Biology Reference
In-Depth Information
A major open question is how these impacts may unfold in the long-term (Strayer
et al. 2006). Impacts can lead to positive feedbacks among invasive species that
lead to a deterioration of reference habitat values (invasional meltdown,
Simberloff and Von Holle 1999). Synergistic interactions with other global
change drivers such as climate change or habitat fragmentation (Didham et al.
2007) may increase the impact of species with novel traits. But it may also be that
the impact of the alien species decreases with time (Morrison 2002). In particular,
the native biota may be able to adapt relatively quickly to novel traits (cf. Dietz
and Edwards 2006), for instance thanks to phenotypic plasticity (Peacor et al.
2006). Or some advantage of the invader may diminish, for instance because it
accumulates pests.
An important aspect for evaluating impacts of alien species in reference habitat
is that the management objective is to conserve specific natural processes, commu-
nities, and rare species that characterize the reference habitat. Such rare, endemic
species or biotic interactions may be most sensitive to impacts of invasion, and
therefore even invasive species that generally only weakly impact native biota may
be of major concern. For instance, Krushelnycky (2007) concluded that “[arthro-
pod] communities that had already lost many endemic species […] were relatively
resistant to further species loss upon [invasive] ant arrival, whereas more intact
communities were vulnerable to substantial declines in richness when ants
invaded.”
Initially small impacts may be more difficult to detect and understand, especially
when considering the feasibility of conducting regular surveys in reference habitat.
Hidden but potentially very important impacts in reference habitats could include
hybridization of alien plants with rare native species (Mooney and Cleland 2001),
an increase of disease incidence in native plants promoted by the presence of an
alien host plant (Malmstrom et al. 2005), or disruption of belowground mutualisms
(Stinson et al. 2006).
5.4.4 Management Action
Where feasible, eradication of small infestations of new alien species should be a
priority in consideration of the precautionary principle. However, for most natural
areas, it will not be possible to regularly search for new introductions of alien spe-
cies. Besides, financial constraints, knowledge about the taxonomy, distribution
and impacts of all but the most disruptive invasive species is usually limited. Rather
than comprehensive invasive species monitoring, rare species and ecosystem health
monitoring programs could be used to indicate invasive species problems that
require management. It may also be promising to develop composite indicators that
track trends in a suite of alien species with similar life histories (Hulme 2006), and
then relate this to indicators of ecosystem health, identify interactions with other
global change drivers, and determine possible management actions. There is a high
potential that control action in reference habitat will have negative impacts on other
