Philopatry, kin clusters, and genetic relatedness in a population of woodrats (Neotoma macrotis)

Studies of highly kin-structured mammal societies have revealedthe importance of natal philopatry in determining the distributionof genetic variation within populations. In comparison, therelationship between philopatry and genetic diversity withinpopulations of moderately kin-structured societies has receivedrelatively little attention. Previous studies of Neotoma macrotishave suggested that females form distinct kin clusters. Eachkin cluster overlaps spatially with the home range(s) of oneor more males that are not related to each other or to the femaleswith which they are spatially associated. To examine interactionsbetween philopatry and genetic structure in this apparentlymoderately kin-structured species, we characterized spatialand genetic relationships among individually marked femalesin a population of N. macrotis from central coastal California.Our field studies revealed that, contrary to expectation, femalesin this population were not strongly philopatric and spatiallyclustered females were not characterized by high levels of geneticrelatedness. Nevertheless, genetic structure was evident withinthe study population; spatial and genetic distances among femaleswere significantly correlated, suggesting that dispersal patternsinfluenced genetic structure even in the absence of marked femalephilopatry. Because females with overlapping spatial distributionswere not typically closely related to one another, opportunitiesfor the evolution of kin-selected social behavior (e.g., cooperativecare of young) appear to be limited in this population.     

Evaluation of Factors Restricting Distribution of the Endangered Key Largo Woodrat

ABSTRACT We examined a suite of models in an information theoretic framework to identify factors restricting presence of the endangered Key Largo woodrat (Neotoma floridana smalli) throughout its remaining habitat. Models containing variables related to availability of nest sites and mammalian predator abundances were supported by our data. Abundance of natural (large overstory trees) and artificial (rock and debris piles) nest substrate were the most important predictor variables, followed by indices of feral cat and raccoon (Procyon lotor) abundance. We recommend increasing abundance of nest substrate in the short term through addition of artificial nest substrate and in the long term through continued protection of remaining forest habitat.     

Evaluating nest supplementation as a recovery strategy for the endangered rodents of the Florida Keys

The Key Largo woodrat (Neotoma floridana smalli) and Key Largo cotton mouse (Peromyscus gossypinus allapaticola) are federally endangered subspecies endemic to the tropical hardwood hammocks of Key Largo, Florida. Woodrats are considered generalists in habitat and diet, yet a steady decline in natural stick nests and capture rates over the past several decades suggests that they are limited by the availability of nesting habitat due to habitat loss and fragmentation. The more specialized Key Largo cotton mouse appears to rely on old growth hammock, a habitat type that is rare following past land clearing. In 2004, the U.S. Fish and Wildlife Service started building supplemental nest structures to restore habitat quality and connectivity for these endangered rodents, but nest use requires evaluation. We used camera traps and occupancy models to evaluate the factors influencing woodrat and cotton mouse use of the supplemental nests. We detected woodrats at 65 and cotton mice at 175 of 284 sampled nest structures, with co‐occurrence at 38 nests. Woodrat nest use followed a gradient from low nest use in the north to high nest use in the south, which might relate to the proximity of free‐ranging domestic cat (Felis catus) colonies in residential developments. Cotton mouse nest use, however, was related positively to mature hammock and related negatively to disturbed areas (e.g. scarified lands). The two species occurred independently of each other. Stick‐stacking behavior was observed at supplemental nests and, although it was correlated with detection of woodrats, it was not a strong predictor of their occurrence. We suggest that nest supplementation can be an important tool for species recovery as habitat quality continues to improve with succession.     

Phylogeographical structure and regional history of the dusky-footed woodrat, Neotoma fuscipes

The dusky-footed woodrat, Neotoma fuscipes, is a medium-sized rodent that inhabits low elevation woodland habitats along the Pacific coast of North America from Oregon, throughout California and into Baja California. Analyses of mitochondrial sequence variation throughout the distribution reveal substantial phylogeographical structure within N. fuscipes. The major mitochondrial lineages are largely concordant with previously identified morphological subdivisions within the taxon. The geographical distribution of distinct clades suggests that a combination of topographic barriers and the expansion and contraction of suitable habitat during the past 2 million years, especially along particular mountain ranges, have played a major role in the diversification of N. fuscipes. Furthermore, relatively low levels of genetic variation across the northern half of the distribution suggest that dusky-footed woodrats may have only recently expanded into this region.     

A 30000 year record of vegetation dynamics at a semi-arid locale in the Great Basin

Abstract. Plant macrofossils extracted from fossil woodrat (Neotoma spp.) middens at a single locale in the northwestern Great Basin were used to examine vegetation dynamics during the last 30 000 yr. Although the modern assemblage of xeric species at the study site is a recent occurrence, a large proportion of the modern plant taxa near the study locale were also found 12 000 - 30 000 yr BP. The persistence of extant species through time was likely facilitated by within-species genetic diversity and the formation of coenospecies. The diverse topographic and microhabitat features in the northwestern Great Basin also allowed different species to coexist during glacial periods. Changes in species composition occurred during two time intervals: 20 000 - 30 000 and 10 000 - 12 000 yr BP. Vegetation changes during 20 000 - 30 000 yr BP were cyclic; community composition oscillated between two groups of taxa. Vegetation changes between 10 000 - 12 000 yr BP occurred during the Pleistocene-Holocene transition and were largely directional from the Pleistocene assemblages through two transition assemblages to a Holocene assemblage. These changes in species composition generally reflect changes in climate. The presence of relatively mesic species during 10 000 - 30 000 yr BP is consistent with the regional late-Pleistocene climate, and the gradual loss of relatively mesic species during the Holocene parallels the change to a more xeric climate. Contrasted with other areas of North America and Europe, the magnitude of vegetation changes at our study area were relatively small. Furthermore, the persistence of many species through time at this site in the northwestern Great Basin also differs from results at other study sites in North America and Europe. These differences are probably related to land form characteristics and genetic diversity within species.     

Characterization of 18 microsatellite loci for woodrats of the Neotoma lepida group (Rodentia,Cricetidae, Neotominae)

The desert woodrat complex (Neotoma lepida group) is a set of four closely related species occupying the arid lands of western North America. We have developed 18 polymorphic microsatellite loci to analyse the population structure, mating patterns, and hybridization at points of contact between the contiguously allopatric species in the complex.     

Implications of Woodrats and Other Scavengers for Avian Telemetry Studies

Abstract: During 2 years of radiotelemetry research on chukars (Alectoris chukar) in western Utah, USA, we found 28% of retrieved radios (n = 78) in rubbish nests of woodrats (Neotoma spp.). Such movement and disturbance of carcasses and radios by woodrats and other species has implications for radiotelemetry studies. We evaluated spatio-temporal movement of 51 radiocollars attached to chukar carcasses in western Utah. Most (80%) carcasses were scavenged within one week and by the end of 3 weeks 25 (50%) had been retrieved from woodrat middens. Scavenging activity can both obscure important clues needed to identify causes of mortality and bias telemetry studies by delaying onset of mortality signals.     

Mating success of male bushy-tailed woodrats: when bigger is not always better

To determine the factors that regulate mating opportunitiesof male bushy-tailed woodrats (Neotoma cinerea), we used stepwisemultiple regression on measurable morphological and behavioraltraits. DNA fingerprinting was used to determine the paternityof juveniles, allowing mating success (the number of femalesmated with), and reproductive success (the number of offspringfathered) to be quantified. Both measures of male success weresignificantly related to the growth rate of males while reproductivelyactive. The most successful males were those that had higher growthrates, indicating that there is relatively little cost (weightloss) associated with successful mating in male woodrats. Ourfindings demonstrate that although this species is highly sexuallydimorphic, large body size does not influence mating success.In addition, it appears that male mating success cannot be predictedfrom morphological measures and may instead be determined bybehavioral or olfactory cues.     

Field Use of Isoflurane for Safe Squirrel and Woodrat Anesthesia

Abstract: We evaluated a chamber and nose cone method of isoflurane delivery for anesthetizing eastern gray squirrels (Sciurus carolinensis; summer n = 43, winter n = 48) and Allegheny woodrats (Neotoma magister; summer n = 24, winter n = 13) for use when pain or stress was possible from sampling procedures. Mean induction time for squirrels (from beginning of isoflurane administration to safe removal from trap), was 4.63 ± 0.58 minutes. Squirrels awoke more quickly in summer (1.40 ± 0.15 min) than in winter (3.62 ± 0.24 min) after removal of the nose cone. We manually restrained woodrats and administered the nose cone for 0.5 minutes to each animal. Woodrats awoke after 4.76 ± 0.58 minutes following the final dose of isoflurane for both seasons. These methods are useful for working with small mammals in the field and provide an appropriate anesthetic when there may be more than slight pain or distress.