摘要:

The habitat hyperspace of a south—facing slope ecosystem in Rocky Mountain National Park, Colorado, USA was characterized by two major gradients, soil depth and soil moisture. Richardson's ground squirrels (Spermophilus richardsonii) were limited in their distribution by areas of shallow soil, and excluded golden—mantled ground squirrels (S. lateralis) from areas of deep soil. The habitat hypervolume of the golden—mantled ground squirrel included that of the least chipmunk (Eutamias minimus); the golden—mantled ground squirrels suppressed the population of least chipmunks. Deer mice (Peromyscus maniculatus), least chipmunks, and golden—mantled ground squirrels were the principal hosts of larval wood ticks (Dermacentor andersoni). The golden—mantled ground squirrels and least chipmunks were the principal hosts of nymphal wood ticks. The circulation of Colorado tick fever virus was maintained through the interactions of the wood ticks, least chipmunks, and golden—mantled ground squirrels. Areas of wood tick abundance were accurately described by a discriminant function of five easily measured habitat hyperspace variables, areas of virus activity with seven variables.

ISSN:0012-9615    

DOI:10.2307/1942476

出版商:Ecological Society of America    

年代:1980

数据来源: WILEY

摘要:

Populations of the Yellow—hooded Blackbird Agelaius icterocephalus (Icteridae) in northern South America fall into two patterns, according to the seasonal duration of nesting and the spacing of males' territories and nests. These differences among populations of the same species result from interacting adaptations for exploiting food resources and reducing nestling mortality from predators and brood parasites. All populations breed in marshes, where males defend territories within which they build nests. In moderately seasonal areas, like Trinidad and Surinam, males' territories were 15—50 m in diameter, active nests were 2—10 m apart, and egg laying continued for most of the rainy season. A male often had a succession of females nesting in his territory, but rarely had more than one or two active at any one time. In an extremely seasonal area, the llanos bajos of central Venezuela, conditions were suitable for nesting blackbirds for no more than 2 mo at the end of the rainy season. Blackbirds migrated to this area several months before breeding, males established territories 4—8 m in diameter in discrete colonies, and females laid eggs within a 3—wk period. A male's territory had as many as five nests active at one time. Many small colonies were soon abandoned after massive brood parasitism by Shiny Cowbirds Molothrus bonariensis; a large colony nested successfully. Cowbirds parasitized 33% of nests in this large colony in Venezuela, the same as in populations in Trinidad and Surinam. Male blackbirds chased cowbirds out of their territories and thus restricted opportunities for uninterrupted searching by female cowbirds for blackbird nests. Blackbirds began incubation with the first egg, so a cowbird had to lay her egg within 1 or 2 d to have any chance of success. In Venezuela, cowbirds failed to respond immediately to the sudden availability of blackbird nests in the large, successful colony. Predation accounted for many nest failures, particularly in Trinidad and Surinam, but starvation of some nestlings, especially those hatched last, occurred in the majority of nests that escaped predation. Females feeding young brought only one item to the nest each trip, an indication that food was difficult to find. They increased their rate of feeding and selected larger items as the nestlings grew. Food for nestlings consisted almost entirely of herbivorous insects, primarily Orthoptera, collected in marshes often several hundred metres from the nest and always outside the male's territory. In Venezuela, suitable insects were sparse and widely distributed in marshes. This situation and the lack of cooperation by females in locating food suggest that aggregated nests probably had disadvantages for foraging. Males helped to feed nestlings at one, or rarely two, nests in their territories. Although males contributed less than the females, nests that received male help on>1 d before day 8 of the nestling period had heavier young on day 8 than did nests that received less male help. Tropical marsh—dwelling Agelaius experience greater nest failure from both predation and starvation of nestlings than do temperate marsh—nesting blackbirds. The staggered hatching of nestling Yellow—hooded Blackbirds, as a result of incubation starting with the first egg, leads to brood reduction, which could have advantages for parents when they confront an unpredictable, sparse food supply, but could also result from parent—offspring conflict over the optimal brood size. Nest building by males permits females to spend all of their time on the best feeding areas until immediately preceding egg laying, presumably an adaptation to sparse food resources at a distance from safe nest locations. The seasonal restrictions on breeding in the Venezuelan Ilanos make Yellow—hooded Blackbirds more vulnerable to brood parasitism by cowbirds, except in large, dense, synchronized colonies. Coloniality reduces brood parasitism as a result of the increase in male vigilance permitted by smaller territories. Blackbirds also obtain a 'head start' on cowbirds as a result of synchronized laying. Coloniality possibly also reduces predation by solitary predators that detect nests at close range, such as mammals and snakes.

