Conservation of an endangered amphibian

: The case of the Natterjack toad (Epidalea calamita) in Ireland

Abstract

Amphibians have been declining globally since at least the 1970s and are the most endangered class of vertebrates with over 40% of species threatened with extinction. The Natterjack toad (Epidalea calamita) is the rarest amphibian in Ireland, regionally Red-listed as Endangered. The species is subject to substantial Government conservation efforts, including regular monitoring and surveillance, a Pond Creation Scheme and an ongoing Head-start and Translocation Programme to facilitate new pond colonisation.

This thesis aimed to update the Natterjack toad’s conservation status in Ireland, establish temporal trends assessing threats and pressures, describe its genetic integrity and population structure and evaluate the efficacy of conservation measures. The new information generated spans habitat selection, spatial ecology, population biology, metapopulation dynamics, genetic diversity, biogeography and effects of climate change.

Natterjack toad annual egg string counts suggested a -23% decline in the number of egg strings between 2004 and 2018 with local extirpation at one site. Assessment of perceived threats and pressures suggests that declines are likely driven by poor habitat quality. Conservation programmes failed to significantly arrest decreases in the number of egg strings offsetting further declines by only 4%. Nevertheless, the conservation value of artificially created ponds should not be underestimated as they had 43% higher aquatic macroinvertebrate species richness and 33% higher macroinvertebrate abundance than natural ponds. Mark-recapture using photo ID and genetic fingerprinting suggested that extrapolation of total population estimates from egg strings alone may underestimate the census size by up to 83% due to substantial sex ratio deviation from 1:1 with up to 7 males per female at breeding ponds. Genetic studies indicated high genetic diversity with no evidence of genetic bottlenecks or inbreeding depression despite considerable declines in the number of egg strings. The Natterjack toad population in Ireland displayed significant genetic spatial structuring, best explained by barriers to dispersal and gene flow inhibited by coniferous forestry plantations, bog, marsh, moor and heath, scrub, anthropogenic presence and rivers, and facilitated by sand dunes and coastal grasslands. Suitable bioclimatic-habitat niche space for the species is likely to expand northward and to higher elevations under projected global climate change with models predicting increase in the number of egg strings and earlier spawning by the end of the 21 century. However, limited dispersal capability and ongoing threats and pressures mean potential benefits of climatic change are unlikely to be realised.

Continued population monitoring and surveillance is recommended while it is suggested that future research should include: estimation of sex ratio variation between metapopulations, use of acoustic monitoring to assess the male population at breeding sites, use of environmental or eDNA in assessing species presence including colonisation of new ponds and calibration of water DNA densities using population abundance derived from egg strings, a greater focus on disease and pathogens, and investigation of terrestrial habitat use and hibernacula availability.

Species conservation strategies should focus on working with landowners and farmers to improve habitat quality, water quality and the availability of breeding ponds to maximise connectivity between breeding sites facilitating dispersal. Recommendations are made to conservation practitioners with respect to genetic structuring and identified genetic entities.

A major challenge lies in breaching the boundaries between academic research, Government and conservation management decision making and practical on-the-ground conservation action by various stakeholders (principally landowners and farmers) to make conservation programmes more effective and efficient.

Date of Award	Jul 2021
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	National Parks & Wildlife Service
Supervisor	Neil Reid (Supervisor), Sarah Helyar (Supervisor) & Mark Emmerson (Supervisor)