Apparent Species Turnover, Probability of Extinction and the Selection of Nature Reserves: A Case Study of the Ingleborough Limestone Pavements

Plant species recorded from two surveys of the Ingleborough limestone pavements in the U.K. 11 years apart, in 1974/75 and 1985, are used to assess the performance of potential reserve networks over time. The minimum set of pavements needed to represent all nationally rare and uncommon species occurring on the pavements in 1974/75 is inadequate in 1985 because of a very high level of apparent turnover in species composition. The number of species lost or gained is not correlated with pavement area and the turnover has not resulted in an equilibrium number of species; overall more species were lost than gained. Even if this turnover is due only to observer bias, it is a real phenomenon when it comes to land use decision-making and should be taken into account when planning reserve networks and developing conservation management strategies. A statistical model of extinction probability is derived by relating the variable "extinct or not in 1985" to frequency of occurrence in 1974/75 using logistic regression. This model is then used to predict that 18, 19, or 20 and 21 species will have become locally extinct by 1994, 1995, and 1996, respectively. The list of species from which these extinctions are likely to be drawn is supplied.