When is it coevolution? The case of ground wētā and fleshy fruits in New Zealand

Both tree and ground wētā have been proposed as potential seed dispersers of some New Zealand fruit. We examine evidence for coevolution of ground wētā and fleshy fruits as suggested by Burns (2006). We found that although ground wētā consume fruits from Gaultheria depressa and G. antipoda, they do not do so in a way that would suggest they had coevolved as dispersers with these or other New Zealand plants (Coprosma, Muehlenbeckia, Leucopogon). In our experiments, ground wētā ate fruits piecemeal and avoided most seeds even when these were very small (<1 mm) as in Gaultheria. We also found a positive preference for eating fruits of plants with seeds that were too big for ground wētā to ingest. Several lines of reasoning we explore lend no support to the proposal that ground wētā have coevolved with New Zealand plants resulting in the unusual characteristics displayed by many species (pale fruit presented within a divaricating canopy).