Rare Species Enhance Niche Differentiation Among Tropical Estuarine Fish Species

Based on the assumption that rare species in estuarine systems may display a different set of traits relative to common species, we hypothesized that the extirpation of rare species would negatively affect functional diversity components of these ecosystems. Therefore, the contribution of rare species to the functional structure of estuarine fish assemblages in a tropical estuarine lagoon was tested using two different simulation scenarios of species loss: (1) losing the rare species first and (2) removal occurring at random. Overall, high functional redundancy among studied estuarine fish species was found, with many species, including some rare species performing similar functions as shown by the consistent and marked species’ overlap in the functional space. Nevertheless, the removal of rare species negatively impacted niche differentiation among assemblages, indicating that while rare species play redundant functions in the studied estuary, they also have a crucial role in increasing niche differentiation among fish assemblages. Such increase in niche differentiation granted by rare species—mostly represented by marine straggler species—appears to be a key component of ecosystem stability by allowing functions to be continued even when the estuary is faced with disturbances.