Biotic Indicators for Ecological State Change in Amazonian Floodplains

Abstract

Riverine floodplains are biologically diverse and productive ecosystems. Although tropical floodplains remain relatively conserved and ecologically functional compared to those at higher latitudes, they face accelerated hydropower development, climate change, and deforestation. Alterations to the flood pulse could act synergistically with other drivers of change to promote profound ecological state change at a large spatial scale. State change occurs when an ecosystem reaches a critical threshold or tipping point, which leads to an alternative qualitative state for the ecosystem. Visualizing an alternative state for Amazonian floodplains is not straightforward. Yet, it is critical to recognize that changes to the flood pulse could push tropical floodplain ecosystems over a tipping point with cascading adverse effects on biodiversity and ecosystem services. We characterize the Amazonian flood pulse regime, summarize evidence of flood pulse change, assess potential ecological repercussions, and provide a monitoring framework for tracking flood pulse change and detecting biotic responses.

The structure and organisation of an Amazonian bird community remains little changed after nearly four decades in Manu National Park

“…Thus, periodic inundation of the floodplain may also provide buffer to potential drought conditions. However, aspects of periodicity of flooding and how they are affected by larger climate patterns remains to be studied (Correa et al, 2022). Based on the results reported in Panama, Tiputini and Manaus, changes in rainfall patterns in other sites may be correlated with the decrease in insectivore birds.…”

Feeding habits influence species habitat associations at the landscape scale in a diverse clade of Neotropical fishes

“…Species in feeding guilds that are associated with wider extensions of floodplain and that depend on allochthonous food resources provided by floodplain habitats (i.e. frugivores) are very likely to be affected by the modification of the flow regime due to hydropower damming of large rivers (Arantes et al, 2019; Correa et al, 2022; de Bem et al, 2021) and climate change (Herrera‐R et al, 2020). That is due to the disruption of the connectivity between the river and floodplains, which impedes the lateral exchange of nutrients and organisms.…”

“…Thus, flood duration may not affect whether they remain as open water bodies capable of supporting plankton and planktivores during the dry season. However, changes in hydrology induced by dams and climate change may reduce flow and turn floodplain lakes ephemeral in the future (Correa et al, 2022). Frugivores and piscivores appear to be similar in terms of how much floodplain extent they occupy but are different when we consider the landscape heterogeneity, with frugivores occupying areas with higher levels of heterogeneity at the smallest buffer size (300 m).…”

“…Thus, flood duration may not affect whether they remain as open water bodies capable of supporting plankton and planktivores during the dry season. However, changes in hydrology induced by dams and climate change may reduce flow and turn floodplain lakes ephemeral in the future (Correa et al, 2022).…”

A synthesis of the diversity of freshwater fish migrations in the Amazon basin

“…In large tropical river basins, such as the Amazon, Congo and Mekong, migration of fishes occurring entirely within freshwaters seems to have a higher prevalence as a migratory strategy, as diadromy is poorly represented among fishes in these basins compared to smaller tropical rivers or temperate rivers (Chalant et al., 2019; Vu et al., 2023; Worthington et al., 2022). Large tropical basins experience marked seasonality in discharge driven by regional precipitation and air circulation patterns, and resulting flood pulses act as a significant factor shaping the ecology of fishes in lowland areas (Correa et al., 2022; Jardine et al., 2015; Junk, 1999). The flood pulse and the extensive network of river basins provide temporal and spatial accessibility for aquatic organisms to a heterogeneous mosaic of freshwater habitats ranging from upland tributaries, floodplain forests and meadows and the estuary (Encalada et al., 2019; Harrison et al., 2016).…”