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

Frugivore guild
Diet overlap
Frugivorous animal species shared between 2 and 42 plant species. This corresponds to
a Sørensen’s similarity index of 0.08 to 0.67 (Table 6). Bird and lemur species had more
fruit species in common than flying foxes and rodents. The highest similarity index was
found between M. rufus and Cheirogaleus spp. (Table 6), followed by P. rufus and M.
rufus. The lowest index was found between Treron australis and the rodents. In general,
dietary overlap among mammals was larger than among birds or between mammals and
birds (Table 6). These results have to be interpreted with caution in particular for those
species which dietary diversity is underestimated, such as T. australis and S. picturata.
Both inter- and intra-specific interactions as well as polyspecific feeding associations
were observed.
Table 6. Diet overlap between each pair of consumer species. The number of species consumed
by each frugivore is shown in italics. Above diagonal is the number of species shared between
pairs, below the diagonal is the dietary overlap values calculated according to Sørensen's
similarity index.
N Hm Am Ta Sp Cn Efc Ch 1 Mr Pr Rod 1
N 21 18 9 13 37 111 39 41 39 50
Hypsipetes madagascariensis (Hm) 21 10 5 5 11 14 8 10 9 3
Alectroenas madagascariensis (Am) 18 0.51 7 4 10 14 9 8 9 8
Treron australis (Ta) 9 0.33 0.52 2 5 6 5 4 4 3
Streptopelia picturata (Sp) 13 0.29 0.26 0.18 8 10 7 7 5 2
Coracopsis nigra (Cn) 37 0.38 0.18 0.22 0.32 27 18 16 14 10
Eulemur fulvus collaris (Efc) 111 0.21 0.21 0.10 0.16 0.36 35 35 35 42
Cheirogaleus spp. (Ch) 39 0.27 0.32 0.21 0.27 0.47 0.47 27 20 18
Microcebus rufus (Mr) 41 0.32 0.27 0.16 0.26 0.41 0.46 0.67 23 19
Pteropus rufus (Pr) 39 0.30 0.32 0.17 0.19 0.37 0.47 0.51 0.57 14
Rodents (Rod) 50 0.08 0.24 0.02 0.06 0.23 0.52 0.40 0.42 0.31
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Congeneric species are treated together, as well as both rodent species which could not
always be attributed to a single species
Dispersal and predation role
The ‘true’ frugivorous bird species Alectroenas madagascariensis, Treron australis, and
Hypsipetes madagascariensis dispersed seeds of most of the species they fed on. Ripe
fruits were nearly always swallowed and thus dispersed (Table 2). Streptopelia picturata
was considered a seed predator feeding on seeds on the ground but due to its shy
nature, feeding behaviour could not be observed in detail and thus the fate of consumed
seeds remains unclear. Coracopsis nigra occasionally dropped fruits under the parent
plant or flew away with intact fruits but for the majority of their food resources, they acted
as seed predators, either destroying seeds directly with their beak or feeding on unripe
fruits (Bollen and Van Elsacker, Chapter 3b). In contrast, E. f. collaris is an important
seed disperser for a large number of plant species. During feeding this species was
messy, swallowing numerous seeds while dropping others under the parent plant and this
happened for a third of their consumed plant species (Table 2). Furthermore, for some
plant species it ate unripe fruits, thus destroying the seeds this way. Cheirogaleus spp.
and M. rufus as well as P. rufus act as seed dispersers for smaller seeds and as seed
droppers for larger ones. P. rufus may participate in dispersal at short distances as they
carry larger fruits to nearby feeding roost and drop the seeds there. Rodents often tear off
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