THE MACROINVERTEBRATE COLONIZATION OF LEAF BAGS: IS THERE A PATTERN?

There have been many studies of litter decompocition and the macroinvertebrates associated with litter. Neverthelesc, the reasons why invertebrates colonize leaf bags are still a matter for diccussion. Although invertebrates use leaves as food, i t has been shown that they may use the leaf bag a substrate. In this study, we investigate whcther macroiiivertebrates colonize leaf bags decpite aburidant natural leof litter in the streams aiid whether they discriminate between leaves occurring naturally in the streainc (Alnus glutino.su) and alien spe-cies í in this case, the South American Nurci crepitum). We found no differences in the relative abundance of chredders between Alrzris and HiiIyi leaf baga. In relation to the relative abundan-ce of shredders in the leaf bags and iii the streambed, we fouiid al1 the possible conibinationc. In two streams there were no differences between the benthic camples and the leaf bags. i n another stream. the relative abuiidance of shredders was higher in the benthic samples, and in a further stream, the relative abundance of shredders was higher in the leaf bags. It seeins therefore, that when tliere ia ari abtindant supply «f high qtiality food in the streains. there is no reason for the aggrcgation o í shredders in the leaf bags