Why does heterogeneity matter?

Abstract

Heterogeneity is a popular ‘‘buzzword’’ in ecology, especially landscape ecology. It reminds us that in real systems we do not have the luxury to speak in terms of mean fields or homogenous processes. Heterogeneity does not imply randomness. As Turner & Chapin point out in Chapter 2, when heterogeneity is a manifestation of some process or patterning-agent, we can study it at one scale to help us understand the patterns at a different scale. As we incorporate ideas of scale into ecological analyses, we are often examining heterogeneous processes that at some smaller scale break-down into more predictable continuous processes. Ecosystems Function in Heterogeneous Landscapes is an edited volume from the 10th Cary conference held in 2003. The Cary conference series has been running biennially since 1985; participants are selected due to their substantial contributions to a particular topic and are brought together to synthesize the state of the science for the particular topic. In the five sections of this volume, the authors seek to lay out the sources of heterogeneity in different systems and evaluate how they contribute to our understanding of patterns and processes with regards to system function. Section one contains four chapters outlining some of the challenges arising from heterogeneous landscapes as well as the conceptual approaches for dealing with them. Turner and Chapin discuss heterogeneity in terms of point processes and interacting flows of resources. They start with first principles like Jenny’s theory of soil generation and continue through some of the major heterogeneity generating mechanisms such as current flows, biotic feedbacks, and how the variation they generate promotes new flows within the heterogeneous system. White and Brown, in Chapter 3, pick up on some of these themes by describing the physical template and suggest characterizing landscapes quantitatively as systems of gradients, patches and networks. They describe briefly the primary methods by which these structures are explored: gradient models, scaling laws, and fractals. They also remind us of the fundamental fact that appropriate scale is always relevant to the organisms and processes under consideration. Pastor (Chapter 4) again deals with flows and patches in the context of coupled differential equations to show how Lotka-Volterra dynamics can instill stable heterogeneous states in the absence of a heterogeneous environment and Reiners (Chapter 5) goes so far as to name ten transport mechanisms as an K. B. Pierce Jr. (&) Landscape Ecology, Modeling, Mapping and Analysis Team, USDA Forest Service Pacific Northwest Research Station, 3200 SW Jefferson Way, Corvallis, OR 97331, USA e-mail: kpierce@fs.fed.us