ISSN:0012-9658    

DOI:10.2307/1936143

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

The life cycle and energy relations of the giant fairy shrimp, Branchinecta gigas Lynch, in a turbid, aestival lake in western Canada are described for 1972. Hatching of overwintered eggs began when lake sediments thawed in April, at which time salinity was low as a result of snow runoff; hatching ceased after a few days as salt deposits redissolved and salinity of the water incresed. The population, being of almost uniform age, was treated as a single cohort. Larval and post—larval growth in length followed a sigmoid pattern that could be well described by a logistic curve. Maximum growth rates occurring at 3—4 wk of age were 2.54 mm/day for ♂ ♂ and 2.95 mm/day for ♀ ♀, representing daily length increments of 11.3% and 10.3%, respectively. Corresponding max dry weight increases were 33% of body weight per day in each case. Average max lengths of 47.7 mm for ♂ ♂ and 60.6 mm for ♀ ♀ were attained at ages of 40—45 days; max longevity was 60 days. The species is exclusively predaceous for most of its life cycle, feeding primarily upon Branchinecta mackini and Diaptomus nevadensis. Females were estimated to produce three clutches of eggs, with clutch size being proportional to total body length of the ♂, and average fecundity in 1972 was calculated at 630 eggs. Measurements of feeding rate and O2consumption were made over 24—h periods in the lake and an energy budget was cosntructed for most of the life cycle (46 days) on the basis of logistic growth curves fitted to field data. Males assimilated 67% and ♂ ♂ 94% of ingested food, investing 23% and 22% of assimilated energy, respectively, in somatic growth. Molting losses were estimated at 5%—6%, and an extreme estimate of 14% was calcualted to represent nitrogen excretion, on the assumption of strictly carbohydrate and lipid—based metabolism. Maintenance costs were estimated at 58% in ♂ ♂ and 47% ♀ ♀. The difference (11.3%) corresponded precisely to the costs of egg production.

ISSN:0012-9658    

DOI:10.2307/1936144

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

Distributional patterns and species diversity of benthic insects in an alpine stream in Gunnison County, Colorado, USA were investigated on several levels of spatial scale, from faunal replacement over 1,000 vertical m to microdistribution within the stony substratum. Ecotones including zonation in terrestrial vegetation and in trout distribution did not appear to affect faunal replacement. Competition among congeners accounted for 7—30% of the cases, while in the majority of species, faunal replacement appeared to be associated with gradual changes in the physical gradient. Trout zonation may affect total numbers of insects, however, as the trout—free headwaters had two to six times higher insect densities. Microdistribution was investigated by measures of species and substratum patterning in a series of microhabitats (0.093 m2) at a series of sites (separated by 75—150 vertical m), and by field colonization experiments with various substratum choices. I hypothesize that increased substratum complexity leads to greater species richness based on several lines of evidence: (1) different species showed different substratum preferences, (2) colonization of mixed substrata generally resulted in greater mean species richness than did colonization of a single substratum type, and (3) both species diversity and substratum complexity were greatest at the within—microhabitat level. However, substratum composition showed little variation along the elevational gradient and did not appear to be a cause of faunal replacement. The several scales of investigation were complementary, as congeners exhibiting sharp mutual exclusion in vertical distribution had similar microhabitat preferences, while other congeners showed less exclusion and differed in microhabitat preferences. Most of species diversity as measured by H' was found within habitats rather than between habitats while species richness depended equally upon within—habitat variation (owing to rare species) and between—habitat variation (owing to faunal replacement).

ISSN:0012-9658    

DOI:10.2307/1936145

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

Six Maryland populations of the dusky salamander Desmognathus fuscus were analyzed for differences in several life history and related parameters: timing of reproductive season, age at sexual maturity, reproductive rate, sex ratio, age structure, survival rate, and body size. Life history features are essentially similar in the populations. Adult ♀ ♀ lay eggs every year. Oviposition takes place during summer (June to early August). Larvae transform in late spring and early summer at about 9—12 mo of age. Males mature at 2 yr of age, ♀ ♀ at 3 yr. Survival rates (determined from age structures and sex ratios) differ considerably among the populations. Between—population differences in survival are greater for ♂ ♂ and older animals than ♀ ♀ and juveniles, respectively. Percentages of tail regeneration are in accord with these observations. Reproductive rate is greater in populations where adult survival is lower, Part, but not all, of these fecundity differences can be accounted for by positive size—fecundity relationships. Considerable interlocality variation in body size of transformed animals is evident. Body size and adult survival are negatively correlated, but no significant relationship between body size and juvenile survival exists. Populations in the same physiographic province are the most similar overall, but no general geographic trends are evident. Biotic interactions may account for some of the observed interpopulation variation, but evidence is unavailable to demonstrate any evolutionary significance to this variation. This study suggests that a complete understanding of the magnitude and nature of broad geographic demographic trends in organisms may necessitate a consideration of local variation.

ISSN:0012-9658    

DOI:10.2307/1936146

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

Energy flow through salamander populations in the Hubbard Brook Ecosystem is about 11,000 kcal/ha°yr (= 46,000 kJ/ha°yr). This is °0.02% of the net primary productivity, and is °20% of the energy flow through bird and mammal populations. Salamanders are efficient (60%) at converting ingested energy into new tissue and produce more new tissue annually than do bird populations. Salamanders are insignificant agents as “sinks” for nutrients or as agents for nutrient cycling in the ecosystem. Sodium is the possible exception, as an amount equivalent to>8% of the Na in annual litter fall passes through salamander populations; all other nutrients (Ca, Mg, K, P, N, S, and Zn) arethat of most of their invertebrate prey. There is some evidence that invertebrates rich in Ca content, such as snails and mites, are necessary components of the diet of salamanders. Salamander tissue is higher in protein content than that of birds and mammals and represents a source of high—quality energy for potential predators. Salamanders have restricted home ranges and are not significant agents in the movement of nutrients into or out of the system.

ISSN:0012-9658    

DOI:10.2307/1936147

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

Damselfly naiads were fed Daphnia magna in laboratory predation studies. Anomalagrion hastatum predation rates were highest during the first 2 days of the penultimate instar and then declined until ecdysis. The functional response of final instar Ischnura ramburii was most sensitive to changes in Daphnia densities of 5—50/liter. Many more prey were killed than eaten in both studies; this wastefulness increased significantly as densities rose from 5 to 10/liter. Observations of feeding behavior revealed that damselfly naiads frequently strike at and capture prey and then discard them uneaten or only partially eaten. This is presumed to be the proximate cause of wasteful killing. Photographic documentation of gut contents showed that during feeding the foregut often becomes full before the midgut, leading us to hypothesize that wasteful killing occurs when hunger in the midgut motivates capture, but fullness of the foregut precludes eating. When wasteful killing is a normal component of hunger—motivated feeding behavior, it has sometimes been explained by hypothesizing the existence of a hunger threshold which is higher for eating than for capture (Holling 1966). We propose a two—gut—compartment formulation of Holling's simultion model of invertebrate predation which accounts for dynamic characteristics of wasteful killing without hypothesizing an elevated hunger threshold for eating.

ISSN:0012-9658    

DOI:10.2307/1936148

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

Guppies (Poecilia reticulatus) were given two prey: Drosophila (on the water surface) and tubificid worms (on the aquarium bottom). The densities of the two prey were varied gradually over 12 days, from 4:1 to 1:4, and we measured the predators' diets, time of each meal, and time spent at the top, middle, and bottom of the aquarium. The guppies switched, attacking disproportionately whichever of the two prey was more abundant. Switching resulted when the fish increased the fraction of time spent at the surface as the fraction of Drosophila available increased. They did this in response to changing reward rates. Switching caused density—dependent mortality. Differences between two groups of fish show that switching behavior is more efficient and should be selected for. The result confirms previous generalizations about switching.

ISSN:0012-9658    

DOI:10.2307/1936149

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

The ecology and bioenergetics of a population of Trimerotropis saxatilis (Acrididae) were examined in field and laboratory studies. This grasshopper species occurs on harsh, desert—like rock outcrops in the southeastern United States and constitutes one of the important consumers in those ecosystems. The rock grasshopper population studied was located on Panola Mountain, ° 16 km southeast of Atlanta, Georgia, USA. Supplemental population data were collected from a nearby granite outcrop, Mt. Arabia. The energy budget equation used was: Production = Ingestion — Egestion — Respiration. Production, ingestion and respiration were measured, and egestion was determined by difference. The energy budget and population ecology parameters for T. saxatilis were compared with those reported for other orthopteran species. The parameters for T. saxatilis were smaller than for any other population studied, reflecting their adaptation to the harsh environment in which they live. Efficiencies, including production/ingestion and assimilation/ingestion, calculted for several orthopteran populations, were found to be relatively constant, indicating that herbivorous orthopterans function similarly in different ecosystems.

ISSN:0012-9658    

DOI:10.2307/1936150

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

Water potentials, leaf resistances to water loss, and relative saturation deficits of selected shrub species of chaparral and coastal sage communities were measured each month from June 1973 through May 1974. Measurements were made at coastal and inland sites in southern California, USA with a pressure chamber and a stomatal diffusion porometer, and by floating leaves until saturated. The drought—deciduous Artemisia californica had water potentials<—65 bars by September. The species of evergreen sclerophylls fell into three groups: (1) Arctostaphylos glauca and Ceanothus greggii developed the lowest water potentials (<—65 bars) and showed stomata least responsive to water potential; (2) Rhus ovata, Rhus laurina, and Rhus integrifolia had the highest water potentials (° —25 bars) and stomata most responsive to water potential; and (3) Adenostoma fasciculatum and Heteromeles arbutifolia showed intermediate water potentials and stomatal responses. The coastal and inalnd sites did not differ in water relations within species and genus, although water stress occurred earlier in the summer at the coastal site. At the inland site, soil moisture content and plant water potentials were higher on the south—facing slope, indicating less water stress for species there than on the north—facing slope. Slope differences were not as well defined at the coast.

ISSN:0012-9658    

DOI:10.2307/1936151

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

The mathematical model WEED was derived to study the productivity of the submerged macrophyte Myriophyllum spicatum in the littoral of Lake Wingra, Madison, Wisconsin. The model coordinates four biomass compartments with selected physiological processes evaluated for a stratified meter—squared water coloumn. Light and temperature are the primary environmental forcing functions. The model considers growth form (depth distribution of biomass), total biomass/meter—squared, the depth profile of photosynthesis and macrophyte contributions to dissovled and particulate organic matter pools in the water column. The model output was tested against field data for seasonal patterns of standing crop, depth distribution of biomass and depth profile of photosynthesis for a rooting depth of 150 cm. WEED has permitted the simulation of macrophyte growth response to changes in environmental conditions and has outlined areas of needed research.

ISSN:0012-9658    

DOI:10.2307/1936152

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY