Trait dimensions
We propose four basic trait dimensions to aid in linking rarity to ecological processes: tolerance, movement, interactions, and life history. These dimensions are based in part on the trait dimensions proposed by for the study of metacommunities, and in part on concepts from relevant macroecological theories. Tolerance captures the breadth of conditions that a species can tolerate (or, conversely, the types of conditions it requires). The interactions dimension includes both interspecific and intraspecific interactions. These first two dimensions overlap to some degree: for example, a plant’s requirement for light is both a physiological requirement and a source of competitive interactions. To distinguish between the two, we use tolerance for non-consumable environmental conditions (e.g., pH, temperature), and interactions for consumable resources (e.g., light, food, nesting sites). Movement includes both dispersal and establishment, while life history includes traits related to survival, mortality, sexual and asexual propagation, ontogeny, and growth rates. Together, these four trait dimensions capture numerous key ecological processes, including demography (life history, interactions), colonisation (movement, life history), density-dependence (interactions), competitive exclusion (interactions), and environmental filtering (tolerance).