A life history study of the Snake River plains endemic Lepidium papilliferum (Brassicaceae)

Lepidium papilliferum is an ephemeral species that occupies ""slick spot"" microhabitats in the matrix of sagebrush steppe vegetation of the southwestern Snake River plains, Idaho, USA. We related population demographic data collected from 1993 to 1996 to on-site precipitation data on the Orchard Training Area west of Boise. We also carried out field seed-retrieval and in situ seed bank studies. We found that L. papilliferum has a dual life history strategy. A fraction of each cohort sets seed as summer annuals, while the remaining plants remain vegetative and potentially biennial. Surviving biennials flower and set seed along with the annual cohort of the following year. The switch to flowering as an annual appears to be based on threshold rosette size. Probability of survival to flowering was much lower for biennials than for annuals of the same cohort, but surviving biennials sometimes had enhanced seed production. The summerdry environment of the Snake River plains combined with the slick spot habitat has apparently selected for a primarily summer annual life cycle for this species. Seeds were highly dormant at dispersal and were not responsive to dormancybreaking cues. Those from a given cohort of L. papilliferum remained viable in the soil for at least 11 years. This persistent seed bank provides a buffer against extinction in sequences of years when seed production is low or absent. Estimated seed bank size varied from near zero for a heavily disturbed site that formerly supported the species to 18 viable seeds · dm -2 for an extant population in high-quality habitat. Management for population preservation for L. papilliferum should focus on protecting the seed bank from destruction caused by livestock trampling and other anthropogenic disturbances.     

Drosophila pseudoobscura (Diptera: Drosophilidae) of the Great Basin IV: a release experiment at Bryce Canyon

Some populations of Drosophila pseudoobscura in the Great Basin have very little genetic variation for third chromosome inversion gene arrangements. These populations are essentially monomorphic for the Arrowhead gene arrangement. At Bryce Canyon, Utah, individuals with other gene arrangements (Standard, Pikes Peak, and Treeline) were released and their frequencies monitored. One generation after release, the released arrangements had increased in frequency from 0.7% to almost 10%. After overwintering, the arrangement frequencies were not statistically different from the prerelease samples. The samples did demonstrate a low-level retention of the released Pikes Peak arrangement. The decline in the released arrangements was probably the result of large population size at Bryce Canyon and the bottleneck effects of overwintering. The results do not seem consistent with a model of the released arrangements having a lowered fitness.     

Size, structure, and habitat characteristics of populations of Braya humilis var. humilis (Brassicaceae): an alpine disjunct from Colorado

Size, structure, and habitat characteristics were studied in three populations of Braya humilis var. humilis (C. A. Meyer) Robins, in Gray & Wats. (Brassicaceae), a small, herbaceous perennial of the alpine tundra in central Colorado. There was a significant association between numbers of reproductive, juvenile, and seedling individuals and population location. Plant size within reproductive, juvenile, and seedling size classes varied significantly among three populations. Plots containing Braya had significantly lower total plant cover, a different set of dominant plant species, more rock, bare ground, and less litter than plots without Braya . Braya appears to be restricted to calcareous substrates that experience a moderate level of disturbance, such as solifluction lobes and abandoned roads. Populations are small despite the existence of much potential habitat. Population studies are necessary for active conservation management of Braya .     

The effects of radiation from uranium mill tailings on Tradescantia

To assess the potential hazard from radioactive wastes, a plant with known radiosensitivity, Tradescantia clone 02, was grown in radioactive soil obtained from uranium mill tailings. The levels of radiation on these tailings varied from 0.03mR/hr (background) to a maximum of 3.00 mR/hr. Tradescantia grown in soil with a radiation level greater than 0.10 mR/hr evidenced significantly reduced reproductive integrity and fecundity, as measured by the number of stunted hairs per stamen, pollen viability, and numbers of somatic mutations. Based on these data, the radioactivity from uranium mill tailings has the potential to alter normal plant succession due to its detrimental effect on any species that is relatively radiosensitive.     

Temperature-mediated changes in seed dormancy and light requirement for Penstemon palmeri (Scrophulariaceae)

Penstemon palmeri is a short-lived perennial herb colonizing disturbed sites in semiarid habitats in the western USA. In this study seed was harvested from six native and four seeded populations during two consecutive years. In laboratory germination trials at constant 15 C, considerable between-lot variation in primary dormancy and light requirement was observed. Four weeks of moist chilling (1 C) induced secondary dormancy at 15 C. Cold-induced secondary dormancy was reversed by one week of dark incubation at 30 C. This warm incubation treatment also reduced the light requirement of unchilled, after-ripened seed. Fluctuations in dormancy and light requirement of buried seeds have been linked to seasonal changes in soil temperature. Penstemon palmeri germination responses to temperature appear to be similar to those of facultative winter annuals.     

