Comments on "Resource Distribution and Dynamics: Mapping Herbivore Resources".

What is a resource, how are resources distributed, and how do they change over time, together with the possibilities of mapping these resources through remote sensing, are the subjects of this chapter. Skidmore and Ferwerda (Chapter 4) follow Morrison and Hall (2002) in their definition of what a resource is, namely "a resource is any biotic or abiotic factor directly used by an organism, and includes food, nutrients, water, atmospheric gas concentrations, light, soil, weather (i.e., precipitation, temperature, evapotranspiration, etc.), terrain, and so on". The central notion of a resource is that it is used. However, Morrison and Hall and also Skidmore and Ferwerda confuse ‘use' in the sense of ‘exploit' or ‘consume as material' with ‘use' in the sense of ‘benefit from'. As a matter of fact, the Oxford English Dictionary (OED) defines ‘resource' as "stock that can be drawn on, available assets, or means of supplying what is needed". Assets and stock can dwindle if they are used faster than their replenishment rate, and if that happens they are used up. We think that the term ‘resource' should be limited to this meaning, and thus disagree with Skidmore and Ferwerda the way they apply this key term: ‘weather' cannot be used, ‘temperature' is a state variable, and ‘terrain' cannot increase or decrease. Where light is a non-depletable resource, weather and temperature are environmental conditions. These are variables that describe an organism's habitat, and are therefore sometimes classified as one of the species' niche dimensions, but not its resource. [ABSTRACT FROM AUTHOR]