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

Chapter 5
Animals
The degree of vulnerability of a given species due to forest fragmentation is likely to be
related to its tolerance to habitat change and its capability to use or bridge the grasslands
around the remaining forest fragments. As for frugivores, the large lemur species E. f.
collaris is most vulnerable as it is reluctant to cross these grasslands. Due to the spatiotemporal
patchiness of its food resources, it needs large home ranges (up to 100ha) and
covers long distances daily (1500-3500m, Donati 2002). E. f. collaris only occurs in the
south-eastern region of Madagascar (Tattersall 1982) and risks to decline severely in
numbers as a consequence of fragmentation and degradation of the littoral forest and
through hunting practice. Eulemur fulvus collaris, or Eulemur collaris as debated by some
(Djletati et al. 1997; Wright 1999; Wyner et al. 1999; but see also Pastorini et al. 2000) is
listed as a vulnerable taxon by IUCN (Hilton-Taylor 2000) and needs to be urgently
protected. With respect to this species, there has already been a translocation on several
groups of E. f. collaris in 1999 in Mandena. Their habitat (fragment M3) was almost
completely destroyed by producers of charcoal. Therefore the lemurs were captured and
transferred to an actively protected forest fragment (M15-M16, Mandena Conservation
Zone). Despite the initial loss of some individuals, the groups seem to have adapted to
their new habitat (Ramanamanjato pers. comm.). Translocation and re-introduction of
primates, especially in ‘rescue’ situations such as the one in Mandena will become
increasingly important as a tool for species conservation (Soorae and Baker 2002).
Moreover, this practice has a high popular significance and a very high potential for
educational applications. The nocturnal lemurs are still more abundantly present in
smaller forest fragments (Ganzhorn et al. 2000) but are restricted to a single fragment as
well. Another highly vulnerable species is Pteropus rufus, because a population of 250-
300 flying foxes has its roost in a severely degraded fragment. Therefore, this roost site
should be included in an actively protected zone. Most frugivorous bird species seem to
be less threatened and more abundantly present in small, large, intact and degraded
fragments.
As frugivores face periods of fruit scarcity it is important to collect long-term data on
phenology to understand inter-annual patterns and predict periods of fruit abundance and
scarcity. Interesting as well is to identify keystone species that bear fruit during periods of
fruit scarcity and supply much of the diet of the frugivores in this forest (Terborgh 1986b).
Given the short duration of our studies (Bollen and Donati, Chapter 1) we are unable to
asses true ‘keystone species’ (definition according Terborgh 1986b; Mills et al. 1993) at
the moment. However, a potential candidate may be Syzigium sp. 2 (Myrtaceae) and to a
lesser extent Dypsis prestoniana (Arecaceae). Both species fruit when fruit availability is
low. Syzigium sp. 2 is a large canopy tree species that is very common in the littoral
forest (Razafimizanilala 1996) with numerous odoriferous purple berries characterised by
a soft and juicy pulp and thin husk. These fruits are one-seeded with high sugar
concentrations (43%). This species constituted 80% of the diet of E. f. collaris in June
2000. Dypsis prestoniana is much less abundant as it used to be but can still be find in
the more intact parts of S9. This high palm species has a relatively large fruit crop
considering its small canopy. Within the diet of E. f. collaris fruits of this species
constituted 20% in April (Table 1). The overall importance of these potential keystone
species increases if we consider that they are eaten by all frugivorous species present in
Sainte Luce. Phenology data on important timber species could further be a useful tool to
more ecologically sustainable initiatives as well (Wallace and Painter 2002). As they can
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