Figure 2: Schematic diagram of the Rio Espiritu Santo, Puerto Rico

Figure 2: Schematic diagram of the Rio Espiritu Santo, Puerto Rico, illustrating observed and potential downstream-upstream effects. Barriers, both natural (waterfalls) and artificial (dams and associated water abstraction), act as selective filters along the stream continuum, modifying the distribution of biota upstream. Superimposed on the upstream legacies created by these filters are the legacies created by interactive effects of both natural (e.g., hurricanes and droughts) and artificial (stream poisoning events, fishing, shrimp trapping, pollution) disturbances (From Pringle 1997).