LONG-TERM STUDIES OF TROPICAL STREAM FISH COMMUNITIES - THE USE OF FIELD NOTES AND MUSEUM COLLECTIONS TO RECONSTRUCT COMMUNITIES OF THE PAST

The accurate perception of change requires a period of continuous obse rvation. For species conservation, change has often not been anticipat ed, so such periods of observation are generally not available. We ins tead usually have to deal with the imperfect recollections of individu al investigators, We argue here that it may be possible to do better t han this by making use of old field notes or museum collections. In so me cases, these sources can provide accurate descriptions of at least some aspects of past community structure. Our first example is for fre shwater streams from Trinidad. One of us (JE) has studied these stream s for 19 years and available data include repeated visual censuses of fish communities. These censuses contain at least a qualitative index of change in the fish communities accompanying anthropogenic changes i n the habitat, Our second example includes three types of data gleaned from collections made in Costa Rican streams during the 1960s and 197 0s, and housed at the University of Costa Rica. We show how these coll ections can be used to describe species abundance and diversity for en tire watersheds, yield detailed descriptions of the composition of the community at individual collecting sites, and reveal much about the l ife histories and ecology of resident species. All of these descriptio ns can be used as a frame of reference for evaluating what present com munities are like in the same areas, and hence for evaluating how thes e communities have changed. We argue that similar quantitative descrip tions are available for many fish communities throughout the world, an d for some other groups of organisms.