| Popis: |
Some amphibians respond to climate change by advances in phenology. Previous work at Llysdinam found significant advances in Lissotriton arrival dates in 1997-2005 compared with the 1980s. This study investigated newt migration phenology and whether early arrival reflected earlier breeding. A temporal difference was found in the size of Lissotriton newts arriving to the pond. Large newts made up a greater proportion of early arrivals. Photographic identification of ventral markings of great crested and male smooth newts was used to monitor individual movements. Breeding was not synchronous with arrival because there was a variable delay before breeding. Lissotriton eggs in Llysdinam Pond were detected ten weeks earlier in 2007 than 2006. In contrast great crested females advanced oviposition by four weeks in 2007 and prolonged oviposition by five weeks. The effect of arrival time on breeding for Lissotriton newts was studied in outdoor tanks. There was a greater delay between arrival and egg-laying for earliest Lissotriton arrivals in 2006 than 2007. There was a significant decline in the length of delay between Lissotriton arrival and egg-laying over the season, with late arrivals breeding soon after arrival. The delay between arrival and egg-laying was reduced if mean weekly air temperatures were consistently over 2 C. Lissotriton larvae and predatory aquatic invertebrates were surveyed by netting, and data compared with two studies in the 1980s. Invertebrates and newt larvae showed similar advances in phenology, but anuran spawning had not advanced indicating possible asynchronous interactions. In the absence of predators, there were no significant differences in Lissotriton hatching success or hatchling size over the season. Larvae grew faster later in the year, releasing them from predation risk by the smallest predatory invertebrates. Further research on the synchrony between species in pond habitats is suggested. If synchrony is maintained, other implications of climate change, including changes in range, susceptibility to disease and length of hydroperiod will have greater impacts on amphibian populations and possibly amphibian declines than phenological change. |
