Hemphill Nina, Cooper Scott D
Department of Biological Sciences, University of California, 93106, Santa Barbara, CA, USA.
Oecologia. 1983 Jun;58(3):378-382. doi: 10.1007/BF00385239.
We examined the importance of disturbance in determining the relative abundances of two lotic filter-feeders, Simulium virgatum and Hydropsyche oslari, in a small, coastal stream in southern California, USA.In most years, winter spates effectively scour substrata in fast-flowing areas, thereby drastically reducing stream insect populations. Newly-opened space in these areas is quickly colonized by simuliids. The abundance of simuliids, however, gradually declines as hydropsychid abundance increases in early summer. To determine if these changes in insect abundance represent seasonal changes or successional changes following disturbance, we performed a field experiment where hard substrates were disturbed at 2 wk, 4 wk, or 8 wk intervals, or were left undisturbed. We found that the numbers of simuliids increased and the numbers of hydropsychids decreased as the frequency of disturbance increased. Although seasonal recruitment patterns and longitudinal position in the strem had important effects on the colonization rates of these insects, time since last disturbance was a prime determinant of the relative abundances of Simulium and Hydropsyche. These results and additional observations suggest that Simulium virgatum is an opportunistic species that quickly colonizes new space, but that it is displaced by the slower-colonizing but competitively superior Hydropsyche oslari. Disturbance promotes the coexistence of these two species by preventing the attainment of a climax state where Hydropsyche monopolizes available space.
我们研究了干扰对于确定美国南加州一条小型沿海溪流中两种溪流滤食性昆虫——弗吉尼亚蚋（Simulium virgatum）和奥斯氏纹石蛾（Hydropsyche oslari）相对丰度的重要性。在大多数年份，冬季洪水有效地冲刷了水流湍急区域的底质，从而大幅减少了溪流昆虫的数量。这些区域新开辟的空间很快就会被蚋类占据。然而，随着初夏纹石蛾数量的增加，蚋类的数量会逐渐减少。为了确定昆虫数量的这些变化是代表季节性变化还是干扰后的演替变化，我们进行了一项野外实验，以两周、四周或八周的间隔对硬质底物进行干扰，或者不进行干扰。我们发现，随着干扰频率的增加，蚋类数量增加，纹石蛾数量减少。尽管季节性补充模式和溪流中的纵向位置对这些昆虫的定殖率有重要影响，但自上次干扰以来的时间是决定蚋属（Simulium）和纹石蛾属（Hydropsyche）相对丰度的主要因素。这些结果以及其他观察结果表明，弗吉尼亚蚋是一种机会主义物种，能够迅速占据新空间，但会被定殖速度较慢但竞争优势较强的奥斯氏纹石蛾所取代。干扰通过防止达到纹石蛾垄断可用空间的 climax 状态来促进这两个物种的共存。
