Urban wetlands are teeming with life. In addition to frogs and newts, there are many invertebrate species that thrive in ponds, rainwater basins and even seasonal urban wetlands in the middle of the hustle and bustle of city life.
Diving beetles are a common sight in urban ponds, and several species can generally be found.
"There are not as many diving beetle species in urban ponds as in rural environments, but the beetles can still be plentiful. Urbanisation does not seem to reduce the capacity of ponds to support diving beetles, as the number of individuals was similar to that in rural ponds. However, some species are less tolerant of urban environments," says Wenfei Liao from the Faculty of Biological and Environmental Sciences, University of Helsinki.
When the researchers sampled 14 fishless ponds and 11 ponds with fish at ten sites in the Helsinki Metropolitan Area, they found 39 species of diving beetles, or dytiscids, which is about 40 per cent of the dytiscid species known from the Uusimaa Region.
Happy together with fish? Not always!
The results show that diving beetles and fish can share a pond, but only the medium to large-sized diving beetle species manage to co-exist with insect-eating fish such as pike, tench, or carp.
"So, ponds with insect-eating fish have a different diving beetle species composition than fishless ponds. And ponds with gently sloping margins provide cover for different kinds of diving beetles and other macroinvertebrates."
Wenfei Liao, Stephen Venn and Jari Niemelä. Environmental determinants of diving beetle assemblages (Coleoptera: Dytiscidae) in an urban landscape. Biodiversity and Conservation https://doi.org/10.1007/s10531-020-01977-9