Long-term Studies of Tropical Stream Fish Communities:The Use of Field Notes and Museum Collections to Reconstruct Communities of the Past

SYNOPSIS. The accurate perception of change requires a period of continuous observation. For species conservation, change has often not been anticipated, so such periods of observation are generally not available. We instead usually have to deal with the imperfect recollections of individual investigators. We argue here that it may be possible to do better than this by making use of old field notes or museum collections. In some cases, these sources can provide accurate descriptions of at least some aspects of past community structure. Our first example is for freshwater streams from Trinidad. One of us (JE) has studied these streams 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 in the habitat. Our second example includes three types of data gleaned from collections made in Costa Rican streams during the 1960s and 1970s, and housed at the University of Costa Rica. We show how these collections can be used to describe species abundance and diversity for entire watersheds, yield detailed descriptions of the composition of the community at individual collecting sites, and reveal much about the life histories and ecology of resident species. All of these descriptions can be used as a frame of reference for evaluating what present communities are like in the same areas, and hence for evaluating how these communities have changed. We argue that similar quantitative descriptions are available for many fish communities throughout the world, and for some other groups of organisms