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11.
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
12.
Peter A. Abrams 《Evolutionary ecology》1992,6(1):56-72
Summary When foraging has costs, it is generally adaptive for foragers to adjust their foraging effort in response to changes in the population density of their food. If effort decreases in response to increased food density, this can result in a type-2 functional response; intake rate increases in a negatively accelerated manner as prey density increases. Unlike other mechanisms for type-2 responses, adaptive foraging usually involves a timelag, because foraging behaviours do not often change instantaneously with changes in food density or risks. This paper investigates predator-prey models in which there are explicit dynamics for the rate of adaptive change. Models appropriate to both behavioural and evolutionary change are considered. Both types of change can produce cycles under similar circumstances, but under some evolutionary models there is not sufficient genetic variability for evolutionary change to produce cycles. If there is sufficient variability, the remaining conditions required for cycles are surprisingly insensitive to the nature of the adaptive process. A predator population that approaches the optimum foraging strategy very slowly usually produces cycles under similar conditions as does a very rapidly adapting population. 相似文献
13.
Alpina Begossi 《Human ecology: an interdisciplinary journal》1992,20(4):463-475
The community of Gamboa is located on Itacuruçá Island, Sepetiba Bay (State of Rio de Janeiro, Brazil) and includes 26 families, mostly of artisanal fishermen who use paddled or motor canoes, and encircling nets for fishing. In this study, predictions from optimal foraging theory (patch model), in particular of patch residence time, are compared to the observed behavior of fishermen on fishing trips. Fishermen's strategies differ depending on their intended prey. They spend more time in patches and use fewer patches for shrimp than for fish. Gamboa's fishermen tend to leave a patch later than predicted by the model. The difficulty in evaluating stock availability, the comparatively few patches available for shrimp, and the competitive aspects of fishing contribute to the explanation of this behavior. 相似文献
14.
K. C. Malhotra T. S. Vasulu Y. S. Dikshitulu R. C. Gupta 《International Journal of Anthropology》1992,7(1):23-40
An attempt was made to investigate dermatoglyphic variation between four sex-crimes (SC) and four sex and other crime (SOC) convicts. These were compared with 10 endogamous and 11 penal populations. The results indicate that the two closely related sex crime cases IPC-363 and IPC 366 («kidnap» and «abducting») show wide differences in dermatoglyphic characters. A comparison of sex crimes with sex and other crime cases showed least differences in the case of IPC-363, IPC-363 KC and in IPC 366 and IPC-366 AC but wide differences in IPC-354 («molestation») cases. The dendrograms suggest that the eight sex crime cases cluster together and are different from other endogamous and penal populations. The significant low mean finger ridge count observed in the case of IPC-366 is in agreement with other studies, suggesting a strong association between crime (sex) and dermatoglyphics. 相似文献
15.
This study examines the optimal seasonal timing of the life cycle for univoltine and bivoltine insects, assuming that resource
availability has a peak in the middle of a year and is symmetric around it. Results show that if the growth rate increases
in proporrion to the bodyweight, bivoltine life cannot be optimal. If the growth rate is a power function of the bodyweight
with a power smaller than unity, a symmetric bivoltine solution can be the optimal provided that the resource availability
has a plateau in the middle of the season. If the resource availability has a sharp peak, the optimal pattern is an asymmetric
bivoltine solution in which the larval periods of two generations differ in length. The bivoltine life cycle is more likely
to be superior to the univoltine one if: growth is fast, suitable growing season is long, biomass loss during nonlarval stages
is small, and egg size is small. 相似文献
16.
The efficacy of Sizofiran(SPG), a highly purified -1,3-D-glucan from the culture broth of a basidiomycetesSchizophyllum commune Fries, in combination with local irradiation was investigated using squamous-cell carcinoma NR-S1 and syngeneic hosts of OH/He mice. NR-S1 tumor was implanted sc in the thigh of C3H/He mice. When tumor grew to 4 mm in diameter, the local irradiation of 55 Gy was delivered. SPG was injected im at a dose of 5 mg/kg. When SPG was administered after irradiation, remarkable inhibition of tumor growth was observed in comparison with the radiation alone group. Furthermore, the combination effect of radiation and active immunotherapy using mitomycin C-treated NR-S1 cells as vaccine was examined. When radiotherapy and active immunotherapy were combined with SPG, suppression of tumor growth was observed from an early stage in comparison with the group which was not administered SPG. SPG also inhibited the pulmonary metastasis of NR-S1 tumor after radiotherapy. 相似文献
17.
Optimal foraging theory is being used increasingly as a means of understanding human foraging behavior. One of the central assumptions of optimal foraging theory is that prey items or patches are encountered sequentially and as a Poisson process. Using empirical data gathered on the Barí hunters of Venezuela, we assess the validity of this central assumption. We compare our observed distribution of encounter frequencies with an expected Poisson distribution, utilizing chisquare tests and graphic representations. The results are strikingly consonant with the expected Poisson distribution and lend support to the applicability of optimal foraging models to human hunting behavior. 相似文献
18.
19.
The evolution of phage lysis timing 总被引:17,自引:0,他引:17
Summary The effect of host quantity and host quality on the evolution of phage lysis timing is analysed using marginal value theorem of optimal foraging theory. Both factors have been shown to strongly influence the latent period. A high host density selects for short latent period, which is the same result as previous investigators have found. A good host quality also promotes a short latent period. However, elasticity analysis shows that these two factors exert their influences under different sets of conditions. When host density is low, the host density is more important in determining the length of latent period, whereas when host density is high, the host quality is more important. 相似文献
20.
The antitumor effect of the combined administration with recombinant human interleukin-2 (rIL-2) and sizofiran (SPG), a single
glucan of Shizophyllum commune Fries, was studied in vivo in C57BL/6 mice intraperitoneally inoculated with EL-4 lymphoma.
The effect was evaluated by a) comparing the survival time of the mice, b) analysis of the intraperitoneal cell population
in Giemsa-stained specimens, c) surface marker analysis of peritoneal exudative cells with flow cytometry, d) cytotoxic assay
of cells against EL-4 and Yac-1 lymphoma, and e) elimination of some cell populations by monoclonal antibodies, to identify
the antitumor-effector cells showing cytotoxic activity. The survival of mice given both rIL-2 and SPG was significantly longer
than the control mice or those given SPG alone or rIL-2 alone. It was demonstrated that the administration of SPG and/or rIL-2
to the EL-4 lymphoma-bearing mice activated immune-response cells in the peritoneal cavity such as T lymphocytes, NK cells,
or macrophages, which might be effective in reducing lymphoma cells. The combination of rIL-2 and SPG administration appears
to activate the antitumor- immune response at the tumor site more effectively than when either agent was administered alone. 相似文献