Náttúrufræðingurinn - 2023, Síða 18

andarstofna á Mývatni gæti allt eins
átt sér utanaðkomandi orsakir. Voru þá
meðal annars tíndar til landskemmdir
á vetrarstöðvum, of mikið veiðiálag og
breytingar á vatnafari vegna loftslags-
breytinga. Nú, næstum hálfri öld síðar,
er orðið alveg ljóst að kísilgúrnám í Mý-
vatni olli stórkostlegum skemmdum á
vistkerfinu og um leið mikilli fækkun
í stofnum anda og bleikju í vatninu.
Námugreftri var hætt 2004, en set-
myndun í vatninu er það hæg5 að það
getur tekið áratugi og jafnvel aldir fyrir
vistkerfið að ná sér aftur.
ABSTRACT
The ducks of Mývatn
Studies of temporal processes at Lake
Mývatn, Iceland, on three scales, mil-
lennial, centennial and decadal, are
reviewed and a summary is presented
of the main results of waterfowl pop-
ulation monitoring studies conducted
during the period 1975–2005. The char-
acteristics of shallow, subarctic Lake
Mývatn and its volcanic environment,
are outlined, as well as recent conflicts
between development and conserva-
tion. Mining of the bottom sediment
of Lake Mývatn has been a major agent
causing habitat destruction and damage
to the food web. Population limitation
of waterbirds at Mývatn is discussed, as
three research questions and emerging
answers: (1) How is reproductive output
determined? All species studied showed
positive correlations of production of
young with levels of aquatic insects,
catastrophic weather was rarely impor-
tant. (2) How is the dispersion of breed-
ing ducks determined? Densities of mi-
gratory species are determined mainly
by resource levels on the breeding
ground in the year before they return to
the breeding area; a year-round resident
species, Bucephala islandica, adjusts its
density to the current availability of in-
sect food in each of two main habitats
used. (3) How are flyway populations
of ducks determined? For most species,
there is not enough information on to-
tal numbers and the state of the habitat
on a flyway scale. In B. islandica, there
are indications that the total popu-
lation is limited by resources in winter.
The Mývatn study area is dominated
by a single, shallow and eutrophic lake
and for many waterbird species the area
seems to form a single functional unit.
This leads to significant correlations
when comparing demography with en-
vironmental conditions, such as food
resources.
The paper is dedicated to the
pioneering work of Dr. Pétur
M. Jónasson at Mývatn.
Straumönd – Harlequin Duck.
Ljósm./Photo: Daníel Bergmann
Straumönd – Harlequin Duck.
Ljósm./Photo: Daníel Bergmann
Náttúrufræðingurinn Ritrýnd grein / Peer reviewed