Colonization of artificial substrates by stream insects: Influence of substrate size and diversity

A field experiment was performed in a New Mexico (U.S.A.) stream to investigate the relation between size and diversity of substrate and numbers and diversity of colonizing insects. Baskets with either small gravel, large gravel, or a 1 : 1 mixture of the two sizes were placed in a riffle area and colonization was monitored for 19 days.Colonization was rapid, and both total number of individuals and number of species colonizing the substrates had stopped increasing by the end of the experiment. Fewer individuals colonized baskets downstream, suggesting that the drift is a major source of insect colonists. Small substrate supported more individuals and more species than the larger stones. Total number of individuals and the number of species on the mixed substrate were between numbers on small and large substrate. These results do not support previous generalizations on the relation between substrate size and complexity and the structure of invertebrate communities in streams. Results of the study are compared with the findings of recent experimental studies and it is suggested that earlier generalizations on the role of substrate size and complexity need to be reexamined.Order of authors was determined by the flip of a coin. Reprint requests may be sent to either author.