Metacommunity Ecology

Mathew A. Leibold, Jonathan M. Chase

• Publisher: Princeton University Press
• Year: 2017
• Print ISBN: 9780691049168
• eBook ISBN: 9781400889068
• Topic: Biological Sciences
• Subtopic: Ecology
• Index: Biological Sciences

Metacommunity ecology links smaller-scale processes that have been the provenance of population and community ecology—such as birth-death processes, species interactions, selection, and stochasticity—with larger-scale issues such as dispersal and habitat heterogeneity. Until now, the field has focused on evaluating the relative importance of distinct processes, with niche-based environmental sorting on one side and neutral-based ecological drift and dispersal limitation on the other. This book moves beyond these artificial categorizations, showing how environmental sorting, dispersal, ecological drift, and other processes influence metacommunity structure simultaneously.

Mathew Leibold and Jonathan Chase argue that the relative importance of these processes depends on the characteristics of the organisms, the strengths and types of their interactions, the degree of habitat heterogeneity, the rates of dispersal, and the scale at which the system is observed. Using this synthetic perspective, they explore metacommunity patterns in time and space, including patterns of coexistence, distribution, and diversity. Leibold and Chase demonstrate how these processes and patterns are altered by micro- and macroevolution, traits and phylogenetic relationships, and food web interactions. They then use this scale-explicit perspective to illustrate how metacommunity processes are essential for understanding macroecological and biogeographical patterns as well as ecosystem-level processes.

Moving seamlessly across scales and subdisciplines, Metacommunity Ecology is an invaluable reference, one that offers a more integrated approach to ecological patterns and processes.

CHAPTER ONE

Introduction

The Rise, Fall, and Rise Again of Metacommunity Ecology

Prospectus

1. Traditional perspectives of community ecology, including species interactions, coexistence, and biodiversity, have focused on local-scale processes and have met with a great deal of controversy and disagreement.
2. The recognition of the importance of spatial (and temporal) processes has risen dramatically in recent years, although threads of ideas (importance of dispersal) and controversies (stochasticity vs. determinism) are evident throughout the history of ecology.
3. Metacommunity ecology, by explicitly incorporating scale as a critical feature of the outcomes of coexistence and biodiversity, among other variables, has the potential to unify what seems like a largely unresolved field.
4. This unification will require explicitly incorporating spatiotemporal heterogeneities, dispersal, the interactions between stochasiticity and determinism, and a number of complicating variables (e.g., food webs, evolution).

The major weakness of traditional community ecology, and why it has so conspicuously failed to come up with many patterns, rules and workable contingent theory, is its overwhelming emphasis on localness.

—Lawton (1999)

Community ecology is the study of how species interact with each other in ways that determine patterns in the distributions and abundances of different species. It represents the nexus at which individual traits, fitness, and population dynamics scale up to influence the distribution and coexistence among species on local to biogeographic scales and from months to millennia. It influences the role that species play in ecosystems and how they evolve. And it plays a critical role in understanding the destruction and conservation of biodiversity, as well as its restoration, as the human footprint becomes more pervasive. Unfortunately, community ecology has not yet fully lived up to its potential (Lawton 1999, Ricklefs 2008).

Are there any broadly applicable concepts and approaches that can help to resolve the clear limitations of community ecology as much of it continues to be practiced? Elton (1927) suggested four important ones—the niche, the food web, body size relations, and the trophic pyramid—that still serve as key concepts of community ecology (Chase and Leibold 2003). Lotka (1925) introduced the idea that energy relations and the laws of physics (thermodynamics) and chemistry (stoichiometry) could serve as a foundation for biology in general, and although these ideas fell largely silent, their core aspects have been championed in putative “unified” ecological theories of neutral coexistence (Hubbell 2001), metabolism (Brown et al. 2004), and stoichiometry (Sterner and Elser 2002), as well as mathematical principles such as body-size relations (Ritchie 2010), maximum entropy (Harte 2011), and neutrality (Hubbell 2001). Attempts have even been made to unify the unified theories (McGill 2010, 2011). Despite these efforts, there does not seem to be a strong sense that any one of these perspectives is able to adequately address the full scope of the questions at hand.

In this book we argue that we already know many of the key aspects of community ecology but that we do not have a framework that adequately links these in an appropriate context. We argue that the missing link that can provide this context is the combination of spatial and interaction processes that characterize metacommunity ecology. To us, the metacommunity approach allows one to explicitly transit from fitness and population dynamics to community- and ecosystem-level processes, as well as from smaller to larger scales, without the need to artificially designate where one community ends and another begins. Our goal for this book is to motivate others to share this vision of metacommunity ecology as a “synthetic hub” for understanding community and ecosystems ecology. We aim to contribute to a synthesis that is akin to the modern synthesis achieved many decades ago in evolutionary biology, which embraced the multiple roles of selection, drift, mutation, and gene flow.

Some elements of this synthesis have already been vetted. For example, Vellend (2010, 2016) developed an important conceptual connection between the major drivers of diversity in community ecology—niche selection, ecological drift, speciation, and dispersal—and the major drivers of diversity in population genetics—natural selection, genetic drift, mutation, and gene flow. In some ways, our goal is to more deliberately “look under the hood” of the relatively simple framework described by Vellend to identify just how niche selection, stochastic drift, speciation, and dispersal interact with eco-evolutionary processes (Hendry 2016), geometric scaling processes (McGill 2010, 2011), and constraints of energy flow and conservation of matter (Loreau 2010) to influence pattern and process at multiple spatial and temporal scales. We use this framework to discuss and synthesize numerous levels of organization ranging from pairwise interactions, to guilds of multiple competing taxa across scales of space and time, to micro- and macroevolutionary processes, to macroecological patterns, to food webs and ecosystems-level processes and patterns.

1.1 THE INDELIBLE INFLUENCE OF SCALE

Before we begin exploring the advantages of the metacommunity approach, it is useful to first ask, what is a community? When we talk of what a community is, we usually think of an idealized case in which multiple species have populations that interact by affecting each other’s birth and death rates at a particular place and time (Fig. 1.1). A great deal of effort has been aimed at understanding the patterns of species composition, relative abundance, and diversity within such communities, as well as the processes leading to those patterns (e.g., the role of interspecific interactions, spatial effects, and environment). And many would argue that the field of community ecology with this focus has gained considerable insight into the patterns and processes by which species interact and coexist (Morin 2011, Mittelbach 2012).

Unfortunately, the definition of community is always qualified by some phrase like “at a particular place and time” (also “in the same geographic area,” “in the same location,” “coexist together,” etc.). Such qualification is not easily operationalized (and perhaps it should not be) in anything more than an arbitrary way; that is, the qualification “at a particular place and time” is ambiguous and user defined. Recognizing this problem, some ecologists have suggested that perhaps the construct of a community is too artificial to be of use and should be abandoned (Ricklefs 2004, 2008; Fahrig 2013).

Because the delineation of the extent of a community might be user defined, community-level patterns such as coexistence, relative abundance, composition, and diversity could be context dependent, as are the mechanisms that create them. Thus one community ecologist might explore the patterns of coexistence and species interactions among species within a delimited area with a constituent subset of species and associated movement and heterogeneity patterns, while another might ask the same questions but define a community that encompasses more area and thus types of species, as well as different degrees of movements and heterogeneity patterns (Fig. 1.1).

Although any decision that community ecologists make in designating the spatiotemporal extent of their communities may seem innocuous, the substantial “apples and oranges” of scales that occur when they are combined into a singular perspective on the community concept has led to much confusion and debate. The answers to most questions in community ecology turn out to be “it depends” (Lawton 1999, Simberloff 2004). Is competition an important structuring force for coexistence communities? It depends. Are communities dispersal limited? It depends. Are niche or neutral processes more important in driving species abundances and distributions? It depends. And so on.

FIGURE 1.1. What is a community? An illustration indicating the subjectivity of the term “community” and which species are encompassed within that community. Lighter shaded circles indicate increasing scale of inclusion within a community, including larger areas, more species types, and associated heterogeneity and movement patterns. Species interacting at each scale are symbolized by the different illustrations of species.

One of the main reasons that the answers to community ecology’s most fundamental questions have not been very well resolved is because community ecologists have not adequately embraced the pervasive influence of scale in the questions they ask and the results they observe (Chave 2013), even though they appreciate that scale is such an important problem. Indeed, recent explorations have begun to show that almost all of the patterns and processes that they study are inextricably embedded within a scaling framework: patterns and processes at smaller spatial scales are better described by smaller-scale processes (e.g., environmental filters, stochastic drift, and interspecific interactions), whereas patterns at broader spatial scales are better described by larger-scale processes (e.g., the regional species pool, climate, and dispersal limitation) (Rahbek and Graves 2001, Condit et al. 2002, White and Hurlbert 2010, Belmaker and Jetz 2011, Jetz and Fine 2012, Keil et al. 2012). Nevertheless, processes and patterns frequently affect each other across scales as well, and it is this aspect of ecology that makes it such a potentially important concept and the one we claim requires a metacommunity approach.

Community ecology’s history is rife with examples in which a simple recognition of the dependence of the outcomes on scale could have resolved volumes of debate and consternation. How could interspecific competition among similar species produce such strong negative effects on the abundances of species in experimental manipulations (Connell 1983) and yet not appear to influence the spatial distributions of species (Connor and Simberloff 1979)? It depends … on scale (Peres-Neto et al. 2001). How could species partition their niches to enable local coexistence (Schoener 1974) and yet diversity not be saturated when the size of the regional pool increases (Cornell 1985)? It depends … on scale (Loreau 2000). How could neutral processes like ecological drift and dispersal limitation be largely consistent with biodiversity patterns observed in tropical forest plots (Hubbell 1979, Condit et al. 2012) and yet geographic distributions among these same forest plots be highly niche-structured (Pitman et al. 2001, Jones et al. 2013). It depends … on scale (Chase 2014).

1.2. THE METACOMMUNITY FRAMEWORK ALLOWS SIMULTANEOUS CONSIDERATION OF MULTIPLE PROCESSES AT MULTIPLE SCALES

In its simplest form, a metacommunity represents a larger-scale “region” that is made up of several smaller-scale “localities” (i.e., communities); these localities are connected by dispersal and may be heterogeneous in any number of abiotic and biotic variables (Fig. 1.2). Thus, the metacommunity framework explicitly considers more than one scale simultaneously. Although species interactions occur at relatively smaller scales, species coexistence at both smaller and larger scales results from interactions in a spatial context and can be modified by dispersal and spatial heterogeneity. Thus, to understand both the patterns and processes of coexistence and the composition and diversity of species, the interactions between scale, dispersal, and heterogeneity must be considered along with the milieu of local-scale processes (reviewed in Chesson 2000, Chase and Leibold 2003, HilleRisLambers et al. 2012).

FIGURE 1.2. Generalized view of a metacommunity. Each circle is a local community where populations of species grow and interact (symbolized by the different illustrations of species). Dispersal takes place among patches (symbolized by the dashed lines with arrows), and patches can be heterogeneous in environmental conditions (symbolized by the different levels of shading in each patch). Different levels of dispersal are symbolized by arrow size and line width.

As we will describe in more detail in Chapter 2, theoretical ideas about metacommunities have incorporated a variety of different assumptions and thus make a variety of predictions regarding the separate and combined influence of dispersal and heterogeneity. Dispersal rates are highly scale dependent; that is, the numbers of propagules that disperse from each reproductive individual in a population are typically highest nearer the parent and decline with increasing distance (though this can be highly species dependent and may, for example, be unimodal). Dispersal rates also depend on the properties of the species under consideration (i.e., some species move over much broader distances than others) and their abundances (i.e., the net number of dispersers is higher at high densities) as well as on the properties of the environment (i.e., some places are more isolated than others depending on the intervening matrix). Within this general context, however, there are three conceptually distinct ways by which dispersal rates can influence patterns in metacommunities, often interacting with the spatial heterogeneity in the system.

1. Dispersal limitation. If dispersal rates are low for at least some of the species in the metacommunity, those species will not be able to be present in all of the possible microsites where they could otherwise maintain positive growth. Dispersal limitation is the premise behind metacommunity theories such as the theory of island biogeography (MacArthur and Wilson 1967), neutral theory (Hubbell 2001), and competition-colonization-based coexistence (Hastings 1980, Tilman 1994, Chave et al. 2002). Observations and experiments that show increased diversity and spatial structuring of species composition support the view that dispersal is often a limiting process in natural communities (Cadotte 2006, Myers and Harms 2009, Condit et al. 2012). In addition to influencing patterns of diversity, dispersal limitation can alter the nature and strengths of species interactions in a loca...

Table of contents

• Cover Page
• Series Announcement Page
• Title Page
• Copyright Page
• Contents
• Preface
• 1. Introduction: The Rise, Fall, and Rise Again of Metacommunity Ecology
• 2. The Theories of Metacommunities
• 3. Processes in Metacommunities
• 4. Metacommunity Patterns in Space
• 5. Interactions between Time and Space in Metacommunities
• 6. What Can Functional Traits and Phylogenies Tell Us about Coexistence in Metacommunities?
• 7. Combining Taxonomic and Functional-Trait Patterns to Disentangle Metacommunity Assembly Processes
• 8. Eco-evolutionary Dynamics in Metacommunities
• 9. Macroevolution in Metacommunities
• 10. The Macroecology of Metacommunities
• 11. Food Webs in Metacommunities
• 12. Community Assembly and the Functioning of Ecosystems in Metacommunities
• 13. From Metacommunities to Metaecosystems
• 14. A Coming Transition in Metacommunity Ecology
• References
• Index
• Series Page