摘要:

We report on a series of experiments performed on a population of free—living eastern chipmunks, Tamias striatus, inhabiting a forest in northwestern Pennsylvania. The experiments were designed to examine, via pertubations of food supply and/or population density, the relationship between home range size, food availability, and population density. When food levels were increased within an area, a simultaneous effect was noted: mean home range size decreased and population density increased through recruitment from neighboring habitats. Whether the cause of the decreased patterns of movement was the increased food supply or the elevated population density was determined in subsequent experiments. When population density was held constant and food supplies were experimentally increased, there was a significant reduction in mean home range sizes when compared to the normal (control) situation. When food supplies were undistributed, put population density was greatly reduced, there was no change in the mean home range size over that determined at higher mean home range size, whereas population density, at least at the levels we examined experimentally, has no effect on movement patterns. These results are in accord with those theories relating movement patterns to resource abundance, but are not in accord with hypotheses suggesting that the home range sized and population density and inversely associated.

ISSN:0012-9658    

DOI:10.2307/1938940

出版商:Ecological Society of America    

年代:1982

数据来源: WILEY

摘要:

Overlaps in resource use have been used to summarize community structure. It is ofen desirable to compare the amount of intensity of overlaps (or other pairwise measures such as competition coefficients) in different communities, especially in the context of comparing actual communities to "neutral model" simulations. We show that the most commonly used index for such comparisons, the mean pairwise overlap, is often unsuitable, and suggest alternate approaches.

ISSN:0012-9658    

DOI:10.2307/1938941

出版商:Ecological Society of America    

年代:1982

数据来源: WILEY

摘要:

All combinations of 0, 10, 20, and 40 hatchlings of two species of frogs, Hyla femoralis and H. gratiosa, were raised in a replicated experiment in which food and space were controlled. Models of density—dependent growth and metamorphosis can be extended to include the effects of competing species by inclusiion of linear, additive terms. Hyla gratiosa has a strong, negative effect on the rate of metamorphosis and size at metamorphosis of Hyla femoralis. Hyla femoralis has no effect on the survival or mean size at metamorphosis of H. gratiosa, but it does lengthen both the minimum and mean larval period. Interspecific density effects on growth may increase both the risk of predation and the risk of desiccation in natural populations.

ISSN:0012-9658    

DOI:10.2307/1938942

出版商:Ecological Society of America    

年代:1982

数据来源: WILEY

摘要:

Larvae of Aedes triseriatus mosquitoes feed on microbes that decompose leaf litter in tree—hole ecosystems. Scanning electron micrographs indicate that browsing by mosquitoes substantially reduces microbial abundance on decaying leaves. Experiments using laboratory microcosms demonstrate that increased larval density decreases larval survivorship, pupation rates, pupal biomass, and total yield. Rapidly decomposing leaf litter (sugar maple) supports more mosquito growth than slowly decomposing litter (beech and black oak). In our experiments, mosquito yield was apparently regulated by larval density and detrital dynamics.

ISSN:0012-9658    

DOI:10.2307/1938943

出版商:Ecological Society of America    

年代:1982

数据来源: WILEY

摘要:

This study provides evidence that the temporal patterning of disturbance may play an important role in determining the effects of disturbance on species diversity. To describe this temporal patterning, a "phasing parameter" is developed, and mechanisms by which this parameter affects the relative abundances of fugitive and competitively dominant species are discussed.

ISSN:0012-9658    

DOI:10.2307/1938944

出版商:Ecological Society of America    

年代:1982

数据来源: WILEY

摘要:

Phenology and seasonal variations in water stress, as reflected in variations in stem circumference, were monitored throughout 1978 in numerous Tabebuia neochrysantha growing at several dry and wet sites in a lowland deciduous forest in Guanacaste, Costa Rica. The rate of leaf fall during the early dry season was strongly correlated with the decline in soil moisture and increasing water stress of the trees. Without exception, recovery from water stress was required for flowering and shoot emergence. At dry sites rehydration ocurred only after isolated rain showers or irrigation; at wet sites it took place during continued drought, probably as a consequence of the decrease in transpiration during leaf fall. Flowering has been observed to occur at any time between the beginning (December) and end (May) of the dry season. Differences in the timing and intensity of flowering as well as in the timing of leaf fall and shoot emergence can be accounted for by site—dependent differences in the rates of desiccation and rehydration of trees in conjunction with year—to—year variation in the timing and intensity of rainfall. No evidence for the control of seasonal development by other environmental factors, such as variations in temperature of photoperiod, was obtained.

ISSN:0012-9658    

DOI:10.2307/1938945

出版商:Ecological Society of America    

年代:1982

数据来源: WILEY

摘要:

The effect of egg size and laying date on the fledging mass of Thick—Billed Murre chicks was examined at Cape Hay, Bylot Island, and Coburg Island, Northwest Territories, Canada, to test the idea that late—laying females face a trade—off between the time of egg laying and egg size. There was a seasonal decline in egg volume, and egg volume was correlated with mass and size (wing length) of chicks soon after hatching. Partial correlations showed that larger eggs hatch into heavier, but not larger chicks. Chics hatched early in the season fledged at heaver masses than late—hatched chicks. Hatching mass contributed significantly to this effect, but other factors (e.g., energy intake) were probably also important. A model, based on a multiple regression of the effects of hatching mass and hatching date on fledging mass, shows the possible combinations of egg size and timing of breeding while maintaining a constant fledging mass. Data on the replacement interval and size of replacement eggs suggest that females that lay late may do better (in terms of fledging mass of their chick) to minimize the delay in laying by producing a small egg earlier, rather than delay laying further in order to produce a larger egg. This is because they are unable to accumulate nutrients at a fast enough rate to make a delay worthwhile. This suggests that the seasonal decline in egg size is an adaptive response to a seasonal deterioration in environmental conditions.

