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

Frugivore guild
Schmid 2000) Cheirogaleus spp. and M. rufus go into torpor from May through October,
which restricts their feeding and thus also dispersal activity to austral summer. These
species are often found at forest edges and in secondary forest throughout Madagascar
(Petter et al. 1977) as well as in Sainte Luce. This makes them important seed dispersers
for small-seeded plant species that fruit during austral summer. So far, few data are
available on the dispersal role of these nocturnal lemurs but Wright and Martin (1995),
Ganzhorn and Kappeler (1996), Dew and Wright (1998), and Atsalis (1999) have
suggested that they are indeed possible seed dispersers for small and medium sized
fruits, which are found intact in their droppings.
Pteropus rufus feeds on a wide array of endemic plant species in Sainte Luce and is
the most important long distance seed disperser in the littoral forest. A colony of 300
Pteropus rufus eats high quantities of fruit each night, defecates during flight, and covers
great distances between sleeping and feeding roosts (up to 50km) (Bollen and Van
Elsacker 2002a, Chapter 3a). By bridging isolated forest fragments P. rufus helps to
ensure genetic exchange between plant populations and forest fragments and even
regeneration in clearings. Passage through the gut does not seem to destroy the seeds
(Bollen and Van Elsacker 2002a, Chapter 3a).
Few data exist on the diet of both Malagasy fruit pigeon species. However, other
studies in the Paleotropics recorded a frugivorous diet for seed dispersing fruit pigeons
(Van der Pijl 1969; Corlett 1998; Dowsett-Lemaire 1988; Oliviera et al. 2002), even
though Snow (1981) described Treron australis as a seed predator of Ficus seeds.
Goodman et al. (1997b) mentions as well that a large component of the diet of T.
australis ate Ficus fruits. Fruit pigeons have large home ranges and can wander daily 10-
12km from their roost (Dowsett-Lemaire 1988; Fleming 1992). In Sainte Luce, they feed
on ripe fruits only and always swallow the entire fruit, digesting only the fleshy parts and
defecating the seeds, as observed by Van der Pijl (1969), Corlett (1998) and Oliveira et
al. (2002). In the littoral forest fruit pigeons seem to be efficient seed dispersers of
numerous plant species because they have wide gapes (Corlett 1998), cover great
distances and use secondary and disturbed habitats dispersing also seeds from pioneer
and heliophil species from perches in a range of habitats. Both short and long-distance
seed dispersal occurs. Preliminary results of germination trials demonstrate that passage
though the digestive tract of Alectroenas madagascariensis does not have a negative
impact on germination (Bollen unpubl. data).
Hypsipetes madagascariensis is an important seed disperser as well, feeding at
lower heights than fruit pigeons and parrots. This species swallows ripe fruits entirely and
defecates the seeds unharmed (Birkinshaw 2001; Bollen unpubl. data). Bulbuls are very
tolerant to disturbance and often the most common frugivores and dispersal agents in
degraded tropical and subtropical forests including urban areas (Corlett 1998). In Sainte
Luce this species could be encountered in intact forest as well as on forest edges.
Only limited data are available on the diet of Coracopsis nigra (Goodman et al.
1997a; Hampe 1998; Dowsett 2000), thus the 37 food species that were recorded in
Sainte Luce seem to be quite representative. Most data are from C. nigra, which is
present at the site year round, whereas C. vasa is encountered less frequently and during
certain periods of the year only. Coracopsis nigra destroys seeds of many endemic plant
species. They can be considered pre-dispersal seed predators in this ecosystem.
Occasional seed dispersal may occur but for few species and on rare occasions only.
Even though substantial differences occur between the numerous parrot species present
worldwide, they are often referred to as granivores (Janzen 1981; Jordano 1983; Clout
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