摘要:

Populations of the Anolis cybotes species group on Hispaniola behaviorally compensate for changes in the thermal environment associated with altitude. Lizards occupy more open habitats, increase basking frequency, and restrict times of activity at high elevation: a result is that the change in mean cloacal temperature with elevation is very small relative to that known for other anoles. In contrast to this large behavioral variation among populations, physiological differences appear to be minor. In this regard, the cybotes group has several parallels with the well—studied cristatellus group of Anolis on Puerto Rico. However, the cybotes group has no equivalent to Anolis gundlachi, which employs physiological adaptations to compensate for different thermal environments.

ISSN:0012-9658    

DOI:10.2307/1937714

出版商:Ecological Society of America    

年代:1981

数据来源: WILEY

摘要:

Ceramic tiles were submerged in the Indian River, Florida, and observed for 2 yr. Neither simulated increases in predation pressure not variation in initial species composition had any observed effect upon the structure of the fouling communities on the tiles. However, the exclusion of predators changed the species composition of the fouling communities by allowing species that are normally grazed off to predominate.

ISSN:0012-9658    

DOI:10.2307/1937715

出版商:Ecological Society of America    

年代:1981

数据来源: WILEY

摘要:

Several recent studies reveal that foraging animals select resources in response to the probability distributions of rewards obtained and costs expended, rather than the expected values alone. This paper suggests that both the mean and variance of an individual bird's foraging time may depend on flock size. If individuals prefer to avoid variation in foraging time while exploiting a patchy environment, flocking should often be favored. Even subordinate birds, which acquire less than the average amount of food when a patch is discovered, may reduce foraging time variation by flocking. Individuals prefering greater variation, in order to achieve a very small foraging time, should feed as solitaries or seek smaller flocks than do birds which avoid variation.

ISSN:0012-9658    

DOI:10.2307/1937716

出版商:Ecological Society of America    

年代:1981

数据来源: WILEY

摘要:

An evaluation of the geographic distribution of °60% of the 2809 described Nearctic Ichneumonidae shows that of the species whose latitudinal ranges contact a given latitudinal band, the number per million square kilometres is greatest between latitude 37.5° and 42.4°N, with °900 species/106km2. The most severe absolute drop in species richness occurs in moving southward from the 37.5°—39.9° band to the 38.0°—37.4° band, with virtually no change in land mass over the same latitudinal change, and the smallest drop in species richness occurs in moving from the 32.5°—34.9° band to the 30.0°—32.4° band, where the land mass is almost halved. Of species whose southern range ends in a particular latitudinal band, the number per million square kilometres is greatest for 32.5°—34.4°N and drops away gradually in both directions. These results are consistent with the hypothesis that parasitic Hymenoptera do not increase in species richness with decreasing latitude to the same degree as their hosts. Various hypotheses are discussed as to why this might occur in Ichneumonidae.

ISSN:0012-9658    

DOI:10.2307/1937717

出版商:Ecological Society of America    

年代:1981

数据来源: WILEY

摘要:

In many species of animals, foraging individuals depart from and return to a central place. In a test of a model for such central place foragers, the time spent searching at different distances from the nest was recorded in an insect—feeding bird, the Whinchat (Saxicola rubetra), with and without additional food distributed over the foraging area. The following predictions were realized: (a) the search effort per unit area decreased with increasing distance from the central place; (b) with higher initial food density, the birds searched more near the nest, and less farther away; (c) the foraging area decreased when food was added; (d) the birds took more of the available food near the nest than far from it. Further, Whinchats apparently searched for food where it was cheapest for the moment. Rapid adaptation to increased food density indicates that foraging behavior in Whinchats is under strong selection for efficiency.

ISSN:0012-9658    

DOI:10.2307/1937718

出版商:Ecological Society of America    

年代:1981

数据来源: WILEY

摘要:

Five measures of niche breadth (Hurlbert's, Levins', Petraitis', and Schoener's) can be described by a single function similar to Hill's function of diversity. Choice of which measure to used depends on how the experimenter wishes to weight the data. Utilization of a resource divided by the availability of that resource can be viewed as the tangent of an angle. Niche breadth and overlap measures are related to the sum of the tangents and can be presented graphically. The graphical technique is extended to describe the relationship between niche breadth and Ivlev's standardized measure of electivity.

