Aquatic, Semi-Aquatic and Riparian Vertebrates

The course of aquatic vertebrate evolution has been moderated by extreme climatic events such as sea-level rise and flooding, with areas such as floodplains providing productive feeding grounds and refuges in times of drought. Aquatic and semi-aquatic vertebrates in the tropics have achieved a remarkable range of anatomical and physiological adaptations, in contrast to temperate latitudes where rivers froze during the last glaciations. Convergent adaptations across different families has been the norm, dictated by the need to swim and to efficiently exploit aquatic niches inhabited by invertebrates and fish. Most taxa are adapted to the lowland sections of large rivers, while few have evolved within fast streams. The current geographic distribution of aquatic, semi-aquatic and riparian species is a reflection of the abundance and variability of water supply in different regions, the obstacles presented to migration by mountain ranges, and the presence of large rivers which may serve as barriers or biocorridors. These vertebrates include a wide range of taxa, some that are more dependent on water than others, and a survey of the main taxa of herpetofauna and mammals is given here. Tropical streams are characterised by seasonal flows and inundation of the floodplain. Many aquatic and semi-aquatic vertebrates have become highly specialised and dependent upon these seasonal flood pulses conditions. They are vulnerable to habitat degradation or alteration associated with flow regulation, irrigation schemes and the conversion of floodplains to agriculture. Because of their specialism, occupation of more upland habitats is not possible, and aquatic and semi-aquatic vertebrates now include some of the most highly threatened species on Earth. Loss of these species, or large declines in their densities, will impact the ecology of tropical river ecosystems because of the important roles that aquatic, semi-aquatic and terrestrial vertebrates play in energy flow, nutrient cycling and riparian landscape engineering.