Macroevolution in progress: competition between semislugs and slugs resulting in ecological displacement and ecological release

The vitrinids, which represent a probably competitively inferior transitional stage between shelled snails and slugs, and their sister group, the limacoid slugs, are used to investigate a macroevolutionary effect of a microevolutionary process, competition between individuals resulting in ecological displacement of one clade by another, based on patterns in the present-day world. The activity period and the altitudinal distribution of the vitrinids has shifted - to the cold season or to higher altitudes, respectively - in those regions where their range overlaps with that of the limacoid slugs. The diversity of the vitrinids is lower in regions with limacoid slugs. These patterns can be ascribed to the ecological displacement or the exclusion of the vitrinids from some habitats by limacoid slugs. Two vitrinid clades which independently colonized regions without limacoid slugs show patterns attributable to ecological release. The ecological displacement or exclusion of the vitrinids by the slugs is probably due to competition for shelter.