Food tree resources for primates and hornbills

There exist many factors that could have an effect on animal population densities among these food availability (Chapman et al., 2006). Several methods such as transect counts (Struhsaker, 1987), direct observations (Usongo & Amubode, 2001), the raked-trail survey method (Poulsen et al., 2002) have been used to measure the availability of food for animal species in tropical rainforest regions. But none of these methods has studied the availability of food resources for primates and hornbills using logged and unlogged forests as sample to determine food abundance and its impact on primate and hornbill population densities.

At transect level and within the same vegetation type, we found a relatively small difference (ca. 2.8%) in food tree abundance between unlogged and logged forest study sites. This could be mainly attributed to habitat difference (Blom et al., 2005) and human induced activities.

Though located at the same ecological forest region, unlogged II is characterised by trees of the primary forest formation such as Afzelia spp., Lophira alata, Berlinia spp., Irvingia gabonensis, Piptadeniastrum africanum, Baillonella toxisperma which have attained maturity.

Parts of these trees such as leaves (Piptadeniastrum africanum), flowers (Lophira alata), fruits (Irvingia gabonensis, Baillonella toxisperma) constitute an important diet for primates.

The maturity of forest trees in unlogged II could have had a positive effect on fruits/seeds production that are important for primates and hornbills. The highest number of food trees found in unlogged II can also be explained by the higher level of seed dispersal by animals mainly frugivores (Hamilton, 1999; Hubbell et al., 1999). However, the fact that the difference in food tree abundance between unlogged II and unlogged I is not significant, indicates that habitat difference is not the only determining factor for food tree abundance between the two study sites.

Forests in unlogged I have undergone large scale disturbance caused by the establishment of large plantations of palm oil and coffee, activities affecting wildlife habitat quality and quantity, but also responsible of the reduction of trees that constitute an important food source for primates and hornbills (Stuhsaker, 1987).

Within logged forest study sites, there was a relatively high abundance of food trees in both logged I and logged II compared to non food trees. This high abundance of food trees in logged forests can be explained by both ecological and disturbance factors. Ecologically, logged forests are predominated with secondary vegetation of pioneer species. Some of these fast growing species belong to families such as Amaranthaceae (Xylopia aethiopica, Uvariopsis bakiriana), Caesalpiniaceae (Anthonotha spp), Euphorbiaceae (Uapaca

guineensis), Moraceae (Musanga cecropioides), Sterculiaceae (Cola spp) and Myristicaceae (Pycnanthus angolensis). After the removal of shade tolerant species which constitute the main economic timber: Lophira alata (Ochnaceae), Entandrophragma cylindricum (Meliaceae), Nauclea diderrichii (Rubiaceae) and Afzelia Africana (Caesalpiniaceae), the forest is invaded by fast growing tree species, the majority of them fruiting at earlier stage and tree parts (fruits, seeds, leaves, flowers) constituting an important food resource for frugivores species.

At study site levels (n= 12) we found relatively more food trees in unlogged forests (ca. 28%) compared to logged forests (ca. 24.6%) and this pattern was reduced at large scale level (n=

24) with 51.6% of non food and 48.6 % of food for primates and hornbills. Rode et al. (2006) also reported a high abundance of food for the Redtail monkeys in the unlogged areas compared with logged areas of the Kibale National Park, Uganda. Our findings suggest that despite logging activities, logged forests of our study sites remained with a high potential of trees that could ensure a suitable habitat for the survival of many species that depend on the habitat value of disturbed forests (Weisenseel et al., 1993). These forests are also predominated by pioneer tree species such as Musanga cecropioides, Pycnanthus angolensis, Ficus spp. which fruit at earlier stage. Fruits, leaves and seeds of these trees constitute an important food source for primates and hornbills, but as well as for other frugivore species.

Several authors have studied the relationship between animals and their tree food resources.

Fairgrieve and Muhumuza (2003) observed a difference between the feeding and dietary composition of Blue monkey in unlogged and logged forest of Budongo forest reserve with a higher proportion of unripe fruits in logged forests while unlogged forests were predominated by young leaves, invertebrates and seeds. Colin et al. (2002) study on variation in the diets of Cercopithecus species in different forests suggested that Cercopithecus species depend mainly on fruits rather than seeds, flowers, leaves and insects. Furuichi et al. (2000) study on fruit availability and habitat used by chimpanzees in the Kalinzu forest, Uganda, observed that the number of chimpanzees did not necessarily increase with fruit abundance in the secondary forest and therefore their increase in number could not be explained by the food supply in Musanga predominated forest. Weisenseel et.al (1993) found no relationship between the use of a particular tree species by nocturnal primates and their availability in unlogged and logged forests. Some specific trees in rainforest in Asia (Borneo) and Africa (Kibale) such as fig (Ficus spp), umbrella tree (M. cecropioides) have been reported as keystone food for birds and monkeys (Terborgh, 1986; Tutin et al., 1997), but also for chimpanzees (Yamkoshi,

At transect level (n=6) we observed a negative, but very strong and significant correlation between the C. pogonias, Cercocebus torquatus and their potential food resources in logged II (R= -0.88 and P= 0.019; R= -0.94 and P= 0.005 respectively) while no correlation was observed between the six other studied primates and hornbills with their related food resources in both unlogged and logged forest areas (Appendix 4.1).

At large scale level (n=12), a negative, moderate and significant correlations were observed only between the C. mona, C. nictitans nictitans and their potential food resources in unlogged forests (R= -0.64 and P= 0.02; R= -0.60 and P= 0.04 respectively). Furthermore, the selection of the Pycnanthus angolensis, Cola spp, Irvingia gabonensis and Musanga cecropioides as the most relevant food trees used by primates and hornbills in the Korup region did not show any relevant correlation. Only P. angolensis was negatively correlated with C. mona (R= -0.70 and P= 0.0001), C. nictitans nictitans (R= -0.51 and P= 0.01), Cercocebus torquatus (R= -0.51 and P= 0.01) and Ceratogymna cylindricus (R= -0.82 and P=

0.04). The abundance of food resources and the less primates and hornbills encountered either in unlogged or in logged study sites could be the results of other limiting factor rather than food resources (Boutin 1990, Dobson & Oli 2001). The abundance of food resources and keystone trees (e.g.: M. cecropioides, Ficus spp, P. angolensis), that constitute an important diet for primates and hornbills, could not be the only factors responsible for the increase, decrease or stability of frugivores species in tropical rainforest regions. Furuichi et al. (2000) observed no correlation between fruit availability and the number of chimpanzees in Musanga secondary forest. This suggests that the number of chimpanzee did not necessarily increase with fruit abundance and could not be explained only by the food supply. Other factors such as predation, habitat quality and quantity and hunting may all contribute to regulate wildlife populations in tropical rainforests (Krebs 1978). In our study we did not observe a significant difference in food abundance between unlogged and logged study sites, however population densities of primates and hornbills were very low in these forests. Furthermore, the ecological value of logged forests may vary according to the original vegetation type, the intensity of logging and time since logging (Plumptre and Reynolds, 1994). Logged forests, if properly managed, may help survival of primates, hornbills and other secondary forest wildlife generalists because they contain an important amount of food trees such as M. cecropioides, P. angolensis, B. toxisperma, Cola spp., Ficus spp., that constitute an important diet for primates and hornbills.