摘要:

Pontoporeia affinis, a burrowing amphipod and the predominant macrobenthic invertebrate in the upper Great Lakes, was studied during the summer months of 1960 and 1961 with regard for its association with the bottom sediments. The primary requirement of the sampling method was to obtain an undisturbed sediment sample. A corer was used to achieve this end. The particle size distribution of the sediments in the study area is graded from coarse, well—sorted sands in the shallow water at the mouth of Grand Traverse Bay to fine, less—well—sorted sediments in the deeper water of Lake Michigan. Loss on ignition was utilized to estimate the organic material in the sediments. Over the sandy sediments organic matter was largely restricted to a thin detrital layer. The amount of organic material in the silty sediments of the deep water was several times that of the sandy sediments. Bacteria were counted directly and correlated with depth, particle size, and estimates of the organic content of the sediments. The number of bacteria per gram of dry sediment ranged from 126 x 106to 860 x 106. The distribution of P. affinis in the study area showed no significant correlation with depth, particle size, or organic matter estimates of the sediments, but correlated with the number of bacteria in the sediments. The numbers of P. affinis collected from several of the stations exceeded maximum population densities reported in the literature. In the laboratory P. affinis selected sediment particles smaller than 1 (0.05 mm). There was no apparent resolution of size differences in experiments utilizing sediments finer than 1. There was significant selection of substrates whose surface layers were enriched with organic matter or which were allowed tocondition, assumedly by the growth of bacteria on the substrate surfaces. Relationships of P. affinis to the substrate were shown to be strongly influenced by the presence of bacteria and organic matter in the sediments, one or both of these serving as the energy source for the amphipod populations. The predominance of P. affinis in the benthic community and its high population densities indicate that it accounts for a large part of the energy dynamics of the benthic trophic system.

ISSN:0012-9658    

DOI:10.2307/1934998

出版商:Ecological Society of America    

年代:1965

数据来源: WILEY

摘要:

A carrion study of the baby pig, Sus scrofa Linnaeus, was conducted during the summers of 1962 and 1963 in a mixed mesophytic hardwood—pine community at Clemson, South Carolina. Six stages of decomposition were delimited for carrion exposed to arthropods: fresh, bloated, active decay, advanced decay, dry, and remains. Five stages were recognized for carrion protected from arthropods: fresh, bloating and decomposition, flaccidity and dehydration, mummy, and desiccation and disintegration. Carrion free of insects decomposed and dried very slowly, retaining its form for many months, while 90% of the carrion open to insects was removed in 6 days. Carrion temperature during the bloated through advanced decay stages differed widely from that of air or soil. A definite ecological succession occurred among the fauna of carrion. Each stage of decay was characterized by a particular group of arthropods, each of which occupied a particular niche. Their activities were influenced by physical properties of carrion, rapidity of putrefaction, time of day, and weather. A total and 522 species representing 3 phyla, 9 classes, 31 orders, 151 families, and 359 genera were collected from decomposing pigs. Four orders of arthropods (Coleoptera, Diptera, Hymenoptera, and Araneida) accounted for 78% of the carrion fauna. Two coleopterous families, Histeridae and Staphylinidae and three dipterous families, Sarcophagidae, Calliphoridae, and Muscidae, represented 26% of the fauna.

ISSN:0012-9658    

DOI:10.2307/1934999

出版商:Ecological Society of America    

年代:1965

数据来源: WILEY

摘要:

Populations of the carnivorous opisthobranch Navanax inermis, living in the vicinity of San Diego, California, were studied from September 1961 to August 1962. Three sampling stations were established, one on the open coast and two in relatively sheltered bays. For all stations, population density and prey content of each gut at time of capture are known. Other data, including caloric content of principal prey, rates of Navanax oxygen consumption, and turnover time of food in gut have permitted the energy available to the field population for growth to be estimated. Laboratory studies, including a complete energy budget in which calories of ingestion, egestion, growth, and reproduction are known, gave data on assimilation efficiency (62%) and maximum possible growth rates (small individuals, 7 to 9% wet wt/day; large, 2.1 to 3.8%). Potential growth in the field, determined by assuming complete conversion to new protoplasm of any caloric excess remaining after consideration of the daily metabolic costs, was compared to these maximum laboratory rates and related to density. In bays, an optimum habitat, density and caloric surplus are positively correlated density—dependent cannibalism characterizes populations of small individuals; and all sized individuals are usually food limited. In marginal, open coast habitats, population density appears to be more closely related to events in the physical environment.

ISSN:0012-9658    

DOI:10.2307/1935000

出版商:Ecological Society of America    

年代:1965

数据来源: WILEY

摘要:

Nighthawks, Chordeiles minor, lay their eggs on flat surfaces–in cities on flat roofs–roost in trees, and feed on flying insects which in turn presumably feed on vegetation. Thirteen neighboring nighthawk breeding home ranges in the center of Detroit, Michigan included on the average 10.4 ha total area, 97 small trees (including large shrubs), 70 large trees, and 38 flat roofs, representing 2.25 ha. More or less centrally in each home range and preferentially over flat roofs, whether being used for nesting or not, resident males performed diving and booming displays. High average and minimum distances between the centers of activity of the residents, together with observations of conflict between neighbors indicated that the home ranges were mostly defended and, since including feeding and breeding activities, constituted type A territories. Home range size which varied more than threefold, showed no significant correlation with the density of any environmental feature, including an index of photosynthesis, except for a negative correlation with number of flat roofs per ha. Six of the 13 home ranges bounded a 42 ha area unoccupied by nighthawks, which was, compared with the home ranges, deficient in trees and especially in flat roofs. These six home ranges tended to be larger than the remaining seven, though not to differ from them in density of trees and roofs, and in neither group was there correlation between size and density of these features. Thus, variation in home range size seems best explained by birds settling thickly where flat roofs are numerous, and through mutual aggressiveness having small home ranges, by birds not settling at all where flat roofs are scarce, and by home ranges next to such unoccupied areas expanding into them and/or at the expense of neighbors who must defend their entire boundaries. Although nighthawks do not always defend combined nesting and feeding areas, the apparently primary importance of aggressive interaction in determining home range size, in the present study, suggests that in nighthawks, as well as in other species having more strictly type A territories, aggressiveness at high population levels may reduce the proportion of individuals breeding and population natality rate below what resources would allow. A variety of evidence is reviewed on this point including the interspecific variation of home range size in relation to body mass which suggests that bird home ranges generally contain more food resources than required by the occupants.

ISSN:0012-9658    

DOI:10.2307/1935001

出版商:Ecological Society of America    

年代:1965

数据来源: WILEY

摘要:

Movements of island populations of deer mice were studied by smoked paper tracking supplemented by live trapping. Some mice tracked regularly, others rarely. Some stations were tracked much more than others. The number of track records per night varied greatly, being much greater immediately after trapping than at other times. Tracking was increased when novel track shelters were substituted for familiar ones. Use of shelters is a form of exploratory behavior that occurs most often when the shelters present stimuli strong enough to elicit exploration but not strong enough to repel the mouse. Tracking also was increased when bait was placed in the shelters. The tracking method produces more data than trapping and interferes less with the movements of the mice. However, it has a greater probability of error, produces more variable results, and does not provide data on the condition of the mice.

ISSN:0012-9658    

DOI:10.2307/1935002

出版商:Ecological Society of America    

年代:1965

数据来源: WILEY

摘要:

The nocturnal activity of Armadillidium vulgare in California grassland suggests that this cryptozoan may be very vagile, but earlier attempts to study its lateral movements failed because of its secretive habits. In the present study, assimilated radiophosphorus was used to label isopods and make the recovery of hidden individuals possible. In each of four experiments, cohorts of about 1,000 radioactive animals were released in a grassland area, and the movements and dispersal of the tagged individuals were followed for as long as 25 days. Two of the experiments were conducted during the rainy season and two during summer drought. Activity of the labeled animals, as reflected in their dispersal rates, was greater in summer than in winter. A maximum dispersal rate of 13 m in 12 hr was observed in one of the summer experiments, as contrasted to a maximum of only 10 m in six days in one of the winter experiments. The greatest dispersal distance observed was 25 m (after 20 days in one of the winter experiments). The dispersal patterns can be described by the equation Y = a + c/r, where Y is a measure of the density of labeled animals at distance, r, from point of release, and c is a proportionality constant. A geometrical analogue for this equation, plus a modified dispersal experiment with Porcellio scaber, shows that c/r accounts for density decrease due to the dilution of tagged animals by the increasing area into which they move the constant a is interpreted as affording a relative measure of dropouts, individuals which disappear from the dispersal pattern. Foraging appears to account for the activity of Armadillidium during the winter. In the summer, on the other hand, isopods must search for shelter from desiccative daytime conditions following nightly forages. The search for shelter in addition to the search for food appears primarily responsible for the greater dispersal rate observed during the summer. The physical environment seems to interact importantly with food availability for these isopod populations.

ISSN:0012-9658    

DOI:10.2307/1935003

出版商:Ecological Society of America    

年代:1965

数据来源: WILEY

摘要:

This study investigated the effect of crowding on the survival time and endocrine response of laboratory—reared meadow voles deprived of cover and water. Crowding was experimentally varied in terms of amount of social contact (number of individuals/group) rather than density (number of individuals/unit area). Thecrowded situation consisted of ten animals (five of each sex) in a pen of 15 ft2, theuncrowded situation of two animals (one of each sex) in a pen of 3 ft2–one mouse per 1.5 ftwin both situations. Survival times were recorded for 504 experimental mice. Supplementary data on adrenal weight, spleen weight, thymus weight, body weight, and the amount of wounding were obtained for 888 mice. In the animals provided with an adequate supply of cover, crowding induced hypertrophy of the spleen and of the female adrenal, but it had no adverse effect on wounding or survival. In the absence of cover, however, crowding precipitated much fighting and mortality. Twenty—seven per cent of the crowded animals deprived of cover succumbed whereas none of those with cover died. This mortality was greatest among the males. Crowding lowered the survival time of meadow voles deprived of water with males having a lower survival time than females. Prolongation of the crowding period decreased the survival time in males but not in females. The ill effects of crowding on survival time disappeared within a few days after animals were released from the crowded situation. Crowded animals autopsied after succumbing has slightly enlarged adrenals and greatly enlarged spleens compared with uncrowded animals. The thymus was not affected by crowding. The incidence of wounding in males was greater in the crowded animals. In all cases animal deprived of water showed adrenal hypertrophy, splenic and thymic atrophy, and a loss in body weight. Dominant males in the social hierarchies of stabilized groups showed longer survival times without water than subordinate males. They also showed greater gains in body weight. Adrenal weight, thymus weight, spleen weight, and the amount of wounding in males also varied in relation to social rank but appeared to be more closely related to the stability of a social hierarchy. The females showed very little agonistic interaction and did not organize into recognizable social hierarchies. The low frequency of social conflict and high survival time in females, and the high frequency of social conflict and low survival time in males, suggest that crowding does affect the capacity of an animal to survive in stressful situations. It can be concluded that under the conditions applying in this study crowding operates to regulate populations of voles by increasing the vulnerability of the animals to various deleterious factors. Conclusive evidence remains to be presented that crowding does, in fact, operate to regulate populations in nature.

ISSN:0012-9658    

DOI:10.2307/1935004

出版商:Ecological Society of America    

年代:1965

数据来源: WILEY

摘要:

Niantic Bay and the estuarine basin of the Niantic River were studied as source areas of phytoplankton transported across the shoals which separate the upper estuarine basin from the coastal waters and which support dense populations of bay scallops and other benthic filter feeders. Surface and bottom stations in the bay and estuarine basin and two stations over the shoals, where tidal excursions alternately transport water from offshore and from the estuary, were sampled at 5—week intervals for 1 year. Dinoflagellates predominated in the basin of the estuary and, to a lesser extent, were significant seaward into the Bay. The diatoms were most abundant in the Bay where they followed population trends characteristic of Long Island Sound and coastal waters. Two species of chrysophyceans were abundant, chiefly restricted to these near—shore waters but showing no indications that either the Bay or the more confined estuarine waters were more favorable. When the Bay was the predominant phytoplankton source area, as judged by the counts and population trends, the plankton of the mixed waters over the shoals was similar to that of the Bay in kind and in numbers. When the basin was the predominant source area, the plankton over the shoals, though similar in kind, commonly dropped to one—tenth the abundance found up—estuary. This drop may relate to the vertical migration of the flagellates into deeper waters which do not flow freely across the shoals. The lower plankton counts over the shoals may also result from the mixing of the waters ebbing from the basin with the relatively large volume of water over the shoals following the high tide. In the basin of the estuary the phytoplankton volume fluctuated around a mean of 6.90 mm3/liter. The average for the Bay was 0.23 mm3/liter. Over the shoals the average was 0.63 toward the upper estuary and 0.45 toward the Bay. These averages and other data constitute evidence that the upper estuarine area contributes more phytoplankton to the shoals than do the offshore waters.

ISSN:0012-9658    

DOI:10.2307/1935005

出版商:Ecological Society of America    

年代:1965

数据来源: WILEY

摘要:

Procedures are outlined whereby enthalpy, entropy, and Gibbs' free energy could be determined for biological material from heat of combustion, chemical analysis, and entropy determinations. Some criteria for determining possible energy pathways between species are derived from their free energy concentrations. Rarely will a pathway be thermodynamically impossible.

ISSN:0012-9658    

DOI:10.2307/1935006

出版商:Ecological Society of America    

年代:1965

数据来源: WILEY

摘要:

Four species of bunchgrass were experimentally burned in a portable combustion chamber to determine their resistance to fire as a function of season of burning (June, July, August), intensity of burn (200°F, 400°F), and plant size. Poa secunda was not affected by burning. Sitanion hystrix proved comparatively resistance to burning; it was damaged in July only. This seasonal response correlates with air temperature and relative humidity, which appear to influence the amount of applied heat required to cause damage. Of the species tested, Stipa comata appeared to be most susceptible to fire. The plants suffered high mortality in June, were extremely susceptible to damage from burning in July, but were relatively resistant to fire in August. The seasonal response of Stipa thurberiana was similar to that of Stipa comata, but damage was less severe. Season of burn was the primary determinant of the extent of damage to Stipa species during June and July, but size of plant became increasingly important in determining the effect of burning during the latter part of summer. The difference between maximum soil surface temperatures of 200°F and 400° was apparent only for small Stipa thurberiana plants burned in June.

ISSN:0012-9658    

DOI:10.2307/1935007

出版商:Ecological Society of America    

年代:1965

数据来源: WILEY