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

Chapter 4
considering species number (Table 2). Scharfe and Schlund (1996) also concluded from
their study that in the western forests of Madagascar the majority of fruits are
autochorous or dispersed by mammals while in the east dispersal by birds (that eat
mainly berries and drupes) and mammals prevail. Our results concur with these.
The site-related difference in the representation of fruits with an odour merits further
consideration. In Malagasy forests, frugivorous diurnal and thus visually oriented bird
species are poorly represented and most mammalian frugivores of Madagascar are
cathemeral or nocturnal. Colour is probably less relevant for these lemurs and flying
foxes while olfactory clues are likely to be important (Schilling 1979; Barton et al. 1995;
Hladik and Simmen 1996; Bollen and Van Elsacker 2002a, Chapter 3a; Dominy et al.
2002; Luft et al. pers. comm.). Since comparative data on fruit odour from other forests
are lacking and taste and smell perception differ largely between individuals and species,
the present results - which are based on subjective impressions of different human
individuals - cannot be further interpreted. A more standardised evaluation of olfactory
clues might be worthwhile in future research.
With respect to our predictions we can say that given the almost identical set of
frugivores present at both sites, these large differences in morphological and biochemical
fruit traits between sites are most likely not a consequence of selection for seed dispersal
by animals, as far as the particular lemur species compared. They rather represent the
adaptations of a plant community responding to the need for protection against water loss
during the long and harsh dry season, typical for dry deciduous forest in Madagascar.
Comparison of lemur diets between sites and lemur food selection within a site
Regarding feeding selection within a given site and comparison of diets between sites
several patterns arise from the datasets. First of all, there are several parameters that
seem less important for lemur food selection such as growth form, colour, fruit length,
seed length, number of seeds, seed protection and extractable proteins. They did not
differ at all between sites and did not influence lemurs’ feeding selection. On the contrary,
clear feeding preferences were found according to fruit and dispersal type. Both lemurs
selected almost exclusively zoochorous berries and drupes when fruits with abiotic
dispersal were also available at both sites. Finally and most remarkably, both lemur
species display a high dietary flexibility for certain parameters, both morphological (pulp
type, odour, fruit skin protection) as biochemical (total nitrogen, tannins, ADF and NDF).
For these parameters they would select food items in correspondence to what is most
available at a given site. This seems to indicate that these species can switch their diet to
what is available. This allows them to survive in different forest types on frugivorous diets
with different nutrient compositions and different morphological traits.
Overall, from a chemical perspective these lemur species did not show much
evidence for fruit selection based on consistent chemical properties once site-specific
characteristics were taken into account. In the present analyses E. fulvus avoid fruits with
high lipid contents and fruits eaten by C. medius had lower fibre content than the nonfood
items. These criteria persist even after site-specific effects have been accounted for
(Table 8). Similarly, the preference of C. medius for fruits with high sugar content also
persists at both sites. This has been linked to their need to accumulate fat reserves for
hibernation (Fietz and Ganzhorn 1999). This selectivity however does not result in tight
co-evolution, as a lot of less sugary fruits are present as well at both sites because other
seed dispersers also occur and do not necessarily select sugary fruits.
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