ISSN:0012-9615    

DOI:10.2307/1942477

出版商:Ecological Society of America    

年代:1980

数据来源: WILEY

摘要:

The ecological and behavioral interactions of adults of nine species of Panorpa scorpionflies were studied during 1971—1974 at eight woodland sites in southeastern Michigan, USA. The species overlap considerably in habitat use, diurnal foraging time and location, and diet. All species inhabit primarily the herb stratum of moist forests. Soft—bodied dead arthropods comprise from 88.5 to 100% of the diets of the different species. Panorpa scorpionflies are very aggressive around food. The species can be ranked linearly in relation to their ability to dominate heterospecific individuals at food. The aggressive dominance ranking of the species is related to increasing size (r = .78, P = .04). The study sites vary in Panorpa species richness from three to eight. Panorpa species clearly interact. Mark—recapture data reveal that at the site where only three species occur adults of P. banksi live longer and move less than adults of the same species at a site where six species occur. The adult seasonal distributions of the three species at the site where only three species occur are extended in comparison to the seasonal distributions of the same species at other sites with greater Panorpa species richness. Species or species groups partition the season to some extent by successional emergence. Seasonal overlap, however, is sufficient to result in competitive interactions between some species. Analyses of the seasonalities of the species reveal that the numbers of individuals and species of Panorpa present during a species' adult seasonal period inversely influence the duration of that period. The durations of the adult seasonal period of the more aggressive species are primarily influenced by the number of conspecific individuals present, whereas the durations of the adult seasonal periods of the less aggressive species are primarily influenced by the number of individuals of heterospecific and more aggressive species present. Very aggressive species cause less aggressive species to feed above the herb stratum; this may result in increased exposure to predators and to reduced longevity of the less aggressive species. I suggest that the emergence times of the species allow coexistence and have been selected in the context of interspecific competition for food. The emergence times of the species in relation to each species' aggressive dominance appears consistent with this hypothesis. The variation in species richness between sites is probably not due to the extinction of certain species because of competition, but is the result of different amounts of Panorpa habitat destruction at the sites in the past.

ISSN:0012-9615    

DOI:10.2307/1942478

出版商:Ecological Society of America    

年代:1980

数据来源: WILEY

摘要:

Allocation of energy to growth and heat production was measured by constructing energy budgets of male and female Sigmodon hispidus (x Adult body mass = ABM = 113 g ♂ 105 g ♀) and Neotoma floridana (ABM = 270 g ♂ 184 g ♀) from birth to maturity. Energy ingested and oxygen consumption per gram of body mass of post—weaning animals were not significantly different between sexes within species, but did differ significantly between the species. In all animals the relation between post—weaning ingestion (per gram body mass) and body mass follows a negative power function. Post—weaning metabolic rate as a function of body mass follows a different negative power function. The pattern of change in metabolic rate prior to weaning is different in the two species. In Sigmodon, metabolic rate increases linearly from birth to about 20 g (or about 20% of ABM). The rate at 20 g is about 5 cm3°g—1°h—1. In Neotoma metabolic rate remains constant at 1.7 cm3°g—1°h—1from birth to about 26 g (or about 11% of ABM), then increases linearly to about 2.2 cm3°g—1°h—1at 65 g (29% ABM). In both species, the peak in metabolic rate and nutritional weaning coincide with development of homeothermy, (measured as ability to maintain adult—level body temperatures at an ambient temperature of 20°C). Young Sigmodon become efficient homeotherms by 10—12 d of age whereas Neotoma require 19—22 d. Growth of each sex and species can be described by Gompertz equations. Growth rate constants, K, and asymptotic mass, A, differ between sexes within species and between species. Gompertz equations do not accurately describe growth of pre—weaning Neotoma which was linear from birth to 21—22 d of age. No such period of linearity is seen in Sigmodon growth. Analysis of litter—size dependence of growth of pre—weaning animals indicates that the early linear growth of Neotoma may not be a result of limited milk production, as it seems to be in Sigmodon. The relative total investment of energy in growth for a litter of Sigmodon (° = 4.8 young) between birth and 12 d of age was 416.7 kJ compared to 770.7 kJ for the first 24 d of life of the average Neotoma (x = 2.6 young). Over these same times, a litter of Sigmodon expended 1350.6 kJ on respiration compared with 1296.2 kJ in Neotoma. Thus the total metabolizable energy requirements of 1767.7 kJ and 2066.2 kJ are similar in the two species; however, a litter of Sigmodon requires about twice as much metabolizable energy per day each day they remain with their mother. Neotoma daily requirements are lower but protracted in time. During the pre—weaning period, Neotoma are investing proportionally more of their metabolizable energy in growth, whereas Sigmodon spend more on respiration, perhaps because they depend on their own heat production for thermoregulation while Neotoma rely on their mother's heat. These results are compared with data from the literature on growth and development of homothermy in a variety of small rodents. The hypothesis is advanced that, in general, larger species defer onset of active thermoregulation to larger body masses when lower metabolic rates occur, perhaps as an adaptation to permit more efficient early growth. Small species sacrifice growth efficiency in favor of rapid attainment of early independence and they pay the high energy costs of that speed. The different developmental physiologies of Neotoma and Sigmodon are explainable by inference from current ideas on the evolution of life histories, but much of the difference is also predictable simply from their difference in body size. This may indicate the importance of body size in the complex of life history traits.

ISSN:0012-9615    

DOI:10.2307/1942479

出版商:Ecological Society of America    

年代:1980

数据来源: WILEY

摘要:

Sebastes carnatus and Sebastes chrysomelas are morphologically and ecologically similar residents of rocky reefs off the coast of California. They segregate bathymetrically, with S. chrysomelas occurring shallower than S. carnatus. Each species extended its depth distribution where its congener was removed, and no distributional changes occurred in a control area. Thus both species tolerated conditions beyond their normal depth ranges, and were limited in part of their normal depth ranges by interspecific competition. Their segregation was apparently initiated by the preferential settlement of young fish from the plankton, S. chrysomelas in shallow water and S. carnatus deeper. Their segregation was maintained by interspecific territoriality. The distribution of S. chrysomelas, the socially dominant species, may also have been affected by a strong preference for food—rich areas that occurred mainly in shallow water. I postulate that such a preference would be due to the advantage of smaller home ranges in shallow water, where strong wave surge makes the shelter hole a more important part of a fish's territory. This postulated preference, along with aggression from S. carnatus, limited S. chrysomelas to shallow water. Because of its social dominance, S. chrysomelas aggressively excluded S. carnatus from preferred areas in shallow water.

ISSN:0012-9615    

DOI:10.2307/1942480

出版商:Ecological Society of America    

年代:1980

数据来源: WILEY

摘要:

The populations, foraging behavior, and habitat selection of 20 insectivorous species of subalpine birds were studied during three breeding seasons in the white Mountains, New Hampshire, USA. The object was to clarify how an elevation gradient of environmental adversity affected diversity, dominance, niche, habitat, and species biology. Population densities and territory sizes were measured from census plots. Territory sizes correlated with species body mass, probably in response to size—related food requirements. Lower elevations had more even distributions of densities among species and less steep dominance—diversity curves than did higher elevations. To show habitat selection patterns in the subalpine vegetation, principal components analysis (PCA) was used to develop a model that emphasized elevation and broadleaf—to—coniferous foliage as the two major gradients. Bird species diversity (BSD) reached a maximum in well—developed preclimax red spruce—balsam fir forests with some broadleaf crowns present. Individual species responses were mapped using the model as a base chart, grouping together: (1) five species living at altitudes above 1100 m with small differences in their specific patterns, (2) five other species widely distributed through the mid—subalpine zone (800—1100 m), (3) six more mid—subalpine species segregating along the broadleaf/conifer foliage gradient, and (4) three species found near water. Niche relations were studied using detrended correspondence analysis, a modified version of reciprocal averaging. Resource use was divided by (1) terrestrial vs. arboreal position, (2) a gradient from fine distal (leaves) to coarse proximal (trunk) substrates, and (3) different specializations for food acquisition. BSD was greater in the resource categories requiring less energy and less specialized morphological adaptations to exploit, or having greater insect resource bases. To investigate the relations between habitat and niche, a matrix of the correlations between the niche and habitat variables, using species means for data, was analyzed by PCA. Three relations emerged: (1) the elevation/forest structure gradient was correlated with the terrestrial/arboreal foraging segregation, (2) the niche substrate gradient responded to vegetation structure along the broad—leaf/conifer gradient, and (3) in both cases the response of foraging behavior to habitat structure involved many variables acting together. Niche and habitat were thus closely linked as aspects of species ecotopes; species responses were illustrated for the Blackpoll Warbler and other wood warblers. Food was inferred to limit populations occasionally, so that interspecific competition plausibly underlies niche differentiation. Thermoregulation is hypothesized to affect habitat selection.

ISSN:0012-9615    

DOI:10.2307/1942481

出版商:Ecological Society of America    

年代:1980

数据来源: WILEY