Do frugivorous mice choose where or what to feed on?

Exhaustive analyses of plant–frugivore systems have revealed that few, if any, of these plant–animal interactions are tightly coevolved. Such lack of coevolutionary evidence could be related to frugivores selecting plants based on environmental cues, rather than on plant phenotypic traits. To evaluate this hypothesis, I examined whether the pattern and extent of fruit predation by long-tailed field mice (Apodemus sylvaticus) on the perennial herb Helleborus foetidus was directly related to mouse abundance, to environmental cues, to plant phenotypic traits, or to a combination of these. Thus, I estimated mouse relative abundance (through livetrapping) and percentages of fruit predation by mice, and quantified plant environmental and phenotypic traits in 9 populations of H. foetidus in southeastern Spain during 2 years (overall, 254 plants). I found substantial variation among populations in mouse trapping success (ranging from 0.0 to 21.8 individuals/100 trap nights), size of fruit crops (8.6–28.9 fruits per plant), and percentages of fruit predation by mice (0.0–93.3%). However, no simple relationship was found between mouse abundance (as estimated by trapping success) and strength of fruit predation. None of the 4 measured plant phenotypic traits (e.g., number of fruits or plant size) had a significant effect on mouse foraging. Conversely, 2 of the 6 environmental traits considered (substrate and distance to nearest tree) influenced fruit predation by mice. Plants located on rocky substrates and nearby trees experienced higher percentages of predation and this result was rather consistent across the 2 years and the 2 levels considered (inter- and intrapopulation). Even though mice could have selected other plant phenotypic traits not accounted for (e.g., chemical traits), such hypothetical phenotypic selection appears to be inconsequential as a source of individual variation in H. foetidus maternal fitness because its effects could have been ‘‘diluted’’ by the overwhelming influence of environmental factors. Thus, the results support the initial hypothesis that the net outcomes of the interaction between H. foetidus and mice in southeastern Spain may not have strong coevolutionary consequences.

Peer reviewed