Abstract
Understanding how invasive plants may alter predator avoidance behaviors is important for granivorous rodents because their foraging can trigger ripple effects in trophic webs. Previous research has shown that European beach grass Ammophila arenaria, an invasive species in coastal California, affects the predation of other seeds by the rodents Microtus californicus, Peromyscus maniculatus, and Reithrodontomys megalotis. This may be due to lower perceived predation risk by rodents foraging in close proximity to the cover provided by Ammophila, but this mechanism has not yet been tested. We examined the perceived predation risk of rodents by measuring the ‘giving up density’ of food left behind in experimental patches of food in areas with and without abundant cover from Ammophila and under varying amount of moonlight. We found strong evidence that giving up density was lower in the thick uniform vegetation on Ammophila-dominated habitat than it was in the more sparsely and diversely vegetated restored habitat. There was also evidence that moonlight affected giving up density and that it mediated the effects of habitat, although with our design we were unable to distinguish the effects of lunar illumination and moon phase. Our findings illustrate that foraging rodents, well known to be risk-averse during moonlit nights, are also affected by the presence of an invasive plant. This result has implications for granivory and perhaps plant demography in invaded and restored coastal habitats. Future research in this system should work to unravel the complex trophic links formed by a non-native invasive plant (i.e., Ammophila) providing cover favored by native rodents, which likely forage on and potentially limit the recruitment of native and non-native plants, some of which have ecosystem consequences of their own.
Highlights
As plant invasions continue to alter ecosystems worldwide [1], [2], it becomes increasingly important to understand their effects on trophic relationships of native species
The Bureau of Land Management (BLM) partnered with the California Conservation Corps (CCC) for 14 years to achieve complete removal of Ammophila in the foredunes, making way for ongoing native American dunegrass (Leymus mollis ssp. mollis) recovery efforts [28]
Results of this study support the hypothesis that cover provided by the invasive beach grass Ammophila arenaria lowers the perceived predation risk for foraging rodents
Summary
As plant invasions continue to alter ecosystems worldwide [1], [2], it becomes increasingly important to understand their effects on trophic relationships of native species. Invasive plants can dramatically alter the structure and composition of areas they invade [3], [4], effectively creating novel habitats [5]. Understanding how invasive plants may alter predator avoidance behaviors is especially important for granivorous rodents because their foraging can trigger ripple effects in trophic webs [9], [10]. We are aware of only one previous study that assessed how an abiotic factor (moon phase) may act in concert and possibly interact with effects of invasive plant species on animal foraging. Mattos and Orrock [8] found that the exotic invasive shrub Lonicera maackii decreased perceived predation risk for rodents, but this effect was contingent on both moonlight and temperature
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