STRUCTURE AND DIVERSITY OF STREAM INVERTEBRATE ASSEMBLAGES - THE INFLUENCE OF TEMPERATURE WITH ALTITUDE AND LATITUDE

1. Structure and diversity of the macroinvertebrate fauna were studied in relation to altitude and latitude among three groups of streams fr om Ecuador (lowland: 100-600 m Central Valley: 2600-3100 m, paramo: 35 00-4000 m), and one group from the temperate lowland region of Denmark . The streams in the four regions were comparable with regard to physi cal characteristics such as size, current and substratum. 2. In terms of faunal composition the Ecuadorian highland streams bore more resemb lance to the Danish lowland streams than the Ecuadorian lowland stream s. The greater similarity between the Ecuadorian highland and the Dani sh streams, however, was due to the large number of insect families in the Ecuadorian lowlands, many of which were not found in the other re gions. Of ten physico-chemical parameters measured, maximum stream tem perature explained by far the most variability in faunal composition. 3. The number of insect orders and families increased linearly with ma ximum stream temperature and therefore decreased with altitude and lat itude. A compilation of literature data on insect richness and maximum water temperature from streams around the world confirmed this patter n, yielding a common linear relation for both temperate and tropical s treams. This pattern may arise due to a direct temperature effect on s peciation but is probably also related to geological history and the i nfluence of climatic changes on stream ecosystems. We estimate that sm all, tropical, lowland streams have, on average, a two-to fourfold hig her species richness than temperate lowland streams.