摘要:

A new method for the mapping of the relative locations of organisms as points in a 2—dimensional space is presented. The proposed method is based on a least—squares estimate of the coordinates using observed distances between the objects being mapped (rather than triangulation based on horizontal angles). Only a small subset of the possible interpoint distances need be measured in order to obtain a very accurate map. The method is applied to 3 problems in mapping of trees in a forest.

ISSN:0012-9658    

DOI:10.2307/1936638

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

The structure of 4 populations of a small boreal mammal, the pika (Ochotona princeps), is examined to explore the causal mechanisms of evolution of life—history features of the species. Litter size reflects potential and realized fecundity and is largest at Bodie (low latitude, low altitude), intermediate at Sierra and Colorado (low latitude, high altitude), and smallest at Alberta (high latitude). The age specificity of mortality largely determines the number of sites available for settlement by juveniles, which dictates the feedback to liter size. Populations are stable and habitats continuously saturated at Alberta; mortality of adults is predictable. The Sierra and Colorado sites possess unstable population. At these sites, snowmelt in spring (the harbinger of emergent vegetation and successful weaning) is relatively unpredictable compared to Alberta; adult mortality may be high in years of early or late snowmelt. The unpredictability also selects for asynchronous breeding such that more sites are available in any one year to offspring from certain successfully weaned litters. The habitat at Bodie is temporally and spatially unsaturated. Largely because of poor vagility of pikas, much of the habitat is vacant. Colonization is unable to completely offset extinction of populations on patches of habitat. Here, the selective factor determining litter size is juvenile production and not adult mortality.

ISSN:0012-9658    

DOI:10.2307/1936639

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

Low numbers of Tetrahymena pyriformis provided with °2 x 109Klebsiella pneumoniae or Rhizobium sp. cells/ml reduced the bacterial population only to 107/ml in solution. When 5—7 x 108K. pneumoniae or 1 x 108Rhizobium sp. were preyed upon, 106bacteria/ml survived and coexisted with the ciliate. Low initial densities of the protozoan provided with 3 x 106or 5 x 107K. pneumoniae or 3—4 x 107Rhizobium sp./ml reduced the prey population t 2—3 x 105/ml. However, when the initial number of T. pyriformis was high (2—34 x 104/ml) and the K. pneumonia or Rhizobium sp. density was °107/ml, the animal did not reduce the bacterial population size. The data suggest that the number of K. pneumoniae or Rhizobium sp. cells able to coexist in solution with T. pyriformis was governed by the number of protozoa initially present or developing as a result of predation. By contrast, 105Xanthomonas citri cells/ml coexisted with the ciliate whether this bacterium was provided at 7 x 106or 8 x 108cells/ml. In soil treated with 3.5 x 108and 3.1 x 109Rhizobium sp./g, the density of indigenous protozoa rose to 1—2 x 104and 4—5 x 105/g, respectively, yet the density of rhizobial survivors stabilized at 3—7 x 107/g, a range higher than that observed in solution.

ISSN:0012-9658    

DOI:10.2307/1936640

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

Time and energy budgets were calculated for 16 Phainopeplas (Phianopepla nitens) nesting in the coastal woodlands of southern California. Brood size differed 50%; 4 pairs raised 3 young and 4 pairs raised 2 young. Compared to pairs feeding 2 nestlings, pairs feeding 3 nestlings spent an average of 42% more time flycatching, 16% more time foraging at fruiting shrubs, and 22% more of their active day in flight. Daily energy expenditure of pairs feeding 3 nestlings was increased a surprisingly small amount compared to that of pairs feeding only 2 young–a mean of 7%, or 12 kJ. Over the entire period from egg synthesis to fledging, total parental energy expenditure is estimated to increase only 4.7% associated with a 50% increase in brood size. The Phainopepla may exhibit a unique annual cycle; it apparently breeds twice annually, once in its summer range (where the present study was conducted) and once in its winter range in the Sonoran Desert. Using data from this study plus those from a previous one, the 2 breedings were compared in terms of parental energy expenditure from egg—laying until fledging and parental harvesting requirements during the incubation and nestling periods. (Harvesting requirements = parental energy expenditure + the energy requirements of any young being fed.) Remarkable convergences are seen in the reproductive energetics of Phainopeplas breeding in the 2 habitats. Regardless of the striking differences between the 2 seasonal ranges in parental energy expenditure, habitat, daylength, and social system used, a Phainopepla incubating or feeding 2 nestlings in the coastal woodlands has a mean harvesting rate (kilojoules/hour active) virtually identical to that of a bird in a comparable stage of breeding in the desert. Similarly, total parental energy expenditure from egg synthesis until fledging averages only 2.6% different between populations breeding in the 2 areas, when calculated on an energy expended per young fledged basis.

ISSN:0012-9658    

DOI:10.2307/1936641

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

Physical and Chemical parameters of soils and water, measured on 140 sites in the Delta Marsh, Manitoba between May 1973 and September 1974, were compared with presence and dry—weight standing crop of sago pondweed (Potamogeton pectinatus L.) on those sites. Mean comparisons and discriminant function analyses identified water depth, soil texture and maximum and directional exposure to wave action as important variables affecting plant distribution. Multiple regression analyses suggested that water depth, available soil K, available soil P, soil texture and directional exposure, were important factors affecting growth on colonized sites. A greenhouse experiment demonstrated that sago pondweed grew better on Delta Marsh soils that normally supported the plant, suggesting that some specific edaphic adaptations might exist. Within the euphotic zone of the Delta Marsh, sago pondweed distribution was probably most effected by prevailing winds through their influence on soil distribution and turbulence.

ISSN:0012-9658    

DOI:10.2307/1936642

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

Two annual grassland communities, 1 of which occurred on serpentine soil, were compared as light—competitive habitats for Bromus mollis L. Gramineae, a common component of each. Potential light competition was assessed as the dependence of simulated photosynthetic rate on position within the canopies. The 2 communities were found to differ markedly in foilage canopy structure and light penetration. Incident sunlight was less attenuated by the serpentine canopy. The vertical gradients of light intensity within the 2 communities were such that a plant in the nonserpentine grassland would have to display its leaves as a greater elevation than it would in the serpentine canopy in order to achieve the same rate of photosynthesis. The nonserpentine canopy was thus judged to be potentially more light competitive.

ISSN:0012-9658    

DOI:10.2307/1936643

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

The problem of weighting resource states to make them equally distinct from each other, and thereby improving measures of niche width and overlap, is discussed on the basis of the Colwell—Futuyma (1971) weighting factors. A drawback of their approach appears to be that the distinctness of resource states is not separated from their production in the physical environment. Therefore, a new factor D/P is suggested instead of D, where D stands for the (Colwell—Futuyma) distinctness and P for the production of a resource state. The P value may be approximated by the total number of individuals associated with the resource state, assuming that resources are utilized proportionally to their availability. Information gathered in a study of the community of dung—inhabiting beetles is used in an evaluation of the "summation"and "product" approaches to the estimation of multidimensional niche metrics from unidimensional data. Niche width was measured with the Shannon—Wiener measure, niche overlap with the index of percentage similarity. The multidimensional niche width was well approximated by the summation measure, but the product measure yielded a much better estimate of the multidimensional niche overlap.

ISSN:0012-9658    

DOI:10.2307/1936644

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

Survivorship data can be effectively summarized using the shape and scale parameters of the Weibull frequency distribution. The shape parameter controls the rate of change of the age—specific mortality rate and, therefore, the general form of the survivorship curve. Estimates of shape and scale parameters and their confidence intervals can be easily calculated and used to compare survivorship curves of different populations.

ISSN:0012-9658    

DOI:10.2307/1936645

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

A coring technique was used to intensively sample the litter layer of a red maple (Acer rubrum) woodlot in the vicinity of Ottawa, Canada. Monthly changes in the litter standing crop provided an accurate estimate of the decomposition rate of red maple litter during 2 summers and 1 winter both under natural conditions and when treated with the insecticide Carbofuran®. The Standing crop of litter ranged annually between °275 and 700 g/m2and decomposed at a rate between 1.48 and 2.19 g°m(—2)°day(—1) under natural conditions between May and November. A common carbamate insecticide (Carbofuran®) applied at recommended rates reduced the decomposition rates to between 0.99 and 1.26 g°m(—2)°day(—1) resulting in an increase in standing crop.

ISSN:0012-9658    

DOI:10.2307/1936646

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

Pogonomyrmex rugosus, a group forager, foraged preferentially on seeds of plant species with shed large quantities of seeds at 1 time. Pogonomyrmex desertorum, an individual forager took seeds in relation to their availability but concentrated on grass seeds late in the growing season. Pogonomyrmex californicus selected seed species which allowed it to avoid contact with its congeners. During a dry year, P. rugosus exhibited little selectivity, supporting the idea that selectivity should be decreased under conditions of low food abundance. Pogonomyrmex spp. removed a significant fraction of the seed production of only 1 species, Boutleoua barbata. It is suggested that Pogonomyrmex foraging may affect the relative abundance of plant species.

ISSN:0012-9658    

DOI:10.2307/1936647

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY