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排序方式: 共有235条查询结果,搜索用时 359 毫秒
211.
The interaction of predation pressure with lethal and sublethal effects of temefos (Abate®) an organophosphorous insecticide, were studied in field populations of Uca pugnax (S.I. Smith). Changes in fiddler crab population densities were followed in open-marsh temefos-treated and untreated test plots and in treated and untreated plots which were caged over to reduce predation by marsh birds. Temefos significantly reduced the population density of U. pugnax in the open test plots but not in the caged plots. These results indicate that temefos has a primarily sublethal effect on the crabs, the effect becoming lethal only after interaction with avian predation. Evidence from the presence of a time-lag effect in the population decrease, from a calculated predation index, and from laboratory studies reported elsewhere of behavioral alteration by temefos also supports the conclusion that temefos primarily impairs the escape response of U. pugnax: this leads to increased predation and subsequently to a decreased fiddler crab population. Such studies of sublethal effects of toxicants and field studies of interactions of lethal and sublethal effects of such compounds with natural population dynamics of affected species are necessary to evaluate possible effects of toxicants on populations. 相似文献
212.
M. M. Webster J. Goldsmith A. J. W. Ward P. J. B. Hart 《Behavioral ecology and sociobiology》2007,62(2):273-280
The structure of social animal groups can be dynamic, characterized by high rates of group fission and fusion. Despite this,
group composition is often well ordered by factors such as species, body size and by numerous other phenotypic traits. Research
in shoaling fishes has revealed that individuals refine group membership decisions still further and are capable of assimilating
chemical cues pertaining to recent habitat and prey use by prospective group mates, preferring to associate with others whose
recent resource use history closely matches their own. In this study, we firstly examined the dynamics of the formation and
breakdown of these preferences, revealing that they can be acquired and replaced in a matter of just a few hours. Using such
cues enables individuals to accurately assess the resource use of conspecifics, allowing them to indirectly sample the local
environment while reducing the chances of acquiring outdated information that can precipitate maladaptive behaviors. Secondly,
we found that shoals composed of individuals with shared recent habitat use history were more cohesive compared to those where
the constituent individuals differed in recent habitat use. Increased shoal cohesion may reduce predation risk, and could
enhance the ability of individuals to detect and use social information. 相似文献
213.
214.
The mechanisms and functions of mixed-species shoaling were investigated in two sympatric species of cyprinids, the chub and the European minnow, from the river Wharfe where they comprised approximately 70% of all year 0+ fish over a 20-year survey. Chub preferred conspecific shoals over heterospecific ones with olfactory cues being more important than visual ones for shoal choice. This preference was consistent with measurements of length:flank area ratios and length:weight ratios which suggest that both species are similar in appearance. When presented with mixed-species shoals, chub increased the percentage time spent with stimulus shoals with increasing proportions of conspecifics. Feeding experiments suggest that the preference for conspecific shoals is driven by interspecific competition (with minnows out-competing similar-sized chub) and the oddity effect. The importance of this work in the context of species assortment in free-ranging shoals is discussed. 相似文献
215.
K. M. Mullen C. D. Harvell A. P. Alker D. Dube E. Jordán-Dahlgren J. R. Ward L. E. Petes 《Marine Biology》2006,149(6):1355-1364
Knowledge of host range and mechanisms of disease resistance is fundamental to predicting impacts and spread of marine diseases. Prevalence of signs of aspergillosis, caused by the terrestrial fungus Aspergillus sydowii, was assessed in the Yucatan among three species of sea fan: Gorgonia ventalina, G. cf. mariae, and G. flabellum. The Yucatan is unusual in that ranges of all three sea fan species overlap at many sites along a cline of increasing depth, allowing us to evaluate potential causes of differing prevalence among species. Signs of aspergillosis were observed in all the three species. However, the prevalence of infection in G. cf. mariae, a deep-water species, was consistently low even at sites where G. ventalina was common and had moderate levels of infection. Because G. cf. mariae is a relatively small-stature sea fan, we compared the prevalence of signs in G. cf. mariae to a subset of comparatively sized G. ventalina. G. ventalina had a significantly higher prevalence of aspergillosis, indicating that size does not explain the lower prevalence in G. cf. mariae. Prevalence of disease signs on the shallow-water G. flabellum was also significantly higher than G. cf. mariae, but did not differ from G. ventalina. To test the hypothesis that higher chemical resistance accounts for the low prevalence of disease in G. cf. mariae, we measured the response of A. sydowii in culture to antifungal extracts from each sea fan species. Significantly lower fungal growth rates on extracts of G. cf. mariae than G. ventalina support the hypothesis that G. cf. mariae is more chemically resistant to aspergillosis. When comparing sea fan disease across different regions of the Yucatan, we detected significantly higher prevalence in G. ventalina near Akumal than further north near Cozumel and Puerto Morelos. In Akumal, there was a strong positive correlation between sea fan size and disease, with the largest fans showing the highest prevalence and severity in all three species. In addition, prevalence of aspergillosis in G. ventalina was density-dependent in Ak. 相似文献
216.
