The impact of habitat fragmentation on the interaction between Centaurium erythraea (Gentianaceae) and its specialized seed predator Stenoptilia zophodactylus (Pterophoridae, Lepidoptera)

Habitat fragmentation can affect plant population characteristics and plant traits, which in turn can change biotic interactions, such as plant–insect interactions. Because of this, habitat fragmentation can affect reproductive success and survival of both the plant and seed predators, especially when the predator is rare and specialized. This study focuses on the level of fruit predation in Centaurium erythraea by its specific seed predator, the plume moth Stenoptilia zophodactylus, in a fragmented coastal dune landscape. To investigate the consequences of habitat fragmentation, we assessed the effect of population and plant characteristics of 25 C. erythraea populations on fruit predation by S. zophodactylus. Although the distribution of this specialized predator is poorly documented, our results show that S. zophodactylus occurred frequently in most of the studied C. erythraea populations. We found a strong correlation between the spatial isolation of the host plant and the level of fruit predation, with low predation in isolated populations, most likely due to the limited dispersion capacity of the plume moth. C. erythraea individuals experienced a higher risk of fruit predation when showing a large floral display size, presumably because they are more attractive. However, at fruit level, the risk of predation decreases with increasing floral display at individual plant level, representing a sort of dilution effect. Our findings indicate that maintaining and restoring large, dense and rather connected populations of C. erythraea will be beneficial for the sustainable conservation of the rare specialist seed predator S. zophodactylus, without increasing the predation pressure on the host plant.