ISSN:0012-9658    

DOI:10.2307/1936243

出版商:Ecological Society of America    

年代:1969

数据来源: WILEY

摘要:

Interrelations among temperature, moisture, and viability of grain, and mites, insects, and fungi were studied from 8,135 samples collected at monthly intervals from two 13.6—ton wheat bulks stored in a granary at Winnipeg, Manitoba for 8 years during 1959—67. The bins were fumigated once with phospine (PH3) in August 1965, to determine the effect of the chemical on the existing relationships in the grain bulk ecosystems. Of the 32 possible principal components extracted from 32 variables by the principal—components method, the first 11, accounting for 65.6% of the total variability, were interpreted. The first principal component is a measure of general aging of the grain and fungal succession. The second and third principal components are measures of the major arthropod populations interacting with their physical environment. The analysis shows that Alternaria and its associates Gonatobotrys, Cochliobolus, Nigrospora, which are carried within seeds from the field, gradually disappear in storage and are replaced by Aspergillus versicolor, Aspergillus spp., Penicillium, Absidia, Chaetomium, Rhizopus, and Streptomyces. A grain mite Tarsonemus, which thrives mainly on Chaetomium, is the only arthropod that is positively correlated with the last group of fungi. The abundance of the granary arthropods, Cheyletus, Acarus, Glycyphagus, and Lepinotus is unaffected by time and most fungi, but appears to be regulated by a complex interaction of temperature, moisture, and, in some cases, the depth of the grain bulk. The predatory mite Cheyletus was related to its prey Glycyphagus and Lepinotus, but it did not effectively control the prey population. Interrelations among fungi and between some fungi and some arthropods in bulk grain ecosystems is confirmed statistically. The biological significance of the most important principal components and variables within these principal components are discussed.

ISSN:0012-9658    

DOI:10.2307/1936244

出版商:Ecological Society of America    

年代:1969

数据来源: WILEY

摘要:

The locomotion of eastern chipmunks and least weasels in activity wheels was studied at various illuminance levels on regimes employing both artificial twilights and abrupt changes between day and night light. Several properties of the running of the chipmunks and weasels, and of the white—footed mice of earlier studies, all show the same qualitative dependence on light level. All three animals have a strong tendency to run in only one direction for extended periods of time. They get their directional bearings for this orientation from sightings of nearby objects. The artificial moon is the preferential orientational reference object for mice, whereas other objects in the enclosure seem to be preferred by chipmunks and weasels. The weasels are stimulated to activity by artificial dusks and inhibited by artificial dawn, but not by sudden onset of bright light. The chipmunks are stimulated to activity by artificial dawn. When the length of the daylight period is comparable to that in the wild, they cease activity several hours before dusk. An early "unexpected" dusk or darkness presented while they are active merely slows down their running. These findings and those with white—footed mice suggest the importance of simulating twilights in laboratory investigations of activity and rhythmicity. The fact that the least weasel was 98% nocturnal in light conditions simulating those in the wild suggests that its visual system is evolving from a nocturnal to an arrhythmic type, for this animal is arrhythmic in the field.

ISSN:0012-9658    

DOI:10.2307/1936245

出版商:Ecological Society of America    

年代:1969

数据来源: WILEY

摘要:

We investigated the relative densities of granivorous, nocturnal desert rodents in small plots within two arid regions of Arizona to study how sympatric species avoid competitive extinction. The most common rodents were kangaroo rats, Dipodomys spp., and pocket mice, Perognathus spp. We attempted correlating the density of each species with several environmental measurements, derived from the soil's i) depth; ii) texture or iii) resistance to sheer stress; or from the plant's i) species diversity; ii) growth forms or iii) foliage density. Successful variables were derived from plant growth form and foliage density. The soil's resistance to sheer stress also seemed important for a few species. In general, kangaroo rats were associated with sparseness of vegetation; pocket mice with denseness. One group of mice, which we term bush mice, seemed to require bushes and included two Perognathus spp., three Peromyscus spp., and probably a harvest mouse (Reithrodontomys fulvescens). Two other Perognathus spp. were taken in grassy habitats. Some suitable habitats tended to be complementary to others, suggesting that species associated with them are competitors. Comparisons of the density and distribution of D. merriami, present in both regions but under different biotic circumstances, reinforces the opinion that competition is responsible for the complementariness of habitats. In some cases the evidence suggests that competitive coexistence is accounted for by the fact that different specializations are needed to escape predation in different environments. We use variables which correlate with the relative density of various species to construct a model of habitat complexity. The rodent species diversities obtained in our plots can be approximately accounted for by this model. The model is based on the premises that the rodents collectively discriminate four qualities of soil surface, and three heights and two densities of vegetation. In general, specializations based on biotic variables appear most important.

ISSN:0012-9658    

DOI:10.2307/1936246

出版商:Ecological Society of America    

年代:1969

数据来源: WILEY

摘要:

The object of this paper is to discuss the relationship of the Weddell seal (Leptonychotes weddelli) to its habitat, the fast ice of Antarctica. Movements and distribution of Weddell seals during summer are governed by presence of fast ice and availability of breathing and exit holes. It is suggested that this applies during winter also. Local populations are relatively discrete and there is limited emigration and immigration. This is supported by demonstration of significant genetic differences in blood serum transferrins from seals at McMurdo, Mawson, and Wilkes. My data support the hypothesis that the Weddell seal is not migratory but moves as the distribution of breathing holes during winter dictates. Subadults were shown to be distributed further out on the fast ice than adults. Inaccessibility and potential danger involved in reaching this area have resulted in a paucity of sightings of subadults and given rise to the theory that they migrated to the pack ice. The location of pupping colonies is determined by physical factors, mainly glacial movement and tidal action, independent of biological considerations such as exposure or accumulation of drift snow. Adult females show a high degree of fidelity to particular colonies for pupping in successive years. During the pupping season, seals are spaced in the pupping colonies and nonbreeding seals and subadults are excluded from these areas. After weaning of pups, and probably mating of adult females, the mean distance between seals on the sea ice is reduced and subadults are tolerated in these areas by adults. Even so, there is a higher proportion of adults than subadults at new cracks which continually form south of the pupping colonies through the summer. This is probably due to competition for a new food source. The behavior and movements of the Weddell seal in the fast ice of the Antarctic are almost identical to those of its ecological counterpart, the ringed seal (Phoca hispida) in the Arctic and are interesting examples of parallel evolution.

ISSN:0012-9658    

DOI:10.2307/1936247

出版商:Ecological Society of America    

年代:1969

数据来源: WILEY

摘要:

Microtus pennsylvanicus and M. ochrogaster are sympatric in southern Indiana grasslands. From June 1965 to August 1967 four populations were lived trapped, three of them in 0.8—hectare (2—acre) outdoor pens. Both species increased during 1965 and reached peak densities in summer 1966. Microtus ochrogaster declined abruptly that fall and remained low; M. pennsylvanicus declined the following spring. One of the fenced populations increased to a density about three times that of its unfenced control. By early fall 1966 it had nearly destroyed its food resources and then suffered a severe decline associated with obvious overgrazing and starvation. No such overgrazing has been seen on any unfenced grasslands in this area. Dispersal is probably necessary for normal population regulation in these voles, since fenced populations seem unable to regulate their density below the limit set by starvation. Both species bred extensively in the winter of 1965—66 during the phase of population increase. There was little or no breeding during the winter after the peak. Survival of females in the trappable population of both species was high and relatively constant until the end of the cycle. In males, periods of low survival punctuated the increase and peak phases, and these periods of low male survival did not occur at the same time in the two Microtus species. Some mortality processes are thus highly specific for sex and species. In the fenced populations survival rates were very high and no sporadic male losses occurred. Increasing and peak populations of M. pennsylvanicus and M. ochrogaster are characterized by adults of large body size. During the increase and peak phases some voles stopped growing at low weights (30—40 g) while others reached high asymptotic weights (45—55 g). The demography of these Microtus species in southern Indiana is similar to that of other cycle voles and lemmings in temperate and arctic areas.

