Changes in distribution of birches and birch-feeding Eriocrania moths in St Petersburg, Russia, between 1986 and 2001
Abstract:Aim and location
I aimed to assess changes in number and quality of suitable habitats, as well as in habitat occupancy by Eriocrania leafminers (Lepidoptera, Eriocraniidae), which have occurred in central parts of the city of St Petersburg between 1986 and 2001. Methods
The study compares results of 2000/2001 with the data of 1986 (published by Kozlov, M.V., Zhurnal Obzsej Biologii (Moscow), 1988, 49, 670; Journal of Biogeography, 1996, 23, 95) and is based on (1) mapping of birch trees in two representative plots (20–25 ha) in downtown and on the periphery of the densely built city area, (2) survey of 133 isolated or semi-isolated habitats that were found suitable for Eriocrania in 1986, and (3) presence/absence records of birches (Betula pendula and B. pubescens) and Eriocrania miners in Petrogradskaya area by using 160 × 160 m regular grid (same as in 1986; 379 cells). Results
Both number of habitats suitable for Eriocrania and number of birch trees in these habitats increased since 1986. Colonization of vacant habitats in the area of sporadic distribution in the years 2000/2001 exceeded the extinction rate by a factor of 4; probability of extinction was highest in low density Eriocrania populations associated with small habitat patches, like solitary birch trees in densely built areas. Proportion of the occupied habitat patches within the zone of sporadic distribution in 2000 (92.4%) was much higher than in 1986 (50.4%); thus the area of the lacuna in distribution range of Eriocrania species, associated with the historical centre of St Petersburg, has decreased since 1986. Main conclusion
The data of 2000/2001 fit the prediction ( Kozlov, 1996) that Eriocrania moths are able to re-colonize the city areas built before 1950s, where they have been extinct or almost extinct by the mid-1980s.