仙女圈演讲稿 2精选.pptVIP

The Biological Underpinnings of Namib Desert Fairy CirclesNorbert JuergensScience 339, 1618 (2013); 摘要 The sand termite Psammotermes allocerus generates local ecosystems, so-called fairy circles,through removal of short-lived vegetation that appears after rain, leaving circular barren patches. Because of rapid percolation and lack of evapotranspiration, water is retained within the circles. This process results in the formation of rings of perennial vegetation that facilitate termite survival and locally increase biodiversity. This termite-generated ecosystem persists through prolonged droughts lasting many decades. 背景介绍 1.仙女圈的外形与地理位置： With a bare patch devoid of vegetation in the center of FCs. At the margin possess a perennial belt. FCs occur in large numbers along a narrow belt at the eastern margin of the Namib Desert, running from mid-Angola to northwestern South Africa. Fig. 1. (A) Spatial pattern of FCs. Fig. 1.(B) Geographical distribution of FCs (black dots) and hotspots of FC occurrences at wider landscape scale (yellow clusters). Note the proximity of the occurrences to the 100-mm isohyet. (C) Schematic sketch showing the structural elements within a FC. The PB is formed by a ring of much larger perennial plants located around the bare patch. The grass outside the FC dies and disappears during drought. The PB remains the only surviving vegetation biomass during drought periods. 2.前人的研究： Early observers considered poisonous plants, ants, or termites as causal factors 3.研究方法： Used a long-term data set describing the environmental and biogeographical characteristics and dynamics of FCs to identify the most likely cause of these unique formations. 研究过程及分析: 1.FCs内含水量研究过程及分析 Imeasur the volumetric soil water content (m3/m3 × 100) from 2006 to 2012 within and around FCs. Higher temporal resolution of water flux was gained by automatic measurements recorded every hour within the bare patch and the grass matrix at 10-, 30-, 60-, and 90-cm depths using