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Ecology and evolution go hand in hand. However, since evolution occurs over relatively long time scales, ecologists had long thought it unlikely that evolutionary events could affect population dynamics or species interactions in ecological time. This view is changing. Today, there are multiple areas of research examining how evolutionary processes feedback directly on ecology. For example, eco-evolutionary dynamics focus on the cyclical interaction between ecology and adaptive evolution, such that changes in ecological interactions drive selection on organismal traits that, in turn, alter the outcome of ecological interactions. Striking examples of eco-evolutionary feedbacks are found in predator–prey interactions of laboratory populations. However, less is known about eco-evolutionary feedbacks in nature. Evolutionary rescue describes a process whereby rapid adaptation may prevent extinction in a changing environment. Other topics covered in this chapter are community phylogenetics and the evolution of regional species pools.

Selection arises from the encounter between phenotypes, which are environmentally influenced, and environments, which in turn are modified by the organisms themselves. This chapter examines selective evolution in the context of these reciprocal effects. First, new insights into phenotypic variation and heredity are summarized to expand a strictly allelic evolutionary model. A key point is that immediate as well as inherited environmental influences affect fitness variation and, consequently, play an evolutionary role. A section on the evolution of reaction norms explains environmentally contingent patterns of genetic variance (G × E interaction and cryptic variation) and argues that plasticity can buffer selective impact, facilitate evolutionary divergence, or both. The impact of heritable epigenetic factors on selective dynamics is then discussed. A section on selective feedbacks due to niche construction (eco-evolutionary feedbacks) provides case studies and reviews theoretical insights, including coevolutionary implications. A final section considers how reciprocal organism–environment effects can be integrated to inform studies of adaptation and selection.

As G. G. Simpson wrote, organisms and their environments are “not really separable.” This chapter examines the biologically intimate organism–environment relationship. It begins by critiquing the concepts of ecological niche and adaptation. The chapter then lays out the book’s conceptual framework, drawing on recent examples from the animal, plant, and microbial literature to make the following points. Environments shape the phenotypes of individuals (whether positively or negatively) through ecological development. In turn, the presence and activities of individuals affect their environments (again, these impacts can be positive or negative) through two modes of niche construction. First, the organism’s presence and activities can alter its external biotic or abiotic conditions (habitat construction). Second, the individual’s phenotype mediates how the organism experiences those conditions (experiential niche construction). Adaptation emerges from these reciprocal organism–environment effects. To close the chapter, the porous boundary between organism and environment is discussed in light of internalized elements such as microbial symbionts.