ISSN:0012-9658    

DOI:10.2307/1934694

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

Seasonal changes in the population ecology of Anolis cupreus, a sexually dimorphic lizard, were studied over a 2—yr period in a deciduous and riparian forest ecosystem in western Costa Rica. This tropical environment undergoes strong seasonal changes, including a 6—mo yr dry season during which maximum air temperatures, hours of daily sunshine, and heavy winds occur. Many aspects of the ecology of A. cupreus undergo striking seasonal changes in response to this climatic seasonality. Both sexes were sexually active for about 6 mo of the year, with the ♀ cycle coinciding with the wet season. Fat body cycles in both sexes were inversely related to the reproductive cycles. Males and ♀ ♀ attain sexual maturity at 1 yr or less, and the population apparently undergoes an annual turnover. Population density was high (>1,200 anoles/ha) in the dry season, but in part because of changes in the structural habitat of ♂ ♂ and territorial behavior, density was much lower in the wet season. In the dry season social interactions were rarely seen, both sexes perched at or near ground level, and ♀ ♀. In contrast, in the wet season social interactions occupied a majority of the ♂ ♂ time as they defended territories and courted ♀ ♀. At this time of the year ♂ ♂ perched much higher than ♀ ♀ fed primarily on the ground; ♂ ♂ obtained at least half their food up to 6 m aboveground in the wet season. Because of seasonal changes in perch heights and size of prey items eaten, intrasexual (seasonal) values of place x food niche overlap were lower than intersexual values. The response of this anole to stressful climatic conditions is analogous to that of its Temperate Zone congener, Anolis carolinensis. Whereas A. carolinensis hibernates to avoid low winter temperatures, A. cupreus becomes inactive during periods of high winds and air temperatures.

ISSN:0012-9658    

DOI:10.2307/1934695

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

Laboratory microcosms were designed to study phosphorus exchange among lake water, diatoms (Nitzschia palea), snails (Physa sp.), and sand. Mathematical models describing the movement of32P were used to simulate phosphorus behavior in microcosms of varying complexities. The single and combined effects of diatoms, snails, and sand on rate of32P transfer were tested by factorial analysis. Phosphorus behavior varied both among microcosms of different complexities and among microcosms containing the same quantities but different compositions of compartments. All rate transfer constants involving water and one other compartment were significantly affected by another single compartment, by an interaction between two other compartments, or by both a single compartment and its interaction with another. Turnover of phosphorus was compared among different microcosms. Water generally maintained a higher turnover rate of phosphorus than any other compartment. The mean hourly turnover rate of32P in water ranged from 0.00029 in microcosms containing water and a snail to 0.1035 in the four—compartment microcosms. Snails and diatoms tended to maintain high concentrations of432P although there was an active exchange of32P between each biotic compartment and water. A major exception occurred in the four—compartment systems wherein diatoms steadily lost32P after about 24 h following inoculation of32P, into the water. Diatoms and sand competed for, and dominated the movement of,32P, as compared to snails which had a generally less dynamic effect on the cycle. Despite the active exchange of32P between water and sand, the slow diffusion of32P resulted in a net flow of32P into sand.

ISSN:0012-9658    

DOI:10.2307/1934696

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

Optimal exploitation strategies were studied for an animal population in a Markovian (stochastic, serially correlated) environment. This is a general case and encompasses a number of important special cases as simplifications. Extensive empirical data on the Mallard (Anas platyrhynchos) were used as an example of general theory. The number of small ponds on the central breeding grounds was used as an index to the state of the environment. A general mathematical model was formulated to provide a synthesis of the existing literature, estimates of parameters developed from an analysis of data, and hypotheses regarding the specific effect of exploitation on total survival. The literature and analysis of data were inconclusive concerning the effect of exploitation on survival. Therefore, two hypotheses were explored: (1) exploitation mortality represents a largely additive form of mortality, and (2) exploitation mortality is compensatory with other forms of mortality, at least to some threshold level. Models incorporating these two hypotheses were formulated as stochastic dynamic programming models and optimal exploitation strategies were derived numerically on a digital computer. Optimal exploitation strategies were found to exist under the rather general conditions. Direct feedback control was an integral component in the optimal decision—making process. Optimal exploitation was found to be substantially different depending upon the hypothesis regarding the effect of exploitation on the population. If we assume that exploitation is largely an additive force of mortality in Mallards, then optimal exploitation decisions are a convex function of the size of the breeding population and a linear or slight concave function of the environmental conditions. Under the hypothesis of compensatory mortality forces, optimal exploitation decisions are approximately linearly related to the size of the Mallard breeding population. Dynamic programming is suggested as a very general formulation for realistic solutions to the general optimal exploitation problem. The concepts of state vectors and stage transformations are completely general. Populations can be modeled stochastically and the objective function can include extra—biological factors. The optimal level of exploitation in year t must be based on the observed size of the population and the state of the environment in year t unless the dynamics of the population, the state of the environment, and the result of the exploitation decisions are completely deterministic. Exploitation based on an average harvest, or harvest rate, or designed to maintain a constant breeding population size is inefficient.

ISSN:0012-9658    

DOI:10.2307/1934697

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

In Union Bay, a temperate embayment in Seattle, Washington, USA two different kinds of predators maintain a polymorphism of the cladoceran Bosmina longirostris. The boundary separating these two Bosmina populations is unusual because it is maintained in a freely mixing body of water, and important because its distinctness is a consequence of trophic dynamics, a result of the interactions of visual predators (fish) and grasping predators (copepods). Not only do the fish directly affect the morph composition by differentially removing the more conspicuous morphs, they also indirectly control the magnitude of counter—selection forces by regulating the abundance of predatory copepods. The joint action of both predators sets up a spatial situation in which adjacent populations of Bosmina actually diverge phenotypically and genetically during the summer.

ISSN:0012-9658    

DOI:10.2307/1934698

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

Orb—weaving spiders Metabus gravidus (Cambridge) (Araneae: Araneidae) spin, maintain, and defend individual webs. Colonies of 5—70 species form multilayered meshes of orbs connected by common support lines over mountain streams at the study site, Monteverde, Costa Rica. Habitat selection, preference for spinning with a group, and maintenance of year—round population levels result in relatively permanent aggregations. Grouped spiders can build orbs in areas of high prey density more efficiently than single spiders, but they do not cooperate in web construction or food capture. Activity patterns relate closely to prey abundance and also depend upon individual energy demands. Cost—benefit analysis for different positions within the colony suggests no single optimal position on the basis of prey capture and the construction, maintenance, and defense of orbs. Colonies are maintained by the composite movements of unspecialized individuals, which benefit in the exploitation of resources not available to solitary spiders.

ISSN:0012-9658    

DOI:10.2307/1934699

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

The thermoregulatory strategies of two Namib Desert tenebrionid beetles were studied to determine the methods used to attain relatively high and constant body temperatures for several hours each day. In the field thermoregulatory behavior observations were made simultaneously with microclimate data collection and measurement of body temperatures in free—ranging beetles. A thermal model was developed using beetle heat exchange parameters and combined with microclimate data to predict the range of body temperatures available to the insects in their different environments. The accuracy of the model was validated against measurements of body temperature in the population of free—ranging beetles. Observations of thermoregulatory behavior, when coupled with the effect of such behavior on modeled body temperatures, make it possible to evaluate quantitatively the efficacy of various thermal strategies and the degree of habitat selection practiced by the insects to maintain preferred temperatures. Thermoregulation methods include squatting, stilting, exposure of lighter—colored body surfaces, climbing and burrowing. These methods, when combined with the ability to seek out and move to unique microenvironments, enable the beetles to maximize thermoregulatory control and achieve greater independence from thermal variations in their habitat. Both beetle species were living maxithermal strategies in which body temperatures were maintained at high levels for a maximum time each day.

