CHANGES IN DEWPOND NUMBERS AND AMPHIBIAN DIVERSITY OVER 20 YEARS ON CHALK DOWNLAND IN SUSSEX, ENGLAND

The fate of dewponds, the only substantive wetland habitat on the chal k Downs of southern England, was monitored over an area of 150 km(2) b etween 1977 and 1996 together with changes in use by the five species of amphibians that inhabit them. Despite a proactive pond restoration programme there was an overall net loss of seven pools (21% of the ini tial number of 33) by 1996, although a higher proportion and absolute number of surviving ponds were in good condition in 1996 (58%, 15 pond s) compared with 1977 (24%, eight ponds). Anurans (common frogs Rana t emporaria and toads Bufo bufo) were more widespread on the Downs in 19 96 compared with 1977, probably because they colonised new ponds effec tively, whereas urodeles (smooth newts Triturus vulgaris, palmate newt s T. helveticus and crested newts T. cristatus) all declined over the same period. T. cristatus, a species ceded maximum protection under th e European Union Habitats Directive, occurred in nine sites in 1977 bu t in just three by 1996. Total destruction of ponds was the most commo n cause of crested newt extinction, but at two sites the species disap peared following the establishment of fish populations. Various indice s of amphibian diversity in dewponds are also compared. (C) 1997 Publi shed by Elsevier Science Ltd.