摘要:

This paper considers various ecological relationships of three gammarid amphipods (Gammarus minus, Stygonectes emarginatus, and Stygonectes spinatus) and one asellid isopod (Asellus holsingeri) in cave streams of the Greenbrier Valley in West Virginia. Two clear—cut cases of reduction of realized niche due to the presence of other species were found: S. emarginatus is limited to small trickles of water when G. minus is present in the stream and A. holsingeri is limited to gravel—bottomed pools when G minus is present in riffles. S. spinatus prefers smaller rocks than do the larger amphipod species. All four species maintained weight equally well on rotting leaves or mud, so feeding differences appear to be minimal. Using Levins' matrix of competition coefficients as a framework, interference and exploitation competition were quantified and separated. From these data, it is indicated that the community is closed to immigration by similar species into the microhabitats occupied by the four crustacean species. Field evidence supports this. Some unused microhabitats may be available, but the aquatic insects that might potentially use them are not present.

ISSN:0012-9658    

DOI:10.2307/1933622

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

Solar radiation, evaporation, air— and soil—temperature extremes, soil moisture, and precipitation were measured on four aspects (SSE, S, SSW, SW) of constant slope in the desert foothills of the Santa Catalina Mountains over a 1—year period. The sequence of warmest and driest aspects based upon annual means was S, SSW, SW, SSE. The warmest and driest aspect may change with the environmental factor considered or the time of year. Drought extremes reached a high peak on the SW aspect during the arid spring, although during all other seasons the SW aspect had the mildest drought conditions. The warmest and driest aspect during the summer rainy season was SSE, during the winter rainy season it was S, and during the fall arid season S and SSE were nearly equal. Few significant differences were found throughout the year between S and SSW aspects. When vegetation and environment are considered, the warmest and driest aspect may also change with the species because plants may utilize different microenvironments at different seasons and vary in their response to similar environmental changes.

ISSN:0012-9658    

DOI:10.2307/1933623

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

The bioenergetics of a detritus—feeding stonefly Pteronarcys scotti, were invetigated. The nymphs were collected from a north Georgia trout stream and held under simulated field conditions of temperature and photoperiod in a laboratory stream. Rates of respiration and egestion were measured at temperatures approximating those in the field at the time of collection. An estimate of the growth rate of nymphs was made from a statistical analysis of monthly field samples. Calorimetric determinations were made of nymphs, molted exoskeletons, and feces. A 17—month energy budget for the average nymph was tabulated on the basis of the data collected. Assimilation and growth efficiencies were found to be low with mean values of 10.6%, 34.2%, and 3.6% for assimilation and net and gross growth efficiencies, respectively. An assessment was made of the rate of leaf breakdown by the nymphs, and a value of approximately 29.1% of the dry body weight per day was calculated. The functional importance of the organism to the stream community is discussed.

ISSN:0012-9658    

DOI:10.2307/1933624

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

Unhandled larvae of Tribolium castaneum (genetic strain cIV—a) were reared in a whole—wheat flour medium (Fortified with dried powdered brewer's yeast, 5% by weight) in a climate of 29°C and 70% RH at three levels of crowding: 100, 200, and 400 per 8 g of flour. At all three densities the median time for pupation was about 18.15 days. Mortality of the developing stages was 3—4% at the 2 lowest densities and about 8% for 400 larvae. Larvae which were subjected to daily handling and reared at the same densities developed more slowly, the prolongation of the larval stage being greatest at density 400. Handling also induced increased mortality at this density but not at lower densities. Handled larvae which were fed eggs of their own kind grew more rapidly than those not fed eggs, and, at the highest egg—feeding rates, the effects of handling and density were almost completely compensated. Evidence is presented that egg—eating would also accelerate the development of unhandled larvae. This is one of the most convincing demonstrations of a nutritional gain on the part of Tribolium cannibals as opposed to noncannibals. We suggest that cannibalism, which is capable of regulating Tribolium populations, is a form of social parasitism which may be favored by natural selection.

ISSN:0012-9658    

DOI:10.2307/1933625

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

In the region of Barnstable Harbor, Massachusetts, 67 species of larger invertebrates were found in 3 faunal associations characteristic of different tide levels. The number of species per sample was highest at the intermediate tide level. Temperatures of sediments and densities of several species were followed for a year at two intertidal levels (60 cm and 90 cm above mean low water). Temperature variation was lower at the 60—cm level than at the 90—cm level at all times of the year, and at both levels was higher in spring than at any other time of the year. In three of the four species studied, spatial variation in density and rate of density change was significantly higher at the 60—cm location than at the 90—cm location. The mortality rate for adult G. gemma was higher at 60 cm (where density was lower) than at 90 cm, while the reverse was true for young—of—year. Release of young began sooner in the spring at 90 cm than at 60 cm. The growth rate of G. gemma at Barnstable Harbor was much lower than that reported at Union Beach, New Jersey, although at both places virtually all growth took place in summer. At Barnstable Harbor the maintenance requirements were 20—30 times higher in summer than in early spring. The Q10within the temperature range 5—20°C was 4.1. G. gemma at 90 cm had less time to feed than at 60 cm, but had higher requirements for population maintenance because of an older age structure and a higher density. The growth rate of G. gemma was higher at 90 cm than at 60 cm.

