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This chapter shows that organizational ecology is much more sociological and less biological than many critics of organizational ecology think. It argues that organizational ecology and its theory of competition rests heavily on the seminal work of Emile Durkheim on the division of labour, and on the thoughts of Amos Hawley on human ecology. It suggests that the expressions used by the agents of organizational ecology are ‘Darwinian’ but that the theoretical argumentation is ‘Durkheimian’. The chapter highlights the theoretical foundations of organizational ecology and emphasizes that competition — and not the biological aspects of evolution — forms the core of the organizational ecology theory. The most the most important sub-concepts of organizational ecology that deal with competition and market formation are also discussed: density dependence and resource partitioning. The first concept deals with the impact of the number of competitors on the survival and founding chances of organizations. The latter is concerned with the influence of market concentration on the vital rates of specialist and generalist organizations.

Meta-analysis of the first generation of biodiversity experiments has revealed that there is a general positive relationship between diversity and ecosystem processes that is consistent across trophic groups and ecosystem types. However, the mechanisms generating these general patterns are still under debate. While there are unresolved conceptual issues about the nature of diversity and complementarity, the debate is partly due to the difficulty of performing a full-factorial analysis of the functional effects of all species in a diverse community. However, there are now several different analytical approaches that can address mechanisms even when full factorial analysis is not possible. This chapter presents an overview and users' guide to these methods. This chapter concludes that the current toolbox of methods allows investigation of the mechanisms for most, if not all, biodiversity and ecosystem functioning experiments conducted to date that manipulate species within a single trophic level (e.g. plant biodiversity experiments). Methods that can address mechanisms in multitrophic studies are a key need for future research.

Resource competition is common in nature and is often strong. Additionally, heterospecifics frequently interact in ways that impede ability of each species to reproduce successfully. Both types of competitive interactions can have severe fitness costs. Indeed, in some cases, competition can even cause a species to go locally extinct. As a consequence, selection should generally favor resource-use or reproductive traits that enable individuals to obtain resources or to successfully reproduce in the face of interspecific competition. Character displacement thereby leads to resource and reproductive partitioning that fosters species coexistence. Although character displacement is not the only means by which partitioning arises or by which species coexist, character displacement can contribute to diversity in important ways.

Adaptive radiation is the evolutionary divergence of members of a clade to adapt to different ecological niches in a variety of ways. The theory of adaptive radiation in anoles suggests that this diversity is the result of ecological interactions between initially similar species. Three predictions stem from this theory: (1) sympatric species interact ecologically, primarily by competing for resources; (2) as a result of these interactions, species alter their resource use; and (3) as a result of shifts in resource use, species evolve appropriate adaptations. This chapter documents evidence from anoles for the first two of these predictions, first reviewing the structure of anole communities and the ecological relationships among coexisting anole species. It then describes patterns of resource partitioning and niche complementarity in anoles, and finally discusses interspecific competition and different forms of anole interactions, including predation, parasitism, and mutualism.

Character displacement fosters species coexistence by promoting differences between species in resource use (resource partitioning) and in reproductive traits (reproductive partitioning). By promoting niche differences, character displacement lessens costly competitive interactions, reduces the risks of competitive or reproductive exclusion, and thereby increases the chances of species coexistence and diversity within communities. Beyond its effects on species coexistence, character displacement has the further potential to alter population dynamics, extinction risk, and, concomitantly, species’ ranges. Studying character displacement can therefore reveal how the fitness consequences of interactions between species potentially translate into large-scale patterns of species richness, distributions, and diversity. Thus, the study of character displacement provides a unifying framework for understanding the maintenance, abundance, and distribution of biodiversity.

In most places on Earth, many similar species are found coexisting. This key observation is often explained in terms of ecological differences in how species interact with their shared environment, that is, in terms of their niche differences. Niche differences can to lead to stable coexistence in contrast to the ecological drift predicted by the neutral theory of community ecology. Coexistence becomes stabilized as density feedback within species is strengthened relative to density feedback between species. Coexistence is reflective of two distinct niche comparisons, niche overlap, and species relative average fitness. In general, low niche overlap (dissimilarity in use of the environment) and similar average fitnesses (similar average performance) favor coexistence. For a unified theory of species coexistence, it is shown how the Lotka–Volterra competition model can reflect and quantify several types of niche comparison, including comparisons of resource use, susceptibility to natural enemies, and temporal variation in activity.

This chapter relates to the emerging field of evolutionary psychology. Building on past research understanding of the mechanisms underlying animal behavior is presented. Current researches in this field offer many insights into the development of social behaviours displayed among humans. The contribution of animal behaviour research to unravel the evolution of individual and social behaviours including foraging strategies, reproductive systems, social behaviour, dominance hierarchies, social communication, parental investment patterns, evolution of eusociality, among others, are highlighted. Finally, the applications of animal behaviour studies in the area of wildlife such as conservation, management of national parks, and zoo management are indicated. It may be noted that the developments in the area of animal behavior are impressive and are perhaps as good as noted in allied disciplines of anthropology and zoology. However, animal behaviour research is currently an underdeveloped field of psychology. India could perhaps rejuvenate its close association with animal world and nature, a main part of its mythology and real life, by developing this area.