ISSN:0012-9658    

DOI:10.2307/1938946

出版商:Ecological Society of America    

年代:1982

数据来源: WILEY

摘要:

An experimental study, using the minnows Semotilus atromaculatus and Rhinichthys atratulus, was conducted in a seminatural artificial stream to evaluate the interaction of predator presence, habitat structural complexity, and time of day in determining habitat use patterns of prey. Predators were adult S. atromaculatus, while juveniles of both species were used as prey. Prey of both species actively avoid locations in the artificial stream that contain predators. However, structural complexity and time of day each have a mediating effect on the response of the prey fish to the presence of predators. While others have shown differential survivorship of prey, dependent upon structural complexity and time of day, this study shows how prey respond behaviorally to the presence of predators in habitat patches. They are most likely to enter those patches during daylight or when structure is present. In natural headwater streams prey fish are often found in patches of high predator density where prey density is often correlated with the degree of structural complexity. Our findings offer an explanation for this variability in relative abundances of predators and prey, by relating patch use by prey habitat structural complexity and diel activity. Resulting implications for optimal foraging and guild organization are suggested.

ISSN:0012-9658    

DOI:10.2307/1938947

出版商:Ecological Society of America    

年代:1982

数据来源: WILEY

摘要:

This research was conducted to test two predictions about niche and competitive relationships in the structure of plant communities. It has been demonstrated that early successional species of plants have broad, overlapping niche occupation on many gradients whereas later successional species show more niche differentiation. We predicted that, if the differences in resource use were for contested resources in limited supply, the more niche—differentiated species should: (1) experience less biomass reduction in pairwise interspecific competition than should broadly overlapping species of early succession, and (2) be able to convert relatively more of the available resources into plant matter as a heterospecific assemblage than can the conspecific stands from that assemblage. Six species from each of early (annual), mid— (early perennial), and late— (prairie) successional plant communities were grown in containers singly, in con— and heterospecific pairs, and in pure and mixed stands. Competitive interactions were assessed by comparing biomass production of species under the various treatment conditions. The late—successional community, in which we have previously shown more niche separation on several axes, showed a significantly higher mean ratio for the mass of individuals grown in heterospecific pairs divided by the mass of individuals of the same species grown in conspecific pairs than did the early successional community. All heterospecific pairs in the prairie and early perennial communities had a winner (ratio of mass in heterospecific pair to mass in conspecific pair>l.0) and a loser (ratio<1.0), while for most pairs in the annual community both competitors had ratios of<—l.0. Annuals showed the most reduction in total mass and prairie species the least when the mass of an individual grown in a heterospecific pair was compared to the mass of an individual of the same species grown by itself. Therefore, there was less competitive reduction in the more niche—differentiated community, the prairie. There was some evidence that mixtures of the more niche—differentiated late—successional species may be able to convert relatively more of the available resources into plant matter. The prairie assemblage had a slightly greater ratio of mixed stand to pure stand biomass with more variation among species than did the annual assemblage. There was also a tendency for the pairs of prairie species to have higher relative and absolute yields in mixture than in conspecific pairs. Thus members of the late—successional community experienced less competitive reduction in the presence of heterospecific neighbors than did species of early succession. This is strong evidence that niche reduction and separation are effective in reducing competition within a community and that selection to reduce competition could have been more important in the evolution of late—successional species than for early successional species.

ISSN:0012-9658    

DOI:10.2307/1938948

出版商:Ecological Society of America    

年代:1982

数据来源: WILEY

摘要:

The reproductive success of periodical cicadas, measured as the number of offspring produced per adult, is found to increase as adult density increases. The inverse density—dependent pattern at the adult stage occurred over the entire range of adult densities encountered. This result could have been caused by (1) predator satiation, (2) increased fecundity at higher densities, (3) more efficient mating at higher densities, and (4) movement of adults from sites of low initial densities to sites of high densities. The hypothesis of predator satiation was explored in depth. Predation at each site was crudely estimated by collecting cicada wings, which are discarded by avian predators. If predator satiation accounts for the inverse density—dependent mortality, then each cicada's risk of capture will decrease as cicada density increases. The data suggest that this prediction is true; predation did not increase as cicada density increased so that the probability of escaping predation is greater at high—density sites. Estimated predator densities are independent of cicada densities, which indicates that predators cannot respond numerically to the cicada emergence. As cicada density increases, the number of cicada wings recovered per bird does not significantly increase, suggesting that birds are satiated. Significantly more cicada wings were recovered at sites with more birds. Total cicada predation was independent of cicada density but dependent on the density of predators. Some evolutionary consequences of these results are discussed.

ISSN:0012-9658    

DOI:10.2307/1938949

出版商:Ecological Society of America    

年代:1982

数据来源: WILEY