Abstract
Multiple-frugivore
systems are common in deciduous forest communities, but multiple
dispersal has rarely been examined from the perspective of plant
fitness. We compare the consequences of fruit consumption by two
co-occurring vertebrate frugivores (Odocoileus virginianus, white-tailed deer, and Procyon lotor, raccoon) for a fleshy-fruited forest herb (Podophyllum peltatum,
mayapple). Shoot emergence, flowering, and fruit removal were monitored
in natural populations in southeastern Ohio, USA. Survival of ingestion
was tested in feeding trials. Germinability of ingested and
non-ingested seeds was tested by experimental planting. Only 2.6 % of
mayapple shoots flowered. All flowers appeared to initiate fruit, but
66 % aborted after 1–2 weeks. Of the fruits remaining, 82 % were removed
unripe, evidently by deer. Only 5.5 % of fruit survived to ripen in
mid-July at which time all were quickly removed. In feeding trials, 28 %
of seeds survived ingestion by raccoons but only ca. 1 % survived
ingestion by deer. Seeds hand harvested from unripe fruits had a lower
proportion germinating in the following spring than those taken from
ripe fruits as a result of significantly lower over-winter seed
survival. Seeds ingested by raccoons showed significantly higher
germination than non-ingested seeds and were more likely to be taken by
secondary dispersers. It appears raccoons have the capacity to disperse a
large proportion of mayapple seeds, whereas deer are primarily seed
predators. By removing unripe fruit in early summer, deer are preempting
late-summer consumption by raccoons thereby reducing the net fitness
benefit to the forest herb. Frugivore service appears to be additive,
potentially reducing herb fitness in proportion to consumption by the
inferior dispersal agent.
