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

Chapter 4
Most seed dispersal studies and reviews of correlations between frugivore food
selection and fruit characteristics have produced little empirical support for tight
co-evolutionary relationships (Howe and Smallwood 1982; Herrera 1984; Howe 1984;
Gautier-Hion et al. 1985; Fisher and Chapman 1993; Chapman 1995; Erikkson and
Ehrlen 1998; Lambert and Garber 1998), as most plant species do not depend on one
single species of disperser. In most cases a range of taxonomically distinct frugivores
may consume and disperse the seeds of the same fruiting species (Gautier-Hion et al.
1985; Herrera 1986; Ganzhorn 1988; Chapman 1995; Chapman and Chapman 1996;
Bollen et al., Chapter 2, 3). Fruit traits are likely to evolve in response to other selection
pressures or may perform more than one function (Willson and Whelan 1990). Data from
the fossil record suggest that morphological fruit traits often have remained relatively
constant for millions of years (Fisher and Chapman 1993; Chapman 1995).
Primates represent a major group of mammalian seed dispersers in the tropics.
Studies have demonstrated that many primate species rely heavily on fruit and that they
represent a large component of the frugivore biomass (25-40%, Terborgh 1983; Bourlière
1985; Chapman 1995; Julliot 1996; Chapman and Onderdonk 1998; Lambert and Garber
1998). In Madagascar, lemurs have been postulated to be important seed dispersers
(Ralisoamalala 1996; Scharfe and Schlund 1996; Dew and Wright 1998; Overdorff and
Strait 1998; Birkinshaw 1999, 2001; Ganzhorn et al. 1999a) in particular since the guild of
frugivorous birds and bats is depauperate in this island as compared to other continents
(Fleming et al. 1987; Wright and Martin 1995; Goodman and Ganzhorn 1997; Wright
1997a; Böhning-Gaese et al. 1999; Ganzhorn et al. 1999a).
In this study, we investigate whether morphological and biochemical fruit
characteristics can be linked to abiotic conditions or whether there is evidence for
co-evolution between these fruit characteristics and the main consumers that are involved
in seed dispersal, i.e. Eulemur fulvus and Cheirogaleus medius. We selected two types of
forest in Madagascar growing under very different climatic and edaphic conditions:
evergreen littoral wet forest and dry deciduous forest. Both sites had a similar
complement of frugivore species, having six genera and five species in common.
The following predictions were tested:
1. If fruit characteristics evolved mainly in response to abiotic conditions we expect
different morphological and biochemical fruit characteristics at the two sites
2. If fruit characteristics co-evolved in response to selective pressure of consumers
we expect that characteristics of food items at both sites do not differ, as the guild
of frugivorous vertebrates is very similar at both sites.
3. The second prediction listed above requires that selection criteria of frugivores
are species-specific. We therefore predict that these consumers will have a
specialised diet irrespective of fruit availability, as is supposed by co-evolution.
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