H. Ronald Pulliam

The Sustainable Biosphere Initiative: An Ecological Research Agenda: A Report from the Ecological Society of America

In this document, the Ecological Society of America proposes the Sustainable Biosphere Initiative (SBI), an initiative that focuses on the necessary role of ecological science in the wise management of Earths resources and the maintenance of Earths life support systems. This document is intended as a call to arms for all ecologists, but it will also serve as a means to communicate with individuals in other disciplines with whom ecologists must join forces to address a common predicament. This document focuses primarily on the acquisition of ecological knowledge. It identifies the ecological research programs of highest priority and recommends steps required to pursue research objectives. The document also lays the groundwork for improving the communication and application of ecological knowledge. The SBI proposes three research priorities: global change; biological diversity; and sustainable ecological systems.

THE USE OF SPACE BY WINTERING SPARROWS

Differences in microhabitat utilization by sparrows wintering in southeastern Arizona, USA may be sufficient to explain their coexistence. The species either forage in different mac- rohabitats or in the same habitat at different distances from tree or shrub cover. Seed size partitioning within habitats is sufficient to explain coexistence only in one case where the seed size distribution is bimodal. The species that forage in plains grassland habitat differ by foraging in concentric rings about tree or shrub cover. The behavior of each of these species appears to enhance predator avoidance and these behaviors change in a regular pattern with distance to cover both within and between species. Species foraging close to cover are social and tend to be conspicuous both in behavior and morphol- ogy. Two different strategies adapt species to avoiding predators at great distances to cover. In dense grassland, with increasing distance to shrub or tree cover, species in the genus Ammodramus are increasingly solitary and cryptic. In sparse grassland, Chestnut-collared Longspurs are social and cryptic on the ground but conspicuous in flight.

The Feeding Ecology of Five Sympatric Finch Species

Within habitats the overlap of food-size utilization of five sympatric finch species is almost 100% despite considerable differences in culmen lengths. It is suggested that the differences in bill size reflect differences in the proportion of large seeds in the set of habitats in which each species feeds and does not function to reduce competition within habitats. Although seed production was sufficient to maintain the finch populations through winter, the finches did eat at least 40% of the available seeds. Of the five finch species commonly present at least three seem to be limited by their winter food supply. The diversity of finches in the yield was not significantly correlated with either food abundance or food diversity.

FORAGING EFFICIENCY, RESOURCE PARTITIONING, AND THE COEXISTENCE OF SPARROW SPECIES'

The relationship between seed size and handling time was documented for three species of sparrows. Handling times were measured in the laboratory by presenting field-collected seeds to birds caught in the wild. Large species of sparrows were more efficient than small species at handling large seeds, but large and small sparrow species were about equally efficient at handling small seeds. Based on the relationships between seed size and handling time, a function was constructed relating profitability (measured in milligrams per second) to seed size for each sparrow species. These results, with information on the abundance and size distribution of seeds in the habitats frequented by the sparrows, were used to show that different species of sparrows are likely to have broadly overlapping diets whenever seeds are scarce enough for the consumption of seeds by one species to have much impact on the availability of seeds to another species.

A social learning model of conflict and cooperation in human societies

Patterns of conflict and cooperation both within and between societies may be related to the degree of cultural similarity within and between the same societies. A simple model of social learning is used to predict patterns of conflict and cooperation in hypothetical societies that differ in the roles of relatives and nonrelatives in the enculturation of children. The model is illustrated by comparing its predictions to known differences in the patterns of conflict between males inpatrilocal and matrilocal societies.

The Influence of Food Supply on Local Density and Diversity of Sparrows

A long-term study of sparrows in an arid oak woodland in southeastern Arizona demonstrated that local population density of sparrows is independent of local seed abundance during years of moderate to high seed production. Experimental manip- ulation of the abundance and size distribution of seeds during 2 yr of moderate seed production had no discernible influence on the local abundance or diversity of sparrows. These experimental results support the hypothesis, based on previous nonexperimental observations, that sparrow populations in this habitat are locally food limited only during infrequent years of very low seed production.

THE COMPARATIVE FEEDING RATES OF NORTH AMERICAN SPARROWS AND FINCHES

Data on the seed profitabilities (mass of seed ingested per unit time) of captive emberizine sparrows and cardueline finches were used to interpret the underlying factors promoting differences in their ecologies. Sparrows consume seeds that are approx- imately an order of magnitude smaller in size that those consumed by finches of similar body mass. Because sparrows consume such small seeds and because finches are much more efficient at handling large seeds, sparrows need to encounter seeds at rates that are one to two orders of magnitude greater than that required by finches. As a result, sparrows have to spend much more time foraging than do finches, and sparrows are not able to go for as long periods of time searching for new food patches as are finches. Consequently, sparrows are relatively sedentary and restricted to areas of dense seed concentrations, whereas finches are extremely vagile and move over very large geographic areas in search of new patches of food. Furthermore, resource partitioning is more pronounced among finches. Small and large finch species eat very different seed sizes, whereas the diets of small and large sparrows overlap greatly. in the Fringillidae. In this paper, we discuss some dra- matic differences in the foraging ecology of the two groups that occur despite their superficially similar ap- pearances.

ECOLOGICAL COMMUNITY THEORY AND THE COEXISTENCE OF SPARROWS

The predictions of community matrix theory do not agree with the observed patterns of coexistence of grassland and woodland sparrows. Predictions based on the random co-occurrence of species match the observed patterns about as well as do the predictions of community theory. Predictions of both the community theory model and the random co-occurrence model are improved substantially by the addition of thresholds that account for the minimum food requirements of spar- rows of different sizes. The observed patterns of species coexistence appear consistent with a model based on resource abundance and aggressive interference; however, they are also consistent with coexistence based on interspecific partitioning of seeds by size.

Equitability and Resource Limitation

It is suggested that the equitability concept of Lloyd and Ghelardi provides an approach to resolving the question of resource limitation in a specific field situation. The high equitabilities of predaceous insect groups in an annual grassland community indicated that these populations were food limited, whereas the low equitabilities of the herbaceous insects indicated that they were limited by some other factor not directly involved in competition. The increase in equitability of the spiders (all species of which are predatory) during the growing season was tentatively explained on the basis that reaching a resource—limited equilibrium in relative abundances required more time because of the relative immobility of species in this component. These data also demonstrated how the relative abundances of species can undergo a history of adjustment during seasonal succession. See full-text article at JSTOR

Spatially Explicit Population Models

During the last decade, ecologists and particularly mathematical ecologists have focused on different approaches to the problem of spatial distribution of species. When the spatial distribution is not considered explicitly, the mathematical models are called spatially implicit. They consider the proportion of territory occupied by given species, but there is no information on which particular sites this occupation takes place (Caswell & Cohen, 1991; Barradas & Cohen, 1994; Barradas et al., 1996; Barradas & Canziani, 1997; Hanski, 1999; Federico & Canziani, 2000). When the spatial distribution of the species is specified, the models are called spatially explicit (Turner et all., 1995; Marquet & Velasco-Hernández, 1997; Hanski, 1999; Neubert & Caswell, 2000; Ruiz-Moreno et al., 2001).