ISSN:0012-9658    

DOI:10.2307/1934700

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

We examined the patterns of distribution of species of resident fishes in an experimental habitat consisting of 10 small live colonies of the coral Acropora pulchra (L—units), and 10 similar sized pieces of eroded coralline rock (D—units). Approximately every 4 mo for 2 yr, all fish in each unit were collected. Numbers collected were similar at all times to numbers in control units that were not disturbed. A total of 630 fishes and 56 species were collected; most species were rare in our sample. Greater numbers of fish and of species were collected when recruitment had taken place during summer months. Greater numbers of fish and of species were collected from L— than from D—units. Only three species were demonstrated to be seasonal in recruitment. No temperal partitioning of the habitat was demonstrated. Five common species showed marked preferences for L—units, but most species did not make this discrimination. Comparisons of samples from L—units with samples from D—units showed somewhat less faunal similarity than comparisons between samples from the same type of unit. There was no evidence that fishes occupying units of one type partitioned the habitat on the basis of precise microhabitat requirements that would have caused particular species to occur consistently in particular units. There was on indication that any pair of species mutually excluded each other from units. With the exception of those few species which distinguished D— and L—units, we conclude that the distribution of species among units is a result of chance colonization, not of a systematic partitioning of the living space provided. We anticipate this conclusion to have general validity for reef fish communities. Some consequences for our understanding of the small—scale distribution of fishes on coral reefs are discussed.

ISSN:0012-9658    

DOI:10.2307/1934701

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

The European wild boar Sus scrofa L., an exotic species, entered the Great Smoky Mountains National Park during the 1940s. Because of their high reproductive potential and their adverse impact on the native flora and fauna, the wild hogs have become a major management problem within the park. During the summer of 1973, quadrat sampling of the canopy and understory of Gray Beech Forest was conducted in both the hog—free and hog—occupied sectors of the park. Removal of the herbaceous understory and other types of hog rooting damage showed no direct relationship to the importance of any individual canopy species, including beech Fagus grandifolia. Cover reduction was related, however, to the importance of mesic herbs in a plot. Polynomial and Gaussian regressions of cover against indirect ordination axes indicate that hog rooting within Gray Beech Forest is most intense in the mesic portion of the moisture gradient and decreases both on xeric, south—facing slopes and on more mesic, north—facing slopes. Understory cover in the most severely damaged plots was between 2% and 15%, while understory cover in hog—free plots in the same position on the moisture gradient was usually between 80% and 110%. Hog rooting significantly reduced the number of species in the most disturbed plots but had no effect on the H' values of the largest plot sizes sampled. High H' values for the damaged plots are related to the lack of succession after disturbance of the understory without removal of the canopy.

ISSN:0012-9658    

DOI:10.2307/1934702

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

Flights (movements from place to place) were studied in 11 species of Lepidoptera which differed in size, mate—locating behavior, food plants of larvae and adults, oviposition behavior, population size, areal extent of populations, and habitat features possibly limiting flights. and population size were quantified. Mate—locating behavior influences the difference in flights of ♂ ♂ and ♀ ♀; males tend to remain in sites favorable for mating, while ♀ ♀ tend to disperse more than ♂ ♂. Multibrood polyphagous species feeding on early successional plants had the farthest flights. Conversely, single—brood species feeding as larvae on perennial trees or shrubs had short flights. There is apparently a genetic component to flight distances; taxonomically similar species had similar distances, flights of several species were similar in successive years, and flights of reared individuals were similar to those of native individual. Two species in different superfamilies occupying the same habitat convergently developed similar flight distances. A migratory species had more unidirectional flight than the nonmigrants. There is a strong positive correlation between the size of the area in which the majority of individuals of a population are concentrated and flight distances for the 11 species. No correlation exists with population size, but mean densities are inversely correlated with flight distances. The significance of these correlations is discussed. It ispostulated that heritable behavioral mechanisms and local extinction influence the relationships between flights, area, and density.

ISSN:0012-9658    

DOI:10.2307/1934703

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY