ISSN:0012-9658    

DOI:10.2307/1934733

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

This paper describes an investigation into whether or not spring territorial behavior was limiting the breeding density of a population of Great Tits on Wytham Estate, near Oxford. The analysis of distances between neighboring nests showed that nest sites were more spaced out than would be expected from a random distribution; this indicated that interactions between the birds produced at least a local density—limiting effect. In 2 successive years, established territorial pairs were removed from a stable spring population in mixed woodland. The removed birds were rapidly replaced by new pairs. These newcomers were largely first—year birds; they came from territories in the hedgerows that surrounded the wood; the vacated hedgerow territories were not refilled. The hedgerows were found to be suboptimal in terms of reproductive success. Thus territory limited the breeding density in the optimal habitat. Song advertisement is probably important in maintaining territorial boundaries, hedgerow birds being able to detect the presence of individual woodland territory holders by recognizing their songs. The effect of winter food supply on the population was investigated by supplying excess food throughout one winter. This artificial food supplement appeared to have no effect on the number of Great Tits breeding in the wood, but did produce an increase in the case of a related species, the Blue Tit. The results show that territorial behavior influences density; this is not considered to be a function of territory in the evolutionary sense, but rather a consequence of spacing out that has been selected for in some other context. A possible advantage of spacing out in the Great Tit is as a defense against predators. Territory size varies considerably from year to year. These variations are the result of interactions between the birds themselves, rather than direct adjustments of territory size to fluctuations in some environmental resource. Even though territory has an effect on the number of birds breeding in the wood,it is not an important density—dependent factor acting to regulate the population.

ISSN:0012-9658    

DOI:10.2307/1934734

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

A new theoretical approach to the study of distribution is presented in this paper. The central concerns the types of interactions between organisms and their surroundings which may function to impose limits on the occurrence of species on a smooth unifactorial environmental gradient. The theory is constructed of a set of three complementary and mutually exclusive models which arbitrarily are given the power of accounting for all possible distributions. Each of the models predicts a different patter of distribution within a group of organisms and each contains two or more unique features which serve to distinguish it from the others. In their simplest form the models state that the occurrence of species is limited respectively by: (i) physical or biological conditions that vary in parallel with the measured gradient, (ii) competitive exclusion and (iii) environmental discontinuities (ecotones). Predictions of each model include (a) the shape of population density curves, (b) the shape of congruity (faunal attenuation) curves, (c) distributional patterns at the termini of gradients, and (d) the form oft he frequency distribution of ecological amplitudes. Application of the theory is demonstrated with data obtained in a study of the distribution of bird species on a uniform elevational gradient in the Eastern Andes of Peru. A series of four expeditions to the Northern Massif of the Cordillera Vilcabamba, a vast undisturbed mountain wilderness, provided information on the upper and lower limits of occurrence of over 410 species of forest birds. Faunal composition and the relative abundances of many species wee estimated at each of 15 stations through large netted samples of birds (170—604 individuals). Following a protocol described in the text, the upper and lower limits of 261 species were assigned to one or another of the three models. Certain limitations of method result in a small number of unavoidable errors in these assignments; hence the outcome of the partitioning procedure is only a first approximation. As evaluated by this preliminary analysis, the three mechanisms of distributional limitation differ appreciably in their importance in the Vilcabamba avifauna. Ecotones account for less than 20% of the distributional limits, competitive exclusion for about one—third of the limits and gradually changing conditions along the gradient for about one—half of the limits.

ISSN:0012-9658    

DOI:10.2307/1934735

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

Observations on populations of Branchinecta mackini in temporary ponds, which last for as little as 3 days to as long as 4 months, on a desert playa showed that hatching of dehydrated cysts (eggs) follows initial entry of water into the basin if salinity remains low. Salinity ranges from an initial 0.5% to as much as 34% as the pond evaporates. Hatching is continuous at constant low salinity, but since salinity general increases rapidly, initial hatch is usually of short duration. Additional periods of hatching follow further inflows of water or after meeting of ice, that is, after reductions in salinity. The duration of hatching is inversely proportional to rate on increase in salinity. When salinity of small—volume summer ponds increases at rates above 500 ppm (1,000 (mu)mhos) per day, three in virtual inhibition of hatching. Laboratory studies showed that egg hatching was controlled by both salinity and oxygen operating in various combinations to inhibit or stimulate hatch. The hatching characteristics obtained from laboratory cultures after ejection from ovisacs of living females. The finding that a salinity—oxygen complex regulates hatching in a desert pond permits tentative explanation of a difference between branchiopods of humid and arid regions. In both cases the branchiopods are characteristic of astatic waters, and stimulation of the egg to hatch must be by some factor that changes at the time or origin of the temporary pond. In humid regions the factors of concern are temperature and oxygen. If the water undergoes significant changes in salinity, as it does in arid regions, control of egg hatch may be by both salinity and oxygen, with temperature limited to control of rate of development.

ISSN:0012-9658    

DOI:10.2307/1934736

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

Eight sites of known age were sampled in Glacier Bay National Monument, Alaska, to examine the changes in plant diversity during primary succession in that region. Four strata–trees, tall shrubs, low shrubs—herbs, and bryoid—thalloids–were sampled independently. Data suggested a sequence of wave—like invasions on sites by strata, largely in order of increasing size. Bryoid—thalloids were exceptional in demonstrating a late peak in cover values. In general, diversity of a particular stratum declined during the period in which the stratum dominated the community in terms of foliar cover. Richness (species number) of communities increased rapidly in the first 100 years, then more gradually to reach a maximum in the muskeg steady state. Equitability (evenness of distribution of foliar cover among species) was erratic, but tended to increase with age. After initial rises, three diversity indices showed nearly flat curves with two exceptions: marked decreases in the 30— to 50—year period; and a rise to maximum levels in the final steady state. Total information per unit area calculated from diversity and foliar cover increased in a sigmoid manner with peak information in the final muskeg stage.

ISSN:0012-9658    

DOI:10.2307/1934737

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

Overstory and understory data were collected from 49 forest stands in 27 small stream bottoms in the Gulf Coastal Plain region of southwestern Alabama. The stands were arranged in a single—dimensioned ordination on the basis of the importance values of the persistent species in the overstories. Leading dominant species, from the dry end to the wet end of the ordination gradient, were Cornus florida, Pinus palustris, Quercus nigra, Liquidambar styraciflua, Nyssa sylvatica v. sylvatica, Magnolia virginiana, and N. sylvatica v. biflora. Two important seral species, most prominent at the middle of the ordination gradient and of relatively little importance at either end, were Pinus elliottii and Liriodendron tulipifera. The stand position on the ordination gradient, referred to as the moisture—regime index, was significantly related to water—table depth, soil—surface gradient, and soil pH at 63.5 cm. Failure to obtain significant relationship with other soil variables was attributed to the high frequency of fresh soil deposition in the small stream bottoms. As a check on the ordination analysis, species—present data were used to construct a species—correlation diagram. When species moisture—regime numbers from the ordination analysis were inserted in this diagram, good agreement was revealed in the results of the two independent analyses.

ISSN:0012-9658    

DOI:10.2307/1934738

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

Thirty—four relatively undisturbed stands of vegetation in shallow marsh, nonto slightly saline wetlands in south—central Saskatchewan were examined with respect to environmental influence on species distribution. Four environmental gradients account for the bulk of variation in the vegetation in the vegetation. They are, in decreasing order of importance, disturbance (despite the fact that all stands chosen are relatively undisturbed), available nutrients, water regime, and salinity. The greatest variation in the data from these stands as a whole is in their salinity, but this is not reflected in the vegetation. The correlation between water regime and available nutrients is negative. A number of other factors show minor correlations with the vegetation and with each other. The method of application of principal components analysis used in this study was a valuable aid in the interpretation of the data. It provides estimates of the proportions of (1) the variance associated with each principal component and (2) the total variation in the vegetation data that can be assigned to variation in the environmental measurements.

ISSN:0012-9658    

DOI:10.2307/1934739

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

The hypothesis that North Temperate Odonata can be categorized into spring or summer species by the predominant overwintering instars and the position and duration of the adult flight season was tested for 55 species in North Carolina. Over 3,000 larvae of these species, collected at a time of stable instar distribution (winter), were examined and the population structure determined for each species. The composition of the wintering populations varied from a single instar to (probably) the entire spread of instars, known for the species. The peak occurred in any one of the last four instars, depending upon the species. The spring vs. summer species classification is valid at high latitudes but breaks down at the latitude of North Carolina, where there is a continuum of variance from one type of life history to another.

ISSN:0012-9658    

DOI:10.2307/1934740

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

Some of the relationships between a lobster (Homarus americanus) and the dimensions of its shelter have been examined. Field studies showed that lobsters generally occupied shelters in which the height was less than the width, and that there was a correlation between lobster size and shelter size. In the laboratory lobsters chose low profile shelters when given a choice of flat (height = ½ width) versus square (height = width) profile openings. Back doors were often present in the field, and laboratory experiments suggested that some sort of constriction before the rear opening was necessary to qualify it as a back door. The amount of time spent in eight opaque or transparent shelter under bright, dim, and dark illumination was measured. In bright and dim light with opaque shelter, lobsters spent significantly more time in a shelter than in the other treatments, showing darkness to be major factor in shelter selection. Shelters are excavated by pushing sand or gravel with the third maxillipeds in a bulldozing motion or by digging with the first two or three pairs of walking legs, followed by a vigorous fanning of the pleopods.

ISSN:0012-9658    

DOI:10.2307/1934741

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

Embryonic thermal adaptations of the frogs, Rana aurora aurora and Rana pretiosa pretiosa from the Pacific Northwest, are described. Limits of temperature tolerance of young R. aurora embryos are about 4—21 degrees C, both the upper and lower lethals being the lowest for any North American ranid frog. For R. pretiosa, the lethal thermal limits of young embryos are approximately 6—28 degrees C. The tolerance limits broaden as embryos become older, and embryos of both species can survive short—term exposure to normally lethal chronic cold temperatures. The developmental rates for embryos of both species at a wide range of constant temperatures are given. Egg masses of both species are compact and globular. The ova of R. aurora average 3.03 mm, those of R. pretiosa 2.31 mm. R. aurora embryos hatch at stage 21, and R. pretiosa embryos hatch at stage 19, a difference that may reflect the O2needs of the hatching embryos. The O2 consumption by R. aurora embryos between developmental stages 12—15 at 18.5 degrees C averaged 0.59 cmm O2/egg per hour. R. pretiosa embryos at the same stage and temperature averaged 0.57 cmm O2/egg per hour. Field observations of breeding frogs indicate a correlation between breeding habits–such as initiation of breeding season, time of daily sexual activity, male calling behavior, and spawning site–and embryonic thermal requirements. High mortality of R. pretiosa embryos in the field often results from freezing temperatures at night and desiccation of egg masses. These factors do not greatly affect R. aurora embryos. These thermal adaptations of the two western species of Rana are compared with those of species from eastern North America, as an aid in broadening our understanding of the evolutionary strategies within the genus in North America.

ISSN:0012-9658    

DOI:10.2307/1934742

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY