ISSN:0012-9658    

DOI:10.2307/1934183

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY

摘要:

Dipodomys microps, D. merriami, and Perognathus longimembris spend most of their lives solitarily and in the ground, coming out onto the surface only at night and foraging for as little as an hour. However, they are active within their burrows throughout the day, seldom remaining motionless for more than half an hour at a time during the warmer parts of the year. All three species rest at positions in their burrows which are generally at the nearest of available temperatures to the lower end of thermal neutrality, but not warmer than 30 degrees C.To do this, they occupy different depths at different seasons and in some cases different times of day. Daily vertical movements are most common in P. longimembris, because it maintains tunnels as near as 1 cm from the surface, where daily fluctuations in temperature are profound. In late fall, winter, and early spring all three species occupy nests, which serve to reduce metabollic expenditure. Energetic strategies differ interspecifically in relation to differences in bodyweight among the species: D. microps (56 g), D. merriami (35 g), and P. longimembris (7 g). The amount of surface activity in the populations and the frequency of movement measured in individuals decrease during colder parts of the year. This decrease is most apparent in the smaller species, and is related to the decreasing success at foraging later in the season and the increasing costs of metabolism at colder temperatures. Surface activity in D. microps and D. merriami continues throughout the year, at temperatures measured as low as —19 degrees C. However, for P. longimembris the costs of foraging in winter usually far outweight the yield, and the mice become continuously fossorial for up to 5 months of the year, living on seeds that they have cached in their burrows, and spending a great deal of time in dormancy. Seasonal cycles of weight and reproduction are not synchronous in D. microps and D. merriami, because of differences in diet and foraging behavior. Dipodomys merriami, which is primarily a seed eater, requires the green vegetation of annual plants to reproduce, and therefore this species increases body weight and reproduces at sporadic intervals according to the unpredictable availability of annuals. Dipodomys microps, however, reproduces in a brief, annually consistent period because leaves of perennial shrubs are its primary year—round food and water resource. This larger kangaroo rat forages over a smaller area for leaves than D. merriami does for seeds; but D. merriami runs 50% faster, which should compensate for the cost of moving greater distances. Dipodomys microps is most active during the first part of the night, but D. merriami becomes more active during the course of the night as the activity of D. microps decreases. Height and breadth of burrow hillocks and height of shrubs on hillocks were significantly larger for D. microps than the other species, but height of burrow hillocks and shrubs on them did not differ between D. merriami and P. longimembris. Perognathus longimembris resembles D. merriami more than it does D. microps in diet and reproductive pattern, but in winters of great food scarcity competition between P. longimembris and D. merriami is reduced by the total absence of P. longimembris from the surface.

ISSN:0012-9658    

DOI:10.2307/1934184

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY

摘要:

The effects of low soil temperature on photosynthesis and water relations were examined in 17 populations of 12 vascular plant species from native elevations ranging between 10 m and 3,170 m. Root permeability to water was sufficient in the majority of populations studied so that neither transpiration nor net photosynthesis was reduced at 3 degrees C soil temperature compared to the rates at 20 degrees C soil temperature. There was no evidence of differential natural selection along altitudinal gradients for ability to maintain photosynthesis rate when roots were chilled. Leaf relative water content was typically reduced in response to soil cooling. There is a critical relative water content above which both transpiration and photosynthesis are insensitive to water content reductions. Root chilling failed to reduce relative water content below this level in most populations studied. Low soil temperatures which had no adverse effects on transpiration or photosynthesis were found to significantly retard plant growth. The observed relative water content reductions might limit growth despite their failure to affect photosynthesis. Evidence for natural selection for ability to maintain turgor upon root chilling in high elevation populations was provided by an inverse relationship between the magnitude of depression in relative water content and native elevation. Thus, growth reduction at low soil temperatures must result from impaired turgor, decreased root growth and metabolism, or impaired cytokinin synthesis and translocation rather than direct limitation of carbon assimilation.

ISSN:0012-9658    

DOI:10.2307/1934185

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY

摘要:

Numerical classifications and principal components ordinations were performed on species from 57 weekly samples of photoplankton from Lake Wingra. The data were considered in absolute and relative terms before and after transformation to presence/absence and logarithmic quantities. The data were also analyzed, taking into account growth rates in the samples, by means of a transformation that replaced the scores of species present by the productivity of the sample as determined by C_(14) uptake/biomass. It is shown that different transformations can reveal different but biologically meaningful aspects of the data. These different biological aspects are species similarities based on either short—term survival expedients in particular environmental circumstances, species tactics, or long—range growth patterns, involving breadth of tolerance and place in the community, that is, species stratagems. Most phytoplankton species in Lake Wingra adopt one of three stratagems: either ungrazed, slow—growing and very persistent, or ungrazed, fast—growing and of intermediate duration, or grazed fast—growing and ephemeral. Tactical information is relevant to particular systems, while strategic information is needed in ecosystem comparison and for models applicable to several systems.

ISSN:0012-9658    

DOI:10.2307/1934186

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY

摘要:

Last instar larvae of Chaoborus americanus overwinter in a state of developmental arrest (diapause) but remain otherwise active and capable of feeding. The diapausing larvae are developmentally responsive to long—day photoperiod and food. A portion of a wild—caught population responds rapidly to these conditions; the remainder of the population is more conservative. For either morph, the closer an individual approaches adult emergence, the more its rate of development is retarded by a small drop in water temperature. This response to temperature both promotes synchronous adult emergence and insures favorable climatic conditions at that time. Even this individual thermal homeostasis does not ensure survivorship throughout the total range of vernal climates encountered in a single shallow pond. The fast—responding morph predominates following warm, continuous springs; the more conservative morph predominates following a spring where the initial thaw is succeeded by a refreezing of the pond. Response time polymorphism is thus envisioned as an adaptive extension of the individual thermal homeostasis and serves as a model for persistent polymorphism.

ISSN:0012-9658    

DOI:10.2307/1934187

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY

摘要:

Photosynthesis and transpiration were examined in detached leaves of broad—leaved cattail (Typha latifolia L.) ecotypes from a long growing season continental climate in California's central valley and a short growing season continental in northwestern Quebec when grown under identical conditions. The principal difference between the ecotypes were (a) greater temperature dependence of net photosynthesis in the Quebec ecotype, particularly when young leaves were compared, (b) a decline in temperature dependence of Quebec leaves as they aged, but not of California leaves, (c) a downward shift in the photosynthetic temperature curve when California plants were transferred to cooler growing conditions, while the curve was stable in Quebec plants, (d) an increase in photosynthetic rate at the optimum temperature when Quebec plants were transferred to cooler conditions, but a decline in California plants, (e) a more phenotypically plastic acclimation response in the California ecotype, and(f) greater sensitivity to photosynthesis inhibition by high oxygen in Quebec leaves. Differences in net assimilation rates were less than would be expected from previous studies of other species.

ISSN:0012-9658    

DOI:10.2307/1934188

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY

摘要:

Geographic variation in body size (BL) and relative foot size (F/B) was studied across the ranges of two sibling species of cricket frogs, genus Acris (Hylidae)in North America. Acris crepitans has a large range in eastern and central states extending from mesic woodlands to xeric grasslands, whereas A. gryllus has a limited range in southeastern states in mesic woodlands. Measurements of BL and F/B of 5,286 frogs from 108 localities were divided into 11 biogeographical regions and subjected to discriminant and multiple regression analyses. BL varies primarily in A. crepitans, negatively correlated with annual rainfall, which is its best single predictor, accounting for about .50 of size variance. A combination of three humidity variables explains .60 of BL variance.Desiccation experiments indicate that loss of body weight and vital time limit regress linearly on size and are highly correlated with it. Larger frogs lose less water and reach their limit of tolerance in twice as long a time as do small ones. F/B in both species is positively correlated and best predicted by a combination of temperature, precipitation, and longitude or sympatric anuran species. It is suggested that BL is casually related to humidity, large size being an adaptation to arid climates, and that F/B is casually related to predation pressure and/or competition for food, large F/B being an adaptation for increased jumping efficiency.

ISSN:0012-9658    

DOI:10.2307/1934189

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY

摘要:

During the spring and summer of 1971 and 1972 quantitative measurements of temperature, water chemistry, and standing crop of benthic algal mats were made at a series of stations along the Firehold River as it flows through the main geyser basins of Yellowstone National Park. The river is an ideal study area for assessing the long—term effects of thermal additions, since it has been subject to heating effects for hundreds of years. Hot springs and geysers in the geyser basins add to the river heated and nutrient—enriched water of about one—third the volume of river water. As the river flowed through the thermal areas, the temperature gradually increased to a maximum daily midsummer temperature 12 degrees higher than the unheated upper portion of the river (15 degrees to 27 degrees C), and the river began cooling when the thermal additions to the river ceased. The river was coldest in early June, when maximum input from melting snow occurred, and remained relatively warm in the heated areas throughout the winter. Alkalinity, pH, conductivity, phosphate, and chloride also increased markedly; nitrate and ammonium concentrations appeared not to be influenced by the additions of hot spring water. The quantity of chlorophyll per unit area extracted from epilithic algal mats also increased with the amount of thermal water input to 20 times that in the unheated control areas. The apparent growth rates of benthic algae calculated from periodic quantitative sampling of cleaned rocks were over fivefold greater in the warmer than in the cooler portion of the river. The effect of temperature on light—dependent incorporation of(14)CO_2 by epilithic, epipelic, and epiphytic algal communities at different stations was measured. The temperature optimum for CO_2 fixation paralleled the midsummer temperature of the habitat although it averaged about 3 degrees higher at each station. The algae retained their midsummer temperature optima even during the early June period of cold water, suggesting that these optima are controlled by the mid—summer maximum temperature. Photosynthesis with natural populations was measured in the presence of increased concentrations of the algal nutrients to determine whether the increased algal growth rate in the warmer parts of the river might be due to nutrient enrichment rather than to temperature. The results suggest that higher temperatures from the additions of thermal water increase the algal standing crop through increase in growth rate of the algae, and that the algae in the heated portion of the river are optimally adapted to the temperatures of their habitats.

ISSN:0012-9658    

DOI:10.2307/1934190

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY

摘要:

The patterns, quantity, and activities associated with the leaf—cutting of Atta colombica were studied August 20—27, 1971, in a lowland tropical wet forest at Osa Peninsula, Costa Rica (Lat. 08 42'N Long. 83 29'W). The study nest had an area of 44.8 m2and covered 1.4 ha of forest floor. Daily, on a m2of forest floor, the study nest had inputs of 10.17 leaf fragments with an area of 0.0108 m2, a weight of 0.0813 g, an ash content of 0.0039 g, and a potential energy of 0.3455 Kcalories. The ants return to the forest floor 0.0525 g of refuse with a potential energy of 0.0764 Kcalories and an ash content of 0.0212 g/m2day. It was calculated that the leaf—cutting activity of ants reduced the gross production of the forest by 1.76 Kcal/m2day but accelerated net production by at least 1.80 Kcal/m2day through the return of ash rich in phosphorus to the forest floor. The size of the Atta nest may be determined by the balance of the energy input to the nest and the cost of obtaining, carrying (concentrating), and distributing the potential energy into the nest. Of a work force of 12,000 ants/m2of trail, 75% were not carrying leaves and were assumed to be doing trail maintenance work. Rainfall and litter fall were the main obstacles of leaf transport, which was about 70% efficient. The ant's energy allocation for maintenance, which limits growth, and the establishment of reward feedbacks to their energy producers have implications for man's urban system development.

ISSN:0012-9658    

DOI:10.2307/1934191

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY

摘要:

Comparisons of populations of soil microfungi from surface soils of bare, mulched, harvested, and recently burned prairie stands, with those from a dry—mesic control stand (1 year post—burn), revealed some remarkable distribution patterns for various fungal isolates. With the exception of the harvested and the control stands, little similarity could be found among any of the populations. Furthermore, the overall species composition of the populations showed little resemblence to populations isolated from within the dry—mesic segment of the prairie continuum in southern Wisconsin. Numbers of fungi and bacteria also exhibited a great deal of variation depending on the stand treatment. The most significant variations in microbial density included reductions in the numbers of fungi in the bare stand and major increases in fungal densities in the recently fired stand. Bacterial counts were higher in the mulched and the burned stands, but significantly lower in the bare stand, and greatly reduced in the moss—covered harvested stand. Manipulation of the dry—mesic prairie stands so altered the microbial balance that the resulting populations differed more than those reported earlier for the entire prairie continuum. Certain physiochemical properties of the microenvironment are important in the selection of prevalent fungi isolated from these stands. Evidence shows that a post—firefungal bloom occurs following grassland fires. Coniochaeta discospora and C. tetraspora, two pyrenomycetes, accounted for 60% of all isolates recovered from the burned stand. Both of these fungi produce ascospores whose dormancy is not readily broken.

ISSN:0012-9658    

DOI:10.2307/1934192

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY