Do deer and raccoons defecate in the right place? Fitness consequences of vertebrate seed dispersal for a deciduous forest herb

Abstract

Precision of seed placement in a heterogeneous environment is often assumed to select for the evolution of animal-mediated dispersal systems, but this hypothesis has rarely been tested in a multivariate sense. We quantify the microsite fitness benefits of dispersal by white-tailed deer (Odocoileus virginianus) and raccoons (Procyon lotor) for mayapple (Podophyllum peltatum), a shade-tolerant perennial herb, in deciduous forests of southeastern Ohio, USA. Micro-environmental variables were recorded at dung-deposition microsites, at rooting points of mayapple shoots, and at random (control) points in the forest. Fitness was assessed as the degree of overlap in ordinations of microsites by environmental variables. Mayapple occupied a broad sector (56%) of environment space corresponding to low and mid-slope positions, ravines, and proximity to trees. Deer and raccoon defecation placed dung in 71-74 and 86-95% of environment space, respectively, reaching mayapple microsites in 57-60 and 53-54% of cases. Deer placed dung in mayapple environment space 7-9% more often than predicted by random distribution, and raccoons placed dung in mayapple space 0-5% more often, consistent with only a modest degree of directed dispersal. Thus, the precision hypothesis is only weakly supported. The greatest fitness benefit of vertebrate dispersal appears to be the broad distribution of seeds, thereby increasing the probability of randomly reaching a suitable microsite. Imprecise dispersal suggests that secondary mechanisms of seed movement need to be explored in deciduous forest communities.

Molecular phylogeography and historical demography of a widespread herbaceous species from eastern North America, Podophyllum peltatum

“…However, this value of the ratio was still lower than the corresponding average reported for other seed plants (median r = 17; Petit et al, 2005), which was likely associated with the species’ insect‐pollinated flowers and fleshy fruits (Laverty, 1992). Pollen limitation has already been reported in P. peltatum (Laverty, 1992; Whisler and Snow, 1992; Crants, 2008), and its fruits could be dispersed over a long distance by frugivorous vertebrates (Niederhauser and Matlack, 2015, 2017). These traits in sexual reproduction make the role of seed dispersal in the species more significant than in other plants surveyed in Petit et al (2005), but it may still be hard for seeds to be transferred across the Mississippi River.…”

“…But the complex physiographic features of the Appalachians may facilitate two populations with the highest haplotype diversity (E1 and T1) to harbor those rare haplotypes (H5 and H6). Human‐mediated migration or long‐distance dispersal of seeds by frugivorous vertebrates such as white‐tailed deer ( Odocoileus virginianus ) may account for H6 being distributed to two disjunct populations (C1 and E1) from opposite sides of the Appalachians (Niederhauser and Matlack, 2015, 2017).…”