Fruit-frugivore interactions in a Malagasy littoral forest - Universiteit ...

Chapter 3b
behaviour of parrots worldwide, many authors agree on their role as seed predators
(Janzen 1981; Jordano 1983; Clout 1989; Galetti 1993; Saini et al. 1994; Pizo et al. 1995;
Corlett 1998; Renton 2001). C. nigra and possibly also C. vasa can certainly be
considered as granivores in Sainte Luce rather than frugivores, as they are so often
referred to in literature. As such they vary from other seed predators in many different
aspects. C. nigra is a pre-dispersal seed predator, which feeds in the tree crown only
during daylight on both ripe and unripe fruits, which are medium in size. It can further
tolerate high tannin contents and eats non-zoochorous fruits as well without any fruit pulp
at all. S. picturata is a post-dispersal seed predator which eats small seeds of juicy fruits
on the ground only, either with a protective seed coat or not. The rodents both feed on
the ground as in the tree at night, but most often carry seeds away to a feeding site. They
eat the largest seeds of mostly drupes and may occasionally be involved in secondary
seed dispersal as well. Nevertheless they can be mainly considered as post-dispersal
seed predators for the majority of consumed fruit species. As shown in Figure 1 C. nigra
has an almost constant year-round food availability as unripe fruits in particular stay long
periods on the tree before ripening. On the other hand seeds stay longer periods
available on the ground than in the tree, which is favourable for both the rodents and S.
picturata. So, apparently there is a good niche separation among all seed predators in
this ecosystem, which is mainly based on fruit and seed size, feeding height and activity
pattern.
In conclusion, C. nigra destroys seeds of numerous endemic plant species in Sainte Luce
and should therefore be considered a seed predator in this ecosystem. In general, they
split and thus destroy the seed with their bill, eat it and reject the surrounding pulp. Seed
dispersal does occasionally occur when parrots fly away from the parent plant, dropping
several intact fruits or the remains of soft and juicy berries. Zoochorous tree species have
evolved phenological, morphological and biochemical flower, fruit and seed
characteristics to attract efficient pollinators and seed dispersers, which can assure
successful plant regeneration. However, the behaviour of granivorous animals offers the
plant no apparent advantage. Nevertheless, most food species consumed by these
parrots are also eaten by other frugivores, which act as seed dispersers. Dietary overlap
among granivores is limited and the different seed predators seem to occupy separate
trophical niches in this ecosystem.
ACKNOWLEDGEMENTS
We would like to thank QMM (QIT Madagascar Minerals) for providing logistics and infrastructure at
the study site. We are very grateful to Steve Goodman and Jörg Ganzhorn for their extensive
revisions and useful suggestions. This study was carried out under a Collaboration Agreement
between the Department of Animal Biology and the Department of Anthropology of the University of
Antananarivo, the Institute of Zoology of Hamburg University and QMM. The first author was
supported by a grant from the Belgian Fund for Scientific Research, Flanders (FWO). We thank the
Flemish Government for its structural support for the Centre of Research and Conservation (CRC)
of the Royal Zoological Society of Antwerp (RZSA).
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