The population structure and demography of Triturus cristatus in agricultural landscapes of North-West England

Orchard, DG

Abstract

Triturus cristatus is one of Europe’s most rapidly declining amphibians and has been the subject of conservation concern in the UK since 1975. Despite its widespread decline and continued threats from development, T. cristatus remains widely distributed in the UK countryside. Traditional farming practices, such as the digging of ponds for livestock, created suitable habitats for T. cristatus and consequently the species was much more common in the past. Over the last 70 years the nature of farming has fundamentally changed and the modern landscape provides a comparatively degraded habitat for wildlife. The value of farmland for T. cristatus in the UK is often overlooked by conservation efforts for the species, even though it is a valuable habitat and essential for providing connectivity between adjacent populations. Much effort is focussed on the small number of Special Areas of Conservation (SACs) or Sites of Special Scientific Interest (SSSIs) but these cover a very small part of the UK landmass. T. cristatus has been protected by law in the UK since 1981, and as a result an estimated minimum of £45 million is spent each year to avoid killing or injuring individual newts where populations are affected by development. In contrast land in agricultural production covers 71% of the UK but funding for proactive conservation of the species across this habitat is minimal and very difficult to obtain.

This thesis has investigated the ecology of T. cristatus on farmland in North West England. Data were collected from a total of 32 ponds on 11 sites. Population size estimates are presented for eight farm ponds and are compared with those from three non-farmed ponds. Population size varied markedly between ponds and sites, and some farm ponds supported very small numbers of newts. Population estimates fluctuated markedly between years, highlighting the importance of long term studies. Isolated ponds supported relatively large numbers of individuals, and indeed the highest population estimate was recorded in an isolated pond. This demonstrates that isolation in itself is not a limiting factor for population size. In total, 4693 individuals captured during this study were weighed and measured, and the data were used to compare body condition index (BCI) between populations. There was no clear difference between BCI at farmed and non-farmed sites, suggesting that BCI of T. cristatus on farmland was not adversely affected by modern farming practices. There was an inverse relationship between age and body condition.

The age structure of 13 populations was estimated based on skeletochronology of 548 adults. Individuals in the farmed landscape survived to a maximum estimated age of 14 years, only one year less than the maximum age recorded during this study. Twenty individuals were estimated at 12 years or older. Fourteen of these were from farmed and six were from non-farmed populations. This indicates that both the aquatic and terrestrial habitat of the farmed landscape is sufficient to allow newts to fulfil their natural lifespan. The estimated age of sexual maturity for the majority of individuals was 2-3 years. The median estimated age across all populations was 6.5 years for males and seven years for females. It appears that individuals do not breed as soon as they reach sexual maturity and thus remain in the terrestrial habitat for a much longer period of their lives than previously thought. Males always returned to the pond earlier than females of the same age. In both sexes, individuals aged 8 years and over were on average captured approximately three weeks prior to younger individuals.

Whether population isolation has had any measurable effect on T. cristatus was investigated using a genetic study of 23 populations on 13 sites. There was no evidence of a loss of genetic diversity through isolation. This study supported the conclusion of other research that dispersal distances for T. cristatus can be much greater than reported by capture-mark-recapture (C-M-R) studies. At one of the farmed sites (Moss Shaw Farm), populations just over 1 km apart were assigned similar genetic characteristics, indicating genetic mixing of those populations. This shows that the modern agricultural landscape is still capable of facilitating the dispersal of individuals.

The results of this research demonstrate that the agricultural landscape in the UK can continue to provide a suitable habitat for T. cristatus. Efforts to engage with farmers and landowners to enlist their support for the conservation of this species will therefore be worthwhile.

Citation

Orchard, D. The population structure and demography of Triturus cristatus in agricultural landscapes of North-West England. (Thesis). University of Salford

• Thesis Type: Thesis
• Deposit Date: Feb 19, 2018
• Publicly Available Date: Feb 19, 2018
• Additional Information: Projects : The population structure and demography of Triturus cristatus in agricultural landscapes of North-West England
• Award Date: Sep 1, 2017