Ecosystem Structure and Function

I. Ecosystem Structure

A. Trophic Structure

B. Spatial Variability

II. Energy Flow

A. Primary Productivity

B. Secondary Productivity

C. Energy Budgets

III. Biogeochemical Cycling

A. Abiotic and Biotic Pools

B. Major Cycles

C. Factors Influencing Cycling Processes

IV. Climate Modification

V. Ecosystem Modeling VI. Summary

TANSLEY (1935) COINED THE TERM "ECOSYSTEM" TO RECOGNIZE THE integration of the biotic community and its physical environment as a fundamental unit of ecology within a hierarchy of physical systems that span the range from atom to universe. Shortly thereafter, Lindeman's (1942) study of energy flow through an aquatic ecosystem introduced the modern concept of an ecosystem as a feedback system capable of redirecting and reallocating energy and matter fluxes. More recently, during the 1950s through the 1970s, concern over the fate of radioactive isotopes from nuclear fallout generated considerable research on biological control of elemental movement through ecosystems (Golley 1993). Recognition of anthropogenic effects on atmospheric conditions, especially greenhouse gas and pollutant concentrations, has renewed interest in how natural and altered communities control fluxes of energy and matter and modify abiotic conditions.

Delineation of ecosystem boundaries can be problematic. Ecosystems can be described at various scales. At one extreme, the diverse flora and fauna living on the backs of rainforest beetles (Gressitt et al. 1965,1968) or the aquatic communities in water-holding plant structures (Richardson et al. 2000a, b) (Fig. 11.1) constitute an ecosystem. At the other extreme, the interconnected terrestrial and marine ecosystems constitute a global ecosystem (Golley 1993, J. Lovelock 1988, Tansley 1935). Generally, ecosystems have been described at the level of the

Interconnected Terrestrial

| The community of aquatic organisms, including microflora and invertebrates, that develops in water-holding structures of plants, such as Heliconia flowers, represents a small-scale ecosystem with measurable inputs of energy and matter, species interactions that determine fluxes and cycling of energy and matter, and outputs of energy and matter.

| The community of aquatic organisms, including microflora and invertebrates, that develops in water-holding structures of plants, such as Heliconia flowers, represents a small-scale ecosystem with measurable inputs of energy and matter, species interactions that determine fluxes and cycling of energy and matter, and outputs of energy and matter.

landscape patch composed of a relatively distinct community type. However, increasing attention has been given to the interconnections among patches that compose a broader landscape-level or watershed-level ecosystem (e.g., O'Neill 2001, Polis et al. 1997a, Vannote et al. 1980).

Ecosystems can be characterized by their structure and function. Structure reflects the way in which the ecosystem is organized (e.g., species composition, distribution of energy, and matter [biomass], and trophic or functional organization in space). Function reflects the biological modification of abiotic conditions, including energy flow, biogeochemical cycling, and soil and climate modification. This chapter describes the major structural and functional parameters of ecosystems to provide the basis for description of insect effects on these parameters in Chapters 12-14. Insects affect ecosystem structure and function in a number of ways and are primary pathways for energy and nutrient fluxes.

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