Population, Community, and Metacommunity Dynamics of Terrestrial Gastropods in the Luquillo Mountains: A Gradient Perspective

Elevational variation in the Luquillo Mountains of Puerto Rico creates strong environmental gradients that affect the abundance and distribution of species.  Moreover, the geographic mappings of these environmental gradients will likely shift as a consequence of global climate change, subsequently altering patterns of biodiversity.  Because they are taxonomically diverse, numerically abundant, responsive to anthropogenic and natural disturbances, and potentially keystone heterotrophs (detritivores, herbivores, and carnivores) in the Luquillo Mountains, terrestrial gastropods represent a model taxon for exploring variation in biodiversity.  We explore spatial and environmental variation in multiple aspects of gastropod biodiversity at the population (total abundance as well as abundance of each of 14 species), community (richness, evenness, dominance, rarity, diversity), and metacommunity levels.  The abundances of most species varied with elevation, and did so in a consistent manner along a mixed forest (tabonuco – palo Colorado – elfin forest) transect and along a palm forest transect.  Similarly, community level aspects of biodiversity varied with elevation in a consistent manner in both mixed forest and palm forest transects.  Moreover, variation among sites in species composition was similar regardless of whether the ordination was based on incidence (i.e. presence versus absence of species) or abundance (double square root transformed density).  This was true for the mixed forest as well as for the palm forest transects.  In addition, variation among sites in composition was correlated with elevation.  Finally, based on analyses of coherence, range turnover, and boundary clumping, metacommunity structure along the mixed forest transect was Clementsian, whereas along the palm forest transect metacommunity structure was quasi-Gleasonian.  Population- and community-level attributes of biodiversity changed gradually, and paralleled variation in total gastropod abundance and net primary productivity in general.  Similar mechanisms (more individuals hypothesis or passive sampling) explain both elevational variation and the differences between mixed forest and palm forest transects.  Similarly, differences in abundance between mixed forest and palm-dominated transects leads to differences in metacommunity organization.