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

Chapter 3
and do not consume the fibrous flesh, which surrounds nuts. Both rodent species clearly
preyed on seeds of numerous species, but intact and even germinated seeds of four
species were found at feeding sites. No secondary seed dispersal through caching could
be detected (Table 2).
DISCUSSION
Food selection based on taxonomy, morphology, biochemistry and phenology
Even though in the literature numerous examples exist of plant families that are typically
consumed by birds such as Lauraceae Myristicaceae, Areceae, Burseraceae, and others
(McKey 1975; Snow 1981; Corlett 1998; Oliveira et al. 2002) or by flying foxes such as
Moraceae, Anacardiaceae, Guttiferae, Myrtaceae, Areceae, and Sapotaceae (Marshall
1983; Banack 1998; Corlett 1998) no clear dominant plant families could be found within
the diets of any of the consumer species. The families best represented correspond with
the dominant plant families of the littoral forest. This may be linked either to the fact that
Madagascar has a high percentage of endemic plant species which may alter the overall
floral composition compared to other tropical forests (Schatz 2001) or that the
depauperate guild of frugivores does not discriminate its diet taxonomically.
The main food preferences for all consumers are related to morphological fruit traits.
Worldwide in studies on fruit-frugivore interactions size, colour, and fruit protection
seemed to be the most important traits in fruit selection. Among these, fruit and/or seed
sizes were found to be most significant and related to the body size of the consumers.
The gape size of frugivorous birds limits the maximum seed diameter of fruits they can
swallow, while mammals have teeth and have other means to eat larger fruits (Fleming et
al. 1987; Dowsett-Lemaire 1988; Corlett 2002). For this reason, in our study, as in most
studies, birds seem to select significantly smaller fruits than mammals (Snow 1981;
Janson 1983; Knight and Siegfried 1983; Gautier-Hion et al. 1985; Wheelwright 1986;
Herrera 1987; Debussche 1988; Debussche and Isenmann 1989; Jordano 1995; Corlett
1996; Lambert 2002; Pizo 2002; Carlo et al. 2003). Eulemur fulvus collaris in this respect
is very important in the local community as it is the only seed disperser of the larger fruit
species. Nevertheless fruit size distinction is weakened by the fact that some bird species
can pick up broken parts of fruits and eat larger soft fruits in a piecemeal fashion
(Kitamura et al. 2002; Pizo 2002). As a result some studies did not find a significant
difference in size of bird and mammal consumed fruits (Gautier-Hion et al. 1985; Voigt
2001; Poulsen et al. 2002).
As for fruit protection, mammals are able to feed on fruits with a thick husk
(Birkinshaw 2001; Kitamura et al. 2002; Lambert 2002), whereas birds select more
frequently those with a thin husk or dehiscent fruits (Janson 1983; Gautier-Hion et al.
1985; Kitamura et al. 2002). However, it seems that not all mammals eat thick-husked
fruits. In our study E. f. collaris and P. rufus did, whereas the Cheirogaleus spp. and M.
rufus nevertheless preferred thin-husked fruits. Another important trait for feeding
selection is supposed to be represented by the external colour of ripe fruits, though little
agreement exists on this topic. One consistency throughout all studies, including this one,
is that birds eat many red and black fruits (McKey 1975; Charles-Dominique et al. 1981;
Janson 1983; Knight and Siegfried 1983; Gautier-Hion et al. 1985; Debussche 1988;
Dowsett-Lemaire 1988; Horvitz et al. 2002; Kitamura et al. 2002; Poulsen et al. 2002;
Voigt et al. 2001). For primates in particular, different results have been found which is
likely related to their different visual acuity in different parts of the world. Lemurs have no
74