Aridlands offer unique opportunities to compare effects of history, evolution, and local geography on assemblage and dynamics of small mammal communities that have severe environmental constraints. Pioneering work in Northern Hemispheric aridlands resulted in paradigms that were assumed to be general. Because the evolutionary history and biogeography of Southern Hemispheric aridlands have been distinct, they offer unusual opportunities to test this assumption. We present 6 papers in this Special Feature that show that Southern Hemispheric aridlands have developed and evolved in many unique directions.

Rooted in the conceptual revolutions of the 1960s and 1970s, contemporary research on the ecology of desert small mammals has progressed markedly in recent decades. Areas of particular emphasis include the role of extrinsic (e.g., climate) compared with intrinsic (e.g., density-dependence) factors on population growth and associated metrics, the role of competition compared with predation in influencing foraging decisions and habitat selection, the influence of small mammals on community structure and composition via consumption and redistribution of plant materials, and as ecological engineers and keystone species (or guilds). Recent emphasis on the energetic basis of assemblage composition is intriguing and warrants further work, and the generality of zero-sum dynamics requires further assessment. Desert systems continue to be the focus of much ecological research, and small mammals remain central figures in understanding the interplay between biotic and abiotic factors and between intrinsic and extrinsic drivers. Small mammals in deserts worldwide exemplify the importance of diverse approaches to ecological research, including local manipulative field experiments, long-term demographic monitoring, and both laboratory and field-based studies on behavioral and foraging ecology.

Early studies of trophic structure from North American deserts set up a paradigm with granivory as a general and integral phenomenon driving the assembly and structure of small mammal communities. This paradigm encouraged many comparative studies seeking support for convergent evolution. A comprehensive review of studies of dietary habits of aridland mammals provided little support for the paradigm. Subsequent research making use of ternary phase diagrams eventually showed that in small mammal communities trophic structure is strongly related to resource use. A synthesis of results across 5 continents shows a gradation in the distribution of trophic groups across regions. The percentage of species in each dietary category from regional pools shows that no one trophic group is dominant in all desert regions studied: South America has 58% herbivores; South Africa, 52% omnivores; North America, 50% granivores; Australia, 49% insectivores; and Eurasia, roughly equal proportions of granivores, herbivores, and omnivores (∼30% each). Seed availability shows substantial overlap across regions but with greater maxima in North America. Granivory appears to be a less important factor in aridlands subject to disturbance regimes, and this could be a result of reduced reliability of seed resources. The impact of fire upon arid environments is one factor common across the Southern Hemisphere but with a lesser effect in the Northern Hemisphere. Fire, rainfall, and particularly extreme climatic events such as El Niño can, at times, outweigh the importance of biotic factors such as competition or predation, emphasizing the importance of resource pulses associated with disturbances. The concepts of history of place and history of lineage can be important factors determining community structure, as has been well demonstrated with the impact of the extensive evolution of the granivorous Heteromyidae in North America and the radiations of marsupials in aridlands of Australia, 2 extremes of the trophic structure shown by desert small mammal communities.

Populations of small mammals often fluctuate dramatically in arid environments, persisting at very low density during drought and erupting briefly but dramatically after rain. We selected 3 species that exhibit such boom and bust dynamics in spinifex grassland in the Simpson Desert, central Australia, and asked how they survive prolonged dry periods when they are scarce or absent from the trapping record. We postulated that animals persist by retreating to small patches of open woodland that are embedded within the grassland matrix and predicted that these patches would provide more food and shelter for small mammals than the surrounding grassland during dry periods but not at other times. We also predicted that capture rates and activity of the study species would be higher, and risk of predation lower, in the woodland than in the grassland during drought, and that after heavy rain the rate of return of small mammals to spinifex grassland would be correlated with proximity to patches of woodland. Sampling provided partial support for these predictions. Some food resources (seeds) were more abundant in woodland patches irrespective of environmental conditions, but others (invertebrates) showed no clear pattern; shelter resources were mostly invariant between habitats and times. Of the 3 study species, only the sandy inland mouse (Pseudomys hermannsburgensis) behaved largely as we had anticipated, but even this species was not confined to woodland during droughts. Both the spinifex hopping-mouse (Notomys alexis) and brush-tailed mulgara (Dasycercus blythi) continued to use grassland more than woodland during drought and nondrought periods, although N. alexis showed a tendency to increase its activity in woodland during dry conditions. Trappability remained relatively constant among species, habitats, and times, indicating that the temporal patterns of habitat use we uncovered were real and not artifacts of changes in animal behavior or susceptibility to capture. We conclude that woodland patches contribute importantly to the persistence of P. hermannsburgensis during droughts, whereas N. alexis and D. blythi either use other unidentified refugia at such times or occur at such low densities in grassland habitat that their chances of being captured are very small.

Small mammal assemblages in the aridlands of the Southern Hemisphere often have wildly fluctuating dynamics. Previous studies have attributed these fluctuations to climate-driven pulses in food resources resulting in the switching of trophic control from bottom-up (food-limited) to top-down (predation-limited) population regulation, and vice versa. In this study we use a meta-analytic approach to evaluate the evidence for the phenomenon of switching trophic control. If shifting trophic control is a unifying phenomenon that shapes small mammal assemblages in arid Australia, we would expect the abundance and species richness of small mammals to increase with increasing primary productivity and the abundance of small mammals to decrease with increasing predator abundances, which lag behind those of small mammals. We tested these predictions using data compiled from 6 unpublished and 2 published data sets containing time series (3–11 years) of small mammal and predator community dynamics. Our analyses provide moderate support for the notion that switching trophic control is a unifying phenomenon shaping small mammal assemblages. Also, our results provide evidence that top-down and bottom-up control are not mutually exclusive phenomena driving desert small mammal assemblages but rather alternative ecosystem states that exist along a rainfall-driven continuum of ecosystem energy flux through time.

Since 1989 we have monitored small mammal populations at a semiarid site in north-central Chile with a large-scale livetrapping grid complex. Selective exclusions of vertebrate predators or putative small mammal competitors, or both, have yielded relatively small or mostly transitory effects, or both, on small mammal population dynamics and plant community composition. During the study period 5 El Niño–high rainfall episodes have occurred lasting 1–3 years. Resident or core small mammals such as Abrothrix olivaceus, Phyllotis darwini, and Octodon degus experience dramatic fluctuations during and following rainfall pulses. Temporary resident or opportunistic species such as Oligoryzomys longicaudatus and A. longipilis disappear from the thorn scrub for varying periods of time. All species persist in more mesic nearby habitats near dry stream courses (aguadas). Since a 3-year high rainfall event in 2000–2002 mean annual rainfall has increased in this region, mainly due to a lack of prolonged droughts. Under these conditions, and building on a qualitative model proposed by Noy-Meir, long-lived species might become more abundant. Changes in the small mammal assemblage are consistent with these predictions; O. degus, a caviomorph rodent with a long life span, now comprises a more constant proportion of the small mammal biomass in the thorn scrub, and we have documented reduced variation in species diversity. Increased rainfall, a predicted consequence of global climate change in this region, might be leading to changes in small mammal assemblage structure and composition and ultimately will result in a more stable, less oscillatory assemblage in the thorn scrub. Additionally, invasive groups such as introduced lagomorphs and ephemeral plants might become more abundant in this community. The long-term consequences of changes in rainfall patterns due to El Niño Southern Oscillations (ENSOs), with important teleconnections to global-scale phenomena, will lead to diverse changes at the community level here.

