Abstract: Tropical montane ecosystems are frequently dominated by discrete vegetation patches of coffee farms, containing coffee and other crops plus a variety of associated biodiversity (i.e. not specifically planted). To the bane of farmers, one component of that associated biodiversity is volunteer plants, normally called weeds. An important component of these weeds is the morphotype of vines. In the action of weeding, farmers effectively act as disturbance generators, periodically trimming the weed (and vine) community to a low level. Furthermore, vines contain numerous obvious competition-related traits (twining mechanisms, rooting patterns, leaf morphology) that are diverse and suggestive of a range of competitive strategies along a variety of niche gradients. Three currently active subjects in community ecology seem especially relevant to this situation: Metacommunities (each farm housing a distinct subcommunity), the intermediate disturbance hypothesis (farmers regularly weed), and intransitive competition (with the unusually large diversity of competition-related traits in vines).
Preliminary species abundance surveys on small-scale coffee farms in Puerto Rico found that seven vine species are most common. In addition, repeated distinct spatial distribution of five of the seven species was found on one farm, over a 6-month survey period. Based on these initial results, a theoretical model was constructed. Our theoretical results suggest that combining intransitive and transitive components of a community result in two distinct patterns of subcommunities that may emerge, and thus place limits on the nature of metacommunity assembly. First, at equilibrium, seven distinct subcommunities can be expected (associated with independent local extinctions of each of the seven species). Secondly, transient/non-equilibrium behavior (likely when disturbance frequency is high) generates a tendency towards three distinct subcommunities, likewise placing a limit on the nature of metacommunity assembly. These theoretical results generate strong predictions to be expected in vine communities, depending on “weed” management strategies on different farms. The overall metacommunity (vines on all farms in the coffee producing area) is expected to be constrained to either the seven-species subcommunities (when weeding is infrequent) or the three-species subcommunities (when weeding is frequent).
