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排序方式: 共有172条查询结果,搜索用时 234 毫秒
31.
32.
Tommy Kristensen Anders Isberg Nielsen Anders Isak J?rgensen Kim N. Mouritsen Henrik Glenner Jens T. Christensen J?rgen Lützen Jens T. H?eg 《Marine Biology》2012,159(9):2015-2023
Male crabs infected by parasitic barnacles (Rhizocephala) are known to be morphologically feminized. Here, we investigate morphological chances in green crabs, Carcinus maenas, induced by the parasitic barnacle Sacculina carcini. Infected males acquire a broader, longer and segmented abdomen, fringed with marginal setae. Copulatory appendages and pereopods are reduced in length, and the chelae become smaller. The feminization show great individual variation. Males with scars from lost externae, the parasites reproductive organ situated under the abdomen, are less modified than males carrying an externa, and the feminization is more pronounced in smaller than in larger males. No super-feminization is evident in female crabs that remain morphologically unaffected by infection. The protective value of a parasitically induced enlargement of the male abdomen may constitute an adaptation that increases parasite longevity. The additional effects on male morphology are viewed as pleiotropic side effects of the main adaptive value of enlarging the abdomen. 相似文献
33.
Physical and biological disturbances are ecological processes affecting patterns in biodiversity at a range of scales in a variety of terrestrial and aquatic systems. Theoretical and empirical evidence suggest that effects of disturbance on diversity differ qualitatively and quantitatively, depending on levels of productivity (e.g., the dynamic equilibrium model). In this study we contrasted the interactive effects between physical disturbance and productivity to those between biological disturbance and productivity. Furthermore, to evaluate how these effects varied among different components of marine hard-substratum assemblages, analyses were done separately on algal and invertebrate richness, as well as richness of the whole assemblage. Physical disturbance (wave action) was simulated at five distinct frequencies, while biological disturbance (grazing periwinkles) was manipulated as present or absent, and productivity was manipulated as high or ambient. Uni- and multivariate analyses both showed significant effects of physical disturbance and interactive effects between biological disturbance and productivity on the composition of assemblages and total species richness. Algal richness was significantly affected by productivity and biological disturbance, whereas invertebrate richness was affected by physical disturbance only. Thus, we show, for the first time, that biological disturbance and physical disturbance interact differently with productivity, because these two types of disturbances affect different components of assemblages. These patterns might be explained by differences in the distribution (i.e., press vs. pulse) and degree of selectivity between disturbances. Because different types of disturbance can affect different components of assemblages, general ecological models will benefit from using natural diverse communities, and studies concerned with particular subsets of assemblages may be misleading. In conclusion, this study shows that the outcome of experiments on effects of disturbance and productivity on diversity is greatly influenced by the composition of the assemblage under study, as well as on the type of disturbance that is used as an experimental treatment. 相似文献
34.
Michael Tobler Dennis Hasselquist Henrik G. Smith Maria I. Sandell 《Behavioral ecology and sociobiology》2010,64(5):717-727
Hormone-mediated maternal effects play an important role in the formation of a differentiated phenotype. They have been shown
to influence a wide array of offspring traits, both early in life and in adulthood. One important offspring trait that is
under the influence of maternal androgens is the immune system. In birds, a growing number of studies show that yolk androgens
modulate immune function during the chick stage. However, there is a lack of knowledge regarding long-term effects of prenatal
androgens on offspring immunity. In this study, we therefore investigated the influence of prenatal testosterone (T) on several
measures of immunity in fledgling and adult zebra finches (Taeniopygia guttata). Cell-mediated immune response (towards phytohaemagglutinin, PHA) of fledglings hatching from control eggs was negatively
related to brood size, whereas there was no such association for fledglings hatching from eggs with experimentally elevated
T levels (T fledglings). Male control fledglings showed reduced mass gain compared to female control fledglings within 24 h
after the PHA injection. This pattern was reversed in T fledglings. Total antibody levels in fledglings were not affected
by egg treatment. Neither cell-mediated immunity nor total antibody levels in sexually mature zebra finches were influenced
by egg treatment. However, there was an immuno-enhancing effect of elevated egg T on both primary and secondary humoral immune
responses toward diphtheria and tetanus antigens in ca 5 and 7 month old zebra finches. In addition, the covariation between
different immune components differed between T and control offspring, suggesting that egg treatment may have altered the potential
trade-offs between different parts of the immune system. Our results suggest that prenatal androgens could be an important
factor contributing to individual variation in immune function even in adulthood. 相似文献
35.
