Manfred Kraemer

Forest Fragmentation and Selective Logging Have Inconsistent Effects on Multiple Animal-Mediated Ecosystem Processes in a Tropical Forest

Forest fragmentation and selective logging are two main drivers of global environmental change and modify biodiversity and environmental conditions in many tropical forests. The consequences of these changes for the functioning of tropical forest ecosystems have rarely been explored in a comprehensive approach. In a Kenyan rainforest, we studied six animal-mediated ecosystem processes and recorded species richness and community composition of all animal taxa involved in these processes. We used linear models and a formal meta-analysis to test whether forest fragmentation and selective logging affected ecosystem processes and biodiversity and used structural equation models to disentangle direct from biodiversity-related indirect effects of human disturbance on multiple ecosystem processes. Fragmentation increased decomposition and reduced antbird predation, while selective logging consistently increased pollination, seed dispersal and army-ant raiding. Fragmentation modified species richness or community composition of five taxa, whereas selective logging did not affect any component of biodiversity. Changes in the abundance of functionally important species were related to lower predation by antbirds and higher decomposition rates in small forest fragments. The positive effects of selective logging on bee pollination, bird seed dispersal and army-ant raiding were direct, i.e. not related to changes in biodiversity, and were probably due to behavioural changes of these highly mobile animal taxa. We conclude that animal-mediated ecosystem processes respond in distinct ways to different types of human disturbance in Kakamega Forest. Our findings suggest that forest fragmentation affects ecosystem processes indirectly by changes in biodiversity, whereas selective logging influences processes directly by modifying local environmental conditions and resource distributions. The positive to neutral effects of selective logging on ecosystem processes show that the functionality of tropical forests can be maintained in moderately disturbed forest fragments. Conservation concepts for tropical forests should thus include not only remaining pristine forests but also functionally viable forest remnants.

Economic Benefit of Crop Pollination by Bees: A Case of Kakamega Small-Holder Farming in Western Kenya

ABSTRACT In most developing countries, crop production is by small scale farmers, who mainly produce for their own consumption and the extra for market. Pollination in such systems is unmanaged and is usually incidental, supported by nearby ecosystems. One of the reasons of not managing pollination is the lack of understanding of its economic value. The “public-good” nature of pollination in these systems also discourages individual initiatives intended to conserve pollinators. We evaluate the economic returns from bee pollination in small-holder farming systems. To do this we apply the factor of production method, a form of revealed preferences methods available for valuing ecosystem services. Our analyses show that bee pollination enhances the yield of most crops grown in the farmland and improves immensely the quality of produce. Almost 40% of the annual value of crops under consideration represented the net returns derived from bee pollination. More than 99% of this benefit is attributed to pollination by feral bees. We provide in-depth valuation of pollination service and discuss applicability and limitations of the factor of production method in developing countries.

EFFECTS OF HABITAT FRAGMENTATION AND DEGRADATION ON FLOCKS OF AFRICAN ANT‐FOLLOWING BIRDS

Tropical rain forests are rapidly cleared, fragmented, and degraded in sub-Saharan Africa; however, little is known about the response of species and even of key ecological groups to these processes. One of the most intriguing (but often neglected) ecological phenomena in African rain forests is the interaction between swarm-raiding army ants and ant-following birds. Similar to their well-known Neotropical representatives, ant-following birds in Africa track the massive swarm raids of army ants and feed on arthropods flushed by the ants. In this study we analyzed the effect of habitat fragmentation and degradation of a mid-altitude Congo-Guinean rain forest in western Kenya on the structure of ant-following bird flocks. Significant numbers of swarm raids were located in all forest fragments and in both undegraded and degraded forest. Fifty-six different species of birds followed army ant raids, forming bird flocks of one to 15 species. We quantitatively differentiated the bird community into five species of specialized ant-followers and 51 species of opportunistic ant-followers. Species richness and size of bird flocks decreased with decreasing size of forest fragments and was higher in undegraded than in degraded habitat. This was caused by the decrease of the species richness and number of specialized ant-followers at swarms, while the group of opportunistic ant-followers was affected little by habitat fragmentation and degradation. The composition of bird flocks was more variable in small fragments and degraded forest, compared to undegraded habitat in large fragments. The effect of habitat fragmentation on flock structure was best explained by the strong decline of the abundance of specialized ant-followers in small forest fragments. To conserve the association of army ants and ant-following birds in its natural state, vast areas of unfragmented and undegraded tropical rain forest are necessary.

Pollination ecology of the dioecious tree Commiphora guillauminii in Madagascar

In dioecious plant species differences in morphology and resources between female and male flowers can have consequences for flower visitation rates. Female flowers sometimes lack pollen and can be less attractive to pollinators than male flowers. We studied the pollination ecology of the dioecious tree Commiphora guillauminii in a dry deciduous forest in western Madagascar. We recorded floral display, visiting insect species and visitation rates for female and male trees. The results showed that female trees produce significantly larger but fewer flowers per inflorescence than male ones. Number of flowers per tree did not differ between the sexes. During 270 observation-hours we observed 17 insect and two bird species visiting the flowers. Mean visitation rates of male flowers were 6.1 times higher than those of female flowers (1.07 vs. 0.18 visitors per flower h -1 ). Visitation rates to female and male trees showed similar daily and seasonal patterns. Fruit set (2.9%) was low. which could have been caused by pollinator or pollen limitation. This study suggests that dioecy may pose a risk for fruit set and, potentially, reproductive success for plant species with depauperate pollinator faunas on islands such as Madagascar.

Farmers' knowledge of bees and their natural history in Kakamega district, Kenya.

Summary The Kakamega district is endowed with good climatic and soil conditions that have favoured agricultural production, and houses the Kakamega Tropical Rain Forest, the only remaining patch of the easternmost end of the Congo Forest. In efforts to halt its fragmentation and to salvage the remaining fragments, studies are being undertaken to convince farmers of the importance of conservation. This study considers bees and their pollinating importance in the livelihood of farmers, in order to understand the level of knowledge local farmers have about bees, and their role in crop production. A questionnaire was sent in January and February 2006 to representatives of 352 households randomly selected from 19,972 households living around the forest. Respondents were shown pictures and specimens of different insects, and after correct identification, were asked to state the food sources and nesting sites of these bees. They were asked to state how they utilize these bees and about their willingness to conserve them as pollinators. We found that Kakamega farmers could identify bees of different species, and had some knowledge of bee floral and nesting needs. Only about 50% were, however, aware of pollination and could relate it to crop productivity, but after having been introduced to the importance of bee pollination in crop production, they showed willingness to conserve bees for such purposes.

Diversity and activity density of bees visiting crop flowers in Kakamega, Western Kenya

Summary We observed bees visiting bean (Phaseolus vulgaris) flowers, the most widely grown crop in farmland near Kakamega forest, Kenya, which has attracted interest due to the presence of the only remaining tropical rain forest in the country. Two transects were created in the north and south of the forest extending to about eight km into the farmland. Observations were carried out on 14 sites on either side of the forest during the flowering period from April to June in 2005 and 2006. We recorded bees belonging to 20 species visiting beans. The honey bee Apis mellifera L. was the most abundant, followed by two solitary bees, Xylocopa calensand Xylocopa incostans. Bee density was low in the farmland in both sides of the forest, but diversity was significantly (P < 0.05) higher in the southern than in the northern transect. One reason for this is that the southern side is heavily populated so hedges and other land are under higher pressure, giving bees no alternative to crop flowers, whilst in the north, the population is low so there is still much land and hedges for alternative food for bees. Hedge management could be improved to support bees, especially when crops are not in flower, by interconnecting the hedges with the forest, so bees will be able to seek refugia and other needs in the forest and be able to provide pollination in the farmland, hence contributing to food security in the country.

Nectar production patterns and pollination of the Canarian endemic Echium wildpretii Pearson ex Hook. fil.

Summary Like other members of the Canarian flora, Echium wildpretii has often been considered to be pollinated by birds. Although the red flowers of Echium wildpretii secrete relatively large amounts of dilute nectar, birds could not be observed at the species. The main flower visitors are honeybees and the solitary bee Anthophora alluaudi, the latter being the most effective pollinator. Both bee species show an increase in nectar sampling activity during the hot daytime which may be a reaction to higher water demands. The highly concentrated nectar becomes diluted during the course of the day, thus meeting the energetic requirements of Anthophora bees in the morning as well as their water needs later on. Almost all the nectar produced is harvested by the bees, which probably accounts for the absence of bird visits.

Bee diversity along a forest regeneration gradient in Western Kenya

Summary Changes in bee species richness and diversity were studied along a forest regeneration gradient in seven sites in Buyangu Nature Reserve, Kakamega Forest, Kenya. At each site, 12 belt transects of 100 m length and 2 m width were established. The selected sites ranged from relatively undisturbed primary to late secondary forests, bush lands and the surrounding farming areas. A total of 4,485 individuals were identified out of 234 species of bee in four families. A Renyi Diversity Index was used to analyse bee diversity. One-way measures of ANOVA were calculated for bee diversity and species richness, with study sites and year as independent factors. The highest species richness and bee diversity were recorded in the open areas followed by secondary forests while evenness was higher in forested sites. There was a general similarity between sites in bee species composition, especially between those of almost similar vegetation structure. This similarity was suspected to have important implications in promoting current understanding of ecological resilience of bees in tropical ecosystems. The study concludes that the future of forest biodiversity and pollination services are dependent on strategic and holistic management of natural forests, secondary forests and the neighbouring agro-ecosystems.

Diversity and abundance of native bees foraging on hedgerow plants in the Kakamega farmlands, western Kenya

Summary We determined the diversity and abundance of native bees foraging on hedgerow flowers, and documented the plant species composition of those hedgerows, from October 2008 to March 2009 at Kakamega, western Kenya. We made observations on hedgerow sectors located in five different land use types: Kakamega forest; roads; sugarcane plantations; maize/bean fields; and grazing land. Our findings show that a high diversity of bees is supported by the hedgerows, and that bee diversity and abundance significantly (P < 0.05) differed across the five land use types. A total of 82 bee species belonging to three families (Apidae, Megachilidae and Halictidae) were recorded, with Apidae having the highest species richness and abundance. The suitability of hedgerow plants as bee forage sources differed greatly, except for Megachilid bees. Most important bee plants belonged to the families Acanthaceae, Asteraceae and Fabaceae. We conclude that hedgerow plants play an important role in providing bee food resources and can be used for managing bees in Kakamega farmed areas. We also suggest the inclusion of hedgerows in community based management of bees in areas where hedgerows are present or have viability to succeed, as they can support bee life and hence the pollination of crops in agricultural ecosystems.