摘要:

Ten captive dingoes were injected with radioactive NaC1 and the turnover of radio—sodium was compared with the measured intake of sodium in the diet, which consisted of rabbit carcasses. A close correlation was established between food intake and(22)Na turnover (r = .95). The possible uses of the(22)Na turnover technique in measuring food intake in free—living animals are discussed.

ISSN:0012-9658    

DOI:10.2307/1936363

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

Selective predation occurs when the relative frequencies of prey types in a predator's diet differ from the relative frequencies in the environment. A measure of preference is proposed which is derived from a simple stochastic model involving probability of encounter and probability of capture upon encounter. The measure is applicable to any number of prey types and methods of estimation are given for both constant and changing prey numbers. Because the measure is based on a biological model, it can be manipulated and interpreted in a meaningful way.

ISSN:0012-9658    

DOI:10.2307/1936364

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

The hypothesis that morphological structure of a community should reflect ecological structure (trophic relationships) was tested in this paper. An assemblage of closely related sympatric species of Peromyscus was studied to see how closely morphological structuring can describe actual food—use relationships in a community. Animals were collected during 4 different seasons and stomach contents were analyzed to reveal the diet of each species. A morphological analysis of the assemblage of Peromyscus was accomplished through the analysis of 4 external and 69 skeletal characters. Morphological and trophic relationships were computed using principal components and distance analysis. A positive relationship between morphological and ecological packing is shown by a correlation coefficient computed between food—use distances and morphological distances. Microhabitat use and foraging behavior are discussed in an attempt to expose actual mechanisms of competitive interactions.

ISSN:0012-9658    

DOI:10.2307/1936365

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

Larvae of the sessile rotifer Ptygura beauchampi begin substrate selection activities when they chemotactually sense a stimulus associated with the glandular trichomes which cover their preferred substrate, the trap door region of the largest, prey capturing organs of the carnivorous aquatic plant, Utricularia vulgaris. Four other co—occurring congeneric species (U. gibba, U. inflata minor, U. intermedia, and U. purpurea) and 2 smaller, morphologically distinct, trap types of U. vulgaris were not colonized. All of these Utricularia traps (except U. purpurea) have glandular trichomes which are nearly indistinguishable from one another. The stimulus appears to be chemical in nature, arising from the terminal head cells of trichomes as they develop. The chemical stimulus (an allelochemic agent) may be the utricularian prey—lure first proposed by Cohn in 1875. This symbiotic relationship should be termed commensal because rotifers colonize, but do not feed on the plant or its prey, and because the plant is apparently not affected by the colonization.

ISSN:0012-9658    

DOI:10.2307/1936366

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

Reproductive strategies of herbaceous plants were analyzed in three successional communities. The communities were a 1—yr old—field, 10—yr old—field, and forest. Analyses included measurement of community—wide reproductive effort (reproductive dry wt/total dry wt) at 3—wk intervals throughout one growing season. Reproductive effort was highest in the 1—yr field. There was essentially no difference in reproductive effort between plants in the 10—yr old—field and forest communities; both exhibited relatively low reproductive effort. Reproduction in the 1—yr and 10—yr fields was highly synchronous; there was little synchrony of reproduction in the forests. This may indicate a more efficient utilization of resources throughout the growing season in the forest. Analyses also included measurement of numbers of seeds per plant produced by dominant species in each community. Number of seeds per plant in the 1—yr and 10—yr fields was relatively high, while number of seeds per plant was comparatively low in the forest. The ratio of root:total biomass increased with successional age, reflecting a proportionately larger expenditure of energy on competitive structures in the forest. Also, goldenrods, dominants in the 10—yr field, were found to possess 1 characteristic of an r—strategy (i.e., large number of small seeds) and a characteristic of a K—strategy (i.e., low reproductive effort). This apparent paradox was explained by relating these characteristics to the selective pressures that might produce them. In addition, the empirical data provide support for expanded concepts of reproductive strategies.

ISSN:0012-9658    

DOI:10.2307/1936367

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

Experiments which measure seed removal rates of ants, birds, and mammals were conducted in the Sonoran Desert of North America and the Monte Desert of South America. Rodents were the primary consumers in North America, but ants also took large amounts of seeds there. Ants were the major granivores in the Monte, where mammal seed consumption was insignificant. Birds were relatively unimportant consumers in both deserts. Total seed removal rates were more than an order of magnitude larger in the Sonoran Desert. These results are much in contrast with the great overall similarity of the 2 systems in climate and flora. The extinction, 1 or 2 million yr ago, of a marsupial family, Argyrolagidae, which appears to have been the ecological equivalent of the rodent granivores, Heteromyidae, may have cause the differences in granivory either because the Argyrolagidae were mutualistic with the plants or, in an evolutionary sense, with the granivorous ants.

ISSN:0012-9658    

DOI:10.2307/1936368

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

To test the hypothesis that adult voles reduce the survival, growth, and maturation rates of young voles, cohorts of young were introduced at 6—week intervals throughout the spring, summer, and fall of 1975 onto an unmanipulated area, a ♂ removal area, and a total removal area. Young survived best on the total removal area but poorly on both other areas. Growth in young ♂ ♂ was directly related to the density of adult ♂ ♂. The weight at which ♀ ♀ attained sexual maturity was directly related to the density of adult ♀ ♀ but not to the density of adult ♂ ♂. Males showed a similar relationship in response to the density of adult ♂ ♂. I conclude that adult ♀ ♀ reduce the survival of young. Further study of ♀—young interactions is necessary to determine the mechanisms involved.

ISSN:0012-9658    

DOI:10.2307/1936369

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

A model of population growth in a partially predictable environment is developed and analyzed. The essential features of the model are as follows: (1) There are only 2 possible environmental states, and the transitions between the 2 states are the same as for a Poisson process, so that time spent in a state before a transition follows an exponential distribution. (2) Arbitrary rules for population growth in each of the states are assumed. (3) The model is formulated in terms of the joint distribution function of environmental states and population sizes. An equilibrium solution is found, from which it can be determined if there is a stationary joint distribution by whether or not the equilibrium solution exists and can be normalized. Several specific growth models are analyzed, including the effect of variations in the intrinsic rate of increase and in the carrying capacity for the logistic and related models. The main result is that it is possible to have a stationary distribution of populations sizes indicating persistent fluctuations driven by environmental changes only when the correlation time of environmental changes is roughly comparable to the average response time of the population to those changes. Also, in many models of growth the dominant parameter that determines the tendency of the population to go extinct is the mean of the intrinsic rates of increase in different environments. There is no support for earlier conjecture that the relative values of the mean and variance of a parameter determine the extinction tendencies.

ISSN:0012-9658    

DOI:10.2307/1936370

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

The functional roles of Schizoporella, an encrusting bryozoan, and Styela plicata, a solitary tunicate, were investigated by continuously removing each species from the developing community for 15 months. Observations were also made on the undisturbed community after the cessation of removals. Two experiments are reported here, initiated in October 1972 and 1973, respectively, and terminated in December 1976. When dense, Schizoporella excluded other species from the space it occupied, resulting in a patch with fewer species and with fewer changes in species composition through time. The maximum persistence time appeared to be °2 years and Schizoporella was unable to invade space occupied by other species. Styela also excluded other species from the community when dense, but its larvae were capable of invading space occupied by other species. The attachment sites of Styela on other organisms were often unable to support the large animals resulting from a summer of rapid growth. Thus, Styela often sloughed off in the fall, (even though the individuals may have been healthy) taking other organisms with it. In a short time frame, Styela stabilized the community, resisting invasion as did Schizoporella, but destabilized the community on a different time scale because of the approximately annual slough—offs.

ISSN:0012-9658    

DOI:10.2307/1936371

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

Biomass and net primary production were measured in 3 forest communities in northern Wisconsin comprised mainly of Populus tremuloides, Betula papyrifera, Acer rubrum, and Acer saccharum. The estimated total aboveground biomass and production for living plants in the 3 stands, designated as (1) aspen, (2) aspen—maple—birch, and (3) maple—birch—aspen types, were 94.8, 95.6 and 119.0 t/ha [=103kg/ha] and 10.43, 8.45, and 8.69 t°ha(—1)°yr(—1), respectively. Shrub and ground vegetation accounted for minor portions of the total standing crop. The tree:shrub:ground biomass ratios were 1:.019:.015 for aspen, 1:.009:.006 for aspen—maple—birch, and 1:.003:.006 for maple—birch—aspen. The contribution to stand production by shrubs and ground vegetation ranged from 17% of the total aboveground production in the aspen type to 9% in the other stands. Inputs to the production equation often neglected in stand analysis, i.e., plant losses by death, shedding, and consumption, amounted to a maximum of 4.5% of total aboveground production. A comparison of biomass data from forests in the lake states suggests that 100 to 200 t/ha (above—ground dry weight) is inclusive of most second—growth forests. The upper and lower bounds for mature forests were projected to be °600 and 60 t/ha. Estimates of aboveground productivity for a variety of forest ecosystems within the lake states had a narrow range from 7.1 to 10.4 t°ha(—1)@?year(—1).

ISSN:0012-9658    

DOI:10.2307/1936372

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY