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191.
192.
Nicholas M. Kellar Marisa L. Trego Susan J. Chivers Fredrick I. Archer 《Marine Biology》2013,160(12):3113-3124
The northeastern offshore population of the pantropical spotted dolphin (Stenella attenuata) in the eastern tropical Pacific remains listed as depleted under the Marine Mammal Protection Act, and recent estimates of abundance show that recovery has been slow. One hypothesis for the slow recovery is that continued chase and encirclement by the tuna fishery negatively affects reproduction. Insufficient life-history sampling in this region over the last two decades makes traditional estimates of reproductive rates impossible. Here, we examine the current reproductive patterns of these dolphins by measuring blubber progesterone (BP) concentrations in biopsy samples to assess pregnancy state. BP was quantified in 212 biopsies from female offshore spotted dolphins sampled between 1998 and 2003 in the northeastern tropical Pacific, and we found that 11.5 % of the biopsied females (mature and immature) were pregnant. The relationship between pregnancy and fishery exposure was analyzed, and we found that pregnant females were exposed to significantly less fishery activity than non-pregnant ones (p = 0.022), suggesting that the fishery may have an inhibitive effect on pregnancy. Spatial analysis indicated that pregnancy was more aggregated than random (p < 0.05) at a scale up to 180-nmi, with the highest proportion pregnant in the mouth of the Gulf of California, an area with relatively low reported fishery activity. 相似文献
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Despite increasing attention to management of headwater streams as sources of water, sediment, and wood to downstream rivers,
the extent of headwater channels and perennial flow remain poorly known and inaccurately depicted on topographic maps and
in digital hydrographic data. This study reports field mapping of channel head and perennial flow initiation locations in
forested landscapes underlain by sandstone and basalt lithologies in Washington State, USA. Contributing source areas were
delineated for each feature using a digital elevation model (DEM) as well as a Global Positioning System device in the field.
Systematic source area–slope relationships described in other landscapes were not evident for channel heads in either lithology.
In addition, substantial variability in DEM-derived source area sizes relative to field-delineated source areas indicates
that in this area, identification of an area–slope relationship, should one even exist, would be difficult. However, channel
heads and stream heads, here defined as the start of perennial flow, appear to be co-located within both of the lithologies,
which together with lateral expansion and contraction of surface water around channel heads on a seasonal cycle in the basalt
lithology, suggest a controlling influence of bedrock springs for that location. While management strategies for determining
locations of channel heads and perennial flow initiation in comparable areas could assign standard source area sizes based
on limited field data collection within that landscape, field-mapped source areas that support perennial flow are much smaller
than recognized by current Washington State regulations. 相似文献
197.
The attitudes and behaviours of private landholders toward the conservation of a highly transformed and critically endangered
habitat, Overberg Coastal Renosterveld (OCR) (a grassy shrubland of the Cape Floral Region, South Africa) are described. Personal,
semistructured interviews were conducted with landholders, representing 40 properties in the Overberg region, on topics such
as management and utilisation of OCR, the depth of their knowledge of its conservation importance, what they perceive its
value to be, and the extent of their willingness to conserve it. General attitudes toward conservation incentives and provincial
conservation authorities were also investigated. Farmers more willing to conserve were younger, did not necessarily have a
better education, and owned larger farms (>500 ha) with a greater amount of remnant renosterveld (>300 ha) than those less
willing to conserve. Attitudes toward the OCR were largely negative, related to associated problem plants and animals and
the fact that it is believed not to be economically advantageous to retain it. However, farmers are of the opinion that provision
of incentives and increased extension support will provide practical positive inducements for conservation. Landholder education
is paramount to prevent further transformation of critically endangered habitats. The success of private-conservation programs
depends on the attitudes of landowners toward (1) the particular habitat or species to be conserved (which can vary depending
on the type of land use practised and the associated benefits and disadvantages of that habitat type); (2) the conservation
agency or extension officers responsible for that area; and (3) willingness of landowners to participate in a conservation
program, which is influenced by landowner age, farm size, and the amount of natural habitat left to conserve. 相似文献
198.