Winter stomach contents of South Dakota badgers

Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 st1\:*{behavior:url(#ieooui) } /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} Stomach contents of 33 hunter and trapper killed badgers, Taxidea taxus, from northeastern South Dakota were examined during the 1980–81 fur season. Mammal prey species made up the bulk of the ingested food, followed by plant materials. Approximately 40 percent of stomach contents were mammals, 35 percent were of plant origin, 10 percent were birds, 10 percent were insects, while the remainder was mostly inorganic materials. Little significant difference was found in variety of food items consumed by each sex. South Dakota badgers are opportunistic foragers in the wintertime when food is scarce. Individual food items are usually taken in quantity when encountered by badgers.     

Influences of sex and weather on migration of mule deer in California

I examined differences by sex and influences of weather on timing and patterns of migration of Rocky Mountain mule deer ( Odocoileus h. hemionus ) in the eastern Sierra Nevada, California, during 1984-87. Deer initiated spring migration from the winter range at about the same time in all years and made extensive use of holding areas at intermediate elevations. Radio-telemetered deer showed strong fidelity to summer ranges over as many as four years. Fall weather produced different patterns of fall migration. Storms during October produced a pulsed migration, in which most animals mmiiggiraatteedd to the winter range during or soon after the storm; in a year without a storm, fall migration was gradual. Despite the influence of storms on the pattern of fall migration, the median date of fall migration by females did not vary over years; however, among males it was later in a year without fall storms.     

Coordination of branch orientation and photosynthetic physiology in the Joshua tree ( Yucca brevifolia )

Despite the profusion of light in deserts, morphological adaptations to increase light interception are common among desert plants. We studied branch orientation and related physiological parameters in the Mojave Desert Joshua tree, Yucca brevifolia (Agavaceae). Azimuth and inclination were measured on all leaf rosettes of 44 Y. brevifolia trees. Interception of solar radiation was modeled for leaves in hypothetical rosettes facing due south and due north in December, March, and June. Carbon isotope discrimination, nitrogen content, and conductance of water vapor were measured in leaves from north- and south-facing rosettes. Rosette azimuths were nonrandom; rosettes predominantly faced southeast. North-facing rosettes were more steeply inclined than those facing south. The preponderance of south-facing rosettes reduces self-shading and increases interception of solar radiation during the winter-spring growth period. Stomatal conductance was higher for leaves in south-facing than in north-facing rosettes. Nevertheless, discrimination against 13 C was less in leaves of south-facing rosettes, indicating that average intercellular CO 2 concentration was also lower. South-facing whorls had higher leaf nitrogen content. Greater allocation of nitrogen to leaves in south-facing whorls probably results in those leaves having a greater photosynthetic capacity than their north-facing counterparts. Orientation of rosettes to increase interception of sunlight during the period most favorable for photosynthesis, coupled with allocation of nutrients to maintain a higher photosynthetic capacity in those rosettes, should significantly increase whole-plan carbon gain in Y. brevifolia .     

Timing, distribution, and abundance of kokanees spawning in a Lake Tahoe tributary

We counted kokanee spawners and carcasses every 1-7 days from mid-September through mid-November in 1991 and 1992 in Taylor Creek, a tributary to Lake Tahoe, California-Nevada. Less than 1% of the spawning run entered Taylor Creek before flow from Fallen Leaf Lake was increased on 2 October 1991; in 1992 the peak occurred on 30 September or 1 October after flows increased on 29 September. In both years spawners concentrated in the middle three of five stream reaches below the impassable Fallen Leaf Lake dam. From tab-and-recovery experiments, the average longevity of male spawners in the stream was 3.5 days in 1991 and 2.8 days in 1992, whereas the average female longevity was 2.0 days in 1991 and 2.3 days in 1992. Observed carcasses accounted for less than 10% of spawners counted, suggesting removal by scavengers or high predation on prespawners. An estimated 1928 males and 1309 females spawned in 1991, and 8021 males and 8712 females spawned in 1992. Our estimate of 3237 spawners in 1991 compared favorably to our estimate of 3520 ± 1474 prespawners staging in Lake Tahoe in mid-September. An index of kokanee abundance in Lake Tahoe has historically been based on 1-day surveys every 1 November since 1960; however, estimated total spawner abundance was 19 times higher than the annual index of 158 spawners in 1991, 141 times higher than the index count of 100 spawners in 1992. The index count and mean fork lengths of spawners (278 ± 10 mm [2 SE] for males, and 248 ± 3 mm for females) in 1991 and 1992 were the lowest on record.     

Influence of prey movement on the aim of predatory strikes of the western rattlesnake ( Crotalus Viridis )

The purpose of this study was to determine whether the western rattlesnake ( Crotalus viridis ) aims its predatory strike at the head/thorax region of mice primarily on the basis of cues related to the direction of prey movement. We hypothesized that when rattlesnakes strike at anesthetized, backward-moving mice, most strikes would be aimed at the forward-most-moving region, i.e., the posterior (abdomen/tail) region of prey. However, most mice were struck in the anterior (head/thorax) region, implying that the visual-infrared image of mice, rather than directional movement, guides the aim of predatory strikes.