low offspring biomass in Marmota and a short time between conception and weaning in a spermophiline clade of predominantly New World species. Overall, reproductive investment within marmotines has followed 2 patterns: the larger marmotines (Cynomys and Marmota) have a reduced annual energetic investment compared with a higher reproductive investment in the smaller marmotines (Ammospermophilus and Tamias). Thus, body size is a key aspect in the diversification of reproductive patterns in the Marmotini.

Body mass is usually positively associated with reproductive output in females, with larger females having more offspring. However, in gliding or flying species, large body mass is constrained as a result of wing loading, defined as the ratio of body mass to the surface area available to generate lift. Gliding animals may be particularly susceptible to increased wing loading resulting from added mass during pregnancy. We compiled reproductive and morphological data for gliding and related nongliding mammals in all extant taxa where this type of locomotion occurs to test the predictions that gliders will have proportionally lighter litters than related nongliders, and relative litter mass will be negatively associated with wing loading. Contrary to our 1st prediction, gliders had heavier offspring than did nongliders in all taxa examined. Consistent with our 2nd prediction, however, greater relative litter mass was associated with lower wing loading. Maintaining the ability to glide when pregnant may influence investment in reproduction. However, gliding locomotion appears to be associated with increased litter mass, perhaps because of smaller litters of heavy young. Thus, we suggest that gliders may be characterized by K-selected life-history traits such as low mortality, slow metabolism, and fewer offspring per litter, but increased investment in individual young. The findings of this comparative study highlight how major shifts in locomotor mode can have a profound influence on patterns of life history.

In polygynous mammals, mating success of males often depends on intense male–male competition and the use of alternative mating tactics. Because reproduction incurs substantial energetic costs and risks of fight injuries, mate selection by males should be expected, particularly when females vary in their ability to produce offspring but can only be defended 1 at a time. Here, we investigated during 3 ruts how age and social rank of male mountain goats (Oreamnos americanus) affected the formation of consort pairs with females (“tending” tactic) in a marked population at Caw Ridge, Alberta, Canada. Among consort pairs, we quantified the behaviors of males and females, and the use of an alternative mating tactic by competing males, “coursing,” which consists of disrupting the pair to gain temporarily access to the female, often by pursuing her. Mate choice was assessed by testing if old and dominant males observed in consort pairs tended experienced females more often than younger females, because reproductive success of females increases with age. Males in consort pairs were ≥4 years old and most (86%, n = 59) were in the top one-half of the dominance hierarchy. Age and social rank of males were positively related to age of females and the total number of young produced by the tended female. All observed matings (n = 32) occurred between 14 November and 2 December and 91% were between males and females in consort pairs. Subordinate males gained mating access to females through coursing, but this tactic was rare. Our study provides evidences of mate choice by males for experienced females in an ungulate and the 1st quantitative information on the rut of mountain goats.

Many antipredator behaviors advertise honestly an individual's health and awareness of predators, reducing the probability of further attack. We presented full-sized models of felid predators to Columbian black-tailed deer (Odocoileus hemionus columbianus) and observed a unique conspicuous gait pattern, the alarm walk, which has not been described in the literature. We conducted frame-by-frame analyses of gait timing and leg movement from video recordings of alarm walking and normal walking. Compared with normal walking, contact durations of all legs during alarm walking were greater and deer lifted their foreleg carpal joint higher off the ground, suggesting that alarm walking requires a level of control and flexibility in leg movement not possible in arthritic or lame individuals. Although phases of limb movement (i.e., midtime lag between fore and hind legs) were reliably different, there was no difference in the angle of foreleg lifting between the 2 walking styles. Performance of alarm walking was correlated with foot stamping, and was observed more often when the predator model was out of view. Although there was no direct evidence supporting any 1 function of alarm walking, available evidence suggests that alarm walking might have the dual function of signaling to a stealthy predator that it has been detected and that the displaying deer is healthy and capable of escaping, both of which should deter further pursuit.

