Operationalizing Scale: Functional and Observational - Are There Different Types of Scale?

Functional scale, also referred to as the “scale of the phenomenon” (MA 2005), or the “absolute scale” (Turner and Gardner 2015), is the magnitude or rate of a process of interest (Cumming et al. 2006), referring to the extent or duration over which a phenomenon has an impact (MA 2005). For example, grazing by a herd of bison or plant invasions occur in specific dimensions of time and space. Functional scale reflects the “true” scale at which a system property (e.g., forage availability) affects a process of interest (e.g., grazing) (Li and Reynolds 1995; Fuhlendorf et al. 2017).

Observational scale, also referred to as arbitrary scale (Weins 1989), is a human construct used for measurement and consists of grain and extent (MA 2005). Observational scale may or may not accurately depict a functional scale and can influence how patterns are interpreted. Remember, functional scale reflects the scale(s) at which a system property affects a process (Li and Reynolds 1995), thus proper selection of scale affects our ability to understand and manage ecological processes. All observational scales are arbitrary--just because observational scales seems “right” provides no assurance that they perfectly represent the functional scale (Weins 1989). Selection of useful observational scales requires thinking about the functional relationships between a system property and the scale at which that property influences a process of interest. For example, what scales are relevant to a beetle versus a bison selecting a home range? Or a germinating acorn in a forest? Additionally, many natural phenomena are influenced by multiple scales and therefore require multiple observational scales to understand (e.g., real world examples provided earlier in this lesson).

Figure 5. Conceptual example of observational and functional scale. Figure created by Dillon Fogarty