MÉTODO DE TRATAMIENTO DE DATOS

The black lemur disperses a large proportion of the trees and tree

species in Lokobe Forest. The little available evidence suggests that this situation is not unusual i.e.:

- in the frugivore-rich Kibale Forest in Uganda, forest chimpanzees, Pan troglodytes, disperse 56% of tree species in sample plots (Wrangham et ai, 1994);

- on Siberut Island, Indonesia, the fruits of 34% of tree species in sample plots were potential foods for the kloss gibbons, Hyiobates /r/oss//(W hitten, 1982);

- in the Tai Forest, Ivory Coast, 30% of trees in sample plots were dispersed by elephants (Alexandre, 1978); and

- at Nourages, French Guiana, 26% of species whose fru it were

gathered from the forest floor were dispersed by the red howler (Julliot, 1992).

Indeed, many studies provide long lists of fru it species w hich are eaten by frugivores e.g. the agile gibbon, Hyiobates agiiis, at Sungai Dal, Malaya (Gittins, 1982); the orang utan, Pongo pyggmaeus, at Tanjung Puting, Kalimatan (Galdikas, 1982); the cassowary, Casuarius casuarius, in North Queensland (Stocker and Irvine, 1983); various primates at Cocha cashu, Peru (Terborgh, 1983); various birds at Monteverde, Costa Rica (Wheelwright et ai, 1984); palm civets (Macdonald, 1984); the gorilla. Gorilla gorilla gorilla, in Gabon (Tutin and Fernandez, 1985; Tutin et ai, 1991); the cock-of-the-rock, Rupicoia rupicoia, at Nouragues, French Guiana (Théry and Larpin, 1993); the red howler monkey.

Alouatta seniculus, at Nourages, French Guiana (Juillet, 1992 and Julliot and Sabatier, 1993); the red-bellied lemur, Eulemur rubriventer, and the rufous lemur, Eulemur fuivus rufus, at Ranomafana, Madagascar

(Overdorff, 1993); and Lagothrix iagotricha cana at Urucu, Brazil (Peres, 1994).

There are tw o probable reasons w hy, even in frugivore-rich communities, frugivores have not evolved to specialise in the

exploitation of the fru it of a few species: a) most tropical plants produce fru it for just short periods and these periods may be separated by

several months or several years; and b) when fruits are produced they are produced in abundance such that many different frugivore species can feed w ithout competing (Fleming, 1979; W heelwright and Orians,

1982; Leighton and Leighton, 1983; Terborgh, 1986; W heelwright, 1986).

The few tropical frugivores which specialise in exploiting a small number of fru it species are able to do so because they forage over wide areas and in different habitats and exploit species w ith long fruiting seasons or asynchronous fruiting. These species include: the resplendent quetzal in Guatemala which specialises on the fruits of Lauraceae (W heelwright, 1983); fru it pigeons in Queensland w hich specialise on fig fruits (Crome, 1975); and the phyllostomid bat genera Caroiiia, Sturnira and Artibeus which specialise on the fruits of Piper, Soianum and Piper, and Ficus respectively (Fleming, 1986).

5.4.2. Proportion of tree flora dispersed solely by the black lemur The black lemur appears to be the only disperser for a large proportion of the trees and tree species in Lokobe Forest. This situation is unusual because generally, the fruits of tropical species are eaten and potentially dispersed by several frugivores e.g. see Howe and Primack (1975),

Howe (1977), Cant (1979), MacKinnon and MacKinnon (1978), Howe (1980), Cruz (1981), Howe and Kerckhove (1981), Jordano (1983), Mabberley (1983); Pratt and Stiles (1985), W heelwright et a! (1984), Coates-Estrada and Estrada (1986), Coates-Estrada and Estrada (1988), Fleming and Williams (1990). |The exceptions to this generalisation are species w ith large seeds or thick husks w hich are dispersed by one (or a few) frugivore species w ith exceptional fru it processing abilities (see Chapter 11 ).

Presumably, the large proportion of Lokobe's flora dispersed solely by black lemurs is because of the species-poor frugivore fauna at this site compared w ith many rain forests (e.g. see Howe, 1984; Pratt and Stiles, 1985; Terborgh, 1986; W heelwright et al, 1984; Fleming et al, 1987). The small number of frugivore species in Lokobe Forest is a reflection of the low number of frugivores in Madagascar as a whole compared to other parts of the tropics (Fleming et at, 1987), the small area of the Forest, and its location on an island. The low species diversity of frugivores in Madagascar may be relatively recent because a few hundred years ago, the island was inhabited by at least 15 additional species of primate and 3 species of ratite, some of which were probably frugivorous (Albignac et al, 1984; MacPhee et al, 1985; Simons et at,

1992; Richard and Dewar, 1991). Indeed, elements of the extant flora, may have been partly, mainly or w holly dispersed by these species. Similarly, Janzen and Martin (1982) suggest that several South American plants were dispersed mainly by the now extinct

gomphotheres. However, in Lokobe Forest no fleshy fruited species were seen, which at least theoretically, could not be dispersed by extant frugivores.

Given that a large number of tree species in Lokobe Forest are dispersed solely by the black lemur there may be a selective advantage to plants in shifting their fruiting seasons to reduce overlap w ith the fruiting seasons of other black lemur-dispersed species. However, this pressure may be

resisted by the selective advantages in flow ering and fruiting during particular periods in Lokobe's seasonal climate. Evolution to reduce the overlap of fruiting seasons in species sharing dispersera has been

reported for species of Miconia in Trinidad (Snow, 1965).

In Lokobe Forest the species w ith the most seed dispersera was the fig, CB107, which is dispersed by black lemurs, fru it bats, bulbuls and blue pigeons. This is in accord w ith Janzen's observation that figs are consumed by most of the available frugivore species (Janzen, 1979). It might have been hypothesised that the species poor frugivore fauna of Lokobe Forest would lead to an increased number and abundance of wind dispersed species. However, this does not seem to be the case as compared to rain forests elsewhere (e.g. see Foster, 1982; Gentry, 1982), Lokobe Forest has a low number and abundance of wind dispersed species.

5.4.3. Seed dispersal of shrubs in Lokobe Forest

The study did not investigate systematically the importance of different dispersal vectors among the shrubs of Lokobe Forest. However, it seems likely th a t bird dispersal, in particular dispersal by the bulbul, is more frequent among shrubs than black lemur dispersal because: a) the sample of black lemur-dispersed species includes only one shrub (see Appendix IV); b) the sample of fleshy fruited species whose fruits are avoided by black lemurs is dominated by shrubs (see Appendix V); and c) the fru it of several shrub species were seen being eaten by birds, in particular the bulbul.