Fish sampling and physicochemical data for aquatic habitats in the Santarem region of the Lower Amazon, Brazil

Explaining the mechanisms underlying spatial and temporal variation in
community composition is a major challenge. Nevertheless, the processes
controlling temporal variation at a site (i.e., temporal β-diversity,
including its turnover and nestedness components) are less understood than
those affecting variation among sites (i.e., spatial β-diversity).
Short-term temporal turnover (e.g., throughout an annual cycle) is
expected to correlate positively with seasonal environmental variability
and landscape connectivity, but also species pool size (γ-diversity). We
use the megadiverse Amazonian freshwater ichthyofauna as a model to ask
whether seasonality and landscape connectivity drive variation in temporal
species turnover among geomorphological habitat types, while accounting
for between-habitat variation in γ-diversity. 11,397 fish
representing 260 species were collected during a year-long sampling
program from an area containing the lowland Amazon’s four major
geomorphological habitat types: rivers, floodplains, terra firme streams,
and shield streams. River-floodplain systems exhibit strong but
predictable seasonality (via a high-amplitude annual flood pulse), high
connectivity, and high species richness with many rare species. Terra
firme and shield streams exhibit low seasonality, low connectivity, and
low species richness with proportionally fewer rare species. Based on
these parameters we predicted that river-floodplain systems should have
higher temporal turnover than stream systems. Using a null model approach
combined with β-deviation calculations, we confirmed that rivers and
floodplains do exhibit higher turnover (but not nestedness) than terra
firme and shield streams, even when controlling for the potentially
confounding effect of higher species richness in river-floodplain systems.
All habitats exhibit low temporal nestedness, indicating that short-term
changes in community composition result primarily from temporal species
turnover. Our results provide a timely reminder that efforts to conserve
the Amazon’s threatened aquatic biodiversity should account for the
distinct temporal dynamics of habitat types and variation in hydrological
seasonality.