ISSN:0012-9658    

DOI:10.2307/1937719

出版商:Ecological Society of America    

年代:1981

数据来源: WILEY

摘要:

Release of nutrients by bacterial—feeding nematodes may result in increased nutrient availability for plants. Effects of two species of bacterial—feeding nematodes on N and P mineralization and C—substrate utilization were examined in soil microcosms. Both nematodes increased the rate of14C—labelled glucose—C utilization and N and P mineralization after 10d. However, after 65 d incubation, soluble C, Pi and NH4+—N were similar in grazed and ungrazed systems. The bacterial grazers, although not directly affecting total decomposition, act to maintain the dynamic nature of the nutrient cycles.

ISSN:0012-9658    

DOI:10.2307/1937720

出版商:Ecological Society of America    

年代:1981

数据来源: WILEY

摘要:

Eggs of Anolis auratus and Anolis limifrons were incubated on soil substrates differing in matric potential of soil water. Eggs of both species hatched after a mean incubation time of 44 d on soils with matric potentials of —1.48 MPa or greater. On soils with water potentials of —2.13 and —2.74 MPa, eggs gained in mass initially but eventually desiccated. The rate of water storage was greater for A. auratus eggs than for A. limifrons eggs on all treatments. Rates of water loss by transpiration from the surface of eggs exposed to the atmosphere was a linear function of egg mass for both species, with A. auratus eggs losing less water per unit time than A. limifrons eggs. Differences in water flux were correlated with eggshell morphology. Eggshells of A. auratus were thicker, had a greater density of fibrils, and had a thicker matrix of calcium carbonate than eggshells of A. limifrons. Thus, the eggs of A. auratus seem to be adapted to the dryness of their grassland habitat and the eggs of A. limifrons seem to be adapted to the more equitable and humid conditions of their rain forest habitat.

ISSN:0012-9658    

DOI:10.2307/1937721

出版商:Ecological Society of America    

年代:1981

数据来源: WILEY

摘要:

Maximal resistance to winter freezing of trees of the South Temperature Zone, especially subalpine trees of Australasia, was assessed. Most of the tree species which grow in lower altitudes were marginally hardy to —10°. Subalpine and alpine shrubby species such as Podocarpus nivalis, P. lawrencei and Dacrydium bidwillii were the hardiest conifers in New Zealand and Australia, resisting freezing to —20° to —23°. This hardiness was comparable to that of conifers native to the warm temperate or temperate parts of Japan. In Nothofagus, the deciduous, subalpine N. antarctica of South America was the hardiest, resisting freezing at —22°. A New Zealand evergreen timberline species, N. solandri var. cliffortioides was marginally hardly to 15°. Of the Eucalyptus species, E. pauciflora which forms the alpine tree limit on the mainland of Australia was the hardiest, resisting freezing to —15° in the leaves. Other high—altitude angiosperm species tested mostly survived freezing to only —10° or —15°. Very hardy tree species that withstand freezing below —30° seem not to have evolved in the Southern Hemisphere, because the mild, oceanic winters did not provide the stimulus, and because hardy northern genera, with minor exceptions, have been unable to cross the barrier formed by the tropics.

ISSN:0012-9658    

DOI:10.2307/1937722

出版商:Ecological Society of America    

年代:1981

数据来源: WILEY

摘要:

The role of decision in size—selective predation by planktivorous fish is not clear. What causes size selectivity when many prey can be seem simultaneously (high prey density) is also not well understood. Suspended clay particles were used in experiments to control the number of Daphnia pulex that could be seen simultaneously by bluegill sunfish (Lepomis macrochirus) in order to test between alternative hypotheses. In clear pools, °122 Daphnia of two distinct size classes could be seen simultaneously by the fish. In turbid pools, the probability that two or more Daphnia could be seen simultaneously was<.01, although initial density was the same as in the clear pools. Size selectivity exhibited by the bluegills was independent of turbidity level and the number of prey seen simultaneously. A differential encounter rate hypothesis and the apparent—size selection hypothesis, both based on a perceptual bias for the larger size class, are rejected. The outcome of the experiments indicates that size selectivity resulted from decisions by the fish to ignore the smaller size class of Daphnia. The role of decision in prey selection and foraging strategies is discussed.

ISSN:0012-9658    

DOI:10.2307/1937723

出版商:Ecological Society of America    

年代:1981

数据来源: WILEY