農(nóng)業(yè)生態(tài)系統(tǒng)(參考版)
2025-01-03 03:03本頁面
【正文】 it is a natural part of the evolutionary process. When a group of pests is exposed to a toxic chemical, some of them survive. These hardy few reproduce and their offspring inherit genes resistant to this particular chemical. Excessive use of a pesticide speeds up the process by which pests develop resistance. More than 500 insects have now developed resistance to one or more pesticides。 The science of agroecology, which is defined as the application of ecological concepts and principles to the design and management of sustainable agroecosystems, provides a framework to assess the plexity of agroecosystems (Altieri 1995). The idea of agroecology is to go beyond the use of alternative practices and to develop agroecosystems with the minimal dependence on high agrochemical and energy inputs, emphasizing plex agricultural systems in which ecological interactions and synergisms between biological ponents provide the mechanisms for the systems to sponsor their own soil fertility, productivity and crop protection (Altieri and Rosset 1995). Agroecosystems About 40% of terrestrial NPP is directly or indirectly consumed by humans. Agroecosystems are ecosystems which are consciously controlled by humans for the purpose of extraction. They include managed forests, farms, rangelands, and aquaculture systems. While huntinggathering is sustainable at very low human densities, it is extremely damaging at high densities, and cannot be sustained for long. Thus agroecosystems are absolutely necessary. However, most agroecosystems today are not sustainable (yields cannot be maintained indefinitely). Problems with contemporary agroecosystems: PESTICIDES ⑤同時受自然與社會經(jīng)濟(jì)“雙重”規(guī) 律的制約。 ③組成要素簡化，自我穩(wěn)定性較差。新的特點(diǎn)主要表現(xiàn)在： ①受人類控制。 設(shè)施中的環(huán)境與自然環(huán)境相比 ， 溫 、 濕 、 光 、 養(yǎng)分等條件都受到較大的改變 ， 而目有獨(dú)特的特點(diǎn) 。 無論是水體 、 土體 、 氣體甚至輻射 ，在農(nóng)業(yè)生態(tài)系統(tǒng)中都或多或少受到人類不同程度的調(diào)節(jié)和影響 。其他生物種類和數(shù)量一般少于同區(qū)域的自然生態(tài)系統(tǒng) 。 （ 1） 農(nóng)業(yè)生態(tài)系統(tǒng)的生物組分 農(nóng)業(yè)生態(tài)系統(tǒng)的生物組分可以按功能區(qū)分為以綠色植物為主的生產(chǎn)者 ， 以動物為主的大型消費(fèi)者和以微生物為主的小
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