If quantitative data are required, then sampling that must be repeatable by others. In the 1980s the then Nature Conservancy Council had three survey teams (Welsh Peatlands, East Anglian Fens and Dungeness) who all used a combination of pitfall and water traps. I ran the Dungeness survey, which was highly illuminating! If nothing else, it highlighted the huge commitment of time that was needed to set and service traps; and the even larger time commitment needed to sort the sample and get it identified.
Pitfall/Water trap combinations
Pitfall traps sometimes generated huge catches of a single species - many hundreds of isopods, anything up to several hundreds of the ground beetle Calathus fuscipes and large numbers of ants if placed close to a colony. The overall species list for a set of traps was often substantial but it had very few dominant species and a long tail of occasional records that made multivariate analysis unconvincing. Cruder analysis showed the relative frequency of some interesting animals across the sites, but making a match to the NVC communities proved to be almost impossible. The best splits occurred where there was a big difference in environmental parameters; whereas different lichen heath communities showed very little difference in the assemblage.
What about the Malaise trap?
So what are the other alternatives?
- an inventory of species for a site?
- sufficient data to undertake multivariate analysis?
- long-term monitoring?
- autecology of a single species or suite of species associated with a highly defined habitat?