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

Chapter 2
Statistical analyses
To visualise dispersal types and to test for fruit trait co-variation consistent with these
dispersal types, two principal component analyses (PCA) were conducted using
morphological and biochemical fruit trait data of 29 tree species. As data were not
normally distributed, morphological and biochemical traits were log-transformed prior to
analyses. Factor loadings were used to determine the strength of association of each fruit
trait with each principal component. Mann Whitney U tests, Spearman rank correlations
and Kruskal Wallis were carried out according to Siegel (1956) with the statistical
software SAS for Windows.
RESULTS
Fruit traps
Considering fruit trap analyses, there was substantial variation in the three main
categories (neutral, dispersal, predation) among different tree species (Table 2, Fig. 1).
Based on all fruit trap data, a substantial proportion (median: 70%, quartiles 39-98%) of
seeds remained under the parent plant; including unripe, ripe and rotten fruits (47%) that
had not been eaten as well as partially eaten fruits that still contained their seed (13%) or
intact seeds (9%) that were dropped after the fruit pulp had been swallowed (Table 2). In
all these cases the animals had a neutral effect on the seeds, since they were neither
dispersed nor predated. For 18 species the number of fruits or seeds dropped under the
parent plant was higher than 50% (Fig. 1). Evidence of seed dispersal involved empty
fruit husks (median 9%, quartiles 0-61%) that were discarded after consumers swallowed
the fruit pulp and seeds. This proportion was relatively large (>50%) for only eight tree
species. The proportion of predated seeds was low (median 2%, quartiles 0-5%) and
exceeded 5% for only six tree species (Table 2, Fig. 1).
Faecal droppings, collected in fruit traps, provided complementary but nonquantitative
information on seed dispersal. Ninety percent of all faecal samples collected
under focal trees were found to contain seeds from other tree species, thus indicating
seed dispersal. Of the 29 tree species sampled, seeds of 13 species were found in
droppings of Eulemur fulvus collaris and one species in droppings of Alectroenas
madagascariensis. For the majority of these species (9 out of 14) hardly any empty fruit
husks were found in the fruit traps as proof of seed dispersal (0-3%) (Table 2) because
dispersed seeds involve completely swallowed fruits, which are not accounted for in this
method. For the other remaining 5 species, more empty fruit husks (42-89%) were
retrieved in the fruit traps, indicating that, here, consumers most often scooped out and
swallowed fruit pulp and seeds and discarded the remaining fraction.
Fourteen plant species had the majority of their fruits eaten. Non-eaten fruits were
most abundant in eight species and equal percentages of eaten and non-eaten fruits
occur for 7 species (Table 2). Identification of the consumers was based on faecal
droppings or feeding marks. On the species level, faecal droppings of E. f. collaris and A.
madagascariensis are obviously distinguishable and recognizable by size and
consistency. The bill mark is typical for both Coracopsis spp. Stripped off pulp parts are
typical marks of Pteropus rufus’ sharp teeth. Lemur tooth marks can be species-specific
based on their size, but were most often assigned to larger taxonomic group of nocturnal
lemurs (involving Cheirogaleus spp. and Microcebus rufus) or lemurs (involving all four
lemur species) (App. II). Rodents leave typical gnawing marks, but these do not always
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