Adaptive radiation into ecological niches with eruptive dynamics: A comparison of tenthredinid and diprionid sawflies

Abstract

1. We tested the hypothesis that the bottom-up influence of coniferous plant resources promotes the probability of outbreak or eruptive dynamics in sawflies. The literature was examined for three geographical regions - North America north of Mexico, Europe and Japan. 2. In each region tenthredinid sawflies (Hymenoptera: Tenthredinidae) were significantly more likely to be eruptive on conifers than on angiosperms. 3. The diprionid sawflies (Hymenoptera: Diprionidae) that attack conifers exclusively showed a significantly higher probability of eruptive dynamics than the tenthredinid sawflies on angiosperms in two regions, North America and Europe, and in Japan the trend was in the same direction. 4. The probability of species showing eruptive dynamics on coniferous hosts was not significantly different among tenthredinids and diprionids on conifers in North America. Europe and Japan. 5. The weight of evidence supports the hypothesis of conifers supporting a higher percentage of eruptive species than angiosperms. 6. In the adaptive radiation of tenthredinid sawflies from flowering plants onto conifers, larches (Larix) appear to be particularly favourable for colonization, but pines (Pinus) have not been colonized in any region, a pattern likely to be explained by the growth characteristics of the host plants. 7. Among tenthredinid species in Europe, where sawfly/host relationships are best known, there is a significant trend for an increasing proportion of outbreaking species from herbs, to shrubs, to trees. 8. The results indicate for the first time the strong bottom-up effects of plant resources on the population dynamics of sawflies, involving general features of host plant taxa and growth characteristics. © 2005 British Ecological Society.