Identifying Biotic Boundaries Along Environmental Gradients

Abstract

We outline a new procedure for placing boundaries of faunal and floral distributions along environmental gradients. Four data sets on species distributions from the marine literature, each of which had been scrutinized previously for boundaries, were analyzed with the procedure. Placement of boundaries proved straightforward in all cases. Our procedure possesses several attributes that make it superior to other methods of boundary location: (1) it is graphical and amenable to exploratory data analysis, (2) it is based upon taxonomic similarity between locations that is judged in a probabilistic manner, (3) it uses all locations simultaneously, (4) it provides a level of confidence in any boundary, and (5) it is precise: two workers employing it will arrive at the same conclusion.