Environmental Engineering Reference
In-Depth Information
living and nonliving environment, the basis of evolu-
tionary processes such as adaptive differentiation and
speciation. In the case of species richness, we have con-
sidered neutral and functional approaches. Likewise,
genetic diversity can be valued in neutral ways (e.g.
immunity to selection, or non-Darwinian evolution by
random drift of genes that are not expressed in the
phenotype) and by functional approaches (selection
and adaptation, survival of the fi ttest or Darwinian
evolution). In order to be applicable to species reintro-
duction projects pursued as part of ecological restora-
tion (see Chapter 8), it is necessary to identify the
ecological relevance of genetic variation.
A large number of techniques have been developed
to quantify genetic diversity in populations of species.
What is their adaptive value? Most molecular markers
are neutral or nearly neutral to natural selection and
patterns of variation in these markers primarily refl ect
the past gene fl ow and genetic drift. Neutral molecular
variation rarely predicts quantitative genetic variation,
a critical determinant of a population's
evolutionary
potential
(see Chapter 21), and there is no theoretical
basis for assuming that the population with the highest
genetic diversity in molecular markers will be the best
genetic source for restoration (McKay
et al
. 2005 ;
Kramer & Havens 2009). We agree that a combination
of molecular studies of large-scale patterns with eco-
logical studies of
local adaptation
is required to
assess the adaptive value of genetic variation. In view
of application to ecological restoration programmes,
McKay
et al
. (2005) raised the following two key ques-
tions (see also Chapter 7): (1) 'How will existing popu-
lations, adapted to local conditions, be affected by the
introduction of novel genes and genotypes in a geo-
graphic region?' and (2) 'What is the level of genetic
diversity required to ensure the long-term success of
restoration projects?' Note that reinforcement or
reintroduction of a local population only deals with the
problem of introducing genotypes from nonlocal popu-
lations of the same species, which the reader should
clearly distinguish from the introduction of alien
species or even unwanted exotic invaders.
Single populations only seldom live in isolation.
Increasing human impact at the level of landscapes
may have resulted in
habitat fragmentation
and
thus in an increasing risk of isolation of formerly inter-
acting local populations. This has consequences for the
genetic diversity and composition of the local popula-
tions, such as the risk of reduced gene fl ow and inbreed-
ing effects or just the opposite (Young
et al
. 1996 ). As
long as there is migration between two or more local
populations, they can form a
metapopulation
(Hanski 1999). The body of theory and models con-
cerning metapopulations is developing quickly, and
has been applied for example to identify the minimum
number of patches required for population persistence
(e.g. Bascompte
et al
. 2002). In view of the fact that a
metapopulation of any species may interact, in each of
the local patches where it occurs, with members of
metapopulations of other species, the concept of
meta-
community
has been proposed, described as 'a set of
local communities that are linked by dispersal of mul-
tiple potentially interacting species ' (Hanski 1999 ;
Leibold
et al
. 2004). The development of this concept
is still in a theoretical stage and diffi cult to apply to
ecological restoration. We prefer, therefore, to confi ne
the terminology to ' interacting populations ' , either in
biotic communities (within ecosystems) or in meta-
populations (within a landscape).
Something new in science and potentially useful in
restoration ecology is the study of
phylogenetic similar-
ity
(Cavender - Bares
et al
. 2009 ; Gerhold
et al
. 2011 ),
and
phylogenetic signatures
(Verd รบ
et al
. 2009 ) at the
level of biotic communities. Here the mapping and
tracking efforts also include the phylogenesis of taxa,
and would be applied not only to extant but also to
intentionally reintroduced organisms or groups of
organisms, and to the possible interactions to be
expected among them. One issue of note is how and to
what extent 'phylogenetically poor plant communities'
respond to or 'receive' incoming species, and how well
these newcomers co-exist with existing communities
(Gerhold
et al
. 2011 ).
2.6
CHALLENGES
We close this chapter by referring to some of the key
challenges ahead: uncertainty, contingency, chaos and
unpredictability, on the one hand, and then transdisci-
plinary science and problem solving.
2.6.1
Coping with uncertainty
An inspiring essay by Hilderbrand
et al
. (2005) , enti-
tled
The Myths of Restoration Ecology
, points to a
number of simplifi ed and dogmatic 'beliefs' in ecologi-
cal restoration. The goal of the authors clearly was not
to discredit the fi eld but rather to challenge practition-
