The reason for positive interspecific covariation was that these species used the resource similarly. 種對正協(xié)變的存在是由于這些物種對環(huán)境資源的利用具有相似性所致。
Water is essential for human being, economic activities, and important environmental resources as well. 水資源是人類(lèi)生存和社會(huì )經(jīng)濟發(fā)展的重要物質(zhì)基礎，也是重要的環(huán)境資源，水危機已嚴重影響人們生活，損害人類(lèi)健康，阻礙經(jīng)濟發(fā)展，危及人類(lèi)自身生存與發(fā)展。
