187
The Glanville fritillary butterfly
metapopulation, in its fragmented
habitats on Finland’s Åland Islands,
provided the ideal subject for Ilkka
Hanski’s studies into species patches.See also: Animal ecology 106–113 ■ Clutch control 114–115
■ Island biogeography 144–149 ■ Metacommunities 190 –193ORGANISMS IN A CHANGING ENVIRONMENT
contact between the various local
groups is limited, and they remain
partly cut off in their own local
habitat or “patch.” Yet there has to
be at least some interaction. It may
be just a single brave or outcast
member of one group that enters
another patch and mates with the
local population there. Isolation for
too long pushes local populations
apart to the point where they can
no longer mate with one another,
and in time they become separate
species or subspecies.
In the 1990s, Finnish ecologist
Ilkka Hanski showed that at the
core of metapopulation theory is the
notion that local populations are
unstable. The metapopulation as
a whole may well be stable, but the
local populations are likely to rise
and fall in their individual patches
in response to inside and outside
influences. Some patch members
may emigrate and join a much
reduced population in danger
of extinction, giving it renewed
strength—a metapopulation feature
known as the “rescue effect.” Other
groups may completely vanish,leaving vacant patches for another
population to recolonize. Hansk
argued that there is persistent
balance between “deaths” (local
extinctions) and “births” (the
establishment of new populations
at unoccupied sites). He likened
this balance to the spread of
disease, with the susceptible and
the infected representing in turn
empty and occupied “patches”
for disease-carrying parasites.
Ecologists see the concept of
metapopulations as increasingly
important in understanding how
species will survive, particularly
in the face of human influence on
habitats. The theory helps them
analyze the way populations rise
and fall, using mathematical models
to play out interactions, and enables
them to predict how much habitat
fragmentation a species can endure
before it is driven to extinction. ■Ilkka Hanski
Widely seen as the father of
metapopulation theory, Ilkka
Hanski was born in Lempäälä,
Finland, in 1953. As a child, he
collected butterflies, and after
finding a rare species, he
devoted his life to ecology,
studying at the universities
of Helsinki and Oxford.
Ecologists at the time
paid little attention to the
distribution of local species
populations, but Hanski
realized this was crucial,
and spent much of his career
testing his metapopulation
theory by mapping out and
recording more than 4,000
habitat patches for the
Glanville fritillary butterfly
on the Åland Islands. This
work earned Hanski global
fame, and enabled him to
establish the Metapopulation
Research Centre in Helsinki,
which became one the world’s
leading focuses of ecological
research. Hanski died of
cancer in May 2016.Key works1991 Metapopulation
Dynamics
1999 Metapopulation Ecology
2016 Messages from IslandsUS_186-187_Meta_populations.indd 187 12/11/18 6:25 PM