Much of South America consists of diverse arid and semiarid regions characterized by high mammal endemism as a result of a complex interplay between place and lineage histories. In this review we summarize and highlight several biogeographical and ecological features of the small mammals of South America drylands, with special focus on the Monte Desert biome. We provide information on population characteristics, community structure, food and habitat use, and responses to disturbances. Major findings at different scales include the distinctiveness and high species turnover across South American drylands and Monte Desert ecoregions; synchronous population fluctuations with high variability between years; herbivory and omnivory as dominant trophic strategies; community structure organized through habitat and food segregation; and the importance of a landscape mosaic of grazed and ungrazed areas for maintenance of small and medium-sized mammal diversity.

Understanding factors that influence the distribution and abundance of seed dispersers is important because of the role these species play in maintaining plant communities. The temperate forest of Patagonia has an unusually high frequency of mutualisms, including obligate seed dispersal of a keystone mistletoe (Tristerix corymbosus) by the marsupial Dromiciops gliroides. We examined whether the distribution and abundance of D. gliroides was related to the distribution and abundance of this mistletoe, which is a principal food source, or alternatively, whether other habitat features constrain the distribution and abundance of this marsupial. We conducted field surveys for D. gliroides, mistletoe, and other habitat variables and developed a set of habitat models in which model variables were defined a priori. We found that the distribution of D. gliroides was related to bamboo cover. Bamboo is an important source of nest material and nest sites. However, when the minimum requirement for bamboo cover was met, abundance of D. gliroides tracked abundance and fruit production of mistletoe plants. Habitat constraints imposed by bamboo on D. gliroides have important conservation implications because both anthropogenic and natural processes have significant impacts on bamboo in the temperate forest of Patagonia.

In most colonial species of bats individuals emerge en masse from day roosts each evening to begin foraging. Although some aspects of emergence behavior are understood, one previously unexplored area is the specific order in which individuals emerge. The goal of our research was to determine if big brown bats, Eptesicus fuscus, fitted with passive integrated transponder tags emerge from roosts in buildings each evening in a nonrandom order. We assessed relative and absolute order of emergence to determine if order is concordant across nights and whether individuals consistently emerge in close association with specific roost mates. We found significant concordance in rank order among nights at all roosts. At 5 roosts concordance decreased as time between dates increased. Association rates between individuals were low, and temporal analyses revealed that associations rapidly degraded over time, indicating that bats do not emerge each evening consistently with the same group of roost mates. We discuss how social structure, information transfer, and/or individual energetic needs could be responsible for the observed nonrandom patterns of emergence. Our results suggest that emergence order represents behavioral information that traditionally has been overlooked and that might be useful for characterizing aspects of the ecology and social behavior of bats and other species with cryptic behavior.

I investigated sleeping-site preference in habituated wild Japanese macaques (Macaca fuscata) for each season (254 days total) on predator-free Kinkazan Island, northern Japan, during 2000–2007. I focused on the effectsof nonpredatory, environmental factors (vegetation type, altitude, and topography), to which little attention has been paid. Macaques used 24–79 sleeping sites in each season (227 sites in total, all on the ground). The frequencies of sleeping sites in each season followed a Poisson distribution, except for spring when several sites were used repeatedly. In spring macaques preferred sleeping in Zoysia japonica grassland, where several staple food species (Berberis thunbergii and Zelkova serrata) are abundant in this season. In summer and fall macaques avoided sleeping in high-altitude forest dominated by Fagus spp., and in the latter season they also preferred Zoysia grassland; these preferences likely reflect an avoidance of strong winds rather than the lower food availability at higher altitudes. In winter macaques avoided sleeping in Zoysia grassland, mainly due to the poor food supply. Macaques preferred valleys to ridges in spring and winter, possibly due to greater densities of shelters such as rocks and fallen trees that facilitate energy conservation in the face of strong/cold winds at night. Additional quantitative data for other mammalian species are needed for generalizations to be made about the importance of nonpredatory factors on sleeping-site preferences.

