In many cases, the seeds had been taken inside fallen
logs, into small burrows, and under trees. I assumed
these seeds were eaten by small rodents because the
sites were not accessible to Collared Peccaries and
larger rodents such as Agoutis. If a marked seed was
removed but not eaten, it was left in the new location
and included in subsequent censuses.
After 4 weeks, the proportion of seeds remaining
varied widely (Fig. 8.23). Meliosma and Beilschmiedia
had very high survival (100% and 90%, respectively);
Solatia (40%), Guarea (30%), and Ocotea (5%) had low
survival. Survival of Eugenia was intermediate (70%).
Seed removal continued during the next 8 weeks at a
much lower rate for all species. Survival after 12 weeks
ranged widely: 2% in Ocotea, 20% in Guarea and
Salacia, 50% in Eugenia, 80% in Beilschmiedia, and
100% in Meliosma. The Ocotea and Eugenia seeds that
were removed were always eaten. The main predators
were small rodents such as Deer Mice, the most com-
mon terrestrial rodent in the study site. Meliosma
seeds, which remained untouched, germinated several
months later. Once the seeds germinated, they lost the
protective seed coat and many were eaten. Both small
and large rodents were responsible for most of the re-
moval of Beilschmiedia. Partially eaten seeds of both
Beilschmiedia and Salacia were able to germinate. Ro-
dents and birds (Black-breasted Wood-Quail) occasion-
ally chewed or pecked the seeds, damaging the coty-
ledons but leaving the embryo intact. Salacia has a thin
seed coat and the seeds suffered more damage than
Beilschmiedia.
Removal of Guarea seeds was fairly high, but in
contrast to the other species, almost half of the re-
moved seeds were found buried, possibly by scatter-
hoarding rodents. Scatterhoarding is fairly common
for temperate zone species such as oaks (Quercus) in
which individual seeds are buried in many shallow
surface caches by seed predators who later retrieve
most of the buried seeds. Scatterhoarding has been
reported for only a few tropical trees (Forget and
Milleron 1991, Forget 1993). Although peccaries prob-
ably ate some seeds, they were not major predators.
The fate of dispersed seeds in this ecosystem de-
pends on a variety of factors. Both seed size and seed
coat thickness were correlated with seed survival.
Although the smallest seed in this study (Ocotea) had
the lowest survival, seed size is not sufficient to pre-
dict seed survival (D. Wenny, unpubl. data). Regard-
less of seed size, postdispersal seed predation may
play a key role in limiting plant recruitment. Because
postdispersal predation can be 90% or more in some
species, such mortality is a strong selective force that
may be more important than selection on other aspects
of the dispersal phase in plants (Wheelwright 1988a).
This study suggests three topics for future research.
First, the trade-off between physical and chemical
defenses in seeds should be investigated. For example,
seeds of most species of Lauraceae are extremely res-
inous and fragrant when cut and may contain com-
pounds that are toxic to some consumers (Castro
1993). Yet Beilschmiedia is the only neotropical
Lauraceae genus that has a relatively thick seed coat.
In contrast, Meliosma has a very thick seed coat but
no indication of secondary compounds. Second, long-
term studies on the fates of dispersed seeds and sur-
vival of seedlings are needed to determine the rates
of mortality for each stage between dispersal and
recruitment (Herrera et al. 1994). Third, the impact
of rodents on recruitment is poorly understood be-
cause some species are both dispersers and preda-
tors. Scatterhoarding and secondary dispersal by ro-
dents may be important for some tropical tree species
that are considered to be bird dispersed (Forget and
Milleron 1991). Ascertaining which rodent species are
involved in secondary dispersal and measuring their
net impact on dispersal will be useful.Figure 8.23. Postdispersal survival of
seeds of six species of lower montane
trees.287 Plant-Animal Interactions