Ecosystems, paleoecology and human disturbance in subtropical and tropical America.

Human disturbances of ecosystems last a long time and have quantifiable influences on the structure and function of the systems. If long records (e.g. paleoecological) of both disturbances and the responses are available, the array of disturbances provides quasi-experimental treatments useful for the study of factors which govern ecosystems. This paper examines the paleoecology of a series of lake-drainage basin ecosystems that have been subject to disturbances which vary through time and space. In all cases studied, it has been demonstrated that human activities have increased the movement of materials from the catchment to the lake. Examples in Guatemala, Haiti and Florida demonstrate that the flow of macronutrients (nitrogen and phosphorus) is proportional to human population sizes, and that the flow of inorganic particulates is related to the nature of both the disturbances and the catchment. Lake eutrophication is driven by growing human populations, but the rate of increase can be slowed by activities such as urbanization, which increases siltation. Several tropical ecosystems have recovered from severe disturbances, but the rate of recovery was related to the severity and temporal extent of the disturbances