We examined spatial and temporal relationships of 104 raccoons (Procyon lotor) at the northern edge of their distribution to report social organization and to test hypotheses regarding the formation of coalition groups among adult male carnivores. Social tolerance among females varied among years, but adults maintained relatively exclusive home ranges (overlap ranged from 2.2% to 12.5%) that were dispersed in a uniform pattern throughout the duration of the study (Clark–Evans ratios ranging from 1.32 to 1.87, P < 0.001–0.08). Social interactions among males were more complex than previously described for low-density populations of raccoons, with most adults (approximately 80%) forming coalition groups. We identified 9 unique coalitions that had extensively overlapping home ranges and positively associated nightly movements within group members (overlap indices ranging from 85.3% to 97.3%). Coalitions maintained exclusive territories between groups (overlap indices ranging from 0% to 3.2%) and formed distinct spatial boundaries that were highly correlated with home-range boundaries of females. Male coalition groups in the order Carnivora are hypothesized to form in response to aggregations of females, but examination of our data suggests that this is not a prerequisite for their formation. We propose a dominance hierarchy where subordinate males benefit through increased likelihood of inheritance of territories, whereas dominant males benefit through increased efficiency of territorial defense.

The reproductive biology of wild Canis species is often described as unique among mammals because an unusual combination of behavioral and physiological characteristics including a seasonally monestrous cycle, copulatory lock or tie, obligatory pseudopregnancy, social monogamy, and biparental care of the young. We investigated social behavior, endocrine profiles, and vaginal cytology of female coyotes (Canis latrans) during 4 breeding seasons, 2000–2003. Blood levels of estradiol, progesterone, prolactin, and relaxin were measured, and mating behavior and changes in vaginal epithelium were documented. After aligning the data from each individual to her estimated day of ovulation, we compared pregnant coyotes with nonpregnant females and evaluated temporal relationships among hormone levels, behavior, and vaginal cytology. We found that patterns of proceptive and receptive behaviors correlated with the secretion of steroid hormones, as did vaginal epithelial cytomorphosis. In addition, although progesterone levels of pregnant and pseudopregnant coyotes were indistinguishable, prolactin demonstrated a discernible intergroup difference and relaxin was only detectable in pregnant females. Although this study included characteristics not previously published for this species, it also showed how key aspects of reproduction were correlated temporally, and emphasized the importance of an integrated perspective when addressing the reproductive biology of coyotes, or other wild species of canids.

We assessed the accuracy of scat-sampling methods in relation to sources of bias (statistical independence of the data and definition of the sampling unit) and precision (sample size). We developed a method to quantify diets of predators accurately in a study of diet selection by wolves (Canis lupus) during 3 winter seasons (1999–2002) in the Western Alps. The best sampling design to avoid pseudoreplication was the “additive method,” where the presence of a carcass, estimated by either a collection of scats or a carcass itself along the travel route of a wolf, was considered 1 sampling unit. Although roe deer (Capreolus capreolus) were the primary prey used by wolves in the area, red deer (Cervus elaphus), recently reintroduced prey present at low density, were selected in winter 2001. We evaluated the optimal sample size for a given question using Monte Carlo simulations. At small sample sizes, slight increases in sample sizes caused large reductions in the standard error, greatly improving the precision of the estimates of percentage of items in the diet. Estimating the number of rare prey species used by wolves, such as red deer in our case study (<2% of the diet estimates), was possible if the minimum sample size was greater than 10–40% of the population of carcasses. We emphasized the importance of the additive method to improve the accuracy of estimates of diet selection by carnivores.

We examined population dynamics and trophic ecology of a predator–prey system in the Simpson Desert, Australia, consisting of an assemblage of small mammals (body mass < 100 g) and 4 species of predators: the endemic letter-winged kite (Elanus scriptus), a nocturnal-hunting rodent specialist; and 3 introduced mammalian predators (dingo [Canis lupus dingo], European red fox [Vulpes vulpes], and house cat [Felis catus]). This is the 1st comprehensive study of the responses of both the kite and introduced carnivores to a rodent outbreak. The 3.5-year study period included a population outbreak of about 24 months duration involving 3 native rodent species. Mammalian predators and kites exhibited similar population responses. Kites immigrated into the area within 6 months of the outbreak commencing, and remained while rodent abundance was high; however, all birds left the area after rodent populations crashed within a 6-week period. Dingoes and foxes were more abundant than cats and both species increased during the outbreak. All carnivores were resident. The letter-winged kite fed almost entirely on rodents. Rodents were the main prey of the 3 mammalian predators during the outbreak; however, all species had intermediate niche breadths. Dietary overlap between the kite and each carnivore was high during the rodent outbreak. During a nonoutbreak period, predation on rodents by the red fox remained high, whereas that by the dingo declined. We estimated the number of average-sized rodents (body mass 32.65 g) eaten daily by a nonreproducing individual to range from 1 (letter-winged kite) to 6 (red fox). We also estimated that the 3 mammalian predators (combined) captured 11 times as many rodents per day as letter-winged kites. There is considerable potential for food-based competition between the kite and introduced mammalian predators, particularly the red fox and house cat, in arid Australia.

