Environmental Engineering Reference
In-Depth Information
Pre-eradication studies provide useful insights into potential ecosystem responses
to invasive species removal, thus helping managers to reliably avert or plan for the
undesired side effects of eradication (Blossey 1999; Zavaleta 2002). Such studies
should at the very least incorporate both surveys of the species present in the eco-
system, and diet studies in order to obtain an understanding of the interactions and
trophic web links that exist between the species present and an estimation of pos-
sible outcomes of the eradication of the target species (Fig. 15.4). For instance in the
case of a possible herbivore removal programme, food-preference trials can be used
to accurately predicted changes in the plant community (Donlan
et al
.
2002),
All such studies should remain simple, standardized, and easily replicable so that
they can be repeated during and after the programme, on other islands, or by new
researchers/staff in the future. Methods should also be properly recorded in order
to help both replication and future analyses.
Erecting fenced exclosure plots prior to the removal of an herbivore from an ecosys-
tem will provide an indication of how the vegetation may respond post-eradication
(Cabin
et al
. 2000; Donlan
et al
. 2002; Zavaleta 2002).
Alien species
Native species
Alien species
Predators
Prey
Plants
Fig. 15.4
In a simple, three-level, nine-species ecosystem, the presence of more
than one alien species can mean alien removal will trigger other alien species
releases. Here, species are represented by a square if they are native and by
ellipse if they are alien. The grey lines are some of the energy fl ows among them.
The cross represents an eradication. Species which undergo a sudden population
increase (resp. decrease) are surrounded by arrows going outwards (resp.,
inward). Real ecosystems will contain far more species, with less straightforward
outcomes. Depending on which species is removed, different outcomes are
possible, but for many confi gurations most outcomes are globally negative,
with an increase of one or several alien species. The confi guration displayed
here illustrates how the eradication of an alien species to protect a local (prey)
species can in fact have the opposite effect.
