Environmental disturbance and chironomid palaeodiversity: 15 kyr BP of history at Lake Mascardi, Patagonia, Argentina

Abstract

1. Palaeoecological records may be useful in predicting the ecological outcomes for certain communities exposed to natural and human disturbance. In turn, theoretical work has emphasized the importance of baseline information on diversity to establish precise conservation and restoration policies. 2. Lake sediments provide good evidence of long-term changes in community composition, especially of insects from the family Chironomidae. Midge fauna is highly diverse and their remains are well preserved in sequential order allowing the construction of past assemblages. 3. To assess long-term community trends and stability in an environment virtually free from human impact, fossil midge assemblages were collected from a sediment core at Lake Mascardi (Río Negro, Argentina). Shannon's diversity index as well as rank-abundance relationships were estimated for core subsamples (10 cm slices), using a ‘taxonomic minimalist’ approach. 4. Diversity levels are relatively constant along the core. However, sharp reductions in diversity and equitability in midge assemblages are recorded. These reductions appear to be related to natural variability—mainly ash falls (pulse) and climatic (press) disturbing events. During pulse disturbances, both diversity and equitability fall, recovering rapidly after pressure is released. During press events (long-term disturbances) equitability falls whereas diversity remains fairly constant. Subfamily succession between pulse disturbances, follows proposed ecological species rank-abundance models. 5. These findings suggest that at long time-scales, a low level of taxonomic detail may be adequate for the analysis of community responses to environmental change. © 1998 John Wiley & Sons, Ltd.