The Princeton Guide to Ecology

By Simon A. Levin | Go to book overview

IV
Landscapes and the Biosphere

Brian Walker

The aim of this section of the Princeton Guide to Ecology is to provide an understanding of ecology at the scale of landscapes. Viewed in this way, terrestrial landscapes can be thought of as self-organizing systems of topographically determined physical/chemical factors interacting with the biological components that occupy them. The resulting patterns of biological communities are strongly influenced by human use and management activities. This becomes extreme when the landscape is fragmented by human use and consists mostly of agricultural or other nonnative cover with separated patches of native communities. Marinescapes are less subject to fragmentation effects, but their biological communities are also structured by spatial processes and ecological dynamics that are equivalent, albeit markedly different, to those that occur in terrestrial landscapes.

Starting with the terrestrial world, an understanding of ecology at landscape scales begins with the determinants of ecosystem structures and patterns across landscapes. Topography and climate are primary drivers, but the observed patterns of biological communities clearly indicate that biological processes interact strongly with the physical/chemical processes, modifying them to produce the resultant distribution of ecosystems. The first two chapters (chapter IV.1 by Tongway and Ludwig and chapter IV.2 by Fischer, Lindenmayer, and Hobbs) provide an account of how ecosystems in landscapes are structured and how they self-organize over time. The first chapter focuses on the physical-biological interactions. The second deals more with the biological processes and compares five different “models” that have been proposed to explain the structure and dynamics of landscapes.

Fewer and fewer intact landscapes remain. In all but very sparsely populated and specially protected regions, more and more of the world consists of landscapes in which native vegetation cover has been fragmented to varying degrees. The result is a disruption of the ecological processes that produced the original biological patterns, with other processes becoming dominant. Erstwhile large, single populations behave as spatially separated metapopulations in which processes such as immigration and emigration assume much greater significance than they did before. The next several chapters cover different aspects of this disruption effect of human use on the ecology of landscapes.

Chapter IV.3 (Wu) explores the dynamics of ecosystems in fragmented landscapes. As the impacts of land use intensify, landscape ecological processes become further modified, and chapter IV.4 (Moorcroft) takes this up by examining the patterns of biodiversity in managed landscapes. Chapter IV.5 (Peters, Gosz, and Collins) considers it further by focusing on disturbances in landscapes and how changes in disturbance regimes induced through different kinds of land use can result in phase shifts in ecosystem structure and composition. There is considerable overlap in chapters IV.3 through IV.5, but, with each providing its own emphasis, they collectively present an understanding of the effects of human use of ecosystems at the scale of landscapes.

Chapter IV.6 (Maurer) moves the focus up in scale to consider interactions between landscapes, over much larger spatial scales. It addresses the issues of biogeography: how species and communities change across latitudinal and other gradients, both on land and in the oceans.

Up to this point the focus has been on what determines the structure and dynamics of the ecosystems in a landscape. Chapter IV.7 (Woodward) changes the focus to interactions of the biosphere and the atmosphere. It examines how the structure and biological composition of ecosystems at landscape scales influence the physics and chemistry of the atmosphere, and vice versa. It thus provides insights into how changes in landscape cover (as dealt with in the preceding chapters) can result in changes in the chemical composition of the atmosphere and in the climate, sometimes in nonlinear and sudden ways.

The last three chapters deal with marinescapes. Chapter IV.8 (Hughes) examines the structure and

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