Abstract
In their first phase of expanding into new areas, invasive plants often take advantage of the inability of existing herbivores and pathogenic species to exploit them. However, in the longer term local enemies may adapt to using these invasive species as a food source. This study assesses the use of mature acorns of two oak species in Europe (the native Pedunculate Oak Quercus robur and the invasive Northern Red Oak Quercus rubra) by moths Cydia fagiglandana and Cydia splendana and beetles Curculio spp. We show that acorns of invasive oak species can be equally attractive to C. splendana but only partially so to C. fagiglandana where infestation rates where significantly lower (approximately half) compared to the native oak. The infestation by Curculio beetles of Northern Red Oak was marginal, less than 1% of the rate in the native oak species. The larval final weights did not differ significantly between host species, but emergence of C. splendana and Curculio spp. took significantly longer in acorns of Northern Red Oak. It is likely that C. fagiglandana and C. splendana have increased their niche breadths by exploiting invasive oak species and avoiding competition with the Curculio weevils. Furthermore, the occurrence of Northern Red Oak could stabilize food resources during years when native oak species have poor acorn crops.
Highlights
A substantial proportion of deciduous tree species growing in the temperate zone of the Northern Hemisphere produce seeds with large energy reserves that allow their seedlings to successfully compete with other plants
Such significant losses during reproduction have caused a number of morphological and chemical characteristics to evolve that serve as defense mechanisms against seed predators. One of these basic tree strategies is the occurrence of mast years, alternating with periods of very low seed production (Selas 1997), which are spatially synchronized over large areas (Koenig et al 2013). This strategy reduces the availability of food in the years of limited seed production, which results in a decrease in the number of seed predating animals
To test differences in the time to emerge for larvae between Pedunculate Oak and Northern Red Oak acorns we used t tests of each species (Cydia) or genus (Curculio)
Summary
A substantial proportion of deciduous tree species growing in the temperate zone of the Northern Hemisphere produce seeds with large energy reserves that allow their seedlings to successfully compete with other plants Such heavy seeds are a plentiful food resource used by many animals, both invertebrate and vertebrate, which results in high preand post-dispersal seed losses (e.g., Jimenez-Pino et al 2011; Bonal et al 2012; Bieberich 2016). Even if the seeds do not completely lose their ability to germinate, the fitness of seedlings from such infected seeds is significantly reduced by insect feeding compared to sound seeds (Bonal et al 2007; Perea et al 2012) Such significant losses during reproduction have caused a number of morphological and chemical characteristics to evolve that serve as defense mechanisms against seed predators. This strategy reduces the availability of food in the years of limited seed production, which results in a decrease in the number of seed predating animals
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