Spatial patterns of macroinvertebrate diversity in New Zealand springbrooks and rhithral streams

Abstract

Spatial patterns in macroinvertebrate communities were examined in 4 to 5 rheocrene springbrooks and 4 to 5 nearby rhithral streams in 4 different regions of New Zealand. Physicochemical attributes of springbrooks and rhithral streams were similar, but springbrooks were more stable. Standing crops of periphyton biomass, epilithic C, and organic matter were greater and more variable in springbrooks than in rhithral streams. The number of macroinvertebrate taxa and the total number of individuals were greater at more stable sites. Altitude, habitat stability, and food resource levels were the best predictors of the number of macroinvertebrate taxa, whereas pH, PO4 concentration, habitat stability, and food resource levels were the best predictors of the total number of individuals at a site. Differences in the number of macroinvertebrate taxa between Northern Hemisphere and New Zealand springbrooks may be related to the larger diversity of macroinvertebrate predators in New Zealand springbrooks and to the fact that many New Zealand invertebrates do not use temperature-mediated life-history cues. Altitude, which limits invertebrate dispersal, also may play an important role in determining the maximum number of macroinvertebrate taxa in a given stream. A dispersal–stability framework is proposed to explain the observed patterns of macroinvertebrate diversity in these streams. The general pattern of noninsect dominance in lowland springs may be the result of the interaction between dispersal ability and the effects of the last glaciation.