摘要:

Beach hoppers of the genus Orchestoidea, abundant amphipods of the sandy beaches of central California, all live in similar ecological positions on these shores. In this study, differences mainly between the two large species O. californiana and O. corniculata are examined. Competition for burrows between hoppers of the same species is commonly observed. In the early morning hours, large males may be seen fighting for possession of holes left open the night before. Fighting is presumably less energy—consuming than digging a burrow, but since most pugnacity is shown by mature males, possession of a burrow already occupied by a female is also of prime importance. Skirmishes for food items are likewise to be seen. Beach hoppers are eaten by an array of avian predators, mostly diurnal birds, and there is evidence that raccoons, moles, humans, beetles, and other animals take a toll of the hopper populations. Several species of Orchestoidea occur on each of many beaches, but interspecific strife has not been seen often. O. corniculata sometimes occurs at the ends of beaches otherwise dominated by O. californiana, but the reverse situation has never been found. O. californiana is a hopper of long, exposed, flat beaches which are made up of quite fine, well—sorted sands. These shores are commonly backed by dunes or possess wide berms into which the animals can retreat. O. corniculata, on the other hand, is a hopper of short, protected, steep beaches which are made up of fine to coarse, commonly poorly sorted sands. These shores are backed by cliffs or boulder piles preventing escape to the backshore. In the laboratory, individuals of the two species tested for sand size preferences showed O. californiana on the average burrowing in finer sand than did the average O. corniculata. O. californiana has relatively longer appendages than O. corniculata. An analysis, however, indicates no appreciable difference between the two species in the relation of weight and length of the main body mass. Measurements of gill volumes indicate that O. californiana possesses relatively larger gills. Large O. californiana are commonly found in burrows high up on the beach in dry zones relatively far from the reach of the surf, and there they dig holes elliptical in cross section with the entire burrow an open shaft. The sand is actively kicked out onto the surface in two directions. This open burrow, plugged at the top, is used by O. californiana perhaps because oxygen does not percolate so well in the fine sand in which these burrows are constructed, and because these hoppers may need a rapid escape to the surface to avoid cutting surf on their exposed beaches. O. corniculata is never found in the high and dry beach zones; its holes are more nearly circular in cross section; the burrow consists only of an air chamber immediately surrounding the hopper; and the sand is merely pushed onto the surface in a rounded heap. This type of burrow can be dug in fine or coarse sands. In the laboratory, O. corniculata dug faster than O. californiana in both coarse and fine sand, and also faster in coarse than in fine sand. O. californiana dug faster in fine than in coarse sand. O. californiana digs relatively isolated burrows; O. corniculata, closely packed ones. This closeness produces a kind of cooperation in making air spaces and in softening the sand. This lessens the energy expenditure in burrowing in conjunction with the simpler burrowing method, and O. corniculata fights less over used openings in the sand than does O. californiana. In the laboratory, O. californiana tended to dig in wetter sand than did O. corniculata. Wet sands packs more firmly than drier sand and the choice of wet, firm sand by O. californiana mirrors their fine sand beach habitat in which capillarity maintains surface moisture. O. corniculata in nature burrows in softer sand, softer by virtue of its coarser texture, lower water content, and the conditioning by members of the concentrated population. These considerations suggest that the hoppers may locate optimal beach zones by sample digging to estimate the moisture content rather than by using moisture—sensing organs. Test of the relationship between sand particle size, moisture content, and penetrability of sand show that there is an inverse relationship between particle size and total water capacity of sand; there is an inverse relationship between moisture content and penetrability; and there is a direct relationship between sand particle size and penetrability. Osmotic influx represents the lethal factor for these animals in tap water, but sea water has no lethal effects provided enough oxygen is available. O. californiana is more tolerant of fresh water. O. corniculata qualifies for higher success on many beaches because of its high population densities. In contrast, O. californiana may have a larger total population because of the much longer stretched of exposed beach available to it in spite of its much lower concentration at any one point. Although there is some overlap of distribution, the requirements for survival are sufficiently different in two species that Gause's principal is not contradicted.

