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51.
Gordon A. Fox 《Evolutionary ecology》1992,6(6):482-499
Summary Much of life history theory follows from the idea that natural selection acts on the allocation of resources to competing and independent demographic functions. This paradigm has stimulated much research on the life histories of annual plants. Models of whole-plant resource budgets that use optimal control theory predict periods of 100% vegetative and 100% reproductive growth, sometimes with periods of mixed growth. I show here that this prediction follows from the assumption of independence of the competing vegetative and reproductive compartments. The prediction is qualitatively unchanged even after relaxing important simplifying assumptions used in most models. Although it follows naturally from the assumptions of the models, this kind of allocation pattern is unlikely to occur in many plants, because it requires that (1) leaf and flower buds can never simultaneously be carbon sinks; and (2) organs that accompany flowers, such as internodes and bracts, can never be net sources of photosynthate. Thus while resources are doubtless important for annual plants, an exclusively resource-based perspective may be inadequate to understand the evolution of their life histories. Progress in research may require models that incorporate, or are at least phenomenologically consistent with, the basic developmental reles of angiosperms. 相似文献
52.
Gordon A. Fox 《Evolutionary ecology》1992,6(6):500-518
Summary Models of optimal carbon allocation schedules have influenced the way plant ecologists think about life history evolution, particularly for annual plants. The present study asks (1) how, within the framework of these models, are their predictions affected by within-season variation in mortality and carbon assimilation rates?; and (2) what are the consequences of these prediction changes for empirical tests of the models? A companion paper examines the basic assumptions of the models themselves. I conducted a series of numerical experiments with a simple carbon allocation model. Results suggest that both qualitative and quantitative predictions can sometimes be sensitive to parameter values for net assimilation rate and mortality: for some parameter values, both the time and size at onset of reproduction, as well as the number of reproductive intervals, vary considerably as a result of small variations in these parameters. For other parameter values, small variations in the parameters result in only small changes in predicted phenotype, but these have very large fitness consequences. Satisfactory empirical tests are thus likely to require much accuracy in parameter estimates. The effort required for parameter estimation imposes a practical constraint on empirical tests, making large multipopulation comparisons impractical. It may be most practical to compare the predicted and observed fitness consequences of variation in the timing of onset of reproduction. 相似文献
53.
Environmental networks,compensating life histories and habitat selection by white-footed mice 总被引:1,自引:0,他引:1
Douglas W. Morris 《Evolutionary ecology》1992,6(1):1-14
Summary Analysis of 6 years' data on a population of free-living white-footed mice documents both phenotypic and environmental control of litter size. Litter size was positively correlated with maternal body size. Maternal size depended upon both seasonal and annual variation. Paradoxically, the proportion of small versus large litters varied among habitats independently of the effects of body size. The result is an influence of habitat on life history that yields patterns of reproduction and survival opposite to the predictions of demographic theory. The habitat producing the largest litters had a relatively high ratio of adult/juvenile survival. Litter size was small in the habitat where the adult/juvenile survival ratio was smallest. All of these anomalous patterns can be explained through density-dependent habitat selection by female white-footed mice. Life-history studies that ignore habitat and habitat selection may find spurious correlations among traits that result in serious misinterpretations about life history and its evolution. 相似文献
54.
55.
Eville Gorham 《Biogeochemistry》1991,13(3):199-239
The history of how aspects of biology, geology and chemistry came together over the past three centuries to form a separate discipline known as biogeochemistry is described under four major headings: metabolic aspects, geochemical aspects, biogeochemical cycles, and the origin of life. A brief chronology of major conceptual advances is also presented. 相似文献
56.
Ralph J. Larson 《Environmental Biology of Fishes》1991,30(1-2):57-70
Synopsis Seasonal cycles of reserve deposition and utilization in many fishes, amphibians and reptiles alleviate temporal mismatches
of energy supply and demand. Utilization of reserves can be related to maintenance during periods of reduced food supply,
to reproduction, particularly during periods of poor food availability, and to migration. Published data on the seasonal cycles
of reserves and reproduction inSebastes suggest that reserves are important for maintenance during wintertime periods of low food availability. Unlike many other
ectothermic vertebrates, some species ofSebastes deposit fat reserves at the same time as gametogenesis, a pattern consistent with the longevity and iteroparity evident in
the genus. Other species ofSebastes have similar seasonal timing of fat cycles, but since reproduction takes place later in the year, the decline in reserves
during winter coincides with the main period of reproductive activity. The significance of this is not clear. Interspecific
differences in amounts of reserves may be related to geographical differences in the seasonality or abundance of food. Intraspecific
variation in reserves, marked most strongly by allometry of reserves with regard to fish legth, bears further study, since
it may link the proces of sexual maturation and the responses of repeat spawners to variability in food supply and other environmental
factors. 相似文献
57.
David Strayer 《Hydrobiologia》1988,160(2):189-191
The ostracod Cypria turneri has one generation per year in Mirror Lake, New Hampshire. Juveniles hatch in January through May and reach maturity by August. The life history of this ostracod suggests that the turnover rate of the population is low. 相似文献
58.
59.
THE ELM DECLINE AT PAWLAW MIRE: AN ANTHROPOGENIC INTERPRETATION 总被引:2,自引:2,他引:0
60.
FLANDRIAN ENVIRONMENTAL HISTORY OF THE ISLE OF MULL, SCOTLAND. 总被引:4,自引:4,他引:0