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991.
McNamara JM Houston AI 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2008,363(1490):301-319
Organisms in a seasonal environment often schedule activities in a regular way over the year. If we assume that such annual routines have been shaped by natural selection then life-history theory should provide a basis for explaining them. We argue that many life-history trade-offs are mediated by underlying physiological variables that act on various time scales. The dynamics of these variables often preclude considering one period of the year in isolation. In order to capture the essence of annual routines, and many life-history traits, a detailed model of changes in physiological state over the annual cycle is required. We outline a modelling approach based on suitable physiological and ecological state variables that can capture this underlying biology, and describe how models based on this approach can be used to generate a range of insights and predictions. 相似文献
992.
Juvenile anadromous river herring (alewives, Alosa pseudoharengus, and blueback herring, Alosa aestivalis) spend 3–7 months in freshwater before migrating to the ocean, often exhibiting waves of early and late migrations. Migratory
patterns and associated abiotic and biotic factors were examined for both species migrating in 2003 from Herring River in
Bourne Massachusetts. Migrating herring were grouped into two temporal periods and separated by species. Relationships between
abiotic (water temperature, lunar phase, and precipitation) and biotic (size, age, growth rate, and hatch date) factors and
the timing of out-migration (transition to seawater) were examined. Blueback herring migration coincided with a sharp decrease
in temperature consistent with the time of year. Peaks in alewive migration may reflect adaptive traits maximizing likelihood
of survival through seasonal marginal stream habitats and also avoiding lethal water temperatures in winter. Migrating bluebacks
exhibited a single migratory period (late September–October) which occurred between the early and late migratory pulses of
the alewives. These patterns may also represent distinct migration strategies between early and late migrating alewives and
between the two species of river herring. Early migration may be a mechanism by which factors such as competition and low
food availability are mitigated. In contrast, environmental conditions during the post hatching time of late migrators may
allow for a size maximizing strategy that promotes migration from the nursery area as late as possible. 相似文献
993.
贵阳地区黄刺蛾种群发生规律及防治策略 总被引:1,自引:0,他引:1
黄刺蛾Monema flavescens Walker是贵阳地区的园林树木的重要害虫。种群年生活史同时存在1年1代和1年2代现象,其中1年1代的个体数占大多数,大约占虫口总数的3/4。1世代或2世代的个体越冬后的成虫羽化都集中于5月中、下旬;茧内滞育虫态(含预蛹和蛹)长达8~10个月;寄生性天敌昆虫对越冬代有很强的自然控制力,冬季茧的平均寄生率达34%。成虫的黑化个体占2.75%。室内养虫笼中黄刺蛾产下的卵粒有3种形状。研究期间(2004~2007年)发现黄刺蛾在贵阳的寄主植物有所不同,认为不同年份嗜食寄主植物有明显不同。根据黄刺蛾在当地的发生规律及天敌的自然控制力,提出了相应的防治策略和建议。 相似文献
994.
No lizards are strictly aquatic, but at least 73 species in 11 different families can be considered to regularly utilize freshwater
habitats. There are no aquatic lizards in the Nearctic or Palearctic regions, whereas the Neotropics, Southeast Asia, and
the Indo-Australian Archipelago support the greatest diversity of freshwater forms, particularly in the families Gymnophthalmidae,
Scincidae and Varanidae. A number of larger aquatic lizards are harvested for food and for the reptile skin trade and several
are CITES listed.
Guest editors: E. V. Balian, C. Lévêque, H. Segers & K. Martens
Freshwater Animal Diversity Assessment 相似文献
995.
Thorsten Blenckner 《Hydrobiologia》2008,599(1):177-182
Large lakes currently exhibit ecosystem responses to environmental changes such as climate and land use changes, nutrient loading, toxic contaminants, hydrological modifications and invasive species. These sources have impacted lake ecosystems over a number of years in various combinations and often in a spatially heterogeneous pattern. At the same time, many different kinds of mathematical models have been developed to help to understand ecosystem processes and improve cost-effective management. Here, the advantages and limitations of models and sources of uncertainty will be discussed. From these considerations and in view of the multiple environmental pressures, the following emerging issues still have to be met in order to improve the understanding of ecosystem function and management of large lakes: (1) the inclusion of thresholds and points-of-no-return; (2) construction of general models to simulate biogeochemical processes for a large number of lakes rather than for individual systems; (3) improvement of the understanding of spatio-temporal variability to quantify biogeochemical fluxes accurately; and (4) inclusion of biogeochemical linkages between terrestrial and aquatic ecosystems in model approaches to assess the effects of external environmental pressures such as land-use changes. The inclusion of the above-mentioned issues would substantially improve models as tools for the scientific understanding and cost-effective management of large lakes that are subject to multiple environmental pressures in a changing future. 相似文献
996.
Xin Lu 《Journal of Ornithology》2008,149(1):41-47
Reproduction of Tickell’s Leaf Warblers Phylloscopus affinis was studied in an alpine valley (29°27′N, 91°40′E, 3,980–5,600 m) in the Lhasa mountains, Tibet, at the upper elevational
limit of the species’ breeding range. This species is a summer breeder, and is the only breeding Phylloscopus species in the valley. It nested in all types of shrubby vegetation across the altitudinal range of the valley. Most nests
were placed close to the ground (<1 m) in low thorn bushes. Egg-laying dates fell between late May and early July, most within
the first 3 weeks after the commencement of breeding. Mean clutch size was 4.0 (3–5) and mean brood size at fledging 3.4 (2–5).
Incubation was by the females and lasted 13–14 days, and both parents cared for the young for 14–17 days. Nestlings ready
to leave the nest were 13% heavier than the adults. Overall, 76% of nesting attempts produced at least one fledged young.
Some aspects of the breeding biology of this high-altitude warbler were compared with those of lower-altitude Phylloscopus species. 相似文献
997.
Jaana Kekkonen Heikki Kolunen Hannu Pieti?inen Patrik Karell Jon E. Brommer 《Journal of Ornithology》2008,149(1):59-66
Tawny owl reproduction and offspring sex ratios have been considered to depend on the abundance of small voles. We studied
reproductive performance (laying date, clutch and brood size) during 1995–2003 and offspring sex ratios from 1999 to 2003
in relation to the abundance of small voles and food delivered to the nest in a tawny owl population in southern Finland.
Abundance of small voles (field and bank voles) was based on trappings in the field, and estimates of food delivery was based
on diet analysis of food remains in the nest boxes. In this population, reproductive output was not related to the abundance
of small voles. Analysis of food delivered to the nest showed that the prey weight per offspring varied more than twofold
between years and revealed that this difference was mainly related to the proportion of water voles in the diet. Only the
number of water voles correlated with laying dates. Offspring sex ratios were weakly male biased (55%) but did not differ
from parity. Sex ratios were not related to the abundance of small voles, and we found no evidence that parents delivered
more food to nests with proportionally more offspring of the larger (female) sex. Our results underline the notion that populations
may differ in their sex allocation pattern, and suggest such differences may be due to diet. 相似文献
998.
The Lesser Rhea (Pterocnemia-Rhea-pennata pennata) has a complex reproductive system that combines polygyny with sequential polyandry, in which males build the nest, fully
incubate the eggs and care for the young. As occurs with the Greater Rhea (Rhea americana), Lesser Rhea females sporadically lay eggs outside the nest (‘orphan’ eggs), which are not incubated and thus fail to hatch.
We have examined the orphan eggs of Lesser Rhea over two separate breeding seasons to determine their abundance and fertility
status. During 2004 and 2005, weekly ground searches for orphan eggs were conducted in a wild population of Lesser Rhea in
northwestern Patagonia, Argentina. During these searches the total number of nests, eggs in each nest and orphan eggs laid
outside the nests was recorded. Orphan eggs represented approximately 7% of the total eggs laid in a breeding season. Six
fresh orphan eggs were artificially incubated, four of them being fertile. Orphan eggs seemed to have two origins: some were
laid near deserted nests in the early to mid-reproductive season; others were probably laid by first-time breeders and were
found later in the reproductive season. Given the near-threatened status of the Lesser Rhea, harvesting and artificial incubation
of orphan eggs, which otherwise would be unproductive, may contribute significantly to the conservation of this species, i.e.,
‘recovered’ birds could be used for reintroduction or reinforcement of wild Lesser Rhea populations. 相似文献
999.
Constitutive immune defences correlate with life-history variables in tropical birds 总被引:1,自引:0,他引:1
Lee KA Wikelski M Robinson WD Robinson TR Klasing KC 《The Journal of animal ecology》2008,77(2):356-363
1. It has been suggested that immune defences are shaped by life history and ecology, but few general patterns have been described across species. We hypothesized that 'fast' life-history traits (e.g. short development times, large clutch sizes) would be associated with developmentally inexpensive immune defences, minimizing the resource demands of young animals' immune systems during periods of rapid growth. Conversely, 'slow' life histories should be associated with well developed antibody-mediated defences, which are developmentally costly. 2. We therefore predicted that 'fast-living' species would exhibit higher levels of complement proteins, a component of non-specific innate defence, but lower levels of constitutive ('natural') antibodies. Additionally, we predicted that constitutive immune defences in general would be higher in species with ecological characteristics that might increase exposure to pathogens, such as open nests, omnivorous diets, gregariousness, and closed forested habitat. 3. Across 70 Neotropical bird species, we found a strongly positive relationship between incubation period and natural antibody levels in adult birds, suggesting that longer developmental times might allow the production of a more diverse and/or more reactive adaptive immune system. Complement activity was positively, although weakly, correlated with clutch size, providing some support for the hypothesis that faster-living species rely more on innate defences, such as complement. Unexpectedly, solitary species had higher natural antibody titres than species that frequently join flocks. 4. Our results suggest that, despite probably widespread differences in the intensity and diversity of pathogen exposure, species-level variation in constitutive immune defences is understandable within the context of life-history theory. 相似文献
1000.