Abstract
Both predators and parasitoids can have significant effects on species’ life history traits, such as longevity or clutch size. In the case of gall inducers, sporadically there is evidence to suggest that both vertebrate predation and insect parasitoid attack may shape the optimal gall size. While the effects of parasitoids have been studied in detail, the influence of vertebrate predation is less well-investigated. To better understand this aspect of gall size evolution, we studied vertebrate predation on galls of Diplolepis rosae on rose (Rosa canina) shrubs. We measured predation frequency, predation incidence, and predation rate in a large-scale observational field study, as well as an experimental field study. Our combined results suggest that, similarly to parasitoids, vertebrate predation makes a considerable contribution to mortality of gall inducer larvae. On the other hand, its influence on gall size is in direct contrast to the effect of parasitoids, as frequency of vertebrate predation increases with gall size. This suggests that the balance between predation and parasitoid attack shapes the optimal size of D. rosae galls.
Highlights
The dynamics of populations are generally affected by influences from all levels of their food-webs
We observed a remarkable level of vertebrate predation on the galls of Diplolepis rosae, for all sites and years
We found that predation is a major contributor to the mortality of the gall inducer
Summary
The dynamics of populations are generally affected by influences from all levels of their food-webs. It can be difficult to understand population processes without taking full account of the interactions at every level. Galls are growths on plants usually caused by invertebrates as insects or mites. Their morphological diversity is mostly explained as an adaptation to lower the impact of natural enemies as insect parasitoids. The effects of insect parasitoids on abundances of plant galls have been studied extensively [1]. The influence of predators, has received comparatively little attention. It is thought that invertebrate predators’ impact is diminished because of the galls’ architecture. The same may not be true for vertebrate predators
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