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

Intersite comparison
characteristics were analysed with two-way analyses of variance. Data were arcsine
transformed for these analyses. Statistical analyses were run according to Siegel (1956)
with the help of SAS and SPSS software.
RESULTS
Climate and phenology
Figure 2 shows phenology and annual precipitation for both study sites. Annual rainfall
was 2,480mm in STL and 721mm in KIR during the study period. The phenological
patterns considered in this study differ slightly from the overall pattern at both sites as
published previously (Sorg and Rohner 1996; Donati 2002) because only a subset of the
complete phenological dataset was used for comparison.
In KIR ripe fruits are available year round with a minimum in April. ‘Fleshy’ and ‘nonfleshy’
fruit species are equally (50%) represented in KIR (Fig. 2). During the dry season
(May through October) non-fleshy fruits predominate. As indicated before, in STL there
are no clearly defined wet or dry seasons. Fruit abundance here is highest from January
through March, rather limited from April through October with a lean period from June to
August. The majority (81%) of fruit species in STL are characterised as ‘fleshy’. In
contrast to KIR, the representation of the ‘non-fleshy’ fruits remains low but fairly constant
(4-7%) in STL throughout the year.
Soil conditions
In the upper layer (A horizon) soils are more acid and contain higher concentrations of
organic matter, nitrogen and phosphor in STL than in KIR (Table 3). Exchange capacity
has not been measured for STL. The situation at STL is similar to the data available for
Ranomafana, an evergreen rainforest site at higher altitude (Ganzhorn et al. 1999b).
There, growth rate of trees is higher than at Kirindy, probably due to the longer growth
season. However, the probability of fruiting is reduced, indicating that fruit production is
associated with higher stress for the trees of the evergreen forest. It is unclear how these
different constraints affect the type of fruits produced.
Floristics
Both datasets have 30 families (40%) and 19 genera (10%) in common but no tree
species (Table 2). In STL the four most important plant families were Rubiaceae (23
species), Euphorbiaceae (8), Flacourtiaceae (6), and Myrtaceae (6). They accounted for
25% of all species. In KIR Fabaceae (16), Euphorbiaceae (14), Tiliaceae (9), Rubiaceae
(8), and Combretaceae (6) were the five most important plant families. They accounted
for 31% of the species. The representation of these top eight families is not correlated
between the two datasets (rs=0.18; P=0.7, N=8). The representation of large and small
trees, shrubs and other growth forms in the samples did not differ between sites (Table
4).
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