Space use in deserts usually has been considered only along the horizontal dimension; however, vertical structure could be an important variable for habitat segregation among small mammal species. Our study assessed the use of vertical space by small mammals of the Monte Desert by live-trapping animals at different heights. We recorded 1,336 captures of 4 rodent and 1 marsupial species in 27,600 trap nights. All 5 species were captured on the ground and in tree layers, but only the gray leaf-eared mouse (Graomys griseoflavus) and the desert mouse opossum (Thylamys pallidior) used vertical space appreciably. G. griseoflavus used the arboreal space independently of habitat, plant species, or branch diameter, whereas T. pallidior showed a more selective behavior, being present at greater heights and on large-diameter branches of Prosopis trees. All rodent species used lower more than higher parts of arboreal strata. They used vertical space more or only during the dry season when resource availability is low. Our study suggests that vertical structure offers greater opportunities to acquire resources when these are scarce and plays a role in the coexistence of small desert mammals.

We investigated the habitat associations of sea otters (Enhydra lutris) during resting and feeding in an area with a predominately soft- and mixed-sediment benthos supporting infaunal prey populations in a fjord in Alaska during the summer months of 2001–2003. Water depth and benthic sediments were sampled, analyzed, and mapped throughout the bay. Sea otter locations and behavior were determined during boat surveys, and water depth, benthic sediment type, and position in the bay (peripheral compared to central) were determined for each animal location. We used logistic regression analysis to determine whether the use of habitat by sea otters was nonrandom according to these variables. Water depth was the most significant habitat association for feeding behavior, with 39% of feeding dives occurring in water 0–10 m deep. Feeding behavior was not strongly associated with sediment type. Position in the bay was the most significant habitat association for resting behavior, with the majority (63%) of otters resting in the central areas of the bay. Overall, habitat associations were nonrandom, a possible reflection of selective pressure to maximize energy intake, minimize energy expenditure, and avoid terrestrial predators.

We investigated space-use patterns of the West African savanna buffalo (Syncerus caffer brachyceros), a little-studied subspecies occurring at the northern limit of the African buffalo's geographical range. This buffalo generally ranges in small herds (about 45 individuals) and has a low body mass (approximately 400 kg) relative to the Cape buffalo (S. c. caffer). We monitored the movements of 7 breeding herds in W Regional Park (Burkina Faso, Benin, Niger) using global positioning system collars and activity data loggers. Habitat selection was analyzed at both large (interseasonal) and small (intraseasonal) scales in a context where resources are segregated spatially at some times of year. Both biotic (primary production and vegetation types) and abiotic (timing of rainfall and surface water) covariates, and the extent to which neighboring herds shared space, were considered. In the dry season buffalo herds ranged close (within 5.3 ± 2.0 km, mean ± SD) to segments of permanent rivers. At the onset of the monsoon all herds but 1 (which had year-round access to suitable resources) performed a large (35 ± 10 km) directional movement in response to a large-scale gradient of primary production. Spatiotemporal dynamics of forage and water resources thus jointly stimulated interseasonal directional movements and shaped large (335 ± 167 km²) annual home ranges. Furthermore, the establishment of home ranges in the wet season appears to be conditioned by a threshold (about 10%) in the availability of perennial grasses. Habitat-selection analysis at intraseasonal scale also underlines the key role played by perennial grasses for buffaloes. The spatial arrangements of home ranges of neighboring herds also suggest that interherd behavioral avoidance is a high-level constraint on foraging processes. The ability of the African buffalo to cope with contrasting environmental conditions throughout most sub-Saharan ecosystems highlights the high behavioral plasticity of this species.

