1 It is widely recognized that negative effects of anaerobic stress on grow
th and survival of flooded plants influence the distribution of numerous sp
ecies. Less explored is the possibility that heterogeneity in abundance of
plants between habitats with distinct flooding regimes may also result from
variation in rates of herbivory or in the ability of plants to tolerate lo
sses to herbivores.
2 Flooding and herbivores were tested as factors underlying variation in ab
undance of two tropical forest palms, Socratea exorrhiza (which is associat
ed with lowlands adjacent to streams) and Oenocarpus bacaba (which is more
abundant on plateaux and upper edges of slopes).
3 In a bench experiment, seeds of both palms were either completely immerse
d in water for a period of 101 days or not subject to inundation. Flooding
inhibited germination of both species but, as expected, the adverse effects
were much stronger on Oenocarpus.
4 In a field experiment, seeds of both palms were planted with increasing l
evels of protection against herbivores on plateaux and in lowlands. Seeds w
ere either not protected or placed within poultry-netting exclosures, half
of which were sprayed with insecticide.
5 After 17 months, only Oenocarpus had experienced differential mortality b
etween habitats, and this was clearly associated with the negative effects
of flooding on seed germination in lowlands. In contrast, growth differed b
etween habitats only for Socratea seedlings, where average above-ground bio
mass was greater in lowlands.
6 Although protection with exclosures and insecticide increased survivorshi
p of both species, herbivores caused similar proportions of mortality on pl
ateaux and in lowlands, and had no significant effect on seedling growth. T
herefore at this site, herbivores do not appear to influence variation in a
bundance of species between habitats.