ISSN:0012-9658    

DOI:10.2307/1934916

出版商:Ecological Society of America    

年代:1964

数据来源: WILEY

摘要:

Studies of the variation in productivity in inbred strains of Tribolium confusum and Tribolium castaneum were undertaken to determine the effects of inbreeding on different strains of common ancestry. Six strains of each species were tested after eight to ten generations of inbreeding by full sibling crosses. The founding parents of each strain were taken from synthetic populations, on of T. confusum, another of T. castaneum, each of which had been established by systematic crosses involving stocks of different origin. Three pairs of sibling strains, two of T. confusum, one of T. castaneum, each pair derived from the same ancestral parents in the founding generation of inbreeding, were included in the 12 stains investigated. In length of productivity period, significant interstrain variation in means and variances was found for the strains of T. castaneum investigated. Differences between the strains of T. confusum examined were found to be not significant. In total 120—day productivity, significant intraspecies, between—strain variation in means and variances was found for both T. confusum and T. castaneum. Analysis of per—day productivity for a 40—day period revealed significant strain differences in productivity in T. confusum; interstrain differences in variance could not be demonstrated. In T. castaneum, significant interstain variation in means and variances was found. Interstrain differences in productivity reflect genotypic differences due to inbreeding as well as genotypic differences of the founding parents of the different strains. Differences between sibling strains, having the same founding parents, are attributable to inbreeding only. The two sibling strains of one pair T. confusum tested exhibited remarkable similarity in all traits compared. The other pair of T. confusum showed slight though significant differences only in total 120—day productivity period and per—day productivity. Difference in total productivity fell short of significance, but the difference in variances was significant. Apparent interstrain variation is greater in T. castaneum than in T. confusum for all three traits analyzed. T. castaneum appears to perform relatively better and T. confusum relatively less well in competition experiments than would be indicated by their basic productivity.

ISSN:0012-9658    

DOI:10.2307/1934917

出版商:Ecological Society of America    

年代:1964

数据来源: WILEY

摘要:

Three species of hymenopterous parasites of the spotted alfalfa aphid were reared over a range of constant temperatures. At each thermal level, life—table data were obtained for each species. These data were used in computing certain statistics concerning reproduction and rates of potential population increase which are valuable in assaying the effectiveness of each species as an aphid parasite. The temperatures studied ranged from 10 to 35°C, and the relative humidity was held as constant as possible between 40 and 60%. Artificial illumination and photoperiods were identical in all studies. The studies showed that the braconid, Trioxys utilis Muesebeck, generally has the highest mean total fecundity of the three species, although the aphelinid, Aphelinus semiflavus Howard, produced more eggs in the temperature range of 18 to 22°C. The gross reproductive rate and net reproductive rate of T. utilis were also higher than the other parasites throughout most of the temperature range studied, although again A. semiflavus showed higher reproductive rates between 24 and 27°C. The innate capacity for increase, rm, of T. utilis was decidedly the highest of the three parasites at all temperatures. The braconid, Praon palitans Muesebeck, was inferior tot he other two parasites in nearly all phases of these life—table statistics. Its inclination to enter a facultative hibernal diapause at relatively mild temperatures, plus its intolerance of higher temperatures, which the other two species endured, limited its thermal range of effectiveness. Statistics such as total fecundity, gross reproduction, rate, net reproduction rate, and innate capacity for increase are discussed relative to their value in indicating the potential effectiveness parasites can be expected to possess in the field.

ISSN:0012-9658    

DOI:10.2307/1934918

出版商:Ecological Society of America    

年代:1964

数据来源: WILEY

摘要:

MacAthur's model was derived to predict the relative abundance of species in adequately sampled sympatric associations in which niches are contiguous and nonoverlapping, the species are comparable in size and physiology and are maintained in equilibrium so that relative abundances are constant. The model is applicable only to homogeneously diverse biotopes in which the range of the environmental mosaic is small in relation to the requirements of the inhabitant species. These factors require that the niche arrangement be the outcome of competitive exclusion. Data are presented on the adequacy of the MacArthur model in describing the relative abundance of fish, ophiuroids, gastropods, pagurid crabs, and ciliates. In addition, summaries of previously reported tests are included. By comparing groups which are adequately and inadequately described by the MacArthur model, it is possible to examine the characteristics which may establish the equilibrium. It is hypothesized that characteristics of importance are length of life cycle, duration and frequency of reproduction, and relative (to generation time) constancy of environmental conditions. It is shown that when fish or gastropod species are tested, the goodness—of—fit to the model's predictions is related to the taxonomic affinity of the group being tested. Stable associations of species with high taxonomic affinity must be highly organized. A high degree of organization is required to maintain the random distribution of abundances. Density dependent competition for food is the most likely bases of this organization.

ISSN:0012-9658    

DOI:10.2307/1934919

出版商:Ecological Society of America    

年代:1964

数据来源: WILEY

摘要:

During the horn fly seasons of 1959 and 1960, experiments were conducted to determine the relationship of weather conditions to horn fly populations on three breeds of dairy heifers, to correlate the effect of the macroenvironment on the microenvironment within the 1/2 in. mantle of a heifer, and also to correlate the locations of horn flies within this mantle with various factors of the microenvironment. Usually there was a significant difference between the number of horn flies on Holstein and that on Guernsey and Jersey heifers. The flies generally preferred the dark—colored areas of biocolored cattle during daylight hours, and the black of the Holstein to the tan of the Guernsey. When the macrotemperature was above 85°C, many of the flies were found on the white skin of the belly and udder area of heifers. During inclement weather the flies were observed on both the white and dark—colored areas of all heifers. Macrotemperature and relative humidity influenced the horn fly populations within the biocenose. The apparently preferred macroclimate for macroclimate for horn flies was: temperature 73 to 80°F, relative humidity 65 to 90%, scattered light showers, and no wind. The flies apparently sought certain microenvironmental conditions most commonly observed on Holsetin heifers. Within the mantle of microenvironment, horn flies appeared to prefer an air temperature of about 85°F, a skin temperature of about 97°F, and a relative humidity of about 65%. When such conditions were not available to the flies on the sides and backs of Holstein heifers, the flies were usually found in near—optimum conditions along the belly midline for each of the three breeds of heifers.

ISSN:0012-9658    

DOI:10.2307/1934920

出版商:Ecological Society of America    

年代:1964

数据来源: WILEY

摘要:

Territories of birds, usually defended against conspecific individuals, are sometimes defended against individuals of other species. Since such behavior is demanding both of time and energy, natural selection should favor ecological should favor ecological divergence, the establishment of overlapping territories, and the reduction of aggression. Lack of divergence in modes of exploitation could mean that insufficient time has elapsed for the changes to be completed or that the environment imposes some limitation preventing the evolution of the required degree of divergence. Such environmental limitation can be predicted in (a) structurally simple environments, (b) when feeding sites are strongly stratified in structurally complex vegetation, or (c) when the presence of other species in the environment prevents divergence in certain directions. The known cases of interspecific territoriality in birds are analyzed and shown to be largely in accordance with these predictions, although several cases of overlapping territories in situations where interspecific territoriality has been predicted provide relationships worthy of further study. We suggest that Darwinian selection at the level of the individual permits an understanding of the known structure of avian communities and that there is no need at present to invoke new selective mechanisms at the level of the community or ecosystem.

ISSN:0012-9658    

DOI:10.2307/1934921

出版商:Ecological Society of America    

年代:1964

数据来源: WILEY

摘要:

The eight species of lizards of the genus Anolis in Puerto Rico can be divided into four morphological similarities. One, Anolis curvieri, is very different from the rest and has not been discussed here. The other seven species fall into three groups. Each of these groups occupies a different structural habitat which can be defined in terms of perch height and perch diameter. Within each of these three groups the species have very similar but not indential structural habitats but differ very widely in climatic habitat defined in terms of shade. Shade preferences seem to result from the temperature preferences of the species involved. In each group there is one species with high shade preference which is essentially restricted to the mountains. Each group also has a species with a lower shade preference which occurs in the lowlands and extends up into the mountains in exposed or sunny situations. One of the three groups has an additional species which is restricted to the hot and southwest corner of Puerto Rico. When one compares the temperature preferences or eccritic temperatures of the various species, one finds in each group that the highland species has a lower eccritic temperature than does the lowland species. There is little temperature difference between the lowland species and arid southwest species in the group where this additional third species is present. The species within each structural habitat show many morphological similarities which may be the result of their being closely related or may be the result of adaptation to similar environments. The differences in microhabitat between the Puerto Rican anoles separate them spatially though not completely. In species occupying different structural habitats in the same area the overlap may involve part of the home range of most of the individuals in the area. In species occupying the same structural but different climatic habitats the overlap may involve all of the home range of some individuals but of only a small fraction of the individuals in the total population. The spatial separation among Puerto Rican Anolis can be suggested to be of ecological significance because it reduces interspecific competition and because it allows the various species to adapt more precisely to different parts of the available habitat. Thus members of a genus may exploit the habitat more efficiently.

ISSN:0012-9658    

DOI:10.2307/1934922

出版商:Ecological Society of America    

年代:1964

数据来源: WILEY

摘要:

Patterns of settling, growth, gemmule formation, and disappearance of sponges in Hatteras Harbor are presented for a one—year period and related to water temperature. Ten species are represented in the harbor, of which eight were recorded settling on submerged clam shells. Certain water temperatures, critical for some sponges, are realized two months earlier than in Milford Harbor, Long Island Sound. In response to these temperatures, certain events in the life cycles of Microciona prolifera and Haliclona loosanoffi occur two months earlier in Hatteras Harbor. In Hatteras Harbor, the latter species persists throughout the winter, exhibits two periods of settling, and relies on gemmules to survive adverse summer conditions, whereas in Long Island Sound it exhibits a single period of settling and relies on gemmules to survive adverse winter conditions. Observations are also made on competition for space by sponges and by the compound ascidian, Botryllus schlosseri, and on other aspects of the ecology of sponges in Hatteras Harbor.

ISSN:0012-9658    

DOI:10.2307/1934923

出版商:Ecological Society of America    

年代:1964

数据来源: WILEY

摘要:

A reassessment of the difficulties inherent in size—frequency identification of pollen indicates that the reliability of the method is of low order. Accurate identifications assume: (1) Adequate data on size variation for all relevant extant species; (2) a standardized method of preparation for all modern samples; (3) use of mounting medium in which size is stabilized (not glycerine or glycerine—jelly); (4) preparation of all samples from a given fossil profile by an identical technique (not necessarily the same as that employed for modern material); (5)cognizance of the fact that size of modern and fossil grains cannot be compared directly and that the size changes may occur as a function of sediment type within a profile; and (6) presentation of size—frequency curves for the fossil material. New Pollen size measurements for the 13 eastern pines indicate that no single species can be identified on a size—frequency basis. The mode for small pine grains described by Frey from the full—glacial portion (M Zone) of the Singletary Lake profile could have been contributed to by either jack pine or red pine (or both). These data and new pollen analyses from the M Zone sediments suggest that the dominant full—glacial forest type in the region consisted of widely spaced pines (jack and/or red pine) associated with heliophytic herbs and shrubs (Artemisia, Polygonella, Plantago, Ambrosia, caryophylls, and chenopods). Boreal elements (Picea, Abies, Schizeae pusilla, Sanguisorba canadensis, Lycopodium annotinum, L. lucidulum) may have occurred on more mesic sites surrounding the lakes or on the poorly drained inter—Bay regions.

ISSN:0012-9658    

DOI:10.2307/1934924

出版商:Ecological Society of America    

年代:1964

数据来源: WILEY

摘要:

Arctostaphylos myrtifolia is a California endemic plant limited to only certain outcrops of an Eocene laterite in the Sierra Nevada foothills near Ione and to a kaolin—altered rhyolite and an acid sericitic schist eastward at higher altitudes of 500 m. Taxonomically the diploid species is isolated. Morphologically it resembles a low, sclerophyllous heath. The plants are killed by fire, but seedlings are favored by the ensuing bare areas. It flowers in late winter or very early spring. The climate where A. myrtifolia occurs is dry in summer, wet in winter. Frosts are infrequent and slight, but summer heat is severe. Only some 350 mm of actual evapotranspiration of water is calculated to take place in these environments, but leaching may amount to 200 mm at lower elevations and to 400 mm at higher. The stations for A. myrtifolia do not differ greatly in climate from surrounding areas where the plant does not occur, but they have a somewhat more maritime temperature regime. The soils at these stations are acid and presumably so low in nutrients as to exclude the normal, zonal, climax vegetation. The endemic plant thus is presumed to be a better competitor on the nonzonal sites of acid soil parent material. Many cases of similarly disjunct plant distribution can be related to regionally peculiar soil parent materials whose evident effect is to exclude the regionally climax vegetation. With competition by zonal vegetation thus weakened, disjunct plants can and do occur. The vegetation associated with A. myrtifolia is poor, therophytic, and adapted to acid, seasonally wet sites. Its shows similarities to the Cisto—Lavanduletea of the Mediterranean region. Historical factors of some kind, and not the contemporaneously acting ecologicalfactors alone, are assumed to help account for the limited distribution of the species.

ISSN:0012-9658    

DOI:10.2307/1934926

出版商:Ecological Society of America    

年代:1964

数据来源: WILEY