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921.
Genetic variation was examined in Helonias bullata , a threatened perennial plant species that occurs in isolated wetland habitats. Fifteen populations representing the species' geographic range were sampled. Genetic diversity was low for the species ( H es = 0.053) as well as within populations ( H ep = 0.029). Of the 33 allozyme loci examined, 11 (33%) were polymorphic, while on average only 12.8% (4) of the loci were polymorphic within populations. The number of alleles per polymorphic locus was 2.36 for the species and averaged 2.09 across populations. For every genetic parameter calculated, variation in H. bullata was lower than that typically found for narrowly distributed plant species. The lowest levels of genetic diversity were found in northern areas that were colonized following the last glacial epoch. The number of genotypes detected per population ranged from three to 21, with a mean of 13 for this clonally reproducing species. We found a relatively high proportion of total genetic diversity (30.6%) among populations and a significant correlation (p < 0.002) between genetic distance and geographic distance. Genetic drift phenomena appear to play a major role in the population genetics of this species. Anomalously, several populations that appeared most limited in size and vigor were genetically most variable, perhaps because they represent older, relictual populations. Life-history characteristics of H. bullata coupled with low levels of genetic diversity and the degradation and disappearance of wetlands threaten the existence of this species. 相似文献
922.
Regina Keller Jason A. Tetro V. Susan Springthorpe Syed A. Sattar 《Food and environmental virology》2010,2(2):97-100
Human noroviral infections are generally more common during winters in temperate regions. This study used a murine norovirus
(MNV) as a human norovirus surrogate to test the effect of water temperature (4 and 25°C) on virus survival and its susceptibility
to the levels of monochloramine (~1.89 ppm) to terminally disinfect municipally treated potable waters. The titre of MNV remained
essentially unchanged for at least 24 h in raw river water at both temperatures. The virus became undetectable in <2 h in
monochloramine-containing samples held at 25°C, but its titre remained virtually unaltered at 4°C (P < 0.05) under the same conditions. These findings strongly suggest that water temperature can influence the norovirucidal
activity of monochloramine and its possible impact on the seasonality of outbreaks of noroviral infections. 相似文献
923.
Sharks are apex predators, and their evolutionary success is in part due to an impressive array of sensory systems, including
vision. The eyes of sharks are well developed and function over a wide range of light levels. However, whilst close relatives
of the sharks—the rays and chimaeras—are known to have the potential for colour vision, an evolutionary trait thought to provide
distinct survival advantages, evidence for colour vision in sharks remains equivocal. Using single-receptor microspectrophotometry,
we measured the absorbance spectra of visual pigments located in the retinal photoreceptors of 17 species of shark. We show
that, while the spectral tuning of the rod (wavelength of maximum absorbance, λmax 484–518 nm) and cone (λmax 532–561 nm) visual pigments varies between species, each shark has only a single long-wavelength-sensitive cone type. This
suggests that sharks may be cone monochromats and, therefore, potentially colour blind. Whilst cone monochromacy on land is
rare, it may be a common strategy in the marine environment: many aquatic mammals (whales, dolphins and seals) also possess
only a single, green-sensitive cone type. It appears that both sharks and marine mammals may have arrived at the same visual
design by convergent evolution. The spectral tuning of the rod and cone pigments of sharks is also discussed in relation to
their visual ecology. 相似文献
924.
Power-law relationships are among the most well-studied functional relationships in biology. Recently the common practice of fitting power laws using linear regression (LR) on log-transformed data has been criticized, calling into question the conclusions of hundreds of studies. It has been suggested that nonlinear regression (NLR) is preferable, but no rigorous comparison of these two methods has been conducted. Using Monte Carlo simulations, we demonstrate that the error distribution determines which method performs better, with NLR better characterizing data with additive, homoscedastic, normal error and LR better characterizing data with multiplicative, heteroscedastic, lognormal error. Analysis of 471 biological power laws shows that both forms of error occur in nature. While previous analyses based on log-transformation appear to be generally valid, future analyses should choose methods based on a combination of biological plausibility and analysis of the error distribution. We provide detailed guidelines and associated computer code for doing so, including a model averaging approach for cases where the error structure is uncertain. 相似文献
925.
The electrosensory capabilities of wobbegong sharks are of particular interest, partly because very little is known about
their behavioural ecology and specifically because of their unusual ambush predatory strategy and benthic lifestyle. While
several biological functions of electroreception have been proposed, less consideration has been given to the functional significance
of interspecific differences in the morphology and topographic distribution of the ampullary organs. The morphology of the
ampullary organs was examined in four species of wobbegong shark, and the distribution of electroreceptive pores was mapped
in two species. The ampullary systems of wobbegongs are similar in morphology to other marine elasmobranchs. The number of
alveoli per ampullae is not significantly different between the four species; however, differences are seen between ampullary
cell size in some species. Ampullary pore distribution patterns are relatively unique, with the majority of pores occurring
on the dorsal region of the head. Wobbegongs feed primarily on demersal teleost fishes, and as the benthic and well-camouflaged
wobbegong remains motionless, these fish could be easily detected by the dorsal pores when swimming within range. 相似文献
926.
Pollution of water resources by phosphorus (P) is a critical issue in regions with agricultural and urban development. In this study, we estimated P inputs from agricultural and urban sources in 24 catchments draining to the Central Valley in California and compared them with measured river P export to investigate hydrologic and anthropogenic factors affecting regional P retention and export. Using spatially explicit information on fertilizer use, livestock population, agricultural production, and human population, we calculated that net surface balances for anthropogenic P ranged from -12 to 648 kg P km yr in the early 2000s. Inorganic P fertilizer and manure P comprised the largest fraction of total input for all but two catchments. From 2000 to 2003, a median of 7% (range, -287 to 88%) of net annual anthropogenic P input was exported as total P (TP). Yields (kg P km yr) of dissolved inorganic P (DIP), dissolved organic P, particulate P, and TP were not significantly related to catchment-level, per area anthropogenic P input. However, there were significant relationships between mean annual P concentrations and P input from inorganic fertilizers and manure due to the concentration of agricultural land near catchment mouths and regional variation in runoff. Catchment-level P fertilizer and manure inputs explained 4 to 23% more variance in mean annual DIP and TP concentrations than percent of catchment area in agriculture. This study suggests that spatially explicit estimates of anthropogenic P input can help identify sources of multiple forms of P exported in rivers at management-relevant spatial scales. 相似文献
927.
In seasonal environments, vertebrates are generally thought to time their reproduction so offspring are raised during the peak of food abundance. The mismatch hypothesis predicts that reproductive success is maximized when animals synchronize their reproduction with the food supply. Understanding the mechanisms influencing the timing of reproduction has taken on new urgency as climate change is altering environmental conditions during reproduction, and there is concern that species will not be able to synchronize their reproduction with changing food supplies. Using data from five sites over 24 years (37 site-years), we tested the assumptions of the mismatch hypothesis in the Tree Swallow (Tachycineta bicolor), a widespread aerial insectivore, whose timing of egg-laying has shifted earlier by nine days since the 1950s. Contrary to the mismatch hypothesis, the start of egg-laying was strongly related to food abundance (flying insect biomass) during the laying period and not to timing of the seasonal peak in food supply. In fact, food abundance generally continued to increase throughout the breeding season, and there was no evidence of selection based on the mistiming of laying with the seasonal peak of food abundance. In contrast, there was selection for laying earlier, because birds that lay earlier generally have larger clutches and fledge more young. Overall, initial reproductive decisions in this insectivore appear to be based on the food supply during egg formation and not the nestling period. Thus, the mismatch hypothesis may not apply in environments with relatively constant or abundant food throughout the breeding season. Although climate change is often associated with earlier reproduction, our results caution that it is not necessarily driven by selection for synchronized reproduction. 相似文献
928.
