Understanding interactions is fundamental to predicting the distribution and abundance of organisms at spatial and temporal scales appropriate to management. Therefore, this chapter focuses on interactions that are particularly relevant to the management of plant and animal populations. Any or all interactions may assume considerable importance in structuring ecosystems. In general, however, few factors exert primary control over community structure at a specific place and time. Identifying which factor (or factors) primarily affects community structure, particularly in a site-and time-specific manner, is therefore a necessary first step for effective management.

Abiotic factors, such as soil type, hydrology, or weather, assume increasing importance as spatial scales increase beyond the local level and as temporal scales exceed decadal time frames (Prentice 1986; Archer 1993; 1995a). Some abiotic constraints can be overcome with appropriate management, and these are described in the following chapter. This chapter will focus on the methods used to study biotic interactions (i.e., among organisms), discuss the interactions that frequently underlie community structure, and describe techniques that may be used to alter the outcome of interactions (Figure 2.1).

CLASSIFYING INTERACTIONS

Many introductory ecology texts use a conceptually simple strategy to classify interactions (Table 2.1). Five interactions are commonly recognized: competition (mutually detrimental), amensalism (detrimental to one participant, no effect on the other), commensalism (beneficial to one participant, no effect on the other), mutualism or symbiosis (mutually beneficial), and contramensalism (detrimental to one participant, beneficial to the other).