Edward O. Wilson

An equilibrium theory of insular zoogeography

As the area of sampling A increases in an ecologically uniform area, the number of plant and animal species s increases in an approximately logarithmic manner, or s = bAk, (1) where k < 1, as shown most recently in in the detailed analysis of Preston (1962). The same relationship holds for islands, where, as one of us has noted (Wilson, 1961), the parameters b and k vary among taxa. Thus, in the ponerine ants of Melanesia and the Moluccas, k (which might be called the faunal coefficient) is approximately 0.5 where area is measured in square miles; in the Carabidae and herpetofauna of the Greater Antilles and associated islands, 0.3; in the land and freshwater birds of Indonesia, 0.4; and in the islands of the Sahul Shelf (New Guinea and environs), 0.5.

The evolution of eusociality

Eusociality, in which some individuals reduce their own lifetime reproductive potential to raise the offspring of others, underlies the most advanced forms of social organization and the ecologically dominant role of social insects and humans. For the past four decades kin selection theory, based on the concept of inclusive fitness, has been the major theoretical attempt to explain the evolution of eusociality. Here we show the limitations of this approach. We argue that standard natural selection theory in the context of precise models of population structure represents a simpler and superior approach, allows the evaluation of multiple competing hypotheses, and provides an exact framework for interpreting empirical observations.

Rethinking the Theoretical Foundation of Sociobiology

Current sociobiology is in theoretical disarray, with a diversity of frameworks that are poorly related to each other. Part of the problem is a reluctance to revisit the pivotal events that took place during the 1960s, including the rejection of group selection and the development of alternative theoretical frameworks to explain the evolution of cooperative and altruistic behaviors. In this article, we take a “back to basics” approach, explaining what group selection is, why its rejection was regarded as so important, and how it has been revived based on a more careful formulation and subsequent research. Multilevel selection theory (including group selection) provides an elegant theoretical foundation for sociobiology in the future, once its turbulent past is appropriately understood.

Strategic environmental assessment.

The changing context of environmental assessment introduction to SEA national applications case studies critique of SEA techniques SEA and the global future.

Biodiversity Studies: Science and Policy

Biodiversity studies comprise the systematic examination of the full array of different kinds of organisms together with the technology by which the diversity can be maintained and used for the benefit of humanity. Current basic research at the species level focuses on the process of species formation, the standing levels of species numbers in various higher taxonomic categories, and the phenomena of hyperdiversity and extinction proneness. The major practical concern is the massive extinction rate now caused by human activity, which threatens losses in the esthetic quality of the world, in economic opportunity, and in vital ecosystem services.

The number of queens: An important trait in ant evolution

The pervasive social and ecological differences between ant colonies that have a single queen and those that have multiple queens are defined. The evolutionary tendencies which lead to polygyny and the adaptive significance of multiple queens are examined. The discussion of the ecological consequences of polygyny and monogyny leads to a deeper understanding of territoriality, spacing and species packing in ants.

The analysis of olfactory communication among animals

Methods are presented for determining those parameters of olfactory communication systems most closely related to the diffusion process. Four general cases of diffusion are considered: instantaneous release of the communicating substance in still air, continuous release in still air, continuous release from a moving source as in an odor trail, and continuous release in a wind. The techniques have been applied in the analysis of three real communication systems, involving an alarm substance, a recruitment trail, and a sex attractant respectively. It has been possible to demonstrate the effect of differing values of the parameters in fulfilling the design requirements of a particular system with respect to range of the signal, its rate of spread, and its persistence.

Caste and division of labor in leaf-cutter ants (Hymenoptera: Formicidae: Atta)

SummaryThe size-frequency distributions of workers were followed in A. cephalotes colonies from the beginning brood (collected in Costa Rica) through 4 years of growth in the laboratory to a worker population of up to 64,530. Workers in the founding groups had a nearly uniform distribution, with a range in head width of 0.8–1.6 mm (Figs. 1–3, Table 1). This range is the minimum required both to harvest fresh vegetation and cultivate the symbiotic fungus. Thus in founding the colony the queen produces close to the maximum mumber of individual workers that can collectively perform all of the essential tasks.By the time the worker population reaches approximately 500, the size-frequency distribution has begun to shift to the distinctively “adult” form seen in much larger colonies. Yet over a span of 3–4 years, encompassing the growth of the incipient colonies into the largest studied, the pattern of energy investment remains relatively little changed, with the maximum investment placed in the large minor to small media size classes of head width 1.0–1.6 mm, in other words the minimally essential size range (Figs. 2, 3).In spite of the large shifts in size-frequency distribution during the earliest stages of colony growth, only relatively minor shifts occur in division of labor (Table 2).The question was posed: which is more important in the ontogeny of the caste system, the size of the colony or its age? In order to provide an answer, I selected four colonies 3–4 years old and with about 10,000 workers and reduced the population of each to 236 workers, giving them a size-frequency distribution characteristic of natural young colonies of the same size. The worker pupae produced at the end of the first brood cycle possessed a size-frequency distribution like that of small, young colonies rather than larger, older ones. Thus colony size is more important than age.

The encyclopedia of life

Abstract Comparative biology, crossing the digital divide, has begun a still largely unheralded revolution: the exploration and analysis of biodiversity at a vastly accelerated pace. Its momentum will return systematics from its long sojourn at the margin and back into the mainstream of science. Its principal achievement will be a single-portal electronic encyclopedia of life.

Caste and division of labor in leaf-cutter ants (Hymenoptera: Formicidae: Atta): I. The overall pattern in A. sexdens

SummaryAtta sexdens was selected for close study because its caste and polyethism systems, which are among the most complex found in all ants, can be expected to provide an estimate of the upper limits of colonial organization in these insects.A total of 29 tasks were identified. These are performed by an estimated four physical castes, of which three are further subdivided into temporal castes to make a total of at least seven castes overall (Figs. 1–11 and Table 1).The physical castes of A. sexdens were defined on the basis of ‘role clusters,’ which are more or less segregated or distinctively shaped sets of polyethism curves. The four castes can be characterized broadly according to role as gardener-nurses, withinnest generalists, forager-excavators, and defenders, respectively (Fig. 12). This discretization is only partial, and finer, arbitrary subdivisions at the lower end of the size scale are possible.The physical castes have been generated by a large evolutionary increase in size variation accompanied by the adoption of relatively elementary rules in allometry and alloethism. The increase in caste diversity beyond that possessed by monomorphic attines serves the relatively narrow primary function of cutting and treating fresh vegetation for use as the fungal substrate. The material is processed and the fungus cultured in an assembly-line fashion, with the succession of tasks (gathering, degrading, and implanting of substrate, followed by implanting and care for the fungal hyphae) being performed by ever smaller workers (Fig. 13).The rules of allometry and alloethism create far less caste diversity than would be possible by a few additional minor evolutionary adjustments in larval growth and allometry during adult development (Fig. 17). Evidence is presented for the existence of secondary roles possessed by various size ensembles in addition to the primary roles, and for the suboptimal performance of a few size classes. These two phenomena are considered to result from the simplicity and hence restrictiveness of the allometry and alloethism rules (see Discussion).Polyethism has evolved further than polymorphism: the alloethic curves rise and descend more steeply than the size-frequency distributions and they are generally steeper than the allometric curves drawn for any selected pair of physical measurements.A technique is introduced by which the functions of previously unstudided or poorly understood organs can be inferred. It consists of noting in which size classes the organs are maximally developed, then determinig the labor specializations of the size classes. The method is shown to work in the cases of pronotal spination, poison sac, postpharyngeal gland, metapleural gland, and mandíbular gland, and it is extended in a speculation concerning the functions of other exocrine glands (Fig. 16).A distinction is made between fixed tasks, which are attended by relatively limited age-size ensembles of workers, and flexible asks, which are attended by ensembles that vary in size (and perhaps age) according to the objects treated during the performance of the task (Fig. 15).The concept of the primitive caste is introduced; it is the size class that most resembles related monomorphic species and performs the most generalized services for the colony. Evidence is presented that in A. sexdens this class is composed of workers with head widths around 1.4–1.6 mm.