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Biodiversity is regarded as a scientific concept, a measurable entity, as well as a social–political construct (Gaston 1996, Wilson 1993). The aim of this volume is to develop the scientific basis for biodiversity studies, and for the integration of the concept into management practice. We emphasize biodiversity as a powerful, integrative concept—one that requires careful articulation and further conceptualization before application. Diversity is a concept that refers to the range of variation or differences among a set of entities; biological diversity then refers to variety within the living world. An example of biological diversity is “species diversity,” which is commonly used to describe the number, variety, and variability of the assemblage of living organisms in a defined area or space. However, biodiversity as a concept has evolved. Current definitions expand the biological diversity concept to emphasize the multiple dimensions and ecological realms in which biodiversity can be observed. These definitions stress that biodiversity encompasses at least four kinds of diversities: genetic diversity, species or taxonomic diversity, ecosystem diversity, and landscape diversity (McAllister 1991; Solbrig 1993, Stuart and Adams 1991; Groombridge 1992; Heywood 1994, Wilson 1993). Two main problems emerge as a consequence of the broad scope that the biodiversity concept has taken at present. Cast as questions, the problems are: (1) How do we incorporate processes (e.g., foraging, energy and nutrient flows, patch dynamics) into a concept that is based on seemingly static entities (i.e., individual organisms, species, habitat types, patch types)? (2) How do we integrate across ecological subdisciplines (e.g., ecosystem, population, landscape ecology) and across scales that are involved in biodiversity studies? The two problems are not mutually exclusive. Indeed, they are inseparable and complementary. For example, to determine how species diversity and ecosystem processes interact requires incorporation of entities and processes, as well as integration of community and ecosystem ecology. The focus on both entities and processes reflects the long-recognized dichotomy of structure and function in biology and ecology. Clearly, both structure and function must be integrated in order to successfully solve ecological questions. Dealing with biodiversity brings this needed integration into focus.

This chapter examines ecological opportunities that are available to species in various positions within a biological community, with particular emphasis on identifying the criteria necessary for an ecological opportunity to exist. Before discussing what performance capabilities a species must have to fill different types of ecological opportunities and what is required for invasibility of species into different functional positions in a community, the chapter considers the different frameworks that have been used to model species interactions. It then describes resource and apparent competition to show how resource availability from below and predation pressure from above can affect the types of species that can exploit specifc ecological opportunities. It also analyzes communities with three trophic levels, intraguild predation or omnivory, mutualism, the mechanisms that foster coexistence between one plant species and one pollinator species, and the case of one plant species with multiple pollinators.

This chapter discusses the important insights that can be gained from the synthetic analysis of evolution in communities. First, fitness, despite being commonly associated only with evolution by natural selection, also plays a key role in both population and community ecology. Second, the same processes jointly drive the dynamics of species abundances and traits, and these dynamics can only be understood in the context of a community of interacting species. All combinations of abiotic factors and other species' abundances and traits that would permit a species to invade the community without any evolution are contained in the so-called ecological volume of invasibility, in contrast to an evolutionary volume of invasibility that defines the conditions for invasion or adaptation to occur. This chapter also considers speciation, disaggregation and recombination, the traits that influence species interactions, ecological differentiation of species, and the use of phylogeny to elucidate community assembly and structure.

This chapter examines the relationship between biodiversity (most often measured as species richness) and the functioning of ecosystems. Examined in detail are the effects of biodiversity on: ecosystem productivity, nutrient use and nutrient retention, community and ecosystem stability, and invasibility by exotic species. A careful look, over two decades, at experimental results and meta-analyses confirms the positive impact of species richness on productivity, ecosystem stability, and nutrient retention. Thus, we can confidently conclude that biodiversity matters to the healthy functioning of ecosystems, although we do not yet know how many species are needed to ensure the successful functioning of any given ecosystem. The chapter concludes with a discussion of six important, but unanswered question in the study of biodiversity and ecosystem functioning.

Biological invasions have served as an excellent natural experiment, allowing us to explore how species sharpen their weaponries (invasiveness), how recipient ecosystems respond to the intrusion (stability and invasibility), and how invaded ecosystems reorganize their structure (architecture). Previous chapters have discussed the emergence of invasion science as a flourishing transdisciplinary field of study. Significant conceptual and theoretical advances have been made, but to achieve a holistic view of biological invasion, a systems approach is needed. This chapter draws on insights from previous chapters and on progress in network science and complex adaptive systems to offer a fresh view of invasions. In so doing, we shift the understanding of invasion as a linear process, along the introduction–naturalization–invasion continuum, to an adaptive network concept of multiplayer games.