ISSN:0012-9658    

DOI:10.2307/1933626

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

Both larvae and adults of Thinopinus pictus are nocturnal predators, feeding primarily on beach hoppers (Orchestoidea). When the nighttime tide is low, the beetles emerge onto the sand surface and are characteristically inactive, waiting for passing prey. Mark—recapture studies showed that dispersal is low. Some beetles emerge at almost identical times on successive nights, remaining out for only a few hours. The observable density at any one time may be only one per several square meters, while the actual density is several times greater (e.g., 5 p/m2) because some individuals are always buried. Pitfall traps revealed at 15— to 30—m—wide band of beetles which moves seaward with neap tides and landward with approaching spring tides. Laboratory gradients of sand permeability and moisture indicate that preference for soft wet sand could account for the movements.

ISSN:0012-9658    

DOI:10.2307/1933627

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

Plant composition and coverage and small mammal populations were compared in virgin forest (control) and clearcut (experimental) areas from April 1954 to October 1965. Changes in ground cover vegetation were modest on the control area but marked on the experimental area. A late fall burn on the experimental area may have retarded herbaceous plant establishment. Nearly half of the herbaceous species were invaders not found in the virgin Douglas—fir (Pseudotsuga menziesii) forest. Ground plant coverage was less than 23% in the virgin forest; 1 year after the clearcut area was burned, the cover was 2%; and by 10 years it was above 53%. Woody plant coverage (mostly sprouts) was slightly more abundant the first 2 years after burning. Herbaceous species then became dominant for a 3—year period, after which woody plants gradually gained dominance. Deer mice (Peromyscus maniculatus) increased on the experimental area soon after the burn. The populations varied from an estimated 0.9 to 12.8 animals per acre and fluctuated widely and irregularly. Townsend's chipmunk (Eutamias townsendii), Oregon vole (Microtus oregoni), and snowshoe hare (Lepus americanus) populations also increased on the area at different periods after the burn. Trownbridge's shrews (Sorex trowbridgii), vagrant shrews (Sorex vagrans), and ermine (Mustela erminea) were present on both areas in relatively low numbers. Redback voles (Clethrionomys occidentalis), Douglas' squirrels (Tamiasciurus douglasii), and northern flying squirrels (Glaucomys sabrinus) were not found on the clearcut. California ground squirrels (Spermophilus beecheyi) migrated to the clearcut and established a modest population. Richardson's voles (Microtus richardsoni), jumping mice (Zapus trinotatus), bushy—tailed woodrats (Neotoma cinerea), and a pika (Ochotona princeps) were visitors.

ISSN:0012-9658    

DOI:10.2307/1933628

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

The influence of meadow mouse (Microtus californicus) populations on grass—land ecosystems was studied at two sites with similar densities of Microtus, but in different types of grassland–a coastal prairie and an inland valley grassland. Height of vegetation, volume of standing crop, and percentage cover were greater at the dry inland site where the annual grass Bromus rigidus was dominant. At the milder coastal site the annual grass Lolium multiflorum and the perennial bunchgrass Danthonia californica were dominant; forbs and other perennial grasses were more important. During a year with high rainfall and moderate densities of Microtus (1967) total standing crop, average height of vegetation, and weight of seed crop at the coastal site increased. Although 1966 and 1968 were both dry years, standing crop, seed production, and volume and cover of vegetation were less in 1968, when the meadow mouse population was high, than in 1966, when it was low. Exclosure studies demonstrated that these vegetation changes resulted from changes in Microtus density. Major food plants for the mice contributed 85% less volume to the vegetation on unexclosed areas after a high density of 395 Microtus per hectare (160/acre). Seed fall from preferred grasses was diminished 70% on grazed areas.

ISSN:0012-9658    

DOI:10.2307/1933629

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

Bacterial counts were generally higher and molds were much more extensive and widely distributed at Paradise Harbor on the Antarctic Peninsula, well above the Antarctic Circle, than in areas to the south. Thermophilic bacteria were found only in soils that had been disturbed or contaminated by man and other animals. Mesophilic counts on media made with deionized or sea water, with few exceptions, were in the same range as psychrophiles. Spore—forming bacteria were present in regions where contamination had taken place or where birds nested. During the short summer, significant growth response of the soil microflora to organic additives (peptone and glucose) was observed. However, no correlations could be made with physiological and metabolic activity, which showed no measurable increase.

ISSN:0012-9658    

DOI:10.2307/1933630

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

Plant species which have survived fires for tens of thousands of years may not only have selected survival mechanisms, but also inherent flammable properties that contribute to the perpetuation of fire—dependent plant communities. This concept goes by beyond the commonly accepted fire climate—fuel moisture basis of wildland fire occurrence. Plant communities may be ignited accidentally or randomly, but the character of burning is not random. The following hypothesis treats this interaction between fire and the ecosystem: Fire—dependent plant communities burn more readily than non—fire—dependent communities because natural selection has favored development of characteristics that make them more flammable. The hypothesis was experimentally derived following laboratory combustion tests with litter of eucalyptus (Eucalyptus obliqua L'Herit), ponderosa pine (Pinus ponderosa Laws.), and tropical hardwood leaves.

ISSN:0012-9658    

DOI:10.2307/1933631

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY