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

Chapter 2
depressed seeds (Fig. 3a). The distribution of the species along the first axis shows
slightly more variation than on the second axis where the majority of fruits have few
seeds and a spherical or elongated fruit shape. The first axis clearly separates the birdspecies
from all other species. They have smaller and lighter fruits and seeds.
Furthermore the mixed fruits have average or intermediate sizes while the specialist fruits
are clearly larger and more variable in shape and seed number. The mammal fruits are
intermediate in size, all rather spherical in shape and few-seeded. So the different
disperser types can be more or less separated into groups by both axes.
The first two factors of the PCA conducted with the biochemical traits accounted for
73% of the total variance (Table 4). The first axis of the PCA included parameters
associated with sugar and crude protein content and explained 43% of the variance
(eigenvalue=2.17). The second axis was determined by concentrations of fat and acid
detergent fibre and explained 30% of the variance (eigenvalue=1.52; Table 4). When
considering the different disperser types no clear patterns arise according to these axes
(Fig. 3b). Thus, chemical traits failed to group species according to disperser type.
To support the conclusions of this descriptive analyses, a Kruskal-Wallis test was
carried out for the disperser syndromes with the first two principal components of each
PCA. For the morphological parameters, the four disperser syndromes showed a
significant difference for PCA1 (P=0.001), meaning traits related to fruit size but not for
PCA2 (seed number, fruit shape; P=0.31). For the biochemical parameters no significant
difference could be found among the disperser syndromes based on PCA1 (P=0.14),
involving sugar and crude proteins, nor for PCA2 (P=0.31) involving fat and ADF (Table
4).
Table 4. Principal component analyses for morphological and biochemical traits of 29 tree
species. Each factor represents an ordination axis. Kruskal Wallis test results of the
disperser type with the principal components given as well (**P