Náttúrufræðingurinn - 2023, Side 57

birds, geese, and waders. A general de-
cline in seabird populations has driven
the recent decline in Arctic foxes (2008-
2012), especially in coastal habitats. In
inland areas, an increase in ptarmigans
and other terrestrial resources, such
as geese and waders, was observed in
the diet during the most recent period
(2008-2015), where fluctuations in the
Arctic population and shift in diet was
observed. The diet of the Icelandic
Arctic fox population has therefore
mainly been determined by functional
responses to intra- and interannual var-
iation in food resources, by feeding on
whatever prey is found in most abun-
dance and accessible at a given time
and space. Despite the importance of
the ptarmigan, which is known to show
regular cycles, the foxes in Iceland do
not seem to fluctuate regularly. In con-
trast to what is known for the species in
other countries, the fertility of Icelan-
dic Arctic fox vixens has been stable, at
least during the past 60 years, according
to litter size from harvest data (1958-
2021: 4,4 +/- 1,65 cubs) and placental
scar counting (1986-2021: 5,4 +/- 1,63
scars). The stability in the fertility of
Icelandic Arctic foxes calls for other ex-
planations for the population dynamics
than in lemming areas. Indeed, it has
turned out that the Icelandic Arctic fox
has responded to variation in carrying
capacity, through changes in prey popu-
lations, with plasticity in number of lit-
ters but not litter size. This is reflected
in proportion of mature individuals in
the population that take part in breed-
ing each year. The most important con-
tribution is by one year old foxes which
were the largest proportion of breeding
individuals during the steepest increase
phase of the population. Therefore,
fluctuations seen in the population in
the period 2007-2018 can be explained
by the variety in the contribution of
each age group (especially the young
ones) in the breeding part of the pop-
ulation each year, which, in each year/
period is determined by the carrying
capacity in each region (i.e. number
and quality of breeding territories). On
a larger spatial and temporal scale ca-
pacity is determined by food availability
through population dynamics and state
of various potential prey species.
Höfundur þakkar veiðimönnum um allt land sem
sent hafa refahræ til athugunar, og Umhverfis-
stofnun fyrir upplýsingar úr veiðigögnum. Fjöl-
skylda Páls Hersteinssonar veitti aðgang að dýr-
mætum gögnum og er þakkað, einnig ljósmyndurum
sem gáfu leyfi til að nota myndir sínar í greinina. Að
lokum ber að þakka ritstjórn, yfirlesurum (sérstak-
lega Sigurði S. Snorrasyni) og ritstjóra fyrir þeirra
framlag og góðar ábendingar við greinaskrifin.
ÞAKKIR
Ester Rut Unnsteinsdóttir (f. 1968) lauk
BSc-prófi í líffræði við Háskóla Íslands 1999
og kennsluréttindum í náttúrufræðum frá
Kennaraháskóla Íslands árið 2005. Árið 2014
lauk hún doktorsnámi í líffræði við Háskóla
Íslands undir leiðsögn Páls Hersteinssonar
prófessors og var viðfangsefnið stofnvistfræði
hagamúsa. Ester sinnti kennslu í náttúrufræðum
á grunnskólastigi árin 1999–2002 og var stundakennari við Líf- og
umhverfisvísindasvið HÍ á tímabilinu 2002–2013. Árið 2007 stofn-
aði hún Melrakkasetur Íslands í Súðavík, sem opnað var almenn-
ingi árið 2010, og starfaði hún þar til ársins 2013 þegar hún hóf
störf á Náttúrufræðistofnun Íslands. Ester hefur fylgst með refum
á Hornströndum frá árinu 1998 og borið ábyrgð á vöktun íslenska
refastofnsins frá árinu 2012.
UM HÖFUNDINN
Ester Rut Unnsteinsdóttir
Náttúrufræðistofnun Íslands
Urriðaholtsstræti 6–8
210 Garðabæ
Ester.R.Unnsteinsdottir@ni.is
1. Angerbjörn, A., Tannerfeldt, M. & Erlinge, S. 1999.
Predator-prey relationships: Arctic foxes and
lemmings. Journal of Animal Ecology 68(1). 34−49.
2. Gilg, O., Sittler, B., Sabard, B., Hurstel, A., Sané,
R., Delattre, P. & Hanski, I. 2006. Functional and
numerical responses of four lemming predators
in high arctic Greenland. Oikos 113(2). 193–216.
3. Elmhagen, B., Tannerfeldt, M., Verucci P. &
Angerbjörn, A. 2000. The Arctic fox (Alopex
lagopus): An opportunistic specialist. Journal
of Zoology 251(2). 139–149.
4. Angerbjörn A., Páll Hersteinsson & Tannerfeldt,
M. 2004. Arctic foxes: Consequences of resource
predictability in the Arctic fox – two life history
strategies. Bls. 163−172 í: Biology and conservation
of wild canids (ritstj. D.W. Macdonald & C. Sillero-
Zubiri). Oxford University Press, Oxford.
5. Berteaux, D., Thierry, A.-M., Alisauskas, R., An-
gerbjörn, A., Buchel, E., Doronina, L. … Ester Rut
Unnsteinsdóttir & White, P.A. 2017 Harmonizing
circumpolar monitoring of Arctic fox: Benefits,
opportunities, challenges and recommendations.
Polar Research 36. 1−13.
6. Tannerfeldt, M. & Angerbjörn A. 1996. Life
history strategies in a fluctuating environment:
Establishment and reproductive success in the
Arctic fox. Ecography 19(3). 209–220.
7. Barraquand, F. & Ólafur K. Nielsen. 2018.
Predator-prey feedback in a gyrfalcon-ptarmigan
system? Ecology and Evolution 8(24). 12425–
12434. https://doi.org/10.1002/ece3.4563
8. Ester R. Unnsteinsdóttir, Páll Hersteinsson, Snæ-
björn Pálsson & Angerbjörn, A. 2016. The fall and
rise of the Icelandic Arctic fox (Vulpes lagopus): A
50-year demographic study on a noncyclic Arctic
fox population. Oecologia 181. 1129–1138.
HEIMILDIR
57
Ritrýnd grein / Peer reviewed