Estimating population parameters in a threatened arctic fox population using molecular tracking and traditional field methods

Abstract

Comprehensive population parameter data are useful for assessing effective conservation actions. The Fennoscandian arctic fox Alopex lagopus is critically endangered and the population size is estimated at 120 individuals that are fragmented into four isolated populations. Here, we use molecular tracking and visual observations to estimate population size and survival in one of the populations on the Swedish mountain tundra during a year of low food availability. We collected 98 arctic fox faecal samples during the winter of 2006 and recorded visual observations of ear-tagged individuals during the summer of 2005 and 2006. The faecal samples were analysed for variation in nine microsatellite loci and matched to the genetic profiles of previously ear-tagged individuals from 2001 to 2005. During winter 2006, the minimum number alive was 12 individuals using visual observations, 30 using molecular tracking and 36 by combining the datasets.Population size was estimated through mark-recapture for the molecular tracking and visual observation datasets and through rarefaction analyses for molecular tracking data. The mark-recapture estimate for visual observations was uninformative due to the large confidence interval (CI) (i.e. 6-212 individuals). Based on the molecular tracking dataset combined with the minimum number alive for visual observations and molecular tracking, we concluded a consensus population size of 36-55 individuals. We also estimated the age-specific finite survival rate during 1 year (July 2005 to July 2006) by combining molecular tracking with visual observations. Juvenile survival on a yearly basis was 0.08 (95% CI 0.02-0.18) while adults had a survival of 0.59 (95% CI 0.39-0.82). Juveniles displayed a lower survival than the adults during autumn (Po0.01) whereas no age-specific survival difference during spring was found. The risk of negative effects due to the small population size and low juvenile survival is accordingly considerable.

Estimating demographic parameters for capture–recapture data in the presence of multiple mark types

“…The interpretation of the mark-loss probabilities and/or recapture efficiency rates will generally be of interest in any study where different marks can be applied to different animals. There are a number of studies of this kind, for example involving both tagging and DNA-based methods (Meijer et al 2008), and marking methodology may have animal welfare or conservation implications in some cases (McCarthy and Parris 2004).…”

Evolution, ecology and conservation—revisiting three decades of Arctic fox population genetic research

“…Dalén, Götherström et al (2004) demonstrated how mitochondrial analysis of faecal samples can be used to distinguish between Arctic and red (Vulpes vulpes) foxes as well as wolverines (Gulo gulo), and subsequently Dalén, Elmhagen et al (2004) used this method to show that while red and Arctic foxes are sympatric in winter, Arctic foxes retreat to higher altitudes in summer, which most likely is due to the increased risk of red fox predation on Arctic fox cubs at lower altitudes. This method was later developed by Meijer et al (2008), who used microsatellite genotyping of faecal samples to estimate population size and survival in the southernmost Swedish subpopulation. In total, 98 Arctic fox faecal samples were genotyped at nine microsatellite loci.…”

“…Molecular tracking can also be used to estimate other population parameters (Schwartz et al 2007). Meijer et al (2008) estimated the age-specific finite survival rate during one year (summer to summer) by combining molecular tracking with visual observations and matching the faecal genotypes to genotypes of known origin (collected as tissue samples during ear-tagging). Juveniles displayed a lower survival than the adults during autumn, whereas there was no evidence for age-specific survival difference during spring.…”

The impact of maternal experience on post-weaning survival in an endangered arctic fox population

“…The study was conducted on the sub-arctic tundra in Helagsfjällen (62.53 N 12.40 E), Jämtland county, Sweden (see Meijer et al 2008). Since 2001, approximately 75% of all born cubs have been ear-tagged (Dalton Rototags) with unique colour combination which allows individual identification.…”