A Comparison of Spatial and Spectral Image Resolution for Mapping Invasive Plants in Coastal California 总被引:1,自引:1,他引:0
We explored the potential of detecting three target invasive species: iceplant (Carpobrotus edulis), jubata grass (Cortaderia jubata), and blue gum (Eucalyptus globulus) at Vandenberg Air Force Base, California. We compared the accuracy of mapping six communities (intact coastal scrub, iceplant invaded coastal scrub, iceplant invaded chaparral, jubata grass invaded chaparral, blue gum invaded chaparral, and intact chaparral) using four images with different combinations of spatial and spectral resolution: hyperspectral AVIRIS imagery (174 wavebands, 4 m spatial resolution), spatially degraded AVIRIS (174 bands, 30 m), spectrally degraded AVIRIS (6 bands, 4 m), and both spatially and spectrally degraded AVIRIS (6 bands, 30 m, i.e., simulated Landsat ETM data). Overall success rates for classifying the six classes was 75% (kappa 0.7) using full resolution AVIRIS, 58% (kappa 0.5) for the spatially degraded AVIRIS, 42% (kappa 0.3) for the spectrally degraded AVIRIS, and 37% (kappa 0.3) for the spatially and spectrally degraded AVIRIS. A true Landsat ETM image was also classified to illustrate that the results from the simulated ETM data were representative, which provided an accuracy of 50% (kappa 0.4). Mapping accuracies using different resolution images are evaluated in the context of community heterogeneity (species richness, diversity, and percent species cover). Findings illustrate that higher mapping accuracies are achieved with images possessing high spectral resolution, thus capturing information across the visible and reflected infrared solar spectrum. Understanding the tradeoffs in spectral and spatial resolution can assist land managers in deciding the most appropriate imagery with respect to target invasives and community characteristics. 相似文献
199.
OBJECTIVES: To better understand the characteristics of crashes involving senior drivers 65 and older, studies of these crashes were reviewed. METHODS: The review focused primarily on North American studies published since 1990. Studies point to important differences between the crashes of senior drivers and those of younger drivers. RESULTS. Numerous studies have found that senior drivers' crashes are much more likely than crashes of younger drivers to occur at intersections. Senior drivers have particularly high rates of involvement in intersection crashes when they are turning, and even more so when they are turning left. Senior drivers are more likely than younger drivers to have been at fault in these situations, typically because they failed to yield the right-of-way, disregarded the traffic signal, or committed some other traffic violation. Studies also suggest that the extent of overinvolvement of senior drivers in certain types of crashes generally increases with advancing age. CONCLUSIONS. The extent to which the distinctive characteristics of senior drivers' crashes may be due to changing travel patterns associated with aging, or physical or cognitive impairments related to the aging process, is unclear. Further research is needed to understand the pre-crash circumstances of older drivers' intersection crashes. 相似文献
200.
We evaluated the influences of several ecological, biological, and methodological factors on post-fledging survival of a shortgrass prairie bird, the Lark Bunting (Calamospiza melanocorys). We estimated daily post-fledging survival (n = 206, 82 broods) using radiotelemetry and color bands to track fledglings. Daily survival probabilities were best explained by drought intensity, time in season (quadratic trend), ages < or = 3 d post-fledging, and rank given drought intensity. Drought intensity had a strong negative effect on survival. Rank was an important predictor of fledgling survival only during the severe drought of 2002 when the smallest fledglings had lower survival. Recently fledged young (ages < or = 3 d post-fledging) undergoing the transition from nest to surrounding habitat experienced markedly lower survival, demonstrating the vulnerable nature of this time period. Survival was greater in mid and late season than early season, corresponding to our assumptions of food availability. Neither mark type nor sex of attending parent influenced survival. The model-averaged product of the 22-d survival calculated using mean rank and median value of time in season was 0.360 +/- 0.08 in 2001 and 0.276 +/- 0.08 in 2002. Survival estimates that account for age, condition of young, ecological conditions, and other factors are important for parameterization of realistic population models. Biologists using population growth models to elucidate mechanisms of population declines should attempt to estimate species-specific of post-fledging survival rather than use generalized estimates. 相似文献