[1] | A matrix model of an endangered population of the arctic fox from mednyi island / A. M. Brilliantova, L. V. Polishchuk, E. V. Bragina et al. // Принципы экологии (Principy èkologii). — 2016. — Vol. 5, no. 3. — P. 32–32. Mednyi Island (Commander Islands, Pacific Ocean) houses an island subspecies of the Arctic fox (Vulpes lagopus semenovi). This unique population occupies the most southern part of the species’ range and has been isolated from other populations for tens of thousands years. It is included in the Red Book of the Russian Federation as an endangered subspecies. Conservation of the population requires a thorough assessment of its vital rates. Up until the 1970s, the population number was maintained at up to 1000 animals, but an epizootic of ear mange that occurred among juveniles from 1976 to the mid-1980s, wiped out most of the population (Goltsman et al., 1996). Now the population number is about 150 adults only. A long-term population study has covered the southern part of the island where 60–90 marked Arctic foxes have regularly been found (Goltsman, Kruchenkova, 2001; Goltsman et al., 2005). A demographic mechanism underlying population stability observed in the last 20 years is unclear. To reveal it, the one needs to estimate age-specific vital rates and then find out which of them affect the growth rate of our population most strongly. The idea behind this approach is that even small changes in those critical vital rates can destabilize the population and thus potentially lead to extinction. To this end, we build up a female-based Leslie-type population matrix model (Leslie, 1945). Each non-zero element of this matrix is either age-specific survival or fecundity. Age-specific survival is the probability of a female of a given age to survive to the next age class; age-specific fecundity is the average number of female offspring born to a mother of a certain age, accounted for non-breeding females. We analyzed individual life histories of 220 females born in 1997–2010 and marked as juveniles. The study area covers about 26,2 km2 in the southern part of Mednyi Island. We used a mark-recapture framework and registered marked animals every year to assess survival rates. We also conducted multi-day observations of dens to determine the number of juveniles. We excluded families with >1 lactating females as it was not clear how many offspring each female had. We allocated all the animals to 7 age classes: juveniles, yearlings, two- to six-year-old adults. We omitted very few females older than 6 years old. To date, we have obtained preliminary survival and fecundity rates which are, respectively: juveniles – 0,393 and 0 (n = 220); yearlings – 0,865 and 0,070 (n = 86); two-year-olds – 0,757 and 1,074 (n = 64); three-year-olds – 0,659 and 1,259 (n = 40); four-year-olds – 0,611 and 1,364 (n = 26); five-year-olds – 0,4 and 0,225 (n = 17); six-year-olds – 0,5 and 1,436 (n = 6). Population growth rate based on these vital statistics is λ = 1,002, which corresponds very well with count data according to which the population is stable. In the future, we are going to refine the above vital rate estimates and conduct sensitivity analysis of the population growth rate. Sensitivity analysis is a tool to find out which vital rates most severely affect the population growth rate. This knowledge will help prevent extinction of the unique Mednyi Island population of the Arctic fox. |