Population dynamics of a breeding population of great crested newts (Triturus cristatus) in Lincolnshire, UK
Creators: name: Warwick, Tess
Publisher: name: University of Lincoln
Year: 2023
Subjects: C162 - Freshwater biology
C170 - Population biology
C180 - Ecology

description: As many amphibian populations are facing global decline, the great crested newt (Triturus cristatus) is of particular conservation interest in Britain following a widespread loss of numbers in the twentieth century. This thesis aimed to study the population dynamics of great crested newts within a breeding pond in Lincolnshire between 2011-2019. Bottle traps were used to capture newts with digital photography used to identify individual newts from their unique ventral pigmentation pattern. A total of 1,163 individual newts were identified across the eighty-six trapping events conducted across the entire study period. The Schnabel method was used to estimate population size, which was found to remain relatively stable throughout the study period, averaging around 500 adult newts per year. In comparison, the Jolly-Seber method, which is deemed more appropriate for this particular population, showed a steady increase in population size across the study period. Analysis of the sex ratio showed a slight male bias with ordinal day and year showing an effect on number of females caught but having no impact on male numbers. Age estimates of 28 and 23 years were calculated for male and female newts respectively, which are higher than any previous longevity estimates of this species. These estimates allowed age specific effects to be studied. Snout to vent length(SVL)measurements tended to be longer in females and increased with age before beginning to decline at around 16 years for males and 22 years for females. Mass was also found to initially increase before plateauing at around 5 years of age and declining later on. Likewise condition scores increased in younger animals until reaching around 16 years of age when a decline in condition began. Within the breeding season, mass and condition decreased as ordinal day increased, with females losing mass at a faster rate than males. Ventral pigmentation increased with age before gradually slowing and remaining steady from around 17 years of age onwards. Despite pigment development it still remained possible to identify individual newts from their ventral pigmentation. Lateral profiles of male newts were studied to determine the effects of age on crest shape. Characteristics in shape were found to be different between younger and older males with these same characteristics subsequently lost as age increased further suggesting that male attractiveness may possibly wane with old age. No differences in crest shape were found relating to condition, mass or SVL however the small sample size used may not have allowed these variables to be explored fully. The major strength of this study is the rich, long-term data set that has been gathered which allows a deep level of analysis to provide insight into specific dynamics of a well-established population. By gaining information on T. cristatus, a protected species, we can provide a basis for further survey work to ensure the most appropriate levels and techniques of protection are afforded to the habitats required. In particular the change in pigmentation of great crested newts with growth could benefit from further survey and analysis as this is a relatively understudied area of newt morphology.