To understand resource partitioning, essentially a community phenomenon, we require a holistic theory that draws upon models at the individual and population level. Yet some investigators are still content mainly to document differences between species, a procedure of only limited interest. Therefore, it may be useful to conclude with a list of questions appropriate for studies of resource partitioning, questions this article has related to the theory in a preliminary way. 1) What is the mechanism of competition? What is the relative importance of predation? Are differences likely to be caused by pressures toward reproductive isolation? 2) Are niches (utilizations) regularly spaced along a single dimension? 3) How many dimensions are important, and is there a tendency for more dimensions to be added as species number increases? 4) Is dimensional separation complementary? 5) Which dimensions are utilized, how do they rank in importance, and why? How do particular dimensions change in rank as species nuimber increases? 6) What is the relation of dimensional separation to difference in phenotypic indicators? To what extent does the functional relation of phenotype to resource characteristics constrain partitioning? 7) What is the distance between mean position of niches, what is the niche standard deviation, and what is the ratio of the two? What is the niche shape?

https://science.sciencemag.org/content/sci/185/4145/27.full.pdf

Resource Partitioning in Ecological Communities

Enchantment and Disenchantment: The Role of Community in Natural Resource Conservation

Hypotheses that attempt to explain latitudinal gradients in species diversity are reviewed. Some hypotheses are circular, i.e. they are based on the assumption that some taxa have greater diversity in the tropics. These include explanations assuming different degrees of competition, mutualism, predation, epiphyte load, epidemics, biotic spatial heterogeneity, host diversity, population size, niche width, population growth rate, environmental harshness, and patchiness at different latitudes

Latitudinal gradients in species diversity: the search for the primary cause

Measures of niche breadth and overlap that depend on the distribution of individual among resource states (ecological categories) should be independent of the relative abundance of the species and of the number of resource states considered. Such measures should also take into account the degree of distinctness of the resource states from the point of view of the organisms concerned. An ecoassay of the distinctness of resource states may well be easier and more meaningful than measurements of physical and chemical factors. We propose that the species composition of communities utilizing different resource states may be used to develop weighting factors with which each state may be weighted in proportion to its degree of distinctness. The weighting factors are used in the development of indices of niche breadth and overlap that correct for variation in the range and distinctness of resource states and that suffer less from human subjectivity than do the measures used to date. The use of such indices and the relationship of niche overlap to competition are discussed.

On the Measurement of Niche Breadth and Overlap

Spatial genetic structure of a tropical understory shrub, PSYCHOTRIA OFFICINALIS (RuBIACEAE)

La Selva, a nature reserve and field station in Costa Rica, is one of the most intensively studied and best-understood tropical field sites in the world. For over 30 years, La Selva has been a major focus of research on rainforest ecology, flora and fauna. This volume provides a comprehensive review of this research, covering La Selva's geographical history and physical setting, its plant and animal life, and agricultural development and land use. Drawing together a wealth of information, "La Selva" offers a substantive treatment of the ecology of a rainforest. Part 1 summarizes research on the physical setting and environment of the rainforest, as well as the history of the research station. Some chapters in this part focus on climate, geomorphology and aquatic systems, while others look at soils, nutrient acquisition and cycles of energy. Part 2 synthesizes what is known about the plant community. It begins with chapters on vegetation types and plant diversity, and also explores plant demography, spatial patterns of trees, and the impact of treefall gaps on forest structure and dynamics. Other chapters address plant physiological ecology, as well as plant reproductive systems. Part 3 covers the animal community, summarizing information on the six best-known animal taxa of the region: fishes, amphibians, reptiles, birds, mammals and butterflies. This part includes an overview of faunal studies at La Selva and a chapter on animal population biology, which examines animal demography and abundance, and interactions between predators and prey. Part 4 addresses interactions between plants and animals and the effects of these interactions on species diversity. Part 5 considers the impact of land use and agricultural development on La Selva and other areas of Costa Rica. One chapter examines land colonization and conservation in Sarapiqui, another covers subsistence and commercial agricultural development in the Atlantic lowlands region, and a third looks at the forest industry in north-eastern Costa Rica. This part also assesses the role and research priorities of La Selva. "La Selva" provides an introduction to tropical ecology for students and researchers at La Selva, a major source of comparative information for biologists working in other tropical areas, and a resource for conservationists.

La Selva: ecology and natural history of a neotropical rain forest.

To some extent ecologists have differentiated into two groups: one whose primary concern is theory, another whose primary concern is collection of data. Fretwell's engaging analysis of research strategies in ecology (19:x-xix) suggests that special­ ization as theorist or data collector increases prestige, which is almost certainly favored by selective biology faculties in the current era of restricted budgets and PhD oversupply. One corollary of such specialization has been the tendency of theoreticians to test models, not by direct field observation of ecological systems, but by measurement of museum specimens for a morphological characteristic indicating the organism's ecology. Certain types of ecologic analysis over large biogeographic areas can probably be done in no other way short of several man-lifetimes of study (46, 57, 74). How valid is this methodology? The purpose of this review is to scrutinize critically some of the studies in which ecological generalizations have been made or tested on the basis of morphological measurements and to examine the validity of the relationship assumed between morphology and ecology. As is demonstrated in the next section, this area of concern involves a wide range of phenomena, some recently and well reviewed elsewhere. I therefore concentrate attention on two related aspects of this topic: the relationship of prey size to predator size and the phenomenon of character displace­ ment understood in terms of niche width, separation, and overlap.

Ecological Inferences From Morphological Data

Recapitulation des donnees portant sur le cycle de vie, l'ecologie, les parasites des insectes mineurs de feuilles, ainsi que leurs relations avec les plantes hotes

Bionomics of Leaf-Mining Insects

SUMMARY
Analysis of published records of the food of flycatchers (Tyrannidae), swallows (Hirundinidae) and vireos (Vireonidae) of North America, and terns (Laridae) of the Pacific Ocean showed that size, rather than taxonomic, differences in food appear to be the most important ones for these birds. Although the distribution of insect sizes in nature approaches a two-parameter log-normal distribution, the distributions of the sizes of food items taken by birds show no significant differences from log-normal.

Birds of a given feeding type (e.g. flycatchers) show a strong correlation of average prey size with bird body weight, and a significantly less strong correlation with bill characteristics, indicating that body size is a better predictor of prey size than any single bill character.

The slopes and/or intercepts of regressions of food size against body weight are different for birds of different foraging type.

Values of overlap in food preference are proportional to the similarity of the two species compared, expressed as the ratio of their weights.

Because insect taxa differ in size and because the amount of overlap in taxonomic composition of foods is therefore very roughly proportional to the amount of overlap in size, taxonomic differences in food may merely reflect differences in size preferences.

Values for overlap in food are greater than for most cases involving spatial niche parameters, indicating space is more easily divided than food, a conclusion supported by the relative rarity of large flycatchers.

Food preference and the extent of overlap in some insectivorous birds, with special reference to the tyrannidae

Summary

Samples of flying insects were made at three sites and during dry and wet seasons in Costa Rica and at two sites during the wet season in Panama. Compared with these were the diets of three aerially foraging birds: the Band-rumped Swift Chaetura spinicauda and Rough-winged Swallow Stelgidopteryx ruficollis in Costa Rica and the Short-tailed Swift Chaetura brachyura in Panama.



Among insects flying, Diptera accounted for between 52 and 75%, with smaller numbers of Hymenoptera (mean = 15%) and Coleoptera (10%). In bird stomach contents, however, Hymenoptera predominated (59–81%), Coleoptera were less common (mean = 18.5%) and Diptera least common (3.4%) of the three orders. The discrepancy between diets and samples of flying insects could not be accounted for solely on the basis of differential digestion. The composition of the swift and swallow diets was similar; there were no significant seasonal differences in the taxonomic composition of the diet of Chaetura spinicauda.



Size distributions of beetle prey fitted log-normal distributions in every case. Mean size of prey was significantly larger than that of insects available in all comparisons. Although there was no seasonal difference in the mean size of prey of Chaetura spinicauda, the variance in prey size, used as a measure of niche width, was significantly larger in the wet than in the dry season. Although insect densities may be higher, foraging time is reduced and the wet season is likely the worse season. This result therefore supports Emlen's hypothesis of narrower niches under optimal conditions and broader niches under suboptimal conditions.



For increasing altitude above ground published data show a decrease in the density of insects flying, a decrease in the proportions of taxa favoured by the birds, and a significant decrease in the mean size of beetles. None of these trends can explain the differences between the birds' diets and the samples of flying insects.



Preference of prey by these birds is concluded not to be a function of prey size alone, but to involve interaction among prey size, ease of capture, and local density. Because of different flight abilities, insect taxa will differ in ease of capture and, consequently, in mean size preferred by the predator, as well as proportions in the diet. This factor favours Hymenoptera and Coleoptera over Diptera as prey. Local concentrations of winged ants, bees and social wasps, and fig wasps make these prey differentially easy to exploit and explain the preference of Hymenoptera over Coleoptera. Large species of swifts are hypothesized to be the evolutionary consequence of the tendency of aerially foraging birds to exploit local concentrations of single prey species.

Henry A. Hespenheide

Papers

La Selva: ecology and natural history of a neotropical rain forest.

Ecological Inferences From Morphological Data

Bionomics of Leaf-Mining Insects

Food preference and the extent of overlap in some insectivorous birds, with special reference to the tyrannidae

Selective predation by two swifts and a swallow in central america