Multispecies coexistence of trees in tropical forests: spatial signals of topographic niche differentiation increase with environmental heterogeneity.

Neutral and niche theories give contrasting explanations for the maintenance of tropical tree species diversity. Both have some empirical support, but methods to disentangle their effects have not yet been developed. We applied a statistical measure of spatial structure to data from 14 large tropical forest plots to test a prediction of niche theory that is incompatible with neutral theory: that species in heterogeneous environments should separate out in space according to their niche preferences. We chose plots across a range of topographic heterogeneity, and tested whether pairwise spatial associations among species were more variable in more heterogeneous sites. We found strong support for this prediction, based on a strong positive relationship between variance in the spatial structure of species pairs and topographic heterogeneity across sites. We interpret this pattern as evidence of pervasive niche differentiation, which increases in importance with increasing environmental heterogeneity.

[Balloon kyphoplasty for recent vertebral fractures in the elderly]. / Ballonkyphoplastie frischer Wirbelkörperfrakturen bei alten Patienten.

BACKGROUND: An increasing life expectancy is often accompanied by a possible increase of vertebral fractures. If operative therapy is necessary, open procedures might be problematic for elderly patients. In this case, balloon kyphoplasty might be an alternative. METHODS: We present our prospective data of 30 patients with an average age of 72 years (range 65-82). The patients suffered from isolated thoracic and lumbar fractures (T6-L4) without neurological deficits and were operated on with balloon kyphoplasty. They were followed up an average of 13 months after surgery. RESULTS: Before surgery, the patients' average kyphotic angle was 12 degrees . After reduction with balloon kyphoplasty, this angle was significantly improved to 7 degrees , and at follow-up it was 8 degrees . Back pain, which was determined by a visual analogous scale, showed a significant reduction from 8.2 to 2.6 points at follow-up. No significant relationship between preoperative pain and improvement of the kyphotic angle could be found. Patients with a bad fracture reposition showed significantly more pain at follow-up. However, there was no difference between the reference group and the examined patients' quality of life regarding general health. CONCLUSION: Recent fractures of the thoracic or lumbar spine in elderly patients treated by balloon kyphoplasty showed good early results.