摘要:

A comparison of the trichopteran communities of streams associated with aspen, spruce—fir, and mixed—conifer forests demonstrated significant differences in structure. Though tricophteran species composition in aspen—associated and spruce—fir associated streams was virtually identical, relative abundances of shredder and grazer Trichoptera differed significantly in the two types of streams. The ratio of shredder to grazer trichopteran biomass in aspen streams was °1:17 while in conifer streams, the dominance was reversed with a shredder to grazer biomass ratio of 3:1. The difference in dominance of functional groups in the two types of streams was attributed to the order—of—magnitude greater standing crops of detritus found in the conifer streams. It is hypothesized that the greater accumulation of detritus in conifer streams is the result of habitat modification by logs. Five times the number of logs were found in conifer streams as compared to aspen streams. The greater accumulation of logs in the conifer streams is attributed to lower rates of decomposition of conifer wood. The data suggest a general model for long—term structural change in trichopteran communities of the southern Rocky Mountains and I suggest that these long—term changes result from changes in quantity and quality of wood inputs during forest succession.

ISSN:0012-9658    

DOI:10.2307/1937023

出版商:Ecological Society of America    

年代:1982

数据来源: WILEY

摘要:

Plots in an ungrazed, re—established grassland near Omaha, Nebraska, USA, dominated by little bluestem (Andropogon scoparius), were burned at 3—wk intervals from March through November 1976. The amount of vegetative biomass consumed during burning, a measure of flammability, was high throughout the study period, varying from>99% in April to 84% in mid—June. Areas burned in March were able to carry a second fire in October of the same year. High flammability throughout the growing season, in conjunction with current fire and climatic records, suggests that widespread, late—summer fires were probably common in presettlement, ungrazed, bluestem prairies.

ISSN:0012-9658    

DOI:10.2307/1937024

出版商:Ecological Society of America    

年代:1982

数据来源: WILEY

摘要:

An equation independently derived by Edmondson and Paloheimo for estimating instantaneous birth rates without a knowledge of mortality rates has been extensively employed by zooplankton ecologists. This expression is exactly true only under the unlikely conditions that the age distribution is stable and that egg mortality is equal to that averaged across the entire population. Here I compare estimates of instantaneous birth rates (b) using the Edmondson—Paloheimo equation to those determined with a general model which accounts for age structure instability and egg mortality in two Daphnia pulex populations. Despite the fact that the assumptions of the Edmondson—Paloheimo models are rarely met, it mimics the seasonal pattern of b quite well, with few exceptions. An analysis of variance suggests that the model will provide an adequate approximation of the true population birth rate when a variance in b of 0.003 can be tolerated. A much more critical factor in the analysis of instantaneous rates in plankton populations is the development of accurate sampling techniques.

ISSN:0012-9658    

DOI:10.2307/1937025

出版商:Ecological Society of America    

年代:1982

数据来源: WILEY

摘要:

In this paper I outline a method for estimating the sampling variance of estimates of mean daily energy expenditure of free—ranging animals, based on time—energy budgets. This method combines estimated components of variation from laboratory and field observations into a single estimate of the overall sample variance. An approximate confidence region for the mean daily expenditure can be constructed as well. I illustrate these methods by applying them to the energy budget of the Golden—winged Sunbird (Nectarinia reichenowi) originally published by Gill and Wolf (1975). The total sample variance of the mean daily energy expenditure, when that expenditure is estimated from the time—energy budget approach, is a sum of many terms, including the products of the variances of individual variables, the squared estimates of the mean of individual variables, and the products of the estimated means and covariances among the variables. Thus, the estimated sample variance will usually be large. Any biases in estimation will be propagated throughout the calculations, and errors of staggering magnitude can result. Knowlege of the components of total sampling variance and the sensitivity of these estimates to the various sources of bias should aid field biologists in designing time—energy budget studies so that the maximum possible reliability can be achieved.

ISSN:0012-9658    

DOI:10.2307/1937026

出版商:Ecological Society of America    

年代:1982

数据来源: WILEY

摘要:

The feeding ecology of predaceous stoneflies was investigated over 18 mo in Cement Creek, Colorado, USA. Three species were studied at each of three sites over their entire life cycles to elucidate any differences due to species and site. Diet typically changed, over the course of development, from diatoms and chrionomids in the earliest instars, to primarily chironomids, to a broader diet in which mayflies increased in importance relative to chironomids. Stonefly diet was similar in individuals of a given size at a particular site, regardless of species, but differed among size categories and sites within a species. Two factors appeared to determine what prey were eaten. The maximum size of prey ingested increased with size of stonefly, at approximately 10% of predator body mass. No evidence of preference for larger prey was observed within a predator size category, however. Rather, the availability of prey depends upon the abundance of the vulnerable size class, which in turn is affected by the juxtaposition of predator and prey life cycles. The mass of a full foregut was related to mass of stonefly by the power law for each species. By combining these estimates of gut clearance rate, total prey consumption by stoneflies at each site was estimated to range from 2.7 to 3.3 g°m—2°yr—1(dry mass). While prey availability is notoriously difficult to measure, this appears to be substantial predation pressure.

ISSN:0012-9658    

DOI:10.2307/1937027

出版商:Ecological Society of America    

年代:1982

数据来源: WILEY

摘要:

Unconfined Quercus prinus woody litter of three size classes (0—1, 1—3, and 3—5 cm diameter) was placed on forest floors of a control hardwood watershed and on mesic and xeric sites of a clear—cut watershed at Coweeta Hydrologic Laboratory, North Carolina. Exponential decay coefficients for mass loss on the control were .1524, .1728, and .0912 yr—1for 0—1, 1—3, and 3—5 cm branches, respectively. Coefficients for 0—1, 1—3, and 3—5 cm branches were. 1752, .0756, and .1644 yr—1on the mesic and site and .0456, .0948, and .0377 yr—1on the xeric site. The effect of site differences on decomposition rate was greater than the effect of diameter, although an inverse relationship between diameter and decay coefficient is suggested. Time in the field, temperature, moisture, and microarthropod abundance also appeared to influence decomposition rate. Microarthropods dominated the animal community on decaying wood with oribatid mites and collembolans the most numerous. Microarthropod densities were highest on 0—1 cm twigs and lowest on 3—5 cm branches. Microarthropod densities were generally highest on the control, slightly depressed on the mesic site, and greatly depressed on the xeric site. Time in the field and state of decomposition both positively correlated with microarthropod abundance. Calcium concentration and total calcium exhibited transitory increases but little net change at the end of 1 yr in experimental branches. Total potassium decreased on all sites for 6 mo and for 12 mo on the control and xeric sites, with °60% remaining after 1 yr. Total potassium increased rapidly on the mesic site over the last 6 mo and reached 110% of the initial amount. Temperature, moisture, microbes, and microarthropods appeared to control nutrient dynamics. Wood litter dynamics were more important in terms of nutrient conservation on the clear—cut watershed than on the control and contributed to the resilience of the system. Removal or destruction of woody debris after clear—cutting would decrease the nutrient conservation properties of decaying wood and would probably contribute to watershed output of nutrients.

ISSN:0012-9658    

DOI:10.2307/1937028

出版商:Ecological Society of America    

年代:1982

数据来源: WILEY

摘要:

Brine shrimp were subjected to one of four reproductive regimes: complete absence of mating, mating postponed for 20 d or 40 d past sexual maturity, or continuous breeding upon sexual maturity (controls). Each of the four reproductive regimes was further subdivided into low and high feeding groups (1:10 feeding ratio). Under low food, female lifespan was negatively correlated with the length of the reproductive period. However, no such relationship was found among the four high food groups; no intrasex differences were found in survival curves or mean length of lifespan. Fertile females in the delayed reproduction groups gave birth to approximately the same total number of offspring as controls, not by lengthening lifespan but by producing larger broods, with fewer days between broods. The results indicate that although some reproductive costs are unavoidable, nutritional resources play a critical role in determining how extensively reproduction will affect lifespan.

ISSN:0012-9658    

DOI:10.2307/1937029

出版商:Ecological Society of America    

年代:1982

数据来源: WILEY

摘要:

Photosynthetic and stomatal responses of Tamarix chinensis to temperature, light, and humidity were investigated in the field in New Mexico and in the laboratory. Transpiration rates for T. chinensis were similar to those of several herbaceous plants and co—occurring phreatophytes. Net photosynthetic rates and water use efficiency of T. chinesis were lower than for other species. Photosynthesis was light saturated at a photon flux density equal to 44% of full sunlight. Carbon dioxide assimiliation was tightly coupled to irradiance below light saturation. Leaf resistances remained low at photon flux densities above one—third of full sunlight, but increased linearly with decreasing photon flux density below that level. Shading for 5 min resulted in a doubling of leaf resistance. The rapid response of stomata to changing light conditions is probably an adaptation to conserve moisture when light is limiting to photosynthesis. Optimal leaf temperatures for photosynthesis were 23°—28° C, which correspond roughly to ambient temperatures during the early part of the day when evaporative demand was relatively low. T. chinensis stomata appeared to respond directly to changes in the leaf—to—air absolute humidity gradient. At constant temperature, leaf resistance increased linearly with increases in the leaf—air humidity gradient. Midday depressions of gas exchange invariably occurred in the field, despite the fact that the plants had an abundant water supply. These depressions resulted from increases in leaf resistance in response to increasing evaporative demand of the air. This response results in improved water use efficiency during the hottest portion of the day. Plant water potential decreased from pre—dawn values of about —0.9 MPa to minimal values of about —2.6 MPa by midmorning. Improvements in bulk water status were often observed during the afternoon when leaf resistances were higher. Diurnal patterns suggested that leaf resistance was largely a function of temperature, light, and humidity, rather than plant water status.

ISSN:0012-9658    

DOI:10.2307/1937030

出版商:Ecological Society of America    

年代:1982

数据来源: WILEY

摘要:

A study of three species of sceloporine lizards (Sceloporus clarki, S. undulatus, and Urosaurus ornatus) was begun in 1971 and continued into 1977 in a very diverse (at least 11 species) lizard community in central Arizona, USA. The present paper reports the results of a density manipulation experiment carried out with these three lizards to ascertain whether direct evidence for interspecific competition could be found in a community of lizards in which circumstantial evidence suggested its importance. In May 1975 the study area was divided along a natural constriction into an experimental area and a control area and an attempt was made to remove all U. ornatus and S. clarki from the experimental areas. This experimental treatment was maintained until the termination of the experiment in 1977. Patterns of habitat utilization, population density, survivorship, and individual body size of S. undulatus on experimental and control areas both before and after the removals were analyzed for evidence of competitive interactions. There were no detectable effect of the removal of S. clarki and U. ornatus on habitat selection, perch height, survivorship, population density, or individual body size of S. undulatus inhabiting the removal area. Implications of these results for studies of lizard community structure are discussed.

ISSN:0012-9658    

DOI:10.2307/1937031

出版商:Ecological Society of America    

年代:1982

数据来源: WILEY

摘要:

By attracting male euglossine bees with cineole, eugenol, methyl salicylate, methyl cinnamate, and benzyl acetate in Costa Rican lowland deciduous forest and rain forest, we found no indication of change in the composition and numbers of rain forest attractable bee species during different seasons, but within the deciduous forest both abundance and species richness declined in the dry season. Within each major forest type there were substantial differences in the abundance and species composition of attractable bees among habitats: baits in estuarine swamp forest and open pasture in the rain forest attracted very few bees as compared with nearby forest understory sites. In the deciduous forest, at least 15 species of male euglossine bees were attracted that apparently do not have breeding populations in this forest and that do not visit orchids in this forest; we hypothesized that they normally find females and chemical resources elsewhere in distant habitats or forest types.

ISSN:0012-9658    

DOI:10.2307/1937032

出版商:Ecological Society of America    

年代:1982

数据来源: WILEY