Fred Babweteera

Can remnant frugivore species effectively disperse tree seeds in secondary tropical rain forests

Seed dispersal by frugivores in tropical rain forests is important for maintaining viable tree populations. Over the years, vertebrate assemblages in tropical forests have been altered by anthropogenic disturbances, leading to concerns about the ability of remnant vertebrates to substitute for the lost or declining vertebrate populations. We compared vertebrate composition and frugivore visitation rates as an indirect measure of rate of seed dispersal in three tropical rain forests in Uganda, namely Mabira, Budongo and Kibale Forests. Mabira is highly disturbed, Kibale is little and Budongo is intermediate. The aim was to determine whether vertebrate assemblages in differentially disturbed forests had comparable abilities to disperse seeds and whether tree species were equally vulnerable to loss of seed dispersers. Assemblages of forest generalist species were similar in all forests, but specialists were less abundant in the heavily disturbed forest. Remnant frugivores in the heavily disturbed forest were mainly small-bodied species that spat seeds beneath fruiting trees compared to large-bodied species observed in the less disturbed forests that ingested and carried away the seeds. We postulate that the quantity of seeds dispersed in heavily disturbed forests is much reduced due to low visitation rates of frugivores and the absence of large frugivores that consume large quantities of fruit. The quality of seed dispersal is affected as well by the distance over which seeds are moved. Assessment of vulnerability of trees shows no evidence for disperser substitution for trees producing large fruits. Fruit trees with low nutritional contents and digestibility were least visited in frugivore-impoverished forests. The loss of large specialist frugivores is likely to affect recruitment of many trees, especially of species that cannot establish beneath adult conspecifics.

Spatial patterns of tree recruitment in East African tropical forests that have lost their vertebrate seed dispersers

The direct removal of adult trees by logging affects tree recruitment in tropical rain forests. However, secondary effects of logging, such as loss of vertebrate seed dispersers may also affect tree recruitment. We studied the recruitment and spatial distribution of five tree species namely Balanites wilsoniana, Celtis zenkeri, Chrysophyllum albidum, Cordia millenii and Ricinodendron heudelotii in Kibale, Budongo and Mabira Forests in Uganda. These forests have been subjected to varying degrees of disturbance leading to changes in their vertebrate seed dispersers. Vertebrate frugivores of the five tree species were identified. Three 1-ha plots were established around adult trees of the same five species in each forest and the distance from the juveniles to the nearest adult conspecific was measured to generate a recruitment curve. Frugivore visitation rates were high in the less disturbed Budongo and Kibale (2.2 and 1.6 individuals h⁻¹ respectively) compared with the highly disturbed Mabira (0.9 individuals h⁻¹). In the frugivore-impoverished forest, 70-90% of juveniles established beneath adult conspecifics, whereas in the less-disturbed forests juveniles were established up to 80 m from adult conspecifics. Shade-tolerant species capable of recruiting beneath adult conspecifics appeared to maintain their populations without dispersal. Consequently, disturbances leading to significant loss of vertebrates may alter tree recruitment and spatial distribution with consequences for long-term population viability of shade-intolerant tropical trees.

Decaying Raphia farinifera palm trees provide a source of sodium for wild chimpanzees in the Budongo Forest, Uganda.

For some years, chimpanzees have been observed eating the pith of decaying palm trees of Raphia farinifera in the Budongo Forest, Uganda. The reasons for doing this have until now been unknown. An analysis of the pith for mineral content showed high levels of sodium to be present in the samples. By contrast, lower levels were found in bark of other tree species, and also in leaf and fruit samples eaten by chimpanzees. The differences between the Raphia samples and the non-Raphia samples were highly significant (p<0.001). It is concluded that Raphia provides a rich and possibly essential source of sodium for the Budongo chimpanzees. Comparison of a chewed sample (wadge) of Raphia pith with a sample from the tree showed a clear reduction in sodium content in the chewed sample. Black and white colobus monkeys in Budongo Forest also feed on the pith of Raphia. At present, the survival of Raphia palms in Budongo Forest is threatened by the use of this tree by local tobacco farmers.

Wildlife Snaring in Budongo Forest Reserve, Uganda

Snaring is an indiscriminate vertebrate trapping method that has maimed more than 36% of an estimated 700 resident chimpanzees (Pan troglodytes) of Budongo Forest Reserve. This study was conducted in two phases to assess this problem. First, we administered questionnaires to 240 randomly selected households in villages around the reserve to look at socioeconomic and cultural contexts within which snares are set. Second, hunters identified in the first phase were purposefully selected for deeper discussions into snaring; 12% of the farmers set snares. Logistic regression showed a significant relationship between snaring and socioeconomic variables such as education. Hunters considered bushmeat an integral part of their livelihood and thus, snaring may continue or increase from current levels. Alternative sources of protein and cash for local people will be necessary to offset snaring problems. Conservationists need to address in-forest diversity and strategies that improve food security and income for forest edge communities.