FISH COMMUNITY PATTERNS OF LAGOONS AND ASSOCIATED TRIBUTARIES IN THE ECUADORIAN AMAZON

We analyzed fish distribution patterns of 10 lagoons and six of their tributaries between 200 m and 295 m altitude along two parallel headwa ter tributaries of the upper Amazon, within the Napo River basin of ea stern Ecuador. Multivariate methods of Detrended Correspondence Analys is (DCA) and Two-Way Indicator Species Analysis (TWINSPAN) revealed co mmunity patterns that corresponded primarily to altitude and secondari ly to habitat. We identified two altitudinal regions, the lowland betw een 200 m and 220 m and the piedmont between 235 m and 295 m. We recog nized four community types associated with lowland lagoon, lowland tri butary, piedmont lagoon, and piedmont tributary habitats. Tributary fa unas were more closely associated with lagoon faunas within the same r egion, than with tributary faunas of differing regions. Lagoons and as sociated tributaries had high species diversity and evenness. Lowland sites showed higher species richness and had more characteristic speci es than piedmont sites, resulting in a pattern of species addition and species replacement along the altitudinal gradient. Decreased species richness in higher altitudes, coupled with unchanging diversity and e venness, is similar to published findings for riverine sandy beach ass emblages of the Napo River basin. Faunal turnover between lowland and piedmont regions was greater for tributaries than for lagoons. Faunal turnover between tributary and lagoon habitats was greater in the lowl and region than in the piedmont region. In contrast to observations fo r riverine sandy beach assemblages of the Napo basin and floodplain la goons of the Orinoco River basin, separation of lagoon communities bas ed on water type (clearwater vs blackwater) was not well supported. Co mparisons among lagoon, tributary, and riverine sandy beach communitie s of the Napo River basin and Rio Negro (Brazil) communities revealed low similarity. Comparison of numerically dominant characiforms of the Napo, Negro, and Apure River (Venezuela) drainages revealed few share d species but approximately 50% shared genera.