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871.
872.
873.
B. Norton 《Annals of science》2013,70(6):537-553
This paper traces the background to R. A. Fisher's multi-factorial theory of inheritance. It is argued that the traditional account is incomplete, and that Karl Pearson's well-known pre-Fisherian objections to the theory were in fact overcome by Pearson himself. It is further argued that Pearson's stated reasons for not accepting his own achievement has to be seen as a rationalization, standing in for deeper-seated metaphysical objections to the Mendelian paradigm of a type not readily discussed in a formal scientific paper. The apparent, post-Fisherian, continued acceptance of Pearson's objections is presented as an interesting problem for the historian and sociologist. 相似文献
874.
Thirteen Speyeria nokomis apacheana (Edwards) (Nymphalidae) populations from the western Great Basin were assayed for isozyme variability using starch-gel electrophoresis. Eight of the 25 presumptive isozyme loci analyzed were found to be polymorphic. Collections made in 1991and 1992 allowed for between-year comparisons of heterozygosity and the estimation of effective population size for five of the sampled populations. Speyeria nokomis apacheana populations exhibit lower mean heterozygosity levels than other nymphalids. This may be attributed to genetic drift in apparently isolated populations with small effective sizes. 相似文献
875.
We examined diets of Western Burrowing Owls ( Athene cunicularia hypugaea ) based on contents of pellets and large prey remains collected year-round at burrows in each of the 3 regions in south central Nevada (Mojave Desert, Great Basin Desert, and Transition region). The most common prey items, based on percent frequency of occurrence, were crickets and grasshoppers, beetles, rodents, sun spiders, and scorpions. The most common vertebrate prey was kangaroo rats ( Dipodomys spp.). True bugs (Hemiptera), scorpions, and western harvest mice ( Reithrodontomys megalotis ) occurred most frequently in pellets from the Great Basin Desert region. Kangaroo rats ( Dipodomys spp.) and pocket mice (Perognathinae) were the most important vertebrate prey items in the Transition and Mojave Desert regions, respectively. Frequency of occurrence of any invertebrate prey was high (>80%) in samples year-round but dropped in winter samples, with scorpions and sun spiders exhibiting the steepest declines. Frequency of occurrence of any vertebrate prey peaked in spring samples, was intermediate for winter and summer samples, and was lowest in fall samples. With the possible exception of selecting for western harvest mice in the Great Basin Desert region, Western Burrowing Owls in our study appeared to be opportunistic foragers with a generalist feeding strategy. 相似文献
876.
Dispersal plays an important role in the population dynamics of many carnivores, yet little information exists about the dispersal and movement patterns of swift foxes ( Vulpes velox ). We radio-collared and monitored 68 swift foxes for dispersal at 2 study sites in northwestern Texas from January 2002 to April 2004. Dispersal distance for juveniles (13.1 ± 0.3 km, s ), adults (10 ± 4.7 km) and transients (25.4 ± 9.1 km) did not differ by age class ( F = 1.49, df = 2, P = 0.24) or sex ( F = 0.23, df = 1, P = 0.63) but differed by study site ( F = 4.72, df = 1, P = 0.04). Mean dispersal distance from private ranches (PR) was greater than from National Grasslands (NG). Peak dispersal occurred during October– November (13 individuals) and January–February (7 individuals). Dispersal direction was influenced by land-use practices (i.e., toward rangelands and away from anthropogenic features). Direction of dispersal among foxes that occupied the NG was uniform ( n = 16, P = 0.08), whereas foxes from PR dispersed in a northwesterly direction ( n = 18, P ≤ 0.001) away from a town and croplands. Three resident adult foxes made extraterritorial movements. Distances of these movements ranged from 0.2 km to 11.4 km. Distance of extraterritorial movements did not differ by sex ( F = 0.05, P = 0.83), nor by duration of movement ( F = 1.11, P = 0.32). Knowledge of movement distances and patterns is important for conservation and protection of swift foxes and their habitats. 相似文献
877.
American Falls Reservoir in southeastern Idaho is an irrigation reservoir used as an inland feeding stopover by many shorebird species. Six exclosure experiments were conducted during the 1990 drawdown period to investigate shorebird predation impact on benthic macroinvertebrate populations. The study sites differed in sediment composition, sediment slope, invertebrate densities, and shorebird abundance. Shorebird predation significantly affected invertebrate densities in only 1 of 6 experiments (Aberdeen Mouth). This site had higher sediment slope and a lower water recedence than other study sites, resulting in concentration of shorebird predation on a small area of newly exposed sediment. Shorebird predation had the greatest impact on medium size class chironomid larvae at Aberdeen Mouth. Our results suggest that inland sites such as American Falls Reservoir represent viable shorebird habitat and may be managed to insure consistent prey availability. Drawdown rate, sediment slope, invertebrate densities, and shorebird abundance are all important factors influencing shorebird predation. Monitoring shorebird abundance and predation impact on invertebrate densities may help in manipulating drawdown rate to provide adequate shorebird prey. Management of inland sites for shorebird use may become more important in the future as human encroachment in coastal areas continues. 相似文献
878.
Estimates of site potential for Douglas-fir based on measured site indexes in 450 stands are compared between 10 southwestern habitat types. Significant differences in site potential are found between the habitat types studied. 相似文献
879.
Forests of the southern Rocky Mountains are punctuated by persistent meadows called parks that are dominated by grasses and forbs. In an attempt to elucidate the maintenance of subalpine parks in the Gunnison Basin, Colorado, soil texture and tree morphology differences along 60-m transects spanning the forest-park ecotone were studied in 6 representative parks. Seedling survivorship, percent seed germination, and soil moisture available to plants were also studied along one of the transects in Willow Park. Soil analyses revealed 40% more silt and significantly less sand and clay in all 6 parks ( P P = 0.011), with 54% more water in forest than in park soils. Measures of growth rate obtained from tree height, dbh, and age were significantly higher nearer the ecotone ( P P = 0.002). These results suggest that stress of mature Engelmann spruce ( Picea engelmannii ) and lodgepole pine ( Pinus contorta ) is an unlikely explanation of park maintenance. P. engelmanii percent seed germination and seedling survivorship were significantly higher in the forest than in the park ( P < 0.001). This may be largely due to the more severe seedling microclimate observed in the park. Results indicate that limited seedling establishment is primarily responsible for maintenance of subalpine parks in the Gunnison Basin. 相似文献
880.
The Shoshone sculpin ( Cottus greenei ) is found only in springs of the Thousand Springs formation along the Snake River in Idaho. In 1983 a small population of Shoshone sculpin was introduced into an unnamed spring in the Thousand Springs formation in an attempt to increase the range of the species. Previously, the only sculpin in that spring was the mottled sculpin ( Cottus bairdi ). The Shoshone sculpin was able to establish itself and become the predominant fish within 8 years. 相似文献