The population dynamics of the crested newt (Triturus Cristatus Cristatus (Laurenti)).

Bielinski, Andrew (1986). The population dynamics of the crested newt (Triturus Cristatus Cristatus (Laurenti)). MPhil thesis The Open University.



This thesis describes studies carried out on the crested newt, Triturus cristatus, and the smooth newt, T. vulgaris, at two localities in the vicinity of Milton Keynes, Buckinghamshire, between 1980 and 1983. The first study site was a pond within the grounds of the Open University at Walton Hall and the second was some 8 miles away from this near the village of Milton Bryan.

At Walton Hall crested newts were intercepted during migration to the breeding pond using drift fencing and pitfall traps and by picking animals up off the road during evening searches. In this way it was found that movement was significantly correlated with daily temperature, but not with daily rainfall. In addition, it was observed that males entered the breeding pond significantly earlier than the females.

At Milton Bryan a program of mark-recapture analyses was carried out on both species as the basis for the study of their population dynamics. Animals were trapped using static underwater traps and marked using toe-clips and the recording of belly-patterning. Both species were found to show variable population sizes from year to year. The sex ratio in T. vulgaris showed an excess of females in all years, whilst that of T. cristatus varied from an excess of males in some years to equality in other years. Annual survival of male and female crested newts was calculated as 0.36 for each sex.

From data on weight change during the season it was found that the majority of individuals of both sexes lost weight whilst in the water. Annual growth in the crested newt was found to be highly variable, but positively correlated with body size; smaller individuals had larger increments of growth than larger individuals. However, animals of the same size did not necessarily grow by the same amount. Size-frequency distributions of both species are analysed and morphometric characteristics compared with data from other populations. The problems associated with the the extrapolation of these types of data into age-distributions are discussed, with reference to the data on growth. It is concluded that length cannot be used as reliable indicator of age in T. cristatus. From the size-frequency data it was found that the numbers of juveniles appearing at a breeding site may be highly variable from year to year. The implications of this for the dynamics of crested newt populations are discussed.

Data are also presented from the dissection of preserved animals. These relate gonad size to body size in both species. It is shown that both testes weight and ovary weight are positively correlated with body weight and snout-vent length and that females display size-specific fecundity i.e. larger females produce larger ova and greater quantities of ova than smaller individuals. These findings are discussed with reference to other species of urodele and with regard to the life history tactics displayed by other species.

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