Oecologia

, Volume 58, Issue 3, pp 378–382

The effect of physical disturbance on the relative abundances of two filter-feeding insects in a small stream

  • Nina Hemphill
  • Scott D. Cooper
Original Papers

DOI: 10.1007/BF00385239

Cite this article as:
Hemphill, N. & Cooper, S.D. Oecologia (1983) 58: 378. doi:10.1007/BF00385239

Summary

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.

Copyright information

© Springer-Verlag 1983

Authors and Affiliations

  • Nina Hemphill
    • 1
  • Scott D. Cooper
    • 1
  1. 1.Department of Biological SciencesUniversity of CaliforniaSanta BarbaraUSA

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