Movement patterns and habitat selection are influenced by factors such as resource availability, predation risk, and social interactions, and the relative importance of each of these variables can change over an animal's life span. Although ranging patterns and habitat use of adult dolphins have been explored in some areas, relatively little is known about how these behaviors develop as young dolphins mature. This study explored natal philopatry during the juvenile period and behavioral development of ranging and habitat-use patterns in newly independent bottlenose dolphins (Tursiops truncatus) at a long-term study site in Sarasota Bay, Florida. To achieve this we used both long-term sighting data from the resident dolphin community in Sarasota Bay and new information on movements, habitat selection, and social associations collected through boat-based focal-animal behavioral observations on 27 individually identifiable juveniles during 2005–2008. We documented differences in ranging patterns and habitat use of juvenile dolphins by sex, season, and age, and investigated the degree of maternal influence on these behaviors and the functional significance of juvenile groups. We found that male and female dolphins in Sarasota Bay had similar ranging and habitat-selection patterns during the juvenile period. Both sexes exhibited a high degree of philopatry to natal areas as juveniles, with dispersal occurring only rarely by members of either sex. Seasonal and age-related differences in juvenile behavior were evident, and lasting maternal influences on habitat selection and ranging patterns postindependence are apparent. These findings provide some of the 1st information on juvenile marine mammal behavior that contributes to our understanding of resident inshore dolphin behavior throughout the life history and are potentially important to management and conservation efforts.

Muskrats (Ondatra zibethicus) prey on freshwater mussels, many species of which are threatened or endangered. Muskrat populations have been reduced in some streams where North American river otters (Lontra canadensis) were reintroduced, and it has been hypothesized that otter reintroduction could be used as a tool for conservation of mussels. We used occupancy estimation methods to evaluate the ecological relationship between muskrats and otters by collecting presence–absence data based on field sign found at bridge crossings in eastern and central Kentucky. Mean detection probabilities (ps) and occupancy probabilities (ψ;s) for muskrats were 0.692 (SE  =  0.045) and 0.723 (SE  =  0.071) and for otters were 0.623 (SE  =  0.036) and 0.662 (SE  =  0.069), respectively. Otter occupancy was related negatively to distance from release sites, which suggests that the otter population is still expanding its range. A 2-species interaction model indicated that the occupancy by muskrats and river otters was independent, and we conclude that river otter reintroduction would not be an effective strategy for conserving mussels.

It is important to the conservation and management of threatened or endangered carnivores to recognize interspecific interactions that can influence demography or behavior of the species involved. We studied the Eurasian lynx (Lynx lynx), an efficient predator, and wolverine (Gulo gulo), an opportunistic predator and scavenger, that coexist in the reindeer husbandry area in northern Sweden. Both species are major predators on semidomestic reindeer (Rangifer tarandus), but wolverines frequently scavenge ungulate carcasses. We examined the composition and use of food resources by wolverines and in particular the relative importance of lynx-killed reindeer in wolverine diet. We also examined the influence of wolverine scavenging on lynx kill rate. We found that 52% of carcasses visited by wolverines were lynx-killed reindeer, but only 11% were wolverine-killed reindeer. Of all wolverine locations at carcasses, 28% were on lynx-killed and 24% on wolverine-killed reindeer. Remaining locations were mainly on reindeer that died from accidents (23%) or were killed by unknown carnivores (9%). Lynx predation rate on reindeer was nine times higher than that of wolverines. Wolverines scavenged 68% of available lynx-killed reindeer, 29% of which were still being used by lynx at wolverine arrival. Still, wolverine scavenging had a limited influence on lynx kill rate. Time to next kill decreased only when the lynx kill was an adult reindeer in forest; however, most lynx-killed reindeer were found on tundra. Wolverines appear to benefit from coexistence with lynx through increased scavenging opportunities. We suspect that lynx presence reduces wolverine predation on reindeer due to increased scavenging opportunities. These results may have important implications for carnivore management in reindeer husbandry areas.

Raccoons (Procyon lotor), like most carnivores, are nocturnal and secretive and consequently difficult to observe. We used proximity-detecting collars to determine effects of sex, age, and season on contact rate and duration; document patterns of seasonal contact rates by dyad type and determine whether patterns were random; identify dyads that exhibited contact rates significantly greater than expected and document the persistence of these positive associations across seasons; and document frequency of den sharing as an additional measure of positive associations at an urban study site with a high-density raccoon population. Contact rate and duration were affected by dyad type, season, and their interaction. Male–male (MM) dyads exhibited higher contact values than male–female (MF) or female–female (FF) dyads, and contact parameters were greater during winter and spring than summer and autumn. Contact parameters for MM and FF dyads were not affected by age of dyad members, whereas those of MF dyads were affected by age and its interaction with season. MF dyads with older individuals exhibited greater contact parameters, and this effect was greatest during winter. For all dyad types and seasons, except FF dyads during winter, observed distributions of contact rates differed from expected. Males formed groups, with most positively associated dyads persisting across seasons, and females were associated almost exclusively with members of only 1 male group. Some positively associated MF dyads occurred during autumn and continued through spring. Positively associated FF dyads occurred at a lower rate and were ephemeral, seldom lasting more than 1 season. FF and MF dyads exhibited a greater proportion of low-frequency contacts with conspecifics than expected during all seasons, except winter, which may function to maintain amicable relationships between neighbors or reinforce dominance hierarchies and create a framework for more complex social behaviors. Raccoons appear to live in a fission–fusion society, with many short-term acquaintances and a few long-term associations.

Molecular genetics tools have been used recently to investigate aspects of bat biology, including the degree of male- and female-driven gene flow among populations. However, none of this work has focused on the little brown bat (Myotis lucifugus), one of the most common bats in North America. Previous work using mark–recapture suggests that like many mammals, including other temperate vespertilionid bats, gene flow in this species is largely driven by males, whereas females return to the roosts in which they were born to rear pups. To determine if this species displays a pattern of population genetic structure that is consistent with this hypothesis I sampled 182 female M. lucifugus at 12 maternity colonies throughout Minnesota. Using a portion of the mitochondrial gene cytochrome b and 10 polymorphic nuclear microsatellites, I found significant structure among colonies, and population differentiation was slightly higher for the mitochondrial locus. This supports the hypothesis that female M. lucifugus display some degree of natal philopatry, but the inferred female dispersal rate was high. The pattern of structure was complex and demonstrates that unequal gene flow among maternity colonies is occurring and that the co-occurrence of breeding populations within maternity colonies and/or inbreeding could be confounding estimates of population genetic structure among these colonies. The patterns of population genetic structure and natal philopatry imply that both seasonal migration and dispersal by females should be considered as possible factors in the spread of emerging infectious diseases such as white-nose syndrome.

Tree rats of the genus Phyllomys are arboreal rodents endemic to the Brazilian Atlantic Forest. Previous phylogenetic analysis of mitochondrial DNA resulted in a basal polytomy of species in this genus, suggesting rapid speciation. Here we expanded this data matrix by adding specimens and both nuclear and mitochondrial genes. We found 2 basal clades: P. pattoni P. mantiqueirensis; and a clade split into 6 lineages: southern clade ([P. sulinus P. nigrispinus] P. dasythrix); northeastern clade ([P. brasiliensis P. lamarum] P. blainvilii); Phyllomys sp. 1; Phyllomys sp. 2; Phyllomys sp. 3; and P. lundi. The discovery of 3 potentially new species calls for a reevaluation of the taxonomy of Phyllomys species. The combination of nuclear and mitochondrial markers increased the resolution of the tree, although the basal topology is poorly supported. The patterns of geographic distribution and phylogenetic relationships are compatible with parapatric diversification within Phyllomys through ecological gradients of latitude beginning 3.69 million years ago and of altitude 4.34 million years ago.