Paul I. Ward 《Behavioral ecology and sociobiology》1993,32(5):313-319
Summary The influence of the female on the process of sperm storage and use was examined. Copula duration, the condition of the female and whether or not a copula terminated naturally influenced the number of spermathecae (of three) in which once-mated females stored sperm. Females stored more sperm the larger their mate and the sperm from larger males were stored more unevenly amongst the spermathecae than were those from smaller males. Double-mated females had sperm in fewer spermathecae the larger the second of their mates and these spermathecae tended to be the ones which lay together within the female. The P2 values over three successive clutches were constant and sperm precedence was complete when the larger male was second to mate but began low and increased over subsequent clutches when the smaller male mated second. These results suggest females prefer, and are able, to use the sperm of larger males to fertilise their eggs. It is proposed that multiple spermathecae in Diptera have evolved to give females better control over offspring paternity. 相似文献
217.
Robert C. Ward 《Journal of the American Water Resources Association》1996,32(4):673-680
ABSTRACT: Water quality monitoring, as a function of society's efforts to manage the environment, is the contact mechanism that management and the public has with the actual water quality in the environment. Water quality monitoring has been studied extensively for many years to ensure that it produces information about water quality conditions. Current efforts to reduce government spending will have negative impacts on those government functions deemed to be non-responsive to the needs of the public. How well does water quality monitoring inform taxpayers about the status and trends in water quality conditions in the United States? This paper reviews a number of past efforts to “improve” water quality monitoring, discusses barriers to such improvement, and suggests ways that monitoring can be made more accountable for the information it should be producing for public understanding of water quality conditions. In particular, the need for standardization in data analysis and reporting of information to the public, is highlighted. 相似文献
218.
C. Rhett. Jackson Christopher A. Sturm Jason M. Ward 《Journal of the American Water Resources Association》2001,37(6):1533-1549
ABSTRACT: We evaluated changes in channel habitat distributions, particle‐size distributions of bed material, and stream temperatures in a total of 15 first‐or second‐order streams within and nearby four planned commercial timber harvest units prior to and following timber harvest. Four of the 15 stream basins were not harvested, and these streams served as references. Three streams were cut with unthinned riparian buffers; one was cut with a partial buffer; one was cut with a buffer of non‐merchantable trees; and the remaining six basins were clearcut to the channel edge. In the clearcut streams, logging debris covered or buried 98 percent of the channel length to an average depth of 0.94 meters. The slash trapped fine sediment in the channel by inhibiting fluvial transport, and the average percentage of fines increased from 12 percent to 44 percent. The trees along buffered streams served as a fence to keep out logging debris during the first summer following timber harvest. Particle size distributions and habitat distributions in the buffered and reference streams were largely unchanged from the pre‐harvest to post‐harvest surveys. The debris that buried the clearcut streams effectively shaded most of these streams and protected them from temperature increases. These surveys have documented immediate channel changes due to timber harvest, but channel conditions will evolve over time as the slash decays and becomes redistributed and as new vegetation develops on the channel margins. 相似文献
219.
Eric Pyle Robert C. Ward Graham McBride Beat Huser 《Journal of the American Water Resources Association》2001,37(4):783-793
ABSTRACT: New Zealand is one of the first countries in the world to enshrine the concept of watershed management in law, through institutional arrangements and the Resource Management Act of 1991 ‐ a law constructed on a watershed management legacy begun in 1941. This paper outlines the development of New Zealand's Resource Management Act (as it applies to water management) and the lessons that have been learned in its implementation. 相似文献
220.
Rochelle Constantine Debbie Steel Judy Allen Megan Anderson Olive Andrews C. Scott Baker Peta Beeman Daniel Burns Jean-Benoît Charrassin Simon Childerhouse Michael Double Paul Ensor Trish Franklin Wally Franklin Nick Gales Claire Garrigue Nadine Gibbs Peter Harrison Nan Hauser Amanda Hutsel Curt Jenner Micheline-Nicole Jenner Greg Kaufman Anne Macie David Mattila Carlos Olavarría Adrian Oosterman David Paton Michael Poole Jooke Robbins Natalie Schmitt Peter Stevick Alden Tagarino Kirsten Thompson Juney Ward 《Marine Biology》2014,161(5):1087-1093
Understanding the dynamics of population recovery is particularly complex when an organism has multiple, remote breeding and feeding grounds separated by one of the longest known migration routes. This study reports on the most comprehensive assessment of humpback whale (Megaptera novaeangliae) movements between remote Antarctic waters south of New Zealand and east Australia (EA), and the migratory corridors and breeding grounds of Australia and Oceania. A total of 112 individual whales were identified; 57 from microsatellites and 61 by fluke with 23 % (n = 26) matched to sites outside Antarctica. Despite large datasets from other southern regions being included in the comparison, the whales were predominantly linked to EA (n = 24). Only two matches to the Oceania catalogues directly north was surprising; therefore the primary feeding grounds of these endangered whales still remain unknown. The confirmation of the Balleny Islands as an important feeding ground for EA whales could provide an insight into reasons behind the rapid recovery of this population. Determining the feeding grounds of Oceania’s whales may explain whether prey energetics or migration length are limiting factors to their recovery and will allow an understanding of future ecosystem changes in these whales. 相似文献