Abstract

Diptera surveys have been carried out over a wide range of sites in Cheshire (VC58) and Lancashire (VCs 59 and 60). Over the period 2012-2019 just over 20,000 records representing the occurrence of a species in a specific 100m square on a specific day were collected using a sweep-net and aspirator, together with field observations and individual capture of some species. The taxonomic scope was 3,300 species from families of larger and more readily identifiable species, of which 1,292 were recorded. Six sites with mixed open, wooded and wetland sites and areas between 19 and 972ha were selected for intensive survey consisting of at least 6 visits spread over the period April-September.

Rank-abundance data have been analysed to produce estimates of biodiversity measures both for the full dataset and for the six sites. They approximate to the log-series distribution. Non-parametric methods have been used to estimate Hill numbers of order 0, 1 and 2. It is concluded that for an adequate sample from a site around 1,200 records need to be gathered leading to around 300-400 species. Pair-wise inter-site comparisons using the Sørensen and Morisita-Horn indices show that the strongest diversity difference is between the single coastal site and the other 5 inland sites. The numbers of the 96 species constituting 50% of the overall data over the six sites is assessed against the hypothesis of a uniform distribution. The diversity differences correlate qualitatively with the habit assemblages determined from the site species lists using the PANTHEON database.

Ref. true flies

Published March 2020