The distribution of dragonfly nymphs across a pH gradient in south-central Ontario lakes

Exuviae of 37 species of dragonflies were collected from the emergent vegetation of 19 small (<35 ha) lakes across a pH gradient (range 4.9–8.1) in south-central Ontario to assess the effect of low environmental pH on species richness and diversity. The number of species present in a lake was not significantly correlated with lake pH. Two measures of diversity (Keefe and Bergersen's TU and McIntosh's M) indicate an increase in species diversity with decreasing lake pH. Species shifts in the communities were also correlated with lake pH: five species were apparently excluded from lakes with a midsummer epilimnetic pH below 5.8, and seven species were apparently restricted to lakes with a pH of less than 6.2.