Thomomys atrovarius is redescribed to include the smooth-toothed pocket gophers that inhabit dry, thornscrub vegetation along the Pacific versant of the Sierra Madre Occidental of Mexico from northern Sinaloa into western Durango, northwestern Jalisco, and western Nayarit. Molecular analyses of mitochondrial and nuclear DNA sequences (including historical samples from museum skins) show high levels of genetic differentiation between T. atrovarius and T. umbrinus of the Sierra Madre Occidental (15.4% cytochrome-b divergence) and Mexican Central Plateau (16.9% divergence). Roughly coincident morphometric and genetic gaps divide T. atrovarius into 2 subspecies, T. a. parviceps in the north and T. a. atrovarius in the south, with probable intergradation in between. Most specimens of T. atrovarius, especially those of the southern subspecies, are distinguished easily from specimens of T. bottae and T. umbrinus on the basis of fur texture, and an analysis of cranial morphometrics shows little overlap between T. atrovarius and other Thomomys clades in Mexico. An analysis of niche parameters shows significantly different climate envelopes for T. atrovarius compared with other species of Thomomys, and a biogeographical review suggests that T. atrovarius has ancestral affinities to the south of its current distribution. A synonymy of T. atrovarius and a key to the currently recognized species of Thomomys in mainland Mexico are provided.

Paleontology can provide a deep-time dimension to observations about recent reactions of small mammals to climate change. Obtaining this perspective for voles (Microtus), a common and important constituent of North American mammal communities, has been difficult because species identification based on their dental remains is problematic. Here I demonstrate that geometric morphometrics and discriminant analyses can use commonly fossilized dental features to identify the 5 extant species of Microtus in California: M. californicus (California vole), M. longicaudus (long-tailed vole), M. montanus (montane vole), M. oregoni (Oregon vole), and M. townsendii (Townsend's vole). Analyses of landmarks on the lower 1st molar (m1) provide more accurate identification than those of the 3rd upper molar (M3), and it is important to use jackknife misidentification metrics to assess the precision of discriminant analyses. Addition of semilandmark curves on m1 does not improve accuracy. The utility of these techniques is demonstrated by identifying Microtus specimens from 2 California fossil localities, Pacheco 2 and Prune Avenue, which provides the first evidence for extralimital presence of M. longicaudus at both localities. The presence of M. longicaudus at these low-elevation sites indicates that pronounced geographic range shifts in this species that have been observed in California over the last 100 years also occurred during previous climate changes. Eventually it might be possible to ascertain whether current range shifts are exceeding those that typified responses to past climate changes.

Geometric morphometrics is a powerful tool for the study of morphological variation that possesses numerous advantages over the more traditional approach based on linear measurements. We analyzed skull morphology, comparing traditional with geometric morphometrics, of 3 different developmental pathways in Mastomys natalensis (Rodentia: Muridae) from a single population. During early development growth patterns were influenced by environmental factors, specifically rainfall pattern, consistent with previous reports that growth trajectories vary according to the amount and distribution of rain. Results confirmed that early growth rate is one of the main determinants of size and shape differences in the skull in the 3 developmental pathways (generation types) of M. natalensis. Other factors, such as food quality and consistency, also could play an important role. Overall, geometric morphometrics appeared more sensitive than the traditional method in detecting variation in skull morphology, but both approaches led to very comparable conclusions. Phenotypic plasticity is an alternative explanation to local adaptations for ecogeographical morphological variation.

Teeth move continuously in the occlusal direction after they have approached the occlusal plane, which is considered a compensatory mechanism for loss of tooth crown by wear, although quantitative data have been inadequate. To clarify phenotypic correlation of tooth eruption and wear 10 populations of wild sika deer (Cervus nippon) in Japan were investigated. Mandibles, with ages assigned by cementum annuli of incisor roots, were used to estimate molar wear rate and eruption timing. Molar eruption status was assessed by observation of the buccal side of molars and coded as 3 ordinal levels according to the appearance of a cervical line (a boundary between molar crown and root). Logistic regression of the eruption status revealed that eruption timing of the lower 3rd molar (m3) was significantly different among populations (P < 0.0001) and correlated with m3 wear rate; faster molar wear resulted in faster molar eruption (P < 0.01). Eruption timing of lower 1st (m1) and 2nd (m2) molars did not show significant correlation with wear rate, possibly due to less variation in eruption timing in m1 and m2 than for m3. These findings indicate that the compensatory response of molar eruption occurs for m3 in accordance with wear mediated by environments.