Environmental Engineering Reference
In-Depth Information
21.5.1 Relationships between genetic
and species diversity
attains a particular community or genetic composi-
tion, but one that has the capacity to change in order
to maintain core
ecosystem functions
and
services
over time (Choi
et al
. 2008 ).
Even if communities targeted for restoration are ini-
tially diverse, the processes that maintain diversity also
need to be considered in order keep diversity levels high
over time. Maintenance of high diversity assemblages
requires stabilizing processes - those that lead towards
coexistence among species through niche differentia-
tion (MacDougall
et al
. 2009). Succession often homo-
genizes, rather than diversifi es, over time (Kuiters
et al
.
2009), posing another type of challenge for restora-
tion; in many systems disturbances need to be incorpo-
rated to maintain diversity, yet some of the species that
arrive after a disturbance are undesirable.
The interplay between genetic and species diversity is
just beginning to be explored. Initial studies are fi nding
more complex interactions than anticipated. For
instance, adaptive change, potentially facilitated by
high genetic diversity, could allow species to maintain
their abundance and avoid extinction under changing
conditions, thus maintaining species diversity (Scoble
& Lowe 2010). On the other hand, de Mazancourt
et al
. (2008) used a modelling approach and found that
species diversity increased the chance that some species
were pre-adapted to new conditions, which restricted
the ecological opportunity for evolutionary responses
in all species. Consistent with these results, the work of
Silvertown
et al
. (2009) regarding the 150 - year
Park
Grass Experiment
in England revealed contradictory
changes in species and genetic diversity in response to
nutrient addition: genetic diversity of a population of
Anthoxanthum odoratum
increased, while species diver-
sity decreased, with the number of resources added to
a plot. Thus, it appears that in some cases species living
in species-rich communities are less likely to be able to
evolve in response to environmental change than
species living in species-poor communities because
competition among species may constrain genetic
diversity of any one species.
21.6
PERSPECTIVES
In this period of unprecedented environmental change,
it will be critical to apply understanding of evolution-
ary and community dynamics in order to anticipate
and incorporate future - and largely uncertain -
change in restoration projects. To use an analogy from
Through the Looking Glass
(Carroll 1871, 135; which
also forms the basis of evolutionary Red Queen Hypoth-
esis, proposed by van Valen 1973), intervention may be
needed simply to remain in the same spot along a de-
gradation trajectory in this era of change: 'Now, here,
you see, it takes all the running you can do, to keep in
the same place. If you want to get somewhere else, you
must run at least twice as fast as that!' To deviate a bit
from the analogy, it may also be necessary to change
the nature of the intervention to incorporate expected
changes and consider the increased need to maintain
ecosystem integrity
over a large potential range of
variability; resetting the ecological - and evolutionary
- clock to a historic range of variation may often not
be feasible or sustainable (Hobbs & Cramer 2008).
In this chapter, we have focused on how to run with,
rather than reset, the rapidly ticking ecological clock,
emphasizing two perspectives. First, we may need to
acknowledge that even maintenance of a less-than-
desired system may require intervention just 'to keep
in the same place.' Second, the very nature of the inter-
vention employed in restoration may need to be
changed to refl ect the need to maintain system integ-
rity over a large potential range of variability that does
not necessarily match historic reference conditions.
21.5.2
Role of functional diversity
Evidence is accumulating that high functional response
diversity might be critical to
sustainable
restoration
(Elmqvist
et al
. 2003). The goal of high response diver-
sity would be to have assemblages that contain species
or genotypes that have a diversity of responses to
change. For example, Steiner
et al
. (2006) found that
diversity of functional groups increased community
resilience
in experimental aquatic food webs because
more diverse communities had a greater likelihood of
containing a particularly resilient species. Restoration
projects can increase response diversity by expanding
species mixes to include many seemingly 'redundant'
species from a wider range of environments, increas-
ing emphasis on genetic diversity in addition to local
adaptation, and considering assisted species migration
and reintroduction of species lost from the regional
species pool
. This consideration also implies that a
successful restoration is not necessarily the one that
