摘要:

This study reports the results of a 13—month live—trap study of two rat species, Rattus rattus, the roof rat, and R. exulans, the Polynesian rat, on the island of Oahu, Hawaii. Rats in Hawaii undergo yearly density and reproductive cycles. Reproductive activity reaches a peak in late summer when numbers are low. This is followed by high recruitment, increase in numbers, and then cessation of reproductive activity in middle to late winter. Peak density occurs later in the winter in R. exaluns than in R. rattus. Survival has an inverse relationship with density and movement data confirm a limited home range in both species. The data from our populations confirm a Hawaiian rodent cycle that is unique in the tropical and subtropical Pacific. The Hawaiian populations have relatively low productivity and survival. Comparative data seem to indicate that the relative densities of these populations are lower than others in the Pacific. Delayed maturation in females partially accounts for lower productivity in these species.

ISSN:0012-9658    

DOI:10.2307/1937622

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

Unlike most tundra rodents, the arctic ground squirrel, Spermophilus undulatus, maintains a relatively constant population. The squirrels exist in two types of groupings: (1) breeding colonies, which cannot expand because their members are territorial, the females reacting to the availability of burrow sites (an environmental constant), and (2) refugee populations, which cannot expand because they cannot breed and, living in habitat only periodically suitable for squirrels, are killed off twice each year. The breeding populations have two distinct types of territories: breeding territories from May to August and prehibernation territories from August to November. During each episode, surplus animals are driven from the colonies and enter the refugee populations, where they are subjected to heavy predation by foxes and bears.

ISSN:0012-9658    

DOI:10.2307/1937623

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

When considering cases in which territorial aggression occurs between species, we find that the relationship varies with the species' geographical and ecological distributions. If similarly sized species are narrowly sympatric or are widely sympatric but normally occupy different habitats, they both are interspecifically territorial and maintain mutually exclusive territories. If similarly sized species are widely sympatric and are common in the same habitats, one species is interspecifically aggressive and the other species flies away when chased. In this paper I present a model that explains these observations. I propose that interspecific territoriality can account not only for these differences in behavior and habitat but also for differences in foraging behavior and bill shape between sympatric species. The last three differences have usually been explained to be consequences of interspecific competition for food. The assumptions of the model proposed here are that (i) interspecific territoriality is misdirected intraspecific territoriality, (ii) territorial behavior prevents some individuals from breeding in optimal habitat, (iii) the individuals of one species are usually dominant over the other species in interspecific encounters, and (iv) of the habitats available to two interspecifically territorial species in their area of sympatry, one habitat is optimal for them both. This model is unusual in that a corollary of assumption (i) is that interspecific territoriality is not an adaptive characteristic, contrary to the assumptions of earlier writers. Nevertheless, the model is interesting and worth consideration because of the range of observable phenomena that are predicted.

ISSN:0012-9658    

DOI:10.2307/1937624

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

Eutamias alpinus, E. speciosus, E. amoenus, and E. minimus are contiguously allopatric and altitudinally zoned into habitats with different energy relationships. The total energy budgets of the species were constructed and compared to see if physiological adaptations could partially explain the observed habitat segregation. Radiating surface area and coefficients of convection were measured through the use of internally heated metal casts of the animals which were covered with pelts. Metabolic rates were measured as O_2 consumption. The climate space of an animal is described by all combinations of absorbed radiation, ambient temperature, and wind velocity which a species can tolerate and remain in neutral energy balance. The climate space for each species is constructed by putting realistic mutually compatible limiting values for body temperature, metabolic rate, evaporative water loss, and coefficient of convection into the energy budget equation. The equation is solved for the combinations of radiation absorbed, ambient temperature, and wind velocity which balance the equation. The upper limits of the climate space of E. speciosus are lower than the upper limits of the other three species' climate spaces. The sagebrush habitat is frequently outside of the climate spaces of all four species. E. minimus makes use of hyperthermia, retreats to its burrow, and probably uses transient excursions beyond is average steady—state limits so that its fundamental niche includes the sagebrush desert habitat whereas the fundamental niches of the other three species do not. The accuracy and predictive potential of the climate spaces are revealed by comparisons with field observations.

ISSN:0012-9658    

DOI:10.2307/1937625

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

Parnell (1969) gathered data on foliage type and habitat zone preferences of warbler species during spring migration and the immediate postmigratory period. Occurrences of species were recorded in four data sets: (i) foliage type, spring migration; (ii) foliage type, postmigration; (iii) habitat zone, spring migration; and (iv) habitat zone, postmigration. The present study is a re—analysis of Parnell's data by a number of statistical methods. The species that are most broadly distributed within the habitat have indices of ecological diversity (H) or niche breadth, of from 3 to 5 times greater than the most narrowly distributed forms. There is no correlation between H in foliage types and H in habitat zones within seasons, but there are significant correlations for H between spring migration and post—migration samples within vegetational subdivisions. Average H is not significantly different between seasons for either foliage type or habitat zone data. The dominant component of H is the number of vegetational subdivisions occupied, rather than the equitability of distribution within subdivisions. Ecological similarity (S = complements of average Euclidian distance in hyperspaces defined by vegetational subdivisions) among species is assessed by cluster analysis of each data set. S among species is not correlated between foliage type and habitat zone occurrences within seasons, but is correlated between spring migration and postmigration samples within vegetational subdivisions. Average ecological distance among species is greater in the reproductive season than during spring migration for both foliage type and habitat zone data. Increased segregation among species in the breeding season may be due to the reduction in the number of warbler species in the study area during that time, seasonal shifts in behavior as regards interaction of species, or simple population differences.

ISSN:0012-9658    

DOI:10.2307/1937626

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

Ingestion rates, as influences by temperature, of the four layers of mor (L, F_1, F_2, H) by saprovores, and of saprovores by predators, were estimated in microcosm studies. Taxa used were Symphypleona, Poduromorpha, Entomobryomorpha, total Collembola, mature Oribatei, immature Oribatei, total Oribatei, total saprovores, and total predators. Several linear differential equations were used as models, in which the elimination rates were either held constant or temperature—and—body—sized—adjusted. Estimated ingestion rates for total saprovores, with temperature—and—body—sized—adjusted elimination rates, were 0.009. 0.022, 0.052, and 0.046 day(—1) at 6 degrees, 15 degrees, 25 degrees, and field temperatures, respectively, with 41%, 39%, 17%, and 3% of their food supply coming from the L, F_1, F_2, and H layers, respectively. Estimated ingestion rates for total predators, using one of two models and with temperature—and—body—sized—adjusted elimination rates, were 0.018, 0.023, 0.033, and 0.020 day(—1) at 6 degrees, 15 degrees, 25 degrees, and field temperatures, respectively.

ISSN:0012-9658    

DOI:10.2307/1937627

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

Density—dependent selective values illustrate the evolutionary effect of population—regulating processes that diminish an individual's probability of survival with increased crowding. The selective values, assumed to decrease as a linear function of density, lead in a mild environment to the evolution of phenotypes having a high carrying capacity, K, at the expense of a low intrinsic rate of increase, r. A graphical technique shows that selection causes evolution of phenotypes having a high r at the expense of a low K in harsh seasonal environments. A mathematical technique developed for analyzing evolution in coarse—grained seasonal environments reveals genetic mechanisms, including ones with full dominance, with which a moderately harsh seasonal environment causes stable polymorphism between high—r and high—K genes. The energy balance equation demonstrates the role of high—r and high—K phenotypes in the population's energy flow. A high—r phenotype makes a large expected contribution to the population's productivity under conditions of negligible crowding, and a high—K phenotype has, for a given contribution to the population's productivity under uncrowded conditions, a low sensitivity to having that contribution diminished by crowding.

ISSN:0012-9658    

DOI:10.2307/1937628

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

This paper examines the effect of natural selection on the composition of a population when the expected numbers of offspring of the different genotypes are decreasing functions of population size. It is shown that the eventual outcome of selection (whether there is a stable polymorphism or fixation of one or other allele) is determined by the genotypic K—values, but that the r—values influence the composition of equilibrium populations. With certain r—values there may be permanent oscillations in population size and gene frequency. A different model of selection, where selective differences are unrelated to differences in r and K in a regulated population, is also described and its relevance to the problem of genetic load is discussed.

ISSN:0012-9658    

DOI:10.2307/1937629

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

Four species of Acrasieae (Dictyostelium mucoroides, D. purpureum, Polysphondylium pallidum, and P. violaceum) coexist in forest soils. All are capable of feeding and reproducing on a wide variety of bacteria than exist in their habitat. The four Acrasieae and four strains of food bacteria were isolated from the soil. When the four slime molds were forced to compete on a single strain of bacteria, one species always outcompeted the others. For any particular food the same species of Acrasieae is the consistent winter. Each species uses a different strategy to outcompete its competitors. The consistency of competitive success and the coarse—grained nature of the food distribution allow the coexistence of these four species of Acrasieae in nature.

ISSN:0012-9658    

DOI:10.2307/1937630

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

At northern latitudes the garter snake (Thamnophis sirtalis parietalis) undergoes a prolonged period of hibernation and has access to food only from mid—May to mid—September. An examination of seasonal changes in the body composition of this organism revealed that protein and ash, expressed as percentage of total body weight, remain essentially constant throughout the year. Lipids are low in the spring, increase during the summer, and decrease during the autumn and winter. Percentage water content exhibits a pattern which is the reverse of that of lipids, with the exceptions of a dehydration in the autumn and a rehydration in the spring. Expressed in absolute terms, for an animal of fixed body length, ash remains relatively constant throughout the year, while all other components show a seasonal pattern similar to that of lipids. The data suggest that the animals are near starvation in May, at the end of an 8—month aphagic period. The period of aphagia and low winter temperatures appear to be the most important factors causing seasonal changes in body composition.

ISSN:0012-9658    

DOI:10.2307/1937631

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY