James G. Hallett

Conservation genetics of the fisher (Martes pennanti) based on mitochondrial DNA sequencing

Translocation of animals to re‐establish extirpated populations or to maintain declining ones has often been carried out without genetic information on source or target populations, or adequate consideration of the potential effects of mixing genetic stocks. We consider the conservation status of the fisher (Martes pennanti) and evaluate the potential genetic consequences of past and future translocations on this medium‐sized carnivore by examining population variation in mitochondrial control‐region sequences. We sampled populations throughout the fishers range in North America including five populations unaffected by translocations and two western populations that had received long‐distance translocations. Twelve haplotypes showed little sequence divergence. Haplotype frequencies differed significantly among subspecies and between populations within subspecies. Analysis of molecular variance (amova) and neighbour‐joining analyses of haplotype relationships revealed population subdivision similar to current subspecies designations, but which may reflect an isolation‐by‐distance pattern. Populations in Oregon and in Montana and Idaho received several translocations and each showed greater similarity to the populations where translocations originated than to adjacent populations. Additional sequences obtained from museum specimens collected prior to any translocations suggest historical gene flow among populations in British Columbia, Washington, Oregon, and California. Anthropogenic impacts in that region have greatly reduced and isolated extant populations in Oregon and California. Future translocations may be necessary to recover populations in Washington and portions of Oregon and California; our results indicate that British Columbia would be the most appropriate source population.

Competition and Habitat Selection: Test of a Theory Using Small Mammals

Two hypotheses about community structure were examined for the small mammals occupying a wet grassland in SW North Dakota, USA. First, we ask whether competition occurs between members of this community. Then, an hypothesis concerning the relationship between competitive ability and habitat selection is addressed. Relative densities of Microtus pennsylvanicus, Zapus hudsonius, Spermophilus tridecemlineatus, and Peromyscus maniculatus were determined by live-trapping in July and September 1976. Species interactions and patterns of habitat occupancy were examined using regression analysis. Microtus, Zapus, and Spermophilus were each competitively dominant to Peromyscus. No competitive effects were observed among Microtus, Zapus and Spermophilus. The four species differed markedly in habitat utilization. Microtus, Zapus, and Spermophilus were each specialized on different habitats. Peromyscus was a habitat generalist and its distribution was determined primarily by competitive interactions with the other species.

Comparison of population estimators for medium-sized mammals

We compared direct enumeration, the closed population models of program CAPTURE, the Jackknife estimator, Chaos (1987) moment estimator, and the Jolly-Seber open population model in estimating abundance of Virginia opossums (Didelphis virginiana) and raccoons (Procyon lotor). For 57 months, we used mark-recapture and radio-telemetry methods to study populations in a 600-ha watershed in northern Virginia. Three hundred and sixty-one opossums and 407 raccoons were captured 2,187 times, and 156 individuals were radiocollared. We used the radio-tracking data to examine departures from the assumptions of the various estimators and to obtain an independent estimate of population size as a means for comparing the other estimators. This RADIO estimate is based on the probability of capturing animals known to be in the study area. Direct enumeration typically underestimated population size relative to the RADIO estimates. Movements by animals to outside the study area resulted in direct enumeration occasionally overestimating population size. Low probability of capture in a trapping period resulted in a pronounced negative bias of the estimates produced by the selected model of program CAPTURE. Jackknife estimates were more correlated with the RADIO estimates than those from CAPTURE, but daily capture probabilities were extremely low. Chaos moment estimates were poorly correlated with RADIO and had the highest coefficient of variation of all estimators. Jolly-Seber estimates were highly correlated with RADIO and exhibited the least deviation from RADIO for both species. Goodness-of-fit tests of the Jolly-Seber model indicated that the models assumptions were violated in some months. The cause and direction of the bias could be ascertained for these months. The standard errors of RADIO, CAPTURE, Jackknife, Chao, and Jolly-Seber estimates were all highly correlated with estimate size

Considerations for measuring genetic variation and population structure with multilocus fingerprinting

Multilocus DNA fingerprinting provides a cost‐effective means to rapidly assay genetic variation at many loci. While this makes the technique particularly attractive for studies of evolution and conservation biology, fingerprint data can be difficult to interpret. Measurement errors inherent with the technique force investigators to group similar‐sized alleles (bands) into discrete bins before estimating genetic parameters. If too little error is accounted for in this process homologous alleles will not be grouped in a common bin, whereas overestimated error can produce bins with homoplasic alleles. We used simulations and empirical data for two frog species (Rana luteiventris and Hyla regilla) to demonstrate that mean band‐sharing (S¯xy) and heterozygosity (H¯E) are a function of both bin width and band profile complexity (i.e. number and distribution of bands). These estimators are also sensitive to the number of lanes included in the analysis when bin width is wide and a floating bin algorithm is employed. Multilocus estimates of H¯E were highly correlated with S¯xy and thus provide no additional information about genetic variation. Estimates of population subdivision (F^ and Φ^ST) appeared robust to changes in bin size. We also examined the issue of statistical independence for band‐sharing data when comparisons are made among all samples. This analysis indicated that the covariance between band‐sharing statistics was very small and not statistically different from zero. We recommend that sensitivity analyses for bin size be used to improve confidence in the biological interpretation of multilocus fingerprints, and that the covariance structure for band‐sharing statistics be examined.

The structure and stability of small mammal faunas

SummaryI examined questions about the local and global stability and resilience characteristics of six small mammal faunas and their relationship to connectance, average interaction strength, community covariance, and indirect competitive pathways. Community matrices estimated elsewhere were used in the analyses. The faunas had from three to nine species and represented several habitat types. The following properties were observed: (1) all community matrices were globally stable, (2) return rates to equilibrium were generally maximized, and (3) competitive interactions were strictly hierarchical. Global stability resulted from a reduction in connectance with increasing species and not from structural characteristics (i.e., community covariance). Average interaction strength did not change with the number of species in these faunas. Increased resilience was due largely to reduced community covariance. Two of the six faunas showed some evidence for indirect pathways, but this appeared to be artifactual. Randomizations of the original community matrices showed that indirect pathways have a high probability of occurrence. Monte Carlo simulations indicated that the probability of indirect pathways increases with increasing number of species or magnitude of competition. These results bring into question previous observational studies invoking indirect competitive pathways. Communities without indirect pathways have a special linear hierarchical structure. This structure has greater resilience than when indirect pathways are present. The observed patterns in community structure are discussed with regard to current theories of habitat selection.