摘要:

Data on the population of grizzly bears in the environs of Yellowstone National Park suggest that the population has not recovered from the reductions following closure of garbage dumps in 1970 and 1971, and may continue to decline. A computer simulation model indicates that the risk of extirpation over the next 30 yr is small, if the present population parameters continue to prevail. A review and further analysis of the available data brings out the importance of enhancing adult female survival if the population is to recover, and assesses various research needs. In particular, a reliable index of population trend is needed to augment available data on the population.

ISSN:0012-9658    

DOI:10.2307/1940382

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

A model of spatial population dynamics was developed in which small and large local populations are distinguished. In the model, emigration from small populations is assumed to be inconsequential, but the dynamics of currently small populations are affected by immigration from large ones. If immigration substantially increases the likelihood that a small population will grow large, two alternative stable states are possible in the model corresponding to regional commonness and regional extinction (or regional rarity, if dispersal fromsafe sites or from outside the region is allowed for). Analysis of the model showed that even a small number of large local populations may play a crucial role in the regional dynamics of some species. The process of regional extinction, when it occurs, may show as an unexpected crash in the time trajectory.

ISSN:0012-9658    

DOI:10.2307/1940383

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

Semelparous, iteroparous, periodic, and erratic breeding patterns were observed in montane populations of the red—spotted newt, Notophthalmus viridescens, in western Virginia from 1974 to 1983. Most of the observed absences and gaps in the records of both males and females are explained by a null model that combines the small errors of sampling with independently estimated rates of annual mortality. Most newts naturally breed every year until their deaths, but a significant number of females and males did skip breeding opportunities. Because the variation in breeding histories could have been environmentally induced, no adaptive significance is ascribed to it.

ISSN:0012-9658    

DOI:10.2307/1940384

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

The evolution of character displacement in competition communities was simulated with two quantitative genetic models. The first model is identical to that of Slatkin (1980) but we extend his analysis. The second model allows for the evolution of all niche attributes that affect interspecific competition along a resource axis. These are: the mean position of each species along the axis, the variation in position between phenotypes within each species, and the width of resources used by each phenotype. In addition, explicit dynamics for the resources are included in the model. This model predicts that character displacement can occur in coevolutionary communities. It also predicts that the relative niche separations between species (d/w ratios; d = distance between peaks of two species' niches on the resource (niche) axis, w = total niche width of a species) can be quite large, that the d/w values should decrease as species number increases, that at the evolutionary equilibrium, the within—individual component of the niche width will be much larger than the between—individual component, and that niche separation should be substantially smaller than character separation. These predictions are all in agreement with field observations surveyed from the literature.

ISSN:0012-9658    

DOI:10.2307/1940385

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

Two ecologically similar shrew species, Sorex minutus and S. araneus, were studied in sympatry on the Swedish mainland and in allopatry on Irelend, the Outer Hebrides, and two islands in the Baltic Sea, in order to examine competitive character displacement in skull morphology. Eight skull measures were compared on a total of 228 specimens. S. minutus had significantly smaller jaws in sympatry. It was concluded that this difference is a result of interspecific competition; alternative explanations were tested and rejected. S. araneus did not exhibit morphological differences between sympatric and allopatric populations. The difference in response of the two species, it was concluded, is due to their different relative abundance in sympatry, which implies an asymmetry in their competitive effect on one another. It is suggested that late—Quaternary zoogeographic patterns during periods of low sea level can explain the present distribution of allopatric pygmy shrew populations.

ISSN:0012-9658    

DOI:10.2307/1940386

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

Time—energy budgets (TEB) of Gambel's Quail (Callipepla gambelii) were compiled during two summers in the Colorado Desert of California. Quail spent 6.77 h/d foraging, 6.2 h/d inactive during daylight hours, and 11.02 h/d inactive at night. Field metabolic rate (FMR) calculated from this activity budget was 81.8 kJ/d. Of this, 47.3 kJ/d was expended during foraging, 12.6 kJ/d in daytime inactivity, and 20.4 kJ/d in nighttime inactivity. Despite the extremely hot thermal environment (maximum ambient temperature °45°C), there was no energy cost above resting levels for thermoregulation. FMR was also measured simultaneously with doubly labeled water (DLW), and averaged 90.8 kJ/d. TEB and DLW values agreed to within 6% when differences in measurement period were taken into account. A laboratory validation study indicated that DLW and balance methods agreed to within 5%. The FMR of C. gambelii was only 40% of that predicted for a bird of its body mass. This low FMR is primarily the result of a low resting metabolic rate (RMR): 51% of the predicted basal rate in 1981, and 70% of predicted in 1982. The basis and significance of this low and variable RMR are unclear. Energy assimilation efficiency, measured in laboratory feeding experiments with a mixed seed and arthropod diet, was 60.3%. An individual quail in the field thus required 150.3 kJ/d in its diet, representing a dry matter intake of 8.1 g/d. A diet of seeds alone provides insufficient water for Gambel's Quail in summer, so they must either incorporate moist food items in their diet or drink free water. It was calculated that over the course of a year, a population of Gambel's Quail consumes seeds with a total energy content °15% as great as that in seeds consumed by a population of desert rodents or harvester ants in the same area. Gambel's Quail thus may be important factors in the competition for resources among desert granivores, particularly because they can eat one of their competitors (harvester ants).

ISSN:0012-9658    

DOI:10.2307/1940387

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

The painted turtles, Chrysemys picta, with four subspecies, have the largest range and most northern distribution of any North American freshwater turtle. C. p. bellii in Canada may hibernate for as much as 6 mo, while C. p. dorsalis on the Gulf Coast may not hibernate at all. We subjected both subspecies to simulated hibernation conditions by submerging them in anoxic water at 3°C without access to air to compare physiological responses. Initial acid—base and ionic statuses of animals acclimated to 3° were the same in both subspecies. As anoxia continued, both subspecies showed similar changes in all measured parameters, but the rates of change were greater in dorsalis than in bellii. By day 46, the plasma pH of dorsalis had fallen to 6.96, a change that required °180 d in bellii. By day 38, the acidosis was entirely due to lactate formation in both groups, and it had induced compensatory changes in ionic concentrations, particularly large increases in total Ca and total Mg in the blood. We conclude that the only adaptation required of bellii to enable it to endure longer winters than dorsalis is an ability to limit lactate accumulation, by having either a lower metabolic rate and/or a great ability to eliminate lactate. It is known that hibernation in a normoxic environment would be less stressful physiologically than in an anoxic one, but turtles apparently choose the latter. We suggest that the physiological stress of prolonged anoxia and the requirements of subsequent recovery in the spring are outweighed by considerations of predator avoidance during the winter. Tolerance of the physiological perturbations resulting from prolonged anoxia may limit the northern distribution of freshwater turtles.

ISSN:0012-9658    

DOI:10.2307/1940388

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

On two 1—ha plots, one fenced in and one not, populations of the prairie vole, Microtus ochrogaster, exhibited annual cycles in population density in 1977 and 1978, as they had since 1971. Blood was analyzed by electrophoresis to determine the frequencies of occurrence of several allozymes of polymorphic blood proteins. There was great seasonal and annual variability in how well population density correlated with the frequency of each of two electromorphs of transferrin (Tf) and one electromorph of leucine aminopeptidase (LAP). Also, during some seasons males with certain electromorphs had significantly greater body mass than those with other morphs. Furthermore, of the 137 individuals captured more than once, 40 (29.2%) showed changes in electromorphs of Tf, and 24 (17.5%) showed changes in LAP electromorphs. These data support earlier studies showing these proteins to be physiologically plastic. This study and others suggest that conclusions about the genetic composition of populations based on electrophoretic analyses must be supported by evidence that the protein systems studied do not show lability within individuals under abiotic or biotic stress. This study also suggests that electrophoresis may be a useful tool in assessing the physiological state of individuals exposed to different natural environments.

ISSN:0012-9658    

DOI:10.2307/1940389

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

The use and defense of food and space in the territorial larval caddisfly Leucotrichia pictipes (Trichoptera: Hydroptilidae) were evaluated through field observations and experiments in southwestern Michigan. These grazing stream insects live in silk cases attached to hard substrates and aggressively expel intruders (both conspecifics and other species) that enter their algal—covered foraging areas. Defended areas contained significantly greater algal standing crops, which were a benefit resulting from resource defense. This territorial behavior often led to patterns of uniform spacing between larvae in high—density patches. Exceptions to these patterns tended toprove the rule; when Leucotrichia cases were much closer than normal, at least one of the individuals had entered a nonterritorial life history stage. Larval territory size was determined by food requirements and food availability. For example, territory size is related to the resident's body mass according to the equation: Area = 2.39 Mass0.84. The exponent for this power function is similar to the exponent relating metabolic rate to mass in many insects, further supporting the view that territoriality in Leucotrichia is related to the defense of a limiting food resource. Testing the effect of food availability on territory size provided support for several optimal feeding—territory—size models; when availability was experimentally reduced, residents expanded the size of their territories relative to control larvae. Ordinarily, other competing grazer species (e.g., the mayfly nymph Baetis flavistriga) spent less time per unit area foraging within Leucotrichia's territory than they spent foraging elsewhere. However, when resident caddisflies were experimentally removed from their territories, these mayfly nymphs spent more time inside than outside the territory. The territory of Leucotrichia often provided a resourceoasis containing significantly higher algal standing crops than unprotected areas, which were heavily utilized by a diverse guild of grazers. The mayfly nymphs seem to have adopted a territory—parasite strategy similar to that of some nectar—feeding birds, in that they regularly robbed resources from Leucotrichia territories by a combination of stealth and speed. Other members of the grazer guild were less able to gain access to these limited resources, so that Leucotrichia acted as a dominant competitor in this community.

ISSN:0012-9658    

DOI:10.2307/1940390

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

Small, shallow seepage lakes in northern Wisconsin that have both low winter oxygen concentrations and low pH possess depauperate fish assemblages containing primarily or exclusively central mudminnows, Umbra limi, and yellow perch, perca flavescens. Six times during three years I determined the total densities of fish in five lakes by mark—recapture and catch—per—effort methods. The richness of the fish assemblages in these lakes varied from one to three species in a nested pattern. While seasonal variations in density occurred within and among lakes due to variations of growth, mortality, and recruitment, total densities overall were independent of species richness. the pattern, called complete density compensation, suggests that total densities are expressions of the lakes' similar abilities to support fish and that the species interact rather than being independent. An intense negative correlation between perch and mudminnow densities was found, suggesting a strong interspecific population dominance of perch over mudminnows. There was also indirect evidence that both competition (exploitation and interference) and predation by perch regulate mudminnow populations when the species co—occur. Because these assemblages were unpredictably variable in time and space, conclusions from single censuses would have been unreliable. An exercise simulating single seasonal censuses from each richness class showed that less than one—half of such single censuses would have produced the pattern of complete compensation that was observed in the field study. In general, my results support the idea that the relative importance of the factors that determine community structure, or even the factors themselves, can differ not only from assemblage to assemblage at any one time, but even from season to season or year to year within a single assemblage.

ISSN:0012-9658    

DOI:10.2307/1940391

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY