摘要:

Abstract:The feeding rhythm of the polychaeteNereis diversicolor(O.F. Müller) was studied during tidal cycles (spring and neap tide) at three sites in baie du Mont St-Michel and the Rance estuary in summer 1990. For most of the sites, the polychaetes were mainly feeding during spring tides when immersion occurred. Dietary activity decreased at emersion sites depending on low tide duration. During this period, the physical and chemical conditions in the mud flat sediments are not favourable to polychaetes’activities (high temperature, high desiccation, low oxygen content) and can cause mortality or migration of the population. Repletion indices from polychaetes of the Hirel sector (baie du Mont-St-Michel) showed a decrease of their dietary’s activity during the neap tide period even if the site was permanently immersed.

ISSN:1195-6860    

DOI:10.1080/11956860.1995.11682264

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

Abstract:Researchers have questioned whether variation in population density influences the maintenance of two or more morphs within and between insect populations. Two distinct morphs of femaleNehalennia irene(Hagen) (Odonata: Coenagrionidae) occurred at each of eight sites in eastern Ontario, Canada; one morph (i.e.andromorph) was coloured and patterned like the conspecific male. We found significant differences in relative frequencies of andromorphs and in male density between sites; frequency of andromorphs ranged from 2–28% and was positively correlated with male density. Sites with high densities of males were located closer to low-density sites than to other high-density sites, indicating that high-density sites were somewhat independent of one another. We also found spatial variation in density of males within sites; males were present almost exclusively at edges of ponds or marshes. Proportionally more andromorphs than heteromorphs were found at the edges of sites, where male-female interactions were likely frequent. Sex ratios at the edges of sites were most strongly male-biased at two of three high-density sites, indicating that males may force non-receptive females away from the edge of high-density sites. Spatial and temporal variation in male density ofN. irenemay be an important factor influencing morph coexistence.

ISSN:1195-6860    

DOI:10.1080/11956860.1995.11682265

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

Abstract:Individuals killed by predators often are considered to be in poorer physical condition than those not killed, but little work has been done on behavioural differences between the two. We monitored the behaviour, movements and survival of 15 juvenile red squirrels (Tamiasciurus hudsonicus) from the first day of their emergence through late summer to determine behavioural characteristics associated with predation. Individuals which spent relatively less time vigilant, less time resting, and more time in exposed locations were more likely to be depredated. The distance moved by an individual during observation periods was not related to its survival, but individuals that spent relatively more time off their natal territory were more likely to be depredated. Adult red squirrels spent significantly less time in exposed places than juveniles, which may relate to the lower depredation rates experienced by adults.

ISSN:1195-6860    

DOI:10.1080/11956860.1995.11682266

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

Abstract:Nutritional effects on growth and reproduction of bank volesClethrionomys glareolus(Schreber) were established by laboratory breeding of wild-caught and laboratory-born animals from two Swedish locations. The animals were kept on either a standardized folivore or a standardized granivore diet,C. glareolusbeing intermediate in natural food habits. South SwedishC. glareolusare less cyclic (with fairly stable populations) and more granivorous than northern conspecifics. The body growth of wild-caught animals was favoured by the granivore diet for southern and by a folivore diet for northern animals. South Swedish animals demonstrated greater reproductive output with a granivore diet than with a folivore diet. Young of laboratory-born southern animals became larger when the mothers were given a granivore diet. Instead, young females of wild-caught mothers were mature at weaning to a larger extent if provided with a folivore diet. These differences are interpreted to reflect digestive adaptation just after weaning, with post-weaning diets on roughage (folivore diet or a field diet) favouring animals being kept on rabbit pellets and with cereal diets after weaning still more favouring animals kept on granivore diets. Differences in reactions to food types between origins and generations can be explained by an evidently common inter-generational effect on maturation and breeding.

ISSN:1195-6860    

DOI:10.1080/11956860.1995.11682267

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

Abstract:Linear regression analyses were used to describe the allometric relationships of basal metabolic rate (BMR), field metabolic rate (FMR) and FMR:BMR ratio on body mass in non-reproducing individuals of bird, marsupial and eutherian mammal species. Measurements of FMR were made by the double labelled water method and of BMR by indirect calorimetry using O2consumption. All regressions were significant, including FMR:BMR ratio on body mass. In addition, the slope of BMR on body mass was significantly higher than that of FMR on body mass for each group of animals. This shows that the FMR:BMR ratio is not constant within each group and is greater for smaller than for larger animals. We propose that this difference is due mainly to thermoregulatory costs. The use of a constant FMR:BMR ratio to estimate FMR from BMR, as is commonly done, could result in erronoeus results. However, the ratio found in the allometric relationships between FMR:BMR ratio and body mass for the three groups of homeotherms could be indicative of trends in estimating FMR from BMR.

ISSN:1195-6860    

DOI:10.1080/11956860.1995.11682268

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

Abstract:We studied the relation between light climate and growth strategies in canopy speciesFagus crenataandAcer mono, and subcanopy speciesCarpinus cordata, to evaluate if differences in growth strategy can contribute to coexistence of shade-tolerant tree species. The study was carried out in the Ogawa Forest Reserve in central Honshu, Japan. For saplings of each species, we analyzed the relation between growth patterns and tree-size and light-environment factors. All three species had higher growth-rates in higher light levels, but an increase in light level affected growth rates differently in the three species.Acer monohad the highest growth rates, and was most affected by annual variation in the environment, probably temperature and duration of sunshine.Fagus crenatahad lower growth rates and showed little annual variation in growth. OnlyFagus crenatashowed response in the 90–100% canopy-cover range.Carpinus cordatahad intermediate growth rates, and crown size and growth rate were not much affected by light levels. BothFagus crenataandCarpinus cordatahad conservative growth patterns which may enhance their survival in the shade. Although interaction among the three species is not important, difference in growth patterns affects each species’chances for survival and may help promote coexistence in heterogeneous light environments.

ISSN:1195-6860    

DOI:10.1080/11956860.1995.11682270

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

Abstract:Although increased cloud-cover may reduce global temperature response to trace gas emissions, it is an important climatic change from an ecological perspective. For plants, cloud-cover reduces photosynthesis and alters establishment; these effects differ among species. The differential effects may be modified, however, by pattern at the landscape level, such as forest edges. Here we include cloud-cover and the edge effects of a snow avalanche path in a simulation of the dynamics of a montane forest using a spatially explicit implementation of the JABOWA-FORET model. Cloud cover is simulated by a 10% reduction in ambient light. Alternately we forced constant full sunlight, constant mortality for conifers, or both, on a strip of simulated cells in order to maintain an avalanche path. Higher light levels maintained on the path allow the persistence of shade-intolerant species that otherwise decline under a scenario of increased cloud-cover (deciduous proportion on 800 cells changes from 0.19 to 0.11 rather than 0.15 to 0.04). A constant population on the path maintains temporary populations elsewhere. Diversity would decline with increased cloud-cover (from 2.3 to 2.0 mean richness), but in cloudier conditions an avalanche path supports higher diversity (2.1) across the entire landscape. Similarly, basal area on sites is reduced by cloud-cover with (6 683 cm2- 5 957 cm2) or without (6 180 cm2- 4 988 cm2) the edge effects, but a path does contribute to higher overall basal area. Spatial structure at such fine scale must be considered in projecting the effects of global climatic change on plant communities and the effect of regional diversity on local diversity.

ISSN:1195-6860    

DOI:10.1080/11956860.1995.11682271

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

Abstract:Although trends toward increased woody plant abundance in grasslands and savannas in recent history have been reported worldwide, our understanding of the processes involved is limited. Here I review and integrate a series of studies which quantify the rates, dynamics, spatial patterns and successional processes involved in tree patch and woody plant community development at a savanna parkland site in southern Texas, U.S.A. Stable carbon isotope ratios of soil organic carbon indicate C3woody plants currently occupy sites once dominated by C4grasses. Historical aerial photographs (1941–1990), tree ring analysis and plant growth models all indicate this displacement has occurred over the past 100 to 200 years.Succession from grass–to woody plant–domination occurs when the N2–fixing arborescent, honey mesquite (Prosopis glandulosa(Torr.) var.glandulosa), invades and establishes in herbaceous patches. Over time, this plant modifies soils and microclimate to facilitate the ingress and establishment of additional woody species. The result is a landscape comprised of shrub clusters of varying ages organized around aProsopisnucleus. As new clusters form and existing clusters enlarge, coalescence occurs. This process appears to be in progress on upland portions of the landscape and has progressed to completion on lowlands. Rates of cluster development and patterns of distribution appear regulated by subsurface variations in clay content and by variations in annual rainfall. Simulation models based on reconstructions and forward projections indicate succession from grassland to woodland steady states would require 400–500 years, with the most dramatic changes occurring over a 200-year period. The shrubs initially facilitated byProsopisappear to contribute to its demise and prevent its re–establishment. Structure and function of future communities may therefore depend on how remaining woody plants react to changes in microclimate and nitrogen cycling that occur afterProsopisis gone.

ISSN:1195-6860    

DOI:10.1080/11956860.1995.11682272

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

Abstract:We examined the composition of plant tissues in the stomach and the feces of arctic hares (Lepus arcticusRoss) to obtain an index to digestibility of dietary components. The monocotyledonous sedges and to lesser extent grasses were over-represented in the feces as compared to the stomach, reflecting their lower digestibility in contrast to dicotyledonous willow (Salix arcticaPall.), forbs, and mountain avens (Dryas integrifoliaM. Vahl.). Arctic hares are similar to collared lemmings (Dicrostonyx groenlandicusTraill) and mountain hares (Lepus timidusLinnaeus) in this pattern of digestibility of plants available to them as forage.

ISSN:1195-6860    

DOI:10.1080/11956860.1995.11682273

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor