ISSN:0012-9658    

DOI:10.2307/1934369

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY

摘要:

Populations of Desmognathus ochrophaeus Cope in the vicinity of Mt. Mitchell, Yancey County, North Carolina, differ from one another with respect to age at first reproduction, a trait in which variation can strongly affect individual fitness. Maturity is delayed in high elevation populations relative to low elevation populations, and in low elevation woodland populations relative to low elevation rockface populations. Juvenile growth rate appears to vary but slightly between populations, so that delay maturity results in individuals being larger at maturity. This may be responsible for the altitudinal size clines noted in D. ochrophaeus by other authors. Body size is positively correlated with clutch size, so that delay reproduction enhances subsequent age—specific fecundity. When populations are compared, indications of delayed maturity are usually accompanied by adult male age structures indicative of higher survivorship. In woodland populations such indications occur in samples from habitats where higher survivorship would be expected. High elevation woodland populations also exhibit higher adult growth rates, which in turn enhance female age—specific fecundities. The degree to which interpopulational differences in life history patterns are genetically based is unknown. The differences which occur are however, compatible with predictions drawn from current theory on the adaptive nature of life history patterns. Specifically, theory predicts that delayed maturity should be adaptive in relative stable environments and where it is accompanied by increased survivorship and fertility. The evolutionary ecology of Desmognathus ochrophaeus is such that these conditions may be met in high elevation woodland environments in southern Appalachians. Evidence for earlier maturity on low elevation rockfaces created by man's activities during 1938—39 suggest that, if these differences are genetically based, natural selection affects are at maturity with great effectiveness. Whether interpopulational differences in age at maturity prove to be genetic or not, interdemic variation in a trait to which fitness is potentially so sensitive is of theoretical interest.

ISSN:0012-9658    

DOI:10.2307/1934370

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY

摘要:

Studies of reproduction and pre— and postnatal growth and development in Myotis thysanodes and M. lucifugus showed that female M. lucifugus copulated in the fall prior to their exodus from the summer roost while M. thysanodes copulated sometime after leaving the summer roost but before their spring return. Ovulation, fertilization, and implantation occurred during the first 2 weeks of May for both species. Gestation has been calculated as 50—60 days for both species. Parturition in M. thysanodes is synchronous with nearly all births within a 2—week period at the end of June and beginning of July. Myotis lucifugus, however, gave birth over a period from June through August. Logarithmic regression lines were calculated for daily prenatal weight increase for both species. Myotis lucifugus grow more rapidly and weigh significantly less than M. thysonades. Regression equations for daily postnatal weight, forearm length, wing span, and fifth—finger length increase in M. thysanodes were calculated and found to be good criteria for estimating age to about 21 days, after which this species has attained adult size. Estimated neonate mortality was low, about 1% for M. thysanodes and 2% for M. lucifugus. Myotis thysanodes was capable of limited flight by 16.5 days of age and of adultlike flight by 20.5 days of age. Myotis lucifugus parallels this attainment of flight quite closely. Wing loading for both species increases slightly from birth to 6 days, followed by a decline to half the birth value at day 20. Aspect ratio for both species increases at steady rate from birth to about 16 days, when it decreases slightly to the adult value. There was no relation of fat index to age in either species, but significant decreases in water index were found with increasing age. Both species demonstrated significant decreases in percentage water and increases in percentage organic and mineral content with increasing age of juveniles. Myotis lucifugus exhibited a significant decrease in spleen weight with age, whereas M. thhysanodes showed no such trend. Neither species showed trends in adrenal weights through the growth period. Several guardian M. thysanodes females stayed with the young during the night. They nursed, retrieved, and in general protected the young throughout the night. Myotis lucifugus did not exhibit this behavior, but large groups of adults would return periodically throughout the night to nurse the young. While M. lucifugus juveniles exhibited practice flight behavior at night, M. thysanodes juveniles were never observed performing this learning process.

ISSN:0012-9658    

DOI:10.2307/1934371

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY

摘要:

Ecological isolating mechanisms based on differences in size or breeding season operate in many groups of related sympatric seabirds, but not in the alcid species (Aves: Fam. Alcidae) found together in Washington State. At least three of the six coexisting species have similar diets, and all six breed at the same time of year. They differ, however, in their foraging zones at sea and appear to have reduced interspecific competition by this means. Diverse aspects of the breeding biology, behavior morphology and ecology of these alcids can be explained by reference to two sets of selective factors–interspecific competition for food and predation upon the eggs, chicks and adults. Species that fish inshore guard their chicks in exposed cliff sites grouped into ubiquitous but small colonies. They carry fish to chicks singly and frequently throughout the day. These young develop rapidly to about one—third adult weight, at which time they quit the nest site. At the other extreme, species that feed far offshore provide burrows for the chick and nest in large colonies on only a few off—shore islands. Chicks are visited at night by adults whose bills are adapted for carrying many fish. These chicks grow slowly and reach close to adult weight before leaving the nest. These patterns are repeated with considerable fidelity in the six—species alcid community of Northern Iceland, but southern hemisphere seabirds are, in general,differently organized.

ISSN:0012-9658    

DOI:10.2307/1934372

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY

摘要:

Timed traps and visual observations were used to measure the distribution of activity of desert insects, principally tenbrionid beetles, in southwest Africa. Differences between species as regards seasonal and daily cycles were observed. Summer and winter faunas were almost entirely different. Measurements showed how hot and cold extremes may be avoided and how activity may be correlated with microclimatic variables. Daily activity of the tenebrionid Onymacris rugatipennis was bimodal in the summer, unimodal in the winter, and the difference could be correlated with the temperature regime.

ISSN:0012-9658    

DOI:10.2307/1934373

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY

摘要:

Vegetative changes were documented for 7 years on permanent milacre plots located in three clearcut logged units in the western Cascade Mountains of Oregon. Plant cover and composition were observed the year prior to logging the old—growth Pseudotsuga menziesii forest, after logging but before burning, and during each of five growing seasons following broadcast slash burning. Total plant cover was 15.2 49.3, and 75.5% in the first, second and fifth years after slash burning, respectively. Invading herbaceous species dominated from the second through fourth growing seasons after burning but by the fifth year residual herbaceous species regained dominance. Differences in disturbance from logging and burning strongly influenced successional trends. In undisturbed soil areas, residual species, such as Acer circinatum, Oxalis oregana, and Gaultheira shallon, dominated. Areas disturbed by logging but unburned supported a wide variety of both residual and invader species. Light to severely burned sites were largely occupied by invaders such as Ceanothus velutinus, Epilobium angustifolium, and E. paniculatum. Although often obscured by varying degrees of disturbance, relationships between early stages of succession and prelogging plant community were discernible. For example, of the species considered characteristic of five undisturbed plant communities, only 13 percent were absent from the plots 5 years after burning. The invaders Ceanothus velutinus, Agoseris grandiflora, and Gnaphalium microcephalum var. thermale were restricted to sites previously supporting rather xeric communities; while Rubus leucodermis and Anaphalis margaritacea were found on plots characteristic of the more mesic communities.

ISSN:0012-9658    

DOI:10.2307/1934374

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY

摘要:

Nutrient fluxes within and through watershed ecosystems at the Coweeta Hydrologic Laboratory are under study. This paper describes the annual budgets and seasonal fluctuations for selected cations. Concentrations and flux of cations moving through a hardwood forest stand, a weed to forest succession, a hardwood coppice stand and an eastern white pine stand on steep mountain topography are compared. Stream discharge was greater by 6% for the successional weed stand, and 10% for the second hardwood coppice, but 15% less for the young pine stand in contrast to pretreatment levels. Although concentrations for Ca(++), Mg(++), K+and Na+combined were usually less than 3.5 ppm, over 98% of the loss of each cation was in dissolved form on all four watersheds. Regression analysis showed that 50 to 60% of the variation in monthly weighted average concentration was accounted for by monthly discharge amounts. Annual losses of the four cations from the mature hardwood stand were in the amounts of approximately 7, 3, 5, and 10 kg/ha respectively for the Ca(++), Mg(++), K+and Na+. Annual budgets showed net changes to be —0.8, —2.0, and —4.3 kg/ha, respectively, for this mature hardwood ecosystem. In contrast, the weed stand lost significantly greater amounts, and the young pine and hardwood coppice watersheds showed a net gain in Ca(++) and significantly lower losses than the mature ecosystem for the other three ions. These budgets show that major alterations to these forest ecosystems are not now producing a substantial out—flux for these cations.

ISSN:0012-9658    

DOI:10.2307/1934375

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY

摘要:

Frasera speciosa is a conspicuous perennial in the Rocky Mountains where it forms discrete colonies whose inflorescences are characterized by almost total absence in some years and greater abundance in others. This sporadic yet synchronous flowering was the most conspicuous feature of the reproductive biology of the species and its adaptive value was worth investigation. In a three—mile stretch of the East River Valley, Colorado, the following data were gathered over a period of three years: the distribution and abundance of colonies, the floral biology, the dispersal of insect visitors among the flowers of Frasera and its floral associates, the frequency of floral predation and seed—set. Although the percentage of plants with inflorescences was always very low and despite the occasional wide spatial separation of individuals, Frasera invariably attracted the greatest number and diversity of floral visitors and never yielded less than 52% seed—set. It was also shown that pollination was affected by a wide variety of inset visitors that maintained cross—pollination at a frequency of approximately 15%. In no colonies was floral predation nearly as heavy as in its sympatric associate Lupinus and it was concluded that seed—set Frasera was not significantly affected by predispersal herbivory. The local synchrony revealed by the occurrence of discrete colonies and the overall synchrony revealed in the almost total absence of floral colonies in some years and their abundance in others is viewed as a strategy for predator avoidance. These mechanisms, together with other aspects of the reproductive biology, also reduce pressure from sympatric species competing for pollinators. It is out that they confer reproductive advantage to a minority species which may otherwise rapidly decline to extinction in the presence of intense competition. The flowering regime of Frasera combines a predator avoidance system which yields widely dispersed colonies in space and in time with a pollination system which successfully exploits the maximum diversity of floral visitors and maintains excellent seed—set whenever and wherever the colonies appear. The systems are clearly complementary in preventing the build—up of predator populations while maintaining an attractive forage source for potential pollen vectors. The combined effect is to maintain the abundance of the species in a variety of stress environments, in turn resulting in a remarkably wide geographic success. It is considered likely that similar systems will turn out to be very common among entomophilous plants in both temperate and tropical regions.

ISSN:0012-9658    

DOI:10.2307/1934376

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY

摘要:

A general equation is derived for the quantity of different foods a predator consumes in response to food preference and food abundance. It is supposed the predator apportions its efforts among different search modes in order to minimize the discrepancy between actual and desired quantities of each food consumed. Included are the conflict between quantity and composition of the diet and the competition between feeding and nonfeeding activities. The properties of the equation are examined and discussed in light of the literature.

ISSN:0012-9658    

DOI:10.2307/1934377

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY

摘要:

A model of competition for aquatic cave invertebrates in the southern Appalachians in which competition affects washout rate in the cave stream is presented. The model accounts for two major generalizations about microdistribution of cave isopods and amphipods in the Applachians: species distribution is uncertain and only one species is found in a habitat patch. The model also predicts the amount of habitat overlap various species pair have. Experiments to verify the model were conducted in an artificial stream.

ISSN:0012-9658    

DOI:10.2307/1934378

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY