Search

The article discusses succession of trees in a mixed forest. A predictive model for the succession was developed in study on woods owned by the Institute for Advanced Study in Princeton, New Jersey. The study for the succession involves factors such as the moisture in the soil and the geometry of leaf arrangement.

Discusses how systematic inventories of plots of woodlands and fields can be of practical use in planning how best to conserve wildlife in a given patch of land. Benefits of the technique; Description of a project designed as an exercise for a summer course in mathematical geology and field biology for grade school teachers. INSET: Deriving the species-area curve..

Overlap in foods and foraging of four species of breeding blackbirds in the Potholes of central Washington was estimated from samples of food delivered to the nestings obtained by the pipe—cleaner technique. Prey distribution and availability were sampled with emergence traps for aquatic species and by sweeping with a standard insect net for upland species. Overlap was estimated by the probability than an item of food drawn randomly from the diet of one species would be of the same prey category taken from the same habitat as an item drawn at random from the diet of another species. Because of the diurnal cycle of emergence of aquatic insects, overlaps were calculated for three periods of the day (preemergence, emergence and postemergence) and averaged for the final overlap value. The overall food overlap for three of the species is high for all periods of the day and there is little evidence for differential specialization within habitats. Habitat overlaps, however, are varied, being highest during the emergence period for Redwings and Yellowheads but highest during the afternoon between Redwings and Brewers. The total overlap values are very similar to the theoretical maximum values derived from competition theory by MacArthur and Levins.

The adaptive significance of colonial nesting for the Brewer's blackbird was studied in a sagebrush desert in eastern Washington. The colonies were small enough (5—30 pairs) to allow analysis of the behavior of individual birds and their reproductive success. The structural simplicity of the study site allowed easy access to the nests and accurate measurement of their spatial distribution. The effects of predation on breeding success were analyzed with respect to colony shape and the spatial distribution of the nests. On the study area the predation pattern favored more widely spaced nests in liner colonies, but more closely spaced nests in round colonies. I examined the role of colonial nesting in aiding the exploitation of a spatially and temporally variable food supply by taking food samples from nestling birds, measuring patterns of food availability, and observing the foraging patterns of the adult birds. An idealized model relates the spatial distribution of nests to the efficiency of individual exploitation of different distributions of food. In addition to conforming to the conditions of the model, Brewer's blackbirds take advantage of each other's foraging success. In conclude that colonial nesting in the Brewer's blackbird is primarily adaptive to the variable nature of their food supply.

We examine the qualitative behavior of differential equations for the proportion of insular patches of each of two kinds of habitat occupied by each of two species with characteristics rates of migration between patches and of local extinction within a habitat. Certain migration and extinction rates result in stable coexistence, even of closely similar species; others lead to competitive exclusion, even when each species is competitively superior in one kind of habitat. For a community of many species in many habitats, we surmise qualitative limits to the subdivision of resources, and alternative stable communities. Our results extend to species that live in successional or ephemeral habitats. We therefore conjecture equilibrial theories for the number of patches of habitat occupied by insular species, fugitive plants and invertebrates, or infesting parasites.

Objective, empirical measures of overlap between samples of items distributed proportionally into various qualitative categories are presented and reviewed. These indices of overlap, derived from either probability or information theory, should prove useful to the ecologist in comparative studies of diet, habitat preference, seasonal patterns of abundance, faunal lists, or similar data.

Data resembling either density dependent or density independent control of animal numbers may be generated by models that differ in degree but not in kind.

A technique is described for estimating a foilage profile in a forest by a combination of measurements over random lines of points: (1) counts of leaf contacts on a plumb line below a tripod, (2) sightings on the heights of lowest leaves over grids of points, and (3) the proportions of sky unobscured by leaves.

Presents a letter to the editors of the "American Science" about the article, "Competition, Scientific Method, and Null Models in Ecology," published in March-April 1986 issue of the magazine.

Tropical Rain Forests of the Far East.

Some problems associated with measuring emergence of Odonata are discussed. The authors described a trap made of window screening on a frame of welded-wire fencing which proved satisfactory for their work. This or a similar design may prove useful for analyzing the emergence of other insects.