Surrounding vegetation mediates frequency of plant herbivore interactions in leaf-feeders but not in other herbivore groups
Abstract
The overall impact of herbivores on plant population dynamics is determined by a combination of herbivore impact on individuals and frequency of herbivore occurrence within the plant population. While the first component is well-explored, the second is much less studied and may depend both on plant individual traits and on local environmental conditions.
In the present study, we focus on determinants of occurrence of damage by five herbivore functional groups to a wet meadow perennial, Succisa pratensis. We assess the role of plant individual traits (size and conspicuousness) and the surrounding vegetation (regarded as a proxy of local biotic and abiotic conditions) in a field study spread over several spatial (and partly temporal) scales.
Overall occurrence of damage both by invertebrate and vertebrate folivores and by the specialist folivore Euphydtyas aurinia depended on the surrounding vegetation. The preferences to plant individual traits of the two former groups changed with the surrounding vegetation type as well.
On the other hand, occurrence of stalk grazing did not vary with any of the tested factors and predispersal seed predators responded only to local inflorescence density. Herbivore damage occurrence varied most at the population scale in all five herbivore groups.
The relative importance of the subpopulation scale was lower for vertebrates than for invertebrates. Temporal variation was higher in vertebrate herbivore groups.
Our results demonstrate that occurrence of damage by three important herbivore groups changed substantially on a relatively finely delimited gradient of local conditions even at the spatial scale of metres. Such spatial heterogeneity could give rise to a mosaic of different subpopulations within the plant population each with different dynamics.
This would in turn substantially change the plant species' long-term persistence prospects in landscape.