Fossil insects and ecosystem dynamics in wetlands: implications for biodiversity and conservation

Description/Abstract

We review the uses of fossil insects, particularly Coleoptera (beetles) and
Chironomidae (non-biting midges) from ancient deposits to inform the study of wetland
ecosystems and their ecological and restoration processes. In particular, we focus on two
contrasting ecosystems, drawing upon research undertaken by us on British raised mire
peats and shallow lake systems, one an essentially terrestrial ecosystem, the other aquatic,
but in which wetland insects play an important and integral part. The study of raised mire
peats suggests that faunal stability is a characteristic of these wetland systems, over what
appear to be extensive periods of time (up to several millennia), whilst studies of shallow
lake ecosystems over recent timescales indicates that faunal instability appears to be more
common, usually driven by increasing eutrophication. Drawing upon a series of fossil
Coleoptera records spanning several thousand years from HatWeld Moors, south Yorkshire,
we reconstruct in some detail the mire’s ontogeny and Xuctuations in site hydrology and
vegetation cover, illustrating the intimate association between substrate, topography and
peat development. A comparison between fossil and modern beetle populations indicates
that the faunal characteristics of this mire and its adjacent neighbour, Thorne Moors,
become established during the early phases of peat development, including its rare endemics,
and that the faunal biodiversity on the sites today is dictated by complex site histories.
The over-riding characteristic of these faunas is of stability over several thousand years,
which has important implications for the restoration of degraded sites, especially those
where refugial areas are limited. In contrast, analyses of fossil Chironomidae from shallow lakes allow researchers to track changes in limnological status and while attempts have
been made to reconstruct changes in nutrient levels quantitatively, the chironomids respond
indirectly to such changes, typically mediated through complex ecosystem dynamics such
as changes in Wsh and/or macrophyte communities. These changes are illustrated via
historic chironomid stratigraphies and diversity indices from a range of shallow lakes
located across Britain: Slapton Ley, Frensham Great Pond, Fleet Pond, Kyre Pool and
Barnes Loch. These sites have shown varying degrees of eutrophication over recent timescales
which tends to be associated with a decline in chironomid diversity. While complex
functional processes exist within these ecosystems, our evidence suggests that one of the
key drivers in the loss of shallow lake chironomid diversity appears to be the loss of aquatic
macrophytes. Overall, while chironomids do show a clear response to altered nutrient
regimes, multi-proxy reconstructions are recommended for a clear interpretation of past
change. We conclude that if we are to have a better understanding of biota at the ecosystem
level we need to know more of the complex interactions between diVerent insect groups as
well as with other animal and plant communities. A palaeoecological approach is thus
crucial in order to assess the role of insect groups in ecosystem processes, both in the recent
past and over long time scales, and is essential for wetland managers and conservation
organisations involved in long term management and restoration of wetland systems