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

The effect of physical disturbance on the relative abundances of two filter-feeding insects in a... 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. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Oecologia Springer Journals

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

Oecologia, Volume 58 (3) – Jun 1, 1983

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Publisher
Springer Journals
Copyright
Copyright © 1983 by Springer-Verlag
Subject
Life Sciences; Ecology; Plant Sciences
ISSN
0029-8549
eISSN
1432-1939
DOI
10.1007/BF00385239
Publisher site
See Article on Publisher Site

Abstract

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.

Journal

OecologiaSpringer Journals

Published: Jun 1, 1983

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