Biodiversity and ecosystem services on the African continent – What is changing, and what are our options?

International audienceThroughout the world, biodiversity and nature's contributions to people are under threat, with clear changes evident. Biodiversity and ecosystem services have particular value in Africa– yet they are negatively impacted by a range of drivers, including land use and climate change. In this communication, we show evidence of changing biodiversity and ecosystem services in Africa, as well as the current most significant drivers of change. We then consider five plausible futures for the African continent, each underlain by differing assumptions. In three out of the five futures under consideration, negative impacts on biodiversity and ecosystem services are likely to persist. Those two plausible futures prioritizing environment and sustainability, however, are shown as the most likely paths to achieving long term development objectives without compromising the continent's biodiversity and ecosystem services. Such a finding shows clearly that achievement of such objectives cannot be separated from full recognition of the value of such services

The feeding height preferences of two goat breeds fed Grewia occidentalis L. (Tiliaceae) in the Eastern Cape, South Africa

Nguni goats and Boer goats, which are farmed together in the savannas of the Eastern Cape Province, depend on the same feed resources. The feeding height intake rates and preferences of one of their most preferred browse species, Grewia occidentalis L. (Tiliaceae), were studied in order to indirectly determine resource partitioning between these goat breeds on the basis of feeding height. The two hypotheses tested were that taller Boer goats feed at higher levels than do Nguni goats and that both breeds have feeding height preferences that are related to differences in intake rates. Four individuals of each breed were fed branches attached to a height foraging board. The two breeds showed no particular height preference in either season. Bite rates varied with feeding height, while bite sizes and intake rates increased with feeding height. Boer goats had lower bite rates compared to Nguni goats, although both breeds achieved similar bite sizes and intake rates. Bites sizes and intake rates for both breeds were higher in summer than in winter, possibly because more browse biomass was available per branch in summer than in winter since G. occidentalis is deciduous. There was no evidence to support that feeding height preference was related to differences in intake rates. It is concluded that Boer goats may compete for forage resources during times of resource limitation. Thus, Nguni goats might be a more favourable breed in semi-arid savannas because of their smaller body-size and, therefore, absolute nutrient requirements as well as their better reproductive performance compared to Boer goats

Effects of season and breed on browse species intake rates and diet selection by goats in the False Thornveld of the Eastern Cape, South Africa

Although goats are common domestic browsers in African savannas, factors that affect their diet selection and food intake rate are poorly understood. This study used a cafeteria-style experimental procedure to investigate the effects of season and breed on browse species intake rates and browse species preference by Boer and Nguni goats in the False Thornveld of the Eastern Cape. Six browse species that commonly occur in the study area were used: Grewia occidentalis L. (Tiliaceae), Scutia myrtina (Burm. f.) Kurz (Rhamnaceae), Diospyros lycioides Desf. subsp. lycioides (Ebenaceae), Rhus longispina Eckl. and Zeyh. (Anacardiaceae), Ehretia rigida (Thunb.) Druce (Boraginaceae) and Acacia karroo Hayne (Fabaceae=Leguminosae). Cut branches were offered to goats during winter and summer and instantaneous intake rates and preferences were measured. There were no significant differences between Boer goats and Nguni goats in dry matter intake rates per unit metabolic body weight and in preferences of the six browse species, suggesting a potential for competition should the resources become limiting. However, the intake rates of Nguni goats increased by 50% from winter to summer, while intake rates of Boer goats increased by 87%. The mean intake rate was 69% higher in summer than in winter. Intake rates varied among all browse species, except A. karroo and R. longispina. Intake rates of D. lycioides, G. occidentalis and S. myrtina were higher than those of the other three species. Intake rates tended to increase more among deciduous species than evergreen species in summer, but the effect was not consistent. Likewise, intake rate within seasons was not consistently related to leaf phenology; intake rate of deciduous species was neither lower nor higher than that of evergreen species at any time. However, the increased intake rate in summer was consistent among those deciduous and evergreen species that produce all their new leaves on new long shoots, as opposed to species that produce their new leaves on old short shoots. The consequence of the two shoot morphologies for the browsing animal is that browseable material in the former group consists of shoots and leaves, but in the latter group consists mostly of leaves only. G. occidentalis and S. myrtina were the two most preferred species. Deciduous species were not consistently more preferred than evergreen. In accordance with optimal foraging theory, nutrient intake rates consistently explained preference in winter and summer. Species that offered the highest rates of nutrient intake were most preferred

Effects of condensed tannins on live weight, faecal nitrogen and blood metabolites of free-ranging female goats in a semi-arid African savanna

Current understanding of the effects of condensed tannins (CTs) on productivity of mixed-feeding ruminants is largely based on simple laboratory and feeding experiments. These experiments do not allow mixed feeders such as goats to adequately employ their behavioural and physiological responses to plant secondary metabolites. In a field experiment, we investigated the effects of CTs on growth performance of goats. We hypothesized that CTs reduce blood circulatory nutrient and increase nitrogen in faeces. We divided 45 yearling females into three groups of 15 animals that were orally dosed daily with either CTs, polyethylene glycol 6000 (PEG, a polymer that neutralizes dietary tannins), or water (control). We measured the average daily gains, live weights, faecal nitrogen and four blood metabolites from each goat during dry and wet seasons. Live weights increased over time in both dry (P < 0.001) and wet seasons (P < 0.001). The average daily gain was consistently greatest for animals dosed with PEG and least for those dosed with CTs. Goats dosed with CTs had the greatest faecal nitrogen and the least blood protein concentrations, while the opposite was true for PEG goats in both seasons. Blood urea and non-esterified fatty acids indicated a negative influence of CTs on energy and protein metabolism. We concluded that CTs limit growth and PEG mitigates the negative effects of CTs on growth performance of free-ranging mixed feeding ruminants.</p

Condensed tannins reduce browsing and increase grazing time of free-ranging goats in semi-arid savannas

Tannin concentrations fluctuate spatially and temporally within and among plant species, with consequences for forage quality of herbivores. The extent to which these fluctuations influence foraging activities of goats is not fully understood. While accounting for the effects of the time of the day and season, we tested the hypothesis that goats exposed to high levels of condensed tannins (i) spend less of their foraging time browsing, (ii) spend more time grazing, and (iii) reduce their total foraging time, especially during the dry season when grasses dry out and deciduous trees lose leaves. We orally dosed 15 goats with (i) 20 g of condensed tannins extract dissolved in 50 ml of water (high tannin exposure), another 15 goats (ii) with 20 g of polyethylene glycol dissolved in 50 ml of water, which neutralizes the effects of tannins (low tannin exposure), and the last group of 15 goats (iii) with 50 ml of water (control). We recorded the time spent on grazing, browsing and these two activities together (i.e., foraging) for 30 days in the dry and wet season. As expected, dosing goats with condensed tannins reduced their browsing time and increased the time spent grazing. Goats dosed with polyethylene glycol increased their browsing time and lowered their time spent grazing. Animals dosed with polyethylene glycol foraged for longer than other treatment groups in the dry season, whereas the goats dosed with condensed tannins increased their foraging time in the wet season. Overall, all treatment groups spent a similar amount of time foraging, indicating an instinctive drive by goats to maintain high total foraging time while avoiding over ingestion of tannin-rich forages. We concluded that tannins do not supress total foraging time for free-ranging goats. Instead, they increase the amount of time animals spend on grazing on herbaceous plants and decrease the amount of time animals spend browsing on woody plants. Comparing time spent on different foraging activities by goats is a first step towards understanding how goats utilize feed resources and how tannins influence resource utilization patterns

Biodiversity and ecosystem services on the African continent – What is changing, and what are our options?

Throughout the world, biodiversity and nature's contributions to people are under threat, with clear changes evident. Biodiversity and ecosystem services have particular value in Africa– yet they are negatively impacted by a range of drivers, including land use and climate change. In this communication, we show evidence of changing biodiversity and ecosystem services in Africa, as well as the current most significant drivers of change. We then consider five plausible futures for the African continent, each underlain by differing assumptions. In three out of the five futures under consideration, negative impacts on biodiversity and ecosystem services are likely to persist. Those two plausible futures prioritizing environment and sustainability, however, are shown as the most likely paths to achieving long term development objectives without compromising the continent's biodiversity and ecosystem services. Such a finding shows clearly that achievement of such objectives cannot be separated from full recognition of the value of such services