Fig. 5. Schematic illustration of stress amelioration for plants with different size in a zone-of-influence (ZOI) model.

A and B (yellow ZOIs) are two conspecific beneficiary plants and they are facilitated by a benefactor X (blue ZOI). The stress intensity (e.g., salinity) per unit area is homogeneous across space. The area of overlap of ZOIs (green) is the same for both beneficiary plants (A_fa = A_fb). However, plant A fully benefits from the presence of X while B benefits only partly. Thus, beneficiary A will respond more positively to habitat amelioration than beneficiary B, i.e., the facilitative response is size dependent.