We predicted that more-fragmented habitats are associated with lower diversity of small mammals and higher densities of populations of rodents that are hosts of hantaviruses. We compared diversity and distribution of small mammals that are either hosts or nonhosts of hantaviruses in 6 Panamanian national parks and adjacent areas with varying degree of human impacts. We sampled forest, edge, and anthropogenically disturbed habitats. The generalist rodents Oligoryzomys fulvescens (reservoir of Choclo virus) and Zygodontomys brevicauda (reservoir of Calabazo virus) were more abundant in disturbed habitats, especially in smaller and more isolated patches, where population density and diversity of other rodent species was lowest. In contrast, these 2 species had lower abundances in larger forested areas with more nonreservoir species of small mammals. Our results suggest that the change in the natural environment resulting from tropical deforestation is increasing the abundance and distribution of species that are reservoirs for hantaviruses. Therefore, it is likely that forest fragmentation has contributed to recent outbreaks of hantavirus pulmonary syndrome in tropical areas. Conservation of natural resources becomes all the more imperative, not only for protecting fauna and flora but also for human health.

We surveyed the historic range of pygmy rabbits (Brachylagus idahoensis) in Nevada and California using infrared-triggered cameras to determine the species' current distribution and habitat selection. Areas with potential habitat were mapped using geographical information system coverages for elevation, big sagebrush (Artemisia tridentata) vegetation, and loamy soils. Within this region random sites and field-selected sites with sagebrush islands (prominent clusters of sagebrush higher than the surrounding sagebrush) were surveyed for the presence of pygmy rabbits. Sites were measured for sagebrush height, surrounding sagebrush height, sagebrush cover, and soil composition. Likelihood of pygmy rabbit occupancy at a site increased with the presence of sagebrush islands, increasing sagebrush cover, and decreasing surrounding sagebrush height. Additionally, we surveyed 1,394 other sites across the species' historic range and found current activity of pygmy rabbits at 258 of these sites. We measured sagebrush cover, sagebrush height, understory stem density, and presence or absence of cottontail rabbits, jackrabbits, red soils, cheatgrass, and rodent burrows at 454 sites. We used 80% of the data to create a logistic regression model. The top-ranked Akaike's information criterion–selected model suggested that likelihood of pygmy rabbit occupancy at a site increased with increasing sagebrush cover, decreasing understory stem density, absence of cottontails, absence of reddish soils, absence of cheatgrass, and absence of rodent burrows. This model showed a 79% accuracy rate in predicting occupancy within the remaining data. Current populations of pygmy rabbits were found throughout all of the species' historic range in Nevada and the southern portion of its range in California.

Although the role of animals in altering ecosystem structure and dynamics has received increased attention in the last decade, large gaps in knowledge still exist, limiting our ability to incorporate animals into models of ecosystem dynamics. Our research on the plains vizcacha (Lagostomus maximus, family Chinchillidae), a colonial burrowing herbivore in grasslands and semiarid scrub of southern South America, addresses 3 of these gaps—belowground impacts of vertebrates on soils, net effects of multiple types of animal activities on ecosystem structure, and the scaling up of plot-level effects to the landscape. Our study demonstrated that grazing by vizcachas produced strong spatial patterns in composition, biomass, and nutrient pools in herbaceous vegetation. In burrows, total nitrogen (N), total phosphorus (P), and inorganic N were greater than in undisturbed soil at a similar depth. Burrow soil and foliage of shrubs growing on burrows were depleted in ¹⁵N, reflecting the signature of vizcacha feces. Transport of caliche by vizcachas resulted in significantly greater P concentrations in surface soil on burrows. Indirect effects of vizcachas on shrubs, through alteration of soil nutrients, transport of caliche to the soil surface, and possibly altered fire regimes, resulted in greater biomass, foliar N and P content, and total N and P pools in shrubs. Net effects of vizcachas on ecosystem structure, above- and belowground, are spatially extensive, and likely persist much longer than the colonies of vizcachas that generated these effects. This study demonstrates that the largest impacts of herbivores on ecosystem structure can be through their effects on plants they do not consume and, in systems where biopedturbation is frequent, animal transport is among the key processes that determine vertical distribution of nutrients in the soil profile.

Knowledge of how animals move through the environment is important for predicting effects of habitat change on faunal distributions. Logging of tropical rain forests produces habitat changes on multiple scales that may affect movement and habitat use by small mammals. To explore the effects of such habitat changes, we compared movement and ranging patterns of the long-tailed giant rat (Leopoldamys sabanus) in logged and unlogged rain forests in Borneo. On a small scale, movement was quantified using spool-and-line tracks; on a larger scale, movement was quantified via radiotracking. At the small scale, paths (49 tracks of 55.2 m ± 20.7 SD each) were relatively straight, with similar step (straight-line section) length distributions in both forest types. At the larger scale, the rats (16 individuals tracked for 4 nights each, X̄ = 1,443 ± 991 m of movement per night) moved with similar speed through both forest types (mean distance covered per 10-min interval = 32 ± 45 m). Based on telemetry data, mean nightly activity periods for individual rats averaged 485 ± 109 min (areas covered = 2,083–9,829 m²), with no statistically significant differences between logged and unlogged forests. The large variability in individual movement parameters was not predicted by sex or forest type, suggesting that the paths taken were most likely responses to the local distribution of resources in a heterogeneous rain-forest environment. We conclude that the logged and unlogged forests did not differ with respect to features that are important to movement and ranging patterns of L. sabanus, suggesting that general differences associated with logging may not predict the effects of this type of disturbance on habitat use by individual species of small mammals.

Cavia intermedia may be the mammal with the smallest geographical distribution in the world, because it is endemic to a 10-ha island and therefore vulnerable to extinction. The objective of this study was to understand the population dynamics of C. intermedia in order to define its conservation status and to provide information for its management. The population was sampled monthly using capture–mark–recapture methods and radiotelemetry for 16 months, between March 2004 and June 2005. A total of 5,530 trap-nights resulted in 665 captures of 141 individuals. The population exhibited the main demographic characteristics of the insular syndrome, such as high and stable density, small home ranges, stable age structure composed mostly of adults, and high survival rates. The population dynamics were characterized by density-dependent effects on mortality. C. intermedia can be considered one of the rarest species on the planet because of its limited geographic distribution and very small population size (average estimated population of 42 individuals). We recommend that it be listed as Critically Endangered.

We developed a new data set of enamel microwear for extant caviomorph rodents (i.e., South American hystricognaths) and inferred the diet of an extinct taxon, Neoreomys australis, from data on microwear. To evaluate frequencies of wear features (pits and scratches) in caviomorphs, we employed low-magnification microwear, which has been used successfully by others to distinguish among the diets of ungulates, primates, and sciurid rodents. We developed 3 broad dietary categories for caviomorphs based on behavioral observations reported in the literature: fruit–leaf, fruit–seed, and grass–leaf. Caviomorphs in general all exhibited wear features indicative of processing hard objects (e.g., seed predation, eating hard fruits, and consuming exogenous grit). Among our grass–leaf group, we identified an exogenous-grit subgroup that included fossorial and dust-bathing taxa. We used a discriminant function analysis of wear features to examine post hoc classification of the caviomorph taxa into the 3 dietary categories. Ours is the 1st study to quantify the distribution of microwear features among modern caviomorph rodents; it has the potential to clarify the diets of modern forms that have little behavioral data as well as to infer the diets of extinct species.

Evolutionary relationships among bats of the genus Rhogeessa (Chiroptera: Vespertilionidae) are poorly understood because of the morphological similarity of many of the species and the limited resolution of karyotypes and allozymes in previous studies. Previous karyotypic studies reported several populations that differ by Robertsonian centric fusions, which led to a proposed mechanism of speciation called speciation by monobrachial centric fusions. Here, we present a molecular phylogenetic analysis of 8 of the 10 currently recognized species of Rhogeessa using the mitochondrial DNA gene cytochrome b as well as new karyotypic data. The results are generally consistent with speciation by monobrachial centric fusions because karyotypically distinct populations typically comprise monophyletic maternal lineages. One exception was 2 individuals that were possible hybrids between R. tumida (2n = 34) and R. aeneus (2n = 32). We found ostensible species-level differentiation among 3 karyotypically identical (2n = 34) but geographically separated populations of R. tumida. Examination of new karyotypic data shows a population from western Ecuador to have 2n = 42 and study of molecular data shows it to be phylogenetically distinct from both the karyotypically identical R. genowaysi from Mexico and the South American R. io (2n = 30) to which it was previously allocated. We recognize this population by its available name, R. velilla. We also found an unexpectedly close relationship between Baeodon alleni and R. gracilis.