ISSN:0012-9658    

DOI:10.2307/1936248

出版商:Ecological Society of America    

年代:1969

数据来源: WILEY

摘要:

Partial differential equations which describe the dynamics of single species populations are applied to Daphnia pulex. Whenever possible, experimental results are used to determine pertinent parameters. Tests are performed to find parameters upon which the model has a critical dependence. The model gives results which are qualitatively in agreement with empirical populations.

ISSN:0012-9658    

DOI:10.2307/1936249

出版商:Ecological Society of America    

年代:1969

数据来源: WILEY

摘要:

Distribution of juvenile manini in tide—pools and on reef flats was significantly correlated with water depth and with cover availability. Substratum type, degree of water movement, and presence of conspecifics were also of potential value as stimuli for habitat selection, but water temperature, salinity, and oxygen content were eliminated as possible cues. Laboratory experiments were conducted testing the responses of juvenile manini to light intensity and direction, to substratum texture and color, to the presence of conspecifics, to variations in degree of water movement, and to presence of food algae. Habitat selection by manini was primarily a response towards a substratum containing suitable food and cover, in a depth of water appropriate to the size of the individual fish. Degree of water movement and presence of conspecifics had a minor influence on the selection process.

ISSN:0012-9658    

DOI:10.2307/1936250

出版商:Ecological Society of America    

年代:1969

数据来源: WILEY

摘要:

The tube building polychaete worm, Clymenella torquata, occurs on the Atlantic coast of North America in estuarine situations. Investigations of the physical environment and the density of the worm populations in the Newport River estuary, North Carolina, showed that the species is found in greatest numbers near low water, in areas where the median particle size of the substrate is between 0.2 and 0.32 mm and where the salinity remains above 25%. From laboratory experiments on the survival of worms under controlled conditions a 50% lethal temperature of 39.2°C was recorded; and 15% salinity resulted in a 50% lethal time of 45 hr. The combined effects of temperature and salinity were tested. The efficiency of tube building under different conditions of temperature and salinity and with substrate particles of various sizes was tested and shown to be at a maximum at 25°C and 35% salinity using particles between 0.25 and 0.42 mm in diameter.

ISSN:0012-9658    

DOI:10.2307/1936251

出版商:Ecological Society of America    

年代:1969

数据来源: WILEY

摘要:

The effects of density on growth and survivorship of Bufo americanus tadpoles and the importance of some predators were investigated experimentally in two small ponds in southeastern Michigan. Tadpoles were raised through metamorphosis at different densities and food levels in screened inclosures placed in the ponds. Most inclosures were open to the natural substratum but others were completely screened to exclude larger predators. In one pond experiment, time of metamorphosis, individual growth variability and mortality were directly related to initial tadpole density, and transformation size was inversely related. The addition of food (natural periphyton on plant litter) produced a density—dependent increase in growth rate. The density—related mortality was correlated with variations in growth rate among pens. Growth rate was correlated with submerged plant cover in the pens. Neither survivorship nor growth was correlated with predator densities. The other pond experiment was characterized by a lack of significant density effects and by high mortality rates. Mortality was correlated with abundance of predators, chiefly nymphs of Odonata and the small leech Batrachobdella picta. Comparison of experimental tadpole densities, growth rates, survivorship and environmental conditions with those of tadpoles in undisturbed environments indicates that the conclusions reached should have relevance to natural population dynamics.

ISSN:0012-9658    

DOI:10.2307/1936252

出版商:Ecological Society of America    

年代:1969

数据来源: WILEY