Consequences of competition on the reproduction and mortality of three species of terrestrial slugs

Summary The interaction of three species of terrestrial slugs was studied in six field cages containing monocultures and 2‐way combinations. A. columbianus and A. ater were non‐aggressive species and L. maximus was highly aggressive during the summer. All three species were similar in body design and resource utilization. Reproduction (egg size, eggs/batch, number of batches, wet‐weight productivity) and mortality were monitored through the 1977 season. L. maximus drastically reduced reproductive success of the non‐aggressive slugs and increased their mortality. There were also significant interactions between the non‐aggressive species. Compared to other invertebrates, the life history characteristics of A. columbianus are strongly K ‐selected and probably evolved through intraspecific exploitative competition in predictable, stable forest habitats. A. ater is best classified as a refuging r ‐selected species adapted to less predictable, unstable field environments. L. maximus appears to be α‐selected and its overall design is suited to density‐dependent regulation in fields.