摘要:

Two subpopulations of blue monkeys (Cercopithecus mitis), located 10 km apart, were studied in Kibale Forest, Uganda, for most of a 6—yr period (1978—1984). This study was undertaken (1) to assess and evaluate the major differences in the environment and in the behavioral ecology of blue monkeys living at high and low densities and (2) to explain the differences in blue monkey densities in the two study sites. Methods included the enumeration of trees and primates, and assessments of the availability of fruits and of diets, time budgets, ranging patterns, and demographics of blue monkeys. There was a 10—fold difference in blue monkey densities between the two subpopulations. Major differences were found in the ecology, behavior, demography, and habitats of blue monkeys living at these two densities. Compared to the high—density subpopulation, the low—density subpopulation exhibited shorter tenure lengths for resident males, a greater density of nonresident males, a higher rate of group intrusions by nonresident males, a higher incidence of infanticide by new resident males, hybridization between blue monkeys and redtail monkeys (Cercopithecus ascanius),fewer adult females per adult male, and lower resident male reproductive success. From these observations I conclude that male—male competition for females was more intense where blue monkey densities were low. Predictor variables of food production and food competition indicate that more food was available for the low—density than for the high—density subpopulation of blue monkeys. The habitat containing the low—density subpopulation had a higher tree density and basal cover, greater tree species richness and diversity, and more fruit left uneaten. It also had a lower overall primate density, which, together with assessments of the kinds of foods eaten, dietary overlap and richness, foraging behavior, and home range size, suggests that intra— and interspecific competition for food both were less in the low—density subpopulation. Further evidence that food was more available for the low—density subpopulation is that both the birth rate and the population growth rate of blue monkeys were higher there than in the high—density subpopulations. The low—density subpopulation was apparently below carrying capacity and increasing in a food—rich habitat. In contrast, the high—density subpopulation appeared to be at carrying capacity, stable, and food limited. Therefore, contrary to what was hypothesized, the availability of food does not explain why blue monkey densities differed on these two areas. On this basis I attribute the low density of the one subpopulation to some unknown historical event rather than to current ecological differences between areas. I suggest that, during this study, the low—density subpopulation was recovering from a decline and that the responsible mechanism (e.g., disease) was no longer operating. This paper emphasizes: (1) the considerable variability found in the ecology and behavior of primates–even within one species in the same forest; (2) the need for long—term comparative studies of free—living primates, especially those at low densities; (3) the importance of investigating the density of primate populations relative to the carrying capacities of their environments, and the influence of this relationship on behavior and ecology.

ISSN:0012-9615    

DOI:10.2307/1943024

出版商:Ecological Society of America    

年代:1990

数据来源: WILEY

摘要:

Techniques are developed for the analysis of community organization and bench tested on a set of simple model systems with known structure (i.e., with and without guild structure, with varying degrees of resource partitioning, with and without "core" resources). Proportional utilization coefficients,pi, are positively correlated with the abundance of resources, whereas electivities,ei, correlate negatively with resource abundance. The geometric mean ofpiandei, termedgiis a superior measure of utilization, more nearly independent of biases associated with resource availability than either of its components, and performs better in bench tests. Organization in observed patterns of resource utilization by four desert lizard and four tropical freshwater fish assemblages is critically evaluated via comparisons with results from two randomization algorithms. Randomizations follow a Monte Carlo technique whereby the dimensions of the originalm×nresource matrix are preserved during hundreds of independent runs. The first "scrambled zeros" algorithm rearranges observed values for resource utilization by each consumer and retains consumer dietary niche breadths, but destroys guild structure (zero structure) of observed matrices. The second algorithm ("conserved zeros") also retains observed consumer diet breadths, but only rearranges observed resource utilization coefficients among the particular resources actually used by consumers, thus retaining observed guild structure (i.e., matrix zero structure). By plotting average dietary overlap against ordered niche neighbors, we evaluate (1) relative guild structure using the randomization algorithm that scrambles observed matrix zero structure, and (2) consumer resource segregation within guilds using the algorithm that conserves zero structure. Statistically significant guild structure is evident to varying degrees in all but one low—diversity fish assemblage. All four tropical fish assemblages reveal significant partitioning of food resources during both the wet and dry seasons, particularly among intermediate to distant neighbors. The most species—rich assemblage exhibits extremely high levels of resource segregation during the period of desiccation of aquatic habitat and increased fish densities. Diverse Australian desert lizard assemblages show significant partitioning of microhabitats among ecologically similar species, even though only 15 microhabitat categories are recognized. Analysis of dietary resource matrices based on only 19 prey resources shows that Australian lizards are piled up on certain prey types, forming functional dietary guilds of lizards that eat termites, ants, other lizards, etc. However, no dietary segregation is evident when only 19 prey resource states are recognized. In contrast, when the analysis is redone on more refined resource matrices based on more than 200 prey types, guild structure essentially disappears but niche segregation becomes evident. In the less diverse Kalahari desert, lizard assemblages are more variable and do not appear to be as tightly organized. Patterns of resource utilization in several of these natural vertebrate assemblages are, however, sufficiently organized to suggest broad effects of internal biotic factors, such as ecological constraints of functional morphology and physiology (leading to guild structure), and possibly interspecific competition.

ISSN:0012-9615    

DOI:10.2307/1943025

出版商:Ecological Society of America    

年代:1990

数据来源: WILEY

摘要:

This study examines natural, long—term (≈104yr) acidification processes in New England using paleoecological methods (pollen, diatoms, and the chemistry of three operationally defined sediment fractions) and a paired watershed approach.The primary variable is lithology, and the focus of this study is to illuminate the role of lithology in long—term ecosystem acidification. Unlike most cases of recent (anthropogenic) acidification in which inferred processes of ecosystem acidification occur over short time spans (10—50 yr), natural acidification processes develop over hundreds or thousands of years, providing enough temporal resolution in the stratigraphic record to allow strong inferences about the factors controlling the occurrence, timing, and magnitude of terrestrial and aquatic ecosystem acidification. The two sites in this study are similar in size, lake depth, elevation, aspect, and local climate, but Cone Pond, New Hampshire, is an acidic, clearwater lake in a catchment of thin tills derived from base—poor gneisses and schists, whereas South King Pond, Vermont is a mesotrophic lake in a catchment of thicker tills derived from slates, phyllites, and limestone. Although vegetation history is generally similar between the two sites, the Cone Pond catchment included higher representation of acidophilic vegetation than the South King Pond catchment throughout its 10 000—yr history. There are no known exposures of sulfide minerals in the Cone Pond watershed, nor are the basal inorganic sediments S—rich. Both diatom and geochemical analyses indicated significant long—term acidification of the upland soils and surface waters of the Cone Pond, but not the South King Pond, catchment. At Cone Pond, the uplands exported A1 almost entirely in labile form by 10 000 yr before present (BP). Increases in labile Al 8000—5500 BP, followed by substantial declines in sedimentary MN and in the ratio of Ca to organic matter, indicate soil acidification followed by decreasing lakewater pH. The loss of the Melosira/Cyclotella diatom assemblage ≈7200 BP as hemlock populations began to expand, coupled with the disappearance of the chrysophyte Mallomonas torquata, suggests increasing lakewater transparency possibly accompanied by decreasing lakewater pH. By 5000 BP, all planktonic diatom species has disappeared, and the acidobiontic diatom flora was well established. Diatom—inferred pH reconstructions indicate that the pH of Cone Pond was<5.5 by 6500 BP and may have dropped below 5.0 as long ago as 2000 BP, when spruce recolonized the catchment. A sudden decline in the ratio of acid—labile nonbiogenic Si to acid—labile A1 also occurred ≈2000 BP, and appears to reflect dissolution of an amorphous aluminosilicate complex, providing independent evidence for a precultural pH of ≈5.0. None of these features are found at South King Pond, where the only paleolimnological evidence of acidification is a sharp decline in sedimentary carbonates ≈5000 BP. This decrease, however, appears to be related to climatic factors rather than to lakewater pH. The historical accident of low till deposition in the Cone Pond catchment has been an important predisposing factor for natural, long—term ecosystem acidification, leading to truncated soil profiles, shortened hydrologic flow paths, lower overall supplies of base cations, and an enhanced susceptibility to biogeochemical changes driven by changes in upland vegetation. The potential role of other factors (depletion of base cations, sulfide minerals in the catchment of the aquifer feeding the ephemeral inlet, weathering of peat deposits in the upper reaches of the inlet, and historic A1 acidity) is also discussed.

ISSN:0012-9615    

DOI:10.2307/1943026

出版商:Ecological Society of America    

年代:1990

数据来源: WILEY

摘要:

A steady—state numerical model has been developed for simulating vertical profiles of the concentrations of organic matter, pyritic sulfur, dissolved oxygen, and the carbon isotope composition of organic matter in marsh sediments.In the model organic matter enters the sediment via sedimentation, belowground production of roots, and chemoautotrophic fixation of interstitial CO2associated with pyrite oxidation. Pyrite is formed by sulfate reduction and consumed by oxidation with dissolved oxygen in the interstitial water. Exchanges of organic matter, carbon isotopes, pyrite, and dissolved oxygen between the sediment and surface environment occur via fiddler crab bioturbation. Aeration of the sediment is caused by diffusion of oxygen into the interstitial water from air cavities assumed to be present in roots and in desaturated sediment pores formed in the upper part of the sediment by drainage and/or evapotranspiration. Sensitivity experiments with the model suggest that the accumulation of pyrite and organic matter in marsh sediments is governed in large part by the turnover time of roots and by the mean diameter of roots. The isotopic composition of the sediment was most sensitive to the rate of belowground production and to a lesser extent to the intensity of fiddler crab bioturbation. The model also indicated that fiddler crab burrowing can account for the observed isotope composition of creekbank sediments but not back (mid) marsh sediment. In both back and creekbank marshes, intense aeration of the sediment by roots is required to prevent the buildup of pyrite to unrealistically high concentrations at depth.

ISSN:0012-9615    

DOI:10.2307/1943027

出版商:Ecological Society of America    

年代:1990

数据来源: WILEY

摘要:

We report the results of a 4—yr study of the community dynamics of the annual weed species Abutilon theophrasti (velvet leaf) and Amaranthus retroflexus (pigweed). We calibrated neighborhood population dynamic models for communities of these species in the field and then tested the predictions of the calibrated models against census data from independent observations. We also analyzed the calibrated and tested models to predict long—term dynamics and to assess how spatially local interactions, growth, fecundity, survivorship, germination, seed dormancy, and dispersal each contribute to the community's dynamics and structure. We show that calibrated neighborhood models accurately predict dynamics in the field over a 4—yr period. Because the predictive spatial models reduce approximately to simple nonspatial models of competition, the spatial processes that govern the dynamics of velvet leaf and pigweed communities behave as simple nonspatial processes. The models predict that velvet leaf will eventually exclude pigweed because of an asymmetry in the magnitude of inter—individual interference affecting growth. We also show that velvet leaf monocultures would oscillate perpetually in the absence of delayed germination and that demographic stochasticity (May 1971) has little effect on the dynamics of the experimental species.

ISSN:0012-9615    

DOI:10.2307/1943028

出版商:Ecological Society of America    

年代:1990

数据来源: WILEY