干旱区生态环境知识资源中心

One of the recommended ways to cope with degraded arid areas is the introduction of special biological species termed "ecosystem engineers’’ that can accelerate the rehabilitation and increase the ecosystem fertility by creating beneficial conditions for resettlement and regrowth of the native plant species. However, identifying these species and assessing their effects on the ecosystem (as a primary step for assigning to them an "engineering efficiency’’ property) is a challenging subject. Taking this into account, we present a methodology that enables assessing the effects of different organisms from the flora and insecta classes on arid ecosystems (characterized by patch-matrix pattern). Specifically, this methodology is based on allocating per each of the organisms (or group of them), a representative patch area in relation to their effect. Using this technique one can also estimate the effects of a given organism on its patch neighbors-the so called "hospitality value.’’ Organisms with low value are most likely to appear alone in their respective patches, whereas the ones with high values will encourage other species to settle inside their patches. The methodology described in this study was tested under different climates and grazing regimes in arid shrubland (Chiran area, northern Negev, Israel). We found that in addition to the shrubs, the ants (mainly of Messor sp.) have a high contribution to the size and the fertility of patches in these ecosystems. The methodology developed in this study could be adjusted and applied to other arid shrublands and degraded ecosystems all over the world for better understanding the relationships between them and the surrounding ecosystem.