Tropical forests are vertically complex, and offer unique niche opportunities in the form of climate-, habitat-, and resource-gradients from ground to canopy. Rainforest species organize within this vertical spatial gradient and recent macro-ecological research suggests the highest levels of vertical stratification occur in structurally complex and climatically stable tropical rainforests. Yet, patterns of verticality are typically derived across latitude, linking annual precipitation regimes to canopy utilization and vertical stratification of communities in space. However, although the tropics are not thermally variable, they do have strong seasonality in rainfall—a temporal component that is missed in macro-scale studies. We suggest that verticality of ecological communities responds to seasonality in climate, particularly rainfall.
We performed 121 ground-to-canopy surveys across the wet and dry seasons for amphibians. We calculated species specific and community wide vertical height and abundance shifts between seasons, and separately test the importance of vertical height and season on the vertical distribution of species.
Results/Conclusions
We uncovered a clear downward shift of 5 m in height in amphibian communities from wet season to dry season. We also observe significant changes in species composition across vertical strata in both seasons, driven by nestedness in the dry season (loss of species over height), and genuine turnover in the wet season (loss and addition of species over height).
The exploitation of canopy microhabitats and resources in the wet season resulted in complex patterns of stratification, whereas drying flattened the distribution and simplified the composition of arboreal communities. As such, pattern and process in the vertical dimension is not static in time but rather exists as a dichotomy with inverse patterns between wet and dry seasons. Complex, multidimensional distributions of diverse rainforest communities can be simplified by climatic constraints—an important consideration as anthropogenic climate change increases the magnitude of seasonal swings in temperature and precipitation.