Fish Community Patterns of Lagoons and Associated Tributaries in the Ecuadorian Amazon

Abstract

We analyzed fish distribution patterns of 10 lagoons and six of their tributaries between 200 m and 295 m altitude along two parallel headwater tributaries of the upper Amazon, within the Napo River basin of eastern Feuador. Multivariate methods of Detrended Correspondence Analysis (DCA) and Two-Way Indicator Species Analysis (TWINSPAN) revealed community patterns that corresponded primarily to altitude and secondarily to habitat. We identified two altitudinal regions, the lowland between 200 m and 220 m and the piedmont between 235 m and 295 m. We recognized four community types associated with lowland lagoon, lowland tributary, piedmont lagoon, and piedmont tributary habitats. Tributary faunas were more closely associated with lagoon faunas within the same region, than with tributary faunas of differing regions. Lagoons and associated tributaries had high species diversity and evenness. Lowland sites showed higher species richness and had more characteristic species 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 evenness, is similar to published findings for riverine sandy beach assemblages 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 lowland region than in the piedmont region. In contrast to observations for riverine sandy beach assemblages of the Napo basin and floodplain lagoons of the Orinoco River basin, separation of lagoon communities based on water type (clearwater vs blackwater) was not well supported. Comparisons among lagoon, tributary, and riverine sandy beach communities 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 shared species but approximately 50% shared genera.