Mechanisms of maintenance of tropical freshwater fish communities in the face of disturbance

Community resistance to, and resilience from, perturbation will determine t he trajectory of recovery from disturbance. Although selective timber extra ction is considered a severe disturbance, fish communities from headwater s treams around Danum Valley Field Centre, Sabah, Malaysia, showed few long-t erm changes in species composition or abundance. However, some species show ed short-term (< 18 months) absence or decrease in abundance. These observa tions suggested that both resistance and resilience were important in maint aining long-term fish community structure. Resistance to perturbation was t ested by monitoring fish communities before and after the creation of log-d ebris darns, while resilience was investigated by following the time-course of recolonization following complete removal of all fish. High community r esistance was generally shown although the response was site-specific, depe ndent on the composition of the starting community, the size of the stream and physical habitat changes. High resilience was demonstrated in all recol onization experiments with strong correlations between pre- and post-defaun ation communities, although there was a significant difference between pool and riffle habitats in the time-course of recovery. These differences can be explained by the movement characteristics of the species found in the di fferent habitats. Resilience appeared to be a more predictable characterist ic of the community than resistance and the implications of this for ensuri ng the long-term persistence of fish in the area are discussed.