摘要:

Two bryophyte—dominated communities in the maritime Antarctic are analyzed in terms of the transfer and standing crops of organic matter within them. A moss turf dominated by Polytrichum alpestre and Chorisodontium aciphyllum and a moss carpet composed of Calliergon sarmentosum, Calliergidium austro—stramineum, and Drepanocladus uncinatus with the liverwort Cephaloziella varians were investigated at Signy Island, South Orkney Islands. Biomass, respiration, and production data for the primary producers (mosses, lichens, liverworts, and algae), for the fauna (Protozoa, Rotifera, Tardigrada, Nematoda, Acari, and Collembola), and for the microflora were synthesized, and annual rates of consumption, egestion, assimilation, and production were derived. The two communities showed similar levels of productivity, trophic structure, and efficiencies of organic matter transfer, but different Collembola and Acari standing crops, turnover of mosses, and accumulation of dead organic matter. These features are discussed in relation to the role of biotic and abiotic variables in determining community structure and function.

ISSN:0012-9615    

DOI:10.2307/2937260

出版商:Ecological Society of America    

年代:1981

数据来源: WILEY

摘要:

The mussel Mytilus californianus is a competitive dominant on wave—swept rocky intertidal shores. Mussel beds may exist as extensive monocultures; more often they are an everchanging mosaic of many species which inhabit wave—generated patches or gaps. This paper describes observations and experiments designed to measure the critical parameters of a model of patch birth and death, and to use the model to predict the spatial structure of mussel beds. Most measurements were made at Tatoosh Island, Washington, USA, from 1970—1979. Patch size ranged at birth from a single mussel to 38 m2; the distribution of patch sizes approximates the lognormal. Birth rates varied seasonally and regionally. At Tatoosh the rate of patch formation varied during six winters from 0.4—5.4% of the mussels removed per month. The disturbance regime during the summer and at two mainland sites was 5—10 times less. Annual disturbance patterns tended to be synchronous within 11 sites on one face of Tatoosh over a 10—yr interval, and over larger distances (16 km) along the coastline. The pattern was asynchronous, however, among four Tatoosh localities. Patch birth rate, and mean and maximum size at birth can be used as adequate indices of disturbance. Patch disappearance (death) occurs by three mechanisms. Very small patches disappear almost immediately due to a leaning response of the border mussels (0.2 cm/d). Intermediate—sized patches (<3.0 m2) are eventually obliterated by lateral movement of the peripheral mussels: estimates based on 94 experimental patches yield a mean shrinking rate of 0.05 cm/d from each of two principal dimensions. Depth of the adjacent mussel bed accounts for much of the local variation in closing rate. In very large patches, mussels must recruit as larvae from the plankton. Recovery begins at an average patch age of 26 mo; rate of space occupation, primarily due to individual growth, is 2.0—2.5%/mo. Winter birth rates suggest a mean turnover time (rotation period) for mussel beds varying from 8.1—34.7 yr, depending on the location. The minimal value is in close agreement with both observed and calculated minimal recovery times. Projections of total patch area, based on the model, are accurate to within 5% of the observed. Using a method for determining the age of patches, based on a growth curve of the barnacle Balanus cariosus, the model permits predictions of the age—size structure of the patch population. The model predicts with excellent resolution the distribution of patch area in relation to time since last disturbance. The most detailed models which include size structure within age categories are inconclusive due to small sample size. Predictions are food for large patches, the major determinants of environmental patterns, but cannot deal adequately with smaller patches because of stochastic effects. Colonization data are given in relation to patch age, size and intertidal position. We suggest that the reproductive season of certain long—lived, patch—dependent species is moulded by the disturbance regime. The necessary and vital connection between disturbance which generates spatial pattern and species richness in communities open to invasion is discussed.

ISSN:0012-9615    

DOI:10.2307/2937261

出版商:Ecological Society of America    

年代:1981

数据来源: WILEY

摘要:

Studies of the bioenergetics of the northern pocket gopher, Thomomys talpoides, are coupled with data on demography, activity budgets, and microclimates to model the energy requirements of individuals and populations in the Wasatch Mountains of Utah during 1976—1979. Metabolic rates during rest increased linearly with decreasing ambient temperature, but burrowing metabolic rates (16.3 mL O2°h—1°g—0.75) were independent of both temperature and physical properties of the soil. Radio—telemetry studies indicated that free—ranging gophers are active °50% of each day. Conservative estimates of true energy consumption were calculated using estimates of habitat—specific minimum daily burrowing requirements. Rates of burrowing measures in the laboratory were either °0.0 or °2.0 cm/min. The low burrowing rate was observed when the soil was frozen or saturated with water, as would occur in the field in early winter and in spring, respectively. Gophers burrowed through soil at the study site at an average rate of °1.5 cm/min. Belowground food energy densities at gopher foraging depth declined from 24.6 to 3.2 J/cm3along a successional gradient (subalpine forb meadow to Engelmann spruce dominated forest). We conclude that individual gophers are food limited within the climax spruce seral stage. Further, daily energy costs associated with reproduction in females may exceed the belowground energy supply available in intermediate seral stage (aspen and subalpine fir). Reduction of burrowing rates for any reason will affect gophers in the late seral stages proportionately more than those resident in the meadow. The peak gopher densities recorded (from 62 individuals/ha in the meadow to 2 individuals/ha in spruce forest) support these inferences. Detailed demographic information was obtained only in the meadow seral stage. Adult survivorship was lower in winter than in summer and varied greatly between years (0.18—0.70 yr—1). Juvenile survivorship from weaning through the first winter was comparable to adult annual rates. The fertility rate was 3.75 young°female—1°yr—1. The energy supply and demand analyses indicate that the growth of Thomomys talpoides populations in the early seral stages is seldom directly limited by the amount of food present. From our demographic, environmental, and autecological studies we conclude that stochastic events associated with weather affect energy acquisition (burrowing) rates, and thus survivorship. In montane environments, such events may prevent populations from attaining sizes at which territorial behavior would hypothetically limit further increases. The energy flow through the meadow population at moderate to high (1976—1977) densities (at least 1100 MJ°ha—1°yr—1) indicates that pocket gophers are proficient energy movers relative to nonfossorial small mammals. Subalpine T. talpoides populations appear commonly to attain such densities. More than 30% of the annual primary productivity allocated to belowground parts of meadow forbs may be consumed by gophers.

ISSN:0012-9615    

DOI:10.2307/2937262

出版商:Ecological Society of America    

年代:1981

数据来源: WILEY

摘要:

Seed dispersal of Prunus mahaleb (Rosaceae), a tree producing large fruit crops, was studied in southeastern Spain to establish the degree of reciprocal dependence between the plant and the birds which disperse it. P. mahaleb drupes contain a relatively large seed (pulp: stone ratio 0.62). The water content of pulp is 82.9% and dry flesh contains 3.2% crude fat and 2.8% crude protein, being largely made up of carbohydrates. Four bird species were the main seed dispersers. Visitation rates, feeding efficiency, and degree of dependence on P. mahaleb fruits for food varied substantially among species. Turdus merula and Sylvia atricapilla showed the highest visitation rates, were behaviorally the most efficient, removed the bulk of seeds and, after feeding, tended to fly preferentially towards the apparently safest sites for growth and survival of saplings. They were also most heavily dependent on P. mahaleb fruits for food, whereas the other disperser species relied largely on insects. Individual plant location and dispersers' habitat preferences produced a differential seeding pattern over the patchy habitat surrounding study trees. The "key" dispersers T. merula and S. atricapilla are specialized frugivores, efficiently dispersing seeds of a plant producing large numbers of extremely low—reward fruits. These results conflict with theoretical expectations and suggest that both the nature of the correlation between bird— and plant—related coevolutionary gradients and their amplitudes, as well as the nature of bird—plant coevolutionary interactions, may differ between tropical and temperate habitats.

ISSN:0012-9615    

DOI:10.2307/2937263

出版商:Ecological Society of America    

年代:1981

数据来源: WILEY

摘要:

Under controlled experimental conditions, the influences of light and temperature on the growth and metabolism of Egeria densa Planch, Hydrilla verticillata Royle, and Myriophyllum spicatum L. were comparatively examined. Light was controlled at six levels ranging between 5 and 75% of full sunlight at solar noon. Water temperature was controlled at five levels ranging between 16° and 32°C. Growth considerations included morphology, biomass, and nutrition. Photosynthesis, respiration, and CO2compensation points were determined to evaluate physiological differences in plant growth as affected by the experimental ranges of temperature and light. External morphology in these species was significantly affected by the different experimental light and temperature conditions. Both low light and high temperature promoted extensive shoot elongation and associated canopy formation. Biomass production and carbon metabolism in all species were influenced more by temperature than by light. Each of the species demonstrated metabolic acclimation to light over a broad range. Conversely, the macrophyte species considered here were not strictly capable of acclimating to temperature. Growth rate and the seasonal progression of senescence were interrelated in these species. Higher temperatures stimulated growth and promoted a compression of the growth cycle. The relationship between photosynthesis and respiration (P:R) was appreciably reduced by senescence, but the CO2compensation point did not reflect this condition. In the species examined, CO2compensation points decreased with increasing temperature, suggesting adaptations to low free CO2levels in the environment. Latitudinal differences in integral seasonal temperature, in relation to species—specific ranges of thermal tolerance, appear to be important in influencing the geographical distribution of the species considered here. Light may be the primary determinant of their depth distribution, but its importance in this regard could be somewhat diminished by their significant abilities to extend to the water surface under low light conditions.

ISSN:0012-9615    

DOI:10.2307/2937264

出版商:Ecological Society of America    

年代:1981

数据来源: WILEY

摘要:

Experimental tests of the equilibrium theory of insular biogeography with the terrestrial arthropod fauna of small islands in Northwest Florida are described. Six islets composed of pure Spartina alterniflora (area: 56 m2to 1023 m2; distance from mainland: 29 m to 1752 m) were defaunated with methyl bromide gas after intensive, inclusive censuses of their terrestrial arthropod inhabitants. Two additional islands and a large S. alterniflora stand on the mainland were not defaunated and served as controls. The recolonization process was monitored by weekly nonlethal censuses of all the sites. Four large cages were placed over other, similar, islands to determine the persistence of populations trapped inside the cages in the absence of immigration. In addition, six traps located in the study area showed the general movement patterns of arthropods. A distinction was made between transient and resident species colonizing the islands based partly upon 3 previous yr of data on the arthropod communities of the area. Recolonization of the defaunated islands was rapid. Allowing for seasonal variations typical of the area, the defaunated islands attained a species richness corresponding to the predefaunation levels in approximately 20 wk and oscillated about that level for the rest of the 53—wk experimental period. Extinction probabilities were inversely correlated with area, and immigration rates during the first 20 wk after defaunation were positively correlated with area. Extinctions and immigrations occurred at low levels following week 20, indicating turnover at approximately 0.14 species/wk. No statistically significant effect of isolation on island immigration rates could be demonstrated. Numbers of species collected on the traps were significantly affected by distance from the nearest large land mass and trap orientation. Only area proved to be significantly correlated with insular species numbers.

ISSN:0012-9615    

DOI:10.2307/2937265

出版商:Ecological Society of America    

年代:1981

数据来源: WILEY