The metacommunity framework integrates species-specific responses to environmental gradients to detect emergent patterns of species organization. More specifically, a metacommunity is a set of ecological communities that are potentially linked by dispersal, with each community being a group of species at a particular site. Elements of metacommunity structure (i.e., coherence, species turnover, and range boundary clumping) were used to distinguish among six patterns of species distributions (random, checkerboards, Gleasonian, Clementsian, evenly spaced, and nested) to determine how snail distributions are structured along elevational gradients in the Luquillo Mountains of Puerto Rico. For example, expected structure is different if a metacommunity is molded by idiosyncratic responses to abiotic characteristics (expectation is Gleasonian structure) than if such a metacommunity is molded by strong habitat preferences or specializations (expectation is Clementsian structure).

Elevational gradients are useful for assessing environmental characteristics to which species respond because changes in elevation result in predictable variation in abiotic factors (temperature, precipitation) and in vegetational composition. Moreover, dramatic environmental variation occurs along elevational gradients, but does so within small geographic areas, minimizing the role of biogeographic and historical mechanisms in molding differences in species composition among sites. 

Paired elevational transects (300 m to 1000 m) in the Luquillo Mountains of Puerto Rico were sampled every 50 m to decouple underlying biotic and abiotic gradients that are commonly associated with changes in elevation and that are hypothesized to structure animal communities. One transect reflected changes in abiotic conditions and forest type (Tabonuco, Palo Colorado, and Elfin Forest), whereas the second transect reflected only changes in abiotic conditions, as its constituent plots were all located within a single forest type, Palm Forest, regardless of elevational strata. Gastropod metacommunities comprised 15 species and exhibited positive coherence, positive species turnover and non-significant boundary clumping along each elevational transect, consistent with Gleasonian structure in both cases. More specifically, gastropod species responded to a latent environmental gradient that is correlated with elevation. In so doing, gastropods do not form distinct communities that differ among Tabonuco, Palo Colorado, or Elfin Forest (i.e., are not Clementsian). Rather, gastropod species independently and idiosyncratically respond to the environmental variation along the elevational gradient in each transect. Moreover, variation in species composition along each transect was highly correlated, suggesting that the latent environmental gradients were quite similar in both transects. Thus, environmental characteristics that change with elevation rather than the biotic structure of the forest, per se, play a dominant role in molding the distribution of gastropods in the Luquillo Mountains.