Functional response diversity is defined as the diversity of responses to environmental change among species that contribute to the same ecosystem function. Because different ecological processes dominate on different spatial and temporal scales, response diversity is likely to be scale dependent. Using three extensive data sets on seabirds, pelagic fish, and zooplankton, we investigate the strength and diversity in the response of seabirds to prey in the North Sea over three scales of ecological organization. Two-stage analyses were used to partition the variance in the abundance of predators and prey among the different scales of investigation: variation from year to year, variation among habitats, and variation on the local patch scale. On the year-to-year scale, we found a strong and synchronous response of seabirds to the abundance of prey, resulting in low response diversity. Conversely, as different seabird species were found in habitats dominated by different prey species, we found a high diversity in the response of seabirds to prey on the habitat scale. Finally, on the local patch scale, seabirds were organized in multispecies patches. These patches were weakly associated with patches of prey, resulting in a weak response strength and a low response diversity. We suggest that ecological similarities among seabird species resulted in low response diversity on the year-to-year scale. On the habitat scale, we suggest that high response diversity was due to interspecific competition and niche segregation among seabird species. On the local patch scale, we suggest that facilitation with respect to the detection and accessibility of prey patches resulted in overlapping distribution of seabirds but weak associations with prey. The observed scale dependencies in response strength and diversity have implications for how the seabird community will respond to different environmental disturbances. 相似文献
36.
Partial migration is a common phenomenon among many animals and occurs in many types of ecosystems. Understanding the mechanisms behind partial migration is of major importance for the understanding of population dynamics and, eventually, ecosystem processes. We studied the effects of food availability on the seasonal partial migration of cyprinid fish from a lake to connected streams during winter by the use of passive telemetry. Fish with increased access to food were found to migrate in higher proportion, earlier in the season, and to reside in the streams for a longer period compared to fish with decreased access to food. Furthermore, fewer unfed migrants returned to the lake, indicating higher overwinter mortality. Our results suggest that individual fish trade off safety from predation and access to food differently depending on their body condition, which results in a condition-dependent partial migration. Hence, our main conclusion is that individual decision-making is based on assessment of own condition which offers a mechanistic explanation to partial migration. Moreover, this may be of high importance for understanding population responses to environmental variation as well as ecosystem dynamics and stability. 相似文献
37.
Rosana Moraes Sara Elfvendahl Henrik Kylin Sverker Molander 《Ambio-人类环境杂志》2003,32(4):258-263
1998年11月、1999年3月和2000年元月分别在巴西雨林自然保护区河流的水体、沉积物和鱼体中检测杀虫剂残毒,每种杀虫剂浓度与基于急性毒性测试的生态毒理基准进行了比较,并且还与规定标准进行比较,以确定它们对水生生物和人类潜在影响的程度.在所有的7个调查地点都检测出杀虫剂及其代谢产物,在水体以及沉积物样品中检测出总共27种杀虫剂及其代谢物的残毒,鱼类富集其中某些最持久稳固的残毒.水体和沉积物中检测出的杀虫剂残毒浓度表明水生生物保护的问题需要引起重视,水体中的几种杀虫剂含量超过了巴西以及欧盟当局规定的指标,表明对人类的健康也有影响. 相似文献
38.
本文通过在东非进行的一系列野外和实验室试验,研究了丰富的红树林十足类螃蟹迈纳新胀蟹(Neosarmatium meinerti)对落叶的清理.在地势高的海榄雌(Avicennia meinerti)潮间带,螃蟹掩埋了所有红树林林区海底的落叶,而且会在2小时内平均消耗其中的67%. 相似文献
39.
Plants have different strategies to cope with herbivory, including induction of chemical defences and compensatory growth.
The most favourable strategy for an individual plant may depend on the density at which the plants are growing and on the
availability of nutrients, but this has not been tested previously for marine plant–herbivore interactions. We investigated
the separate and interactive effects of plant density, nutrient availability, and herbivore grazing on the phlorotannin (polyphenolic)
production in the brown seaweed Ascophyllum nodosum. Seaweed plants grown at low or high densities were exposed either to nutrient enrichment, herbivorous littorinid gastropods
(Littorina obtusata), or a combination of nutrients and herbivores in an outdoor mesocosm experiment for 2 weeks. Seaweeds grown at a low density
tended to have higher tissue nitrogen content compared to plants grown at a high density when exposed to elevated nutrient
levels, indicating that there was a density dependent competition for nitrogen. Herbivore grazing induced a higher phlorotannin
content in plants grown under ambient, but not enriched, nutrient levels, indicting either that phlorotannin plasticity is
more costly when nutrients are abundant or that plants responded to herbivory by compensatory growth. However, there were
no significant interactive or main effects of plant density on the seaweed phlorotannin content. The results indicate that
plants in both high and low densities induce chemical defence, and that eutrophication may have indirect effects on marine
plant–herbivore interactions through alterations of plant chemical defence allocation. 相似文献
40.
High levels of DDT residues and hexachlorocyclohexanes (HCHs) were found in soil, well water, and surface water around a collapsed pesticide storage shed at Vikuge Farm, Tanzania. Residues of DDT and HCHs were found at three soil depths down to 50 cm. Surface soil samples contained up to 28% total DDT and 6% total HCH residues. Water samples had concentrations of up to 30 microg L(-1) of organochlorine pesticides. Other compounds detected were aldrin, azinphos-methyl, carbosulfan, gamma-chlordane, chlorprofam, heptachlor, hexazinone, metamitron, metazachlor, pendimethalin, and thiabendazole. Although the visible remains of pesticides have been removed, the remaining soil is itself hazardous waste and poses a risk to the environment and the inhabitants of the surrounding villages. These findings show the necessity to follow up the environmental situation at former storage sites of obsolete stocks of pesticides, and that the environmental problems are not necessarily solved by removing the visible remains. 相似文献