Environmental Engineering Reference
In-Depth Information
6
Populations: intraspecific
interactions
Jelte van Andel
6.1 Introduction: island biogeography
and metapopulations
population is relatively large, as is often the case with
mainland populations.
A metapopulation in the strict sense is an assemblage
of local populations that are connected by mutually
dispersing individuals (see Levins 1969, Hanski &
Gilpin 1991). The concept was elaborated with mobile
animals in mind. For sessile plants, seeds and pollen
are the major dispersal units (Kwak
et al
. 1998).
Hanski (1997) outlined four conditions needed for a
regional population to persist as a metapopulation:
Population dynamics deals with numbers of indi-
viduals and genotype frequencies in different stages
of the life cycle of the local representatives of a species.
An introduction to population processes in a textbook
on restoration ecology, recognizing the often frag-
mented structure of habitat or biotope, cannot but
explicitly place them in the context of processes at
the level of landscapes. This implies a focus on the
dynamics of spatially structured (meta)populations in
a network of habitat patches. The island biogeo-
graphy (MacArthur & Wilson 1967), though developed
to explain species richness and interactions between
species at the community level, also includes such
single-species population aspects as migration, colon-
ization and extinction. The metapopulation model
of Levins (1969) can be characterized as a single-
species version of the island model of MacArthur and
Wilson (1967). According to Hanski and Simberloff
(1997), the main difference between the metapopula-
tion approach and island biogeography is that in the
latter case there is a permanent source population
on the 'mainland', whereas habitat patches of meta-
populations can mutually be temporary sources and
sinks. As soon as patches of varying size and quality
are included in a metapopulation study, the difference
with the island biogeographical approach becomes even
smaller. Migration from one population to another does
reduce the number of individuals in the donor popu-
lation, but this effect becomes negligible if the donor
1
suitable habitat occurs in discrete patches which may
be occupied by local breeding populations;
2
even the largest local populations have a substan-
tial risk of extinction;
3
habitat patches must not be too isolated to prevent
recolonization following local extinctions;
4
local populations do not have completely syn-
chronous dynamics.
Later on, the concept of source/sink populations
was incorporated (Pulliam 1988, Eriksson 1996), in
which ensembles of individuals in sink habitats are
maintained by continuous immigration from source
habitats, but the latter is actually an important aspect
of MacArthur and Wilson's (1967) theory of island
biogeography. Eriksson (1996) discussed concepts of
regional-scale dynamics in plants and added a third
type, termed 'remnant population dynamics', in local
populations that survive long enough to bridge
periods of unfavourable successional development,
including survival in a long-lived seed bank (Figs 6.1
70
