Spatial patterns in lotic invertebrate community composition: is substrate disturbance actually important?

Abstract

Twenty-five forest streams were sampled in August 1994 in Te Urewera National Park, New Zealand, to examine the effect of substrate disturbance on invertebrate community structure. Stream size, flow permanence, and riparian cover were more influential than substrate disturbance in affecting invertebrate composition. Three community types were distinguishable based on these three factors: small (<1 m wide), intermittent streams were dominated by Chironomidae; larger (12-15 m wide), open streams were dominated by Chironomidae, Plecoptera, and Ephemeroptera; and intermediatesized (1-10 m wide) streams with continuous riparian cover were dominated by mayflies and caddisflies. Periphyton biomass was negatively affected by substrate disturbance but not to the same degree as reported by others studying unshaded streams. This may explain why the influence of substrate disturbance on community composition was less than that of stream size, flow permanence, and riparian cover. The key effect of substrate disturbance on postdisturbance community composition in these light-limited New Zealand streams appears to be the removal of animals rather than food loss. Thus, differences between communities that experience high flows and those that do not are far less than they might be in unshaded streams in which the food base is more severely affected by substrate disturbance.Résumé : L'échantillonnage de 25 cours d'eau forestiers en août 1994 dans le Parc national Te Urewera en NouvelleZélande a permis d'évaluer les effets d'une perturbation du substrat sur la structure de la communauté d'invertébrés. La taille du cours d'eau, la permanence du débit et la couverture végétale des rives ont plus d'influence sur la composition des invertébrés que la perturbation du substrat. Trois types de communautés se distinguent d'après ces facteurs: de petits (<1 m de largeur) ruisseaux intermittents dominés par les Chironomidae, des cours d'eau plus grands (12-15 m de largeur) colonisés par les Chironomidae, les plécoptères et les éphéméroptères, et des cours d'eau de taille intermédiaire (1-10 m de largeur) à couverture végétale complète et dominés par les éphéméroptères et les trichoptères. Il y a un effet né-gatif sur la biomasse du périphyton, mais jamais au point mentionné par d'autres chercheurs qui ont étudié des cours d'eau non ombragés. Cela peut expliquer pourquoi l'effet d'une perturbation du substrat sur la composition de la communauté est moindre que les effets de la taille du cours d'eau, de la permanence du débit et la couverture végétale de la rive. L'effet principal de la perturbation du substrat sur la composition de la communauté dans ces cours d'eau néo-zélandais limités par le manque de lumière semble être la perte d'animaux plutôt que la perte de nourriture. Ainsi, les différences entre les communautés qui subissent de forts débits et celles qui n'en subissent pas sont beaucoup moindres que dans les cours d'eau non ombragés où la base alimentaire est plus sévèrement affectée par une perturbation du substrat.[Traduit par la ...

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