Long Term Turnover of a Fossil Community of Chironomids (Diptera) from Lake Mascardi (Patagonia, Argentina)

CORLEY; MASSAFERRO

JOURNAL OF THE KANSAS ENTOMOLOGICAL SOCIETY

KANSAS ENTOMOLOGICAL SOC

Lugar: Kansas; Año: 1998 vol. 71 p. 407 - 413

0022-8567

bstract: For the short-lived aquatic insects, such as the Chironomidae Family, large iso lated lakes act as islands as they sustain "closed" communities. Island Biogeography Theory considers communities in a dynamic equilibrium, where species yearly turnover is an im portant component. Long term community composition studies are limited because turnover is sensitive to the length of the sample interval. Apparent turnover, that by definition is in dependent of census interval, instead considers longer intervals and allows studies to trace communities far back in time. In northern Patagonia, an archipelago of post-glacial lakes originated ca. 15,000 yr BP with little human impact and offers unique conditions for long term ecological studies of aquatic communities. In this study, we used a long-term apparent turnover approach to provide insight into the dynamics of Chironomid communities. Such an approach allows for longer intervals, avoids the bias reported for short term studies, and may be suitable for looking at long term temporal trends in short lived insects. We estimated the apparent turnover for past Chironomid assemblages using data obtained from 11-m long sed iment core collected at Lake Mascardi. Samples taken every 10-cm, covered approximately 100-200 yr intervals. Twenty-eight species, belonging to 4 groups (subfamilies Tanypodinae and Orthocladiinae, tribes Tanytarsini and Chironominini) were identified from the fossil record. Maximum number per assemblage did not exceed 14 species. Turnover, mainly due to local extinction events was important during reported pulse disturbances, such as regional vulcanism. Stable assemblages instead, revealed by minimal turnover pattern, may be asso ciated with favorable environmental conditions or when community composition is 0. We conclude that for midges at the studied lake, the community is indeed under a dynamic equi librium and may not be species saturated. In this sense, the importance of regional physical disturbance should be considered.