Many vertebrate taxa show genetic differentiation between populations in northern and southern California. This genetic pattern may reflect a common environmental history for these species. For example, a previous study of the California vole (Microtus californicus) showed morphological divergence between populations in northern and southern California and decreased fertility in crosses between the populations. To investigate phylogeographic differences in this species, we assessed variation in mitochondrial and nuclear DNA throughout much of its distribution from Oregon to Baja California. We generated molecular data (mitochondrial cytochrome b and nuclear acid phosphatase V intron [AP5]) for 178 individuals. Examination of these data suggests 2 phylogeographic groups that are largely discordant with the boundaries of 17 currently recognized subspecies. Estimates of pairwise genetic divergence between these groups for cytochrome b are as high as 4.46% uncorrected p. Sequence data for AP5 also indicate a division between populations of M. californicus in northern and southern California. Examination of data from the mitochondrial and nuclear markers together suggests limited gene flow between clades. These data are concordant with other studies that suggest that mountain ranges in California were important in within- and possibly between-species divergence and subsequent contact. The general distribution of each clade, combined with a geographic information system analysis of known capture sites, suggests that clade divergence may be correlated with ecological differences. Our study creates a new framework for reevaluating morphological and ecological diversity in this species, and with more diverse markers, possibly the recognition of 2 species of California voles.

Phylogenetic relationships among individuals of 9 taxa of the Akodon varius group of sigmodontine (tribe Akodontini) rodents from Argentina, Bolivia, and Paraguay were examined using nucleotide sequence data from the entire 1,140 base pairs of the mitochondrial cytochrome-b gene to clarify the evolutionary relationships among lineages. Two individuals of A. iniscatus were included to test proposed relationships with the A. varius group. Maximum-parsimony, minimum-evolution, maximum-likelihood (TVM I G), and Bayesian analyses revealed 2 major clades, 1 composed of Yungas Forest taxa and 1 of non-Yungas (lowlands) taxa, and 8 well-supported terminal clades. The Yungas Forest clade includes A. glaucinus, A. simulator, A. tartareus, and A. varius, which are recognized as distinct species. A. iniscatus was the most basal taxon in the lowlands clade containing A. dayi, A. toba, and A. dolores. Results support the proposed conspecificity of A. dolores and A. molinae, and the relationship within the A. varius group, which had not been clearly defined, is clarified. A. dayi and A. toba were found to be more closely related to A. dolores than to the Yungas Forest clade with which they historically have been associated. A low level of percent sequence divergence between A. toba and A. dolores suggests the need for a closer examination of this relationship, as does the high level of within-clade percent sequence divergence for A. dayi.

We present the most comprehensive systematic study to date of Necromys, a rodent genus distributed in open areas north and south of Amazonia and in Andean grasslands. The study is based on sequences of the cytochrome-b gene that were analyzed by parsimony and Bayesian approaches. The analyses include sequences of 62 specimens from 51 localities from Argentina, Bolivia, Brazil, Colombia, Paraguay, Peru, Uruguay, and Venezuela, representing all but 1 of the species currently recognized in the genus. Necromys was recovered as a monophyletic group and we found a large polytomy at its base that involves 3 lineages. One, represented by the Andean N. lactens, shows a marked phylogeographic pattern. The 2nd clade is formed by N. urichi from the northern grasslands of South America and N. amoenus from the central Andes. Results suggest that each of these taxa may represent more than 1 biological species. The 3rd clade is formed by lowland species found south of Amazonia. Within this clade N. obscurus is sister to the remaining species. Haplotypes recovered from specimens assigned to N. benefactus, N. temchuki, and N. lasiurus form a clade, but these taxa do not form reciprocally monophyletic groups, nor does this large clade possess geographic structure. These genealogical results, discussed in the context of genetic variation, are the basis of taxonomic (e.g., N. benefactus and N. temchuki are regarded as junior synonyms of N. lasiurus) and biogeographic considerations.