Chazdon RL Chao A Colwell RK Lin SY Norden N Letcher SG Clark DB Finegan B Arroyo JP 《Ecology》2011,92(6):1332-1343
We develop a novel statistical approach for classifying generalists and specialists in two distinct habitats. Using a multinomial model based on estimated species relative abundance in two habitats, our method minimizes bias due to differences in sampling intensities between two habitat types as well as bias due to insufficient sampling within each habitat. The method permits a robust statistical classification of habitat specialists and generalists, without excluding rare species a priori. Based on a user-defined specialization threshold, the model classifies species into one of four groups: (1) generalist; (2) habitat A specialist; (3) habitat B specialist; and (4) too rare to classify with confidence. We illustrate our multinomial classification method using two contrasting data sets: (1) bird abundance in woodland and heath habitats in southeastern Australia and (2) tree abundance in second-growth (SG) and old-growth (OG) rain forests in the Caribbean lowlands of northeastern Costa Rica. We evaluate the multinomial model in detail for the tree data set. Our results for birds were highly concordant with a previous nonstatistical classification, but our method classified a higher fraction (57.7%) of bird species with statistical confidence. Based on a conservative specialization threshold and adjustment for multiple comparisons, 64.4% of tree species in the full sample were too rare to classify with confidence. Among the species classified, OG specialists constituted the largest class (40.6%), followed by generalist tree species (36.7%) and SG specialists (22.7%). The multinomial model was more sensitive than indicator value analysis or abundance-based phi coefficient indices in detecting habitat specialists and also detects generalists statistically. Classification of specialists and generalists based on rarefied subsamples was highly consistent with classification based on the full sample, even for sampling percentages as low as 20%. Major advantages of the new method are (1) its ability to distinguish habitat generalists (species with no significant habitat affinity) from species that are simply too rare to classify and (2) applicability to a single representative sample or a single pooled set of representative samples from each of two habitat types. The method as currently developed can be applied to no more than two habitats at a time. 相似文献
929.
Maki BE Sibley KM Jaglal SB Bayley M Brooks D Fernie GR Flint AJ Gage W Liu BA McIlroy WE Mihailidis A Perry SD Popovic MR Pratt J Zettel JL 《Journal of Safety Research》2011,42(6):473-485
Problem
Falling is a leading cause of serious injury, loss of independence, and nursing-home admission in older adults. Impaired balance control is a major contributing factor.Methods
Results from our balance-control studies have been applied in the development of new and improved interventions and assessment tools. Initiatives to facilitate knowledge-translation of this work include setting up a new network of balance clinics, a research-user network and a research-user advisory board.Results
Our findings support the efficacy of the developed balance-training methods, balance-enhancing footwear, neuro-prosthesis, walker design, handrail-cueing system, and handrail-design recommendations in improving specific aspects of balance control.Impact on Knowledge Users
A new balance-assessment tool has been implemented in the first new balance clinic, a new balance-enhancing insole is available through pharmacies and other commercial outlets, and handrail design recommendations have been incorporated into 10 Canadian and American building codes. Work in progress is expected to have further impact. 相似文献930.
Christopher William Woodall Michael C. Amacher William A. Bechtold John W. Coulston Sarah Jovan Charles H. Perry KaDonna C. Randolph Beth K. Schulz Gretchen C. Smith Borys Tkacz Susan Will-Wolf 《Environmental monitoring and assessment》2011,177(1-4):419-436
For two decades, the US Department of Agriculture, Forest Service, has been charged with implementing a nationwide field-based forest health monitoring effort. Given its extensive nature, the monitoring program has been gradually implemented across forest health indicators and inventoried states. Currently, the Forest Service??s Forest Inventory and Analysis program has initiated forest health inventories in all states, and most forest health indicators are being documented in terms of sampling protocols, data management structures, and estimation procedures. Field data from most sample years and indicators are available on-line with numerous analytical examples published both internally and externally. This investment in national forest health monitoring has begun to yield dividends by allowing evaluation of state/regional forest health issues (e.g., pollution and invasive pests) and contributing substantially to national/international reporting efforts (e.g., National Report on Sustainability and US EPA Annual Greenhouse Gas Estimates). With the emerging threat of climate change, full national implementation and remeasurement of a forest health inventory should allow for more robust assessment of forest communities that are undergoing unprecedented changes, aiding future land management and policy decisions. 相似文献