Long-term population ecology of the great crested newt in Kent

Climate change has been recognized as one of the causes of global amphibian population declines. Amphibians may be particularly susceptible to climatic changes, as a result of their ectothermic life style and dependence on moisture. Climatic factors may affect amphibian population dynamics deterministically or stochastically, and can act at both local and regional levels. Using capture-mark- recapture (CMR) methods, population dynamics of great crested newts over two decades were compared between two separate populations in Canterbury, Kent in order to explore local and regional drivers of population change. Accurate individual identification is a basic assumption of capture-mark-recapture methods. A comparison of manual and computer-assisted photo identification programs verified that the spot patterns of individual newts did not change significantly through time, and were sufficiently varied to reliably identify individual newts. At a metapopulation located within an agricultural landscape, capture-mark-recapture modelling revealed variations in survival, detectability, and population size between years. Low annual survival of adult newts was related to mild, wet winters which impacted the metapopulation at the regional level. Therefore, survival varied between years but not between subpopulations. Regardless of this regional effect, the four subpopulations were generally asynchronous in their dynamics, but the persistence of the metapopulation depended on a single source pond that was the smallest water body within the system. At a further population two miles away, survival since 2001 was constant and high every year despite mild, wet winters. Management practised through draining and refilling the ponds did have an apparent effect on the number of newts captured over the subsequent years. Population increase could be due to the decrease in predatory invertebrates following pond desiccation and a subsequent increase in recruitment levels. Body condition may be linked to the survival of amphibians. However, there was no influence of climatic conditions on the body condition at either of the populations studied. Nevertheless, body condition was related to survival at one of the populations, and body condition was lower in ponds with high densities of newts. Consequently, the persistence of the two populations relies on a combination of (1) local, population-specific factors - such as population density and pond desiccation, and (2) regional factors, such as climate that affect recruitment and survival from each pond. However, conservation actions at the local scale may offset reduced larval recruitment and adult survival at the regional scale.