Numerous protected areas (PAs) have been created in Africa to safeguard wildlife and other natural resources. However, significant threats from anthropogenic activities and decline of wildlife populations persist, while conservation efforts in most PAs are still minimal. We assessed the impact level of the most common threats to wildlife within PAs in tropical Africa and the relationship of conservation activities with threat impact level. We collated data on 98 PAs with tropical forest cover from 15 countries across West, Central and East Africa. For this, we assembled information about local threats as well as conservation activities from published and unpublished literature, and questionnaires sent to long-term field workers. We constructed general linear models to test the significance of specific conservation activities in relation to the threat impact level. Subsistence and commercial hunting were identified as the most common direct threats to wildlife and found to be most prevalent in West and Central Africa. Agriculture and logging represented the most common indirect threats, and were most prevalent in West Africa. We found that the long-term presence of conservation activities (such as law enforcement, research and tourism) was associated with lower threat impact levels. Our results highlight deficiencies in the management effectiveness of several PAs across tropical Africa, and conclude that PA management should invest more into conservation activities with long-term duration.

Black women have a lower incidence of vertebral and hip fractures than white women, possibly due to differences in skeletal and mineral metabolism. One suggested mechanism is that blacks have decreased skeletal sensitivity to parathyroid hormone (PTH). To test this hypothesis, we infused h(1-34)PTH in healthy premenopausal black (n ‫؍‬ 15) and white (n ‫؍‬ 18) women over 24 h and measured serum and urine indices of bone turnover and calcium metabolism throughout the infusion. At baseline, the mean 25-hydroxyvitamin D (25(OH)D) concentration was significantly lower in black women (46%). There were also nearly significant trends toward higher PTH and lower urinary calcium and pyridinoline levels in black women. During infusion, there were no racial differences in the mean (1-34)PTH levels achieved or in resultant elevations of serum calcium or 1,25-dihydroxyvitamin D (1,25(OH) 2 D) levels. Endogenous parathyroid suppression (measured by (1-84)PTH levels) was also similar between blacks and whites. There was an initial decline in urinary calcium/creatinine in both groups with a greater reduction in black women early in the infusion period ( p < 0.05 at 8 h). Furthermore, blacks had lower levels of urinary calcium/creatinine throughout the infusion ( p < 0.05 group difference). Bone formation markers (carboxy-terminal propeptide of type I procollagen and osteocalcin) decreased within 8 h and continued to decline throughout the infusion with no distinguishable racial differences ( p < 0.05 time trend for both). The most dramatic difference between black and white women in response to PTH infusion was represented by the bone resorption markers. Three separate metabolites of bone resorption (cross-linked N-telopeptide of type I collagen, cross-linked C-telopeptide of type I collagen, and free pyridinoline) all showed substantially greater elevations in white (mean peak increments 399, 725, and 43%) compared with black women (mean peak increments 317, 369, and 17%) during the infusion ( p < 0.05 group differences for all three variables). These data strongly suggest that blacks have decreased skeletal sensitivity to the acute resorptive effects of increased PTH. This finding indicates that calcium homeostasis may be accomplished in blacks (during times of relative calcium deficiency) by greater conservation of calcium from nonskeletal sources (most likely renal) with relative preservation of skeletal tissue. These differences in calcium economy could account, at least in part, for the increased bone mass and lower incidence of osteoporotic fractures in black women. (J Bone Miner Res 1997;12:958-966)

While noninvasive studies of bone mass and turnover in blacks and whites abound, histologic evaluations are very rare. We have performed a comparative bone histomorphometric study of iliac biopsies from 55 healthy, premenopausal women including 21 blacks (mean age 33.4 ؉ 1.2 years) and 34 whites (mean age 32.5 ؉ 0. /day, p ‫؍‬ 0.0001) were all lower in blacks than in whites. These results indicate that there are no differences in bone volume, microstructure, or turnover between black and white premenopausal women. However, there are significant differences in the mechanism of bone formation between the two groups, with a lower rate of mineralized matrix apposition within each remodeling unit and a longer total formation period in blacks than in whites. The differences appear to be the result of more frequent and/or longer inactive periods in the life span of the bone formation units in blacks. These differences may allow a greater overall deposition of bone mineral in black women and therefore help explain a higher bone mass and perhaps better bone quality in black than white women. (J Bone Miner Res 1997;12:948-957)

The basis for the racial difference in bone mass between black and white women is not known. Lower bone turnover, better renal calcium conservation, and decreased sensitivity to parathyroid hormone (PTH) have been proposed as explanations. A dynamic comparison of osteoblast function, utilizing stimulation by 1,25-dihydroxyvitamin D [1,25(OH)2D], has not been tested between these two ethnic groups. We compared well-matched black (n = 15) and white (n = 15) premenopausal women, before and during 5 days of 1,25(OH)2D administration (1.0 microgram/day) in order to assess dynamic indices of bone metabolism. As expected, at baseline, black women had lower levels of serum 25-hydroxyvitamin D and biochemical markers of bone turnover with slightly higher levels of PTH. Black women also had superior renal calcium conservation than white women at baseline. In response to 1,25(OH)2D administration, black women had a slightly greater increase in serum calcium and greater decrement in PTH. Moreover, black women showed a lesser increment in urinary calcium than white women and a more robust increase in two markers of bone formation--osteocalcin and carboxyterminal propeptide of type 1 procollagen--than white women. There were no changes in bone resorption indices in either race upon 1,25(OH)2D administration. These data provide preliminary evidence that black women conserve calcium more efficiently under both static and dynamic conditions, and also appear to have better osteoblastic functional reserve than white women.