1. IntroductionThe susceptibility of an environment to invasion
by new organisms (invasibility; Lonsdale, 1999) has long been
recognised as a major factor influencing the actual establishment
of new species (Davis et al., 2000). Though no general theory
accounts for environmental invasibility, possibly reflecting the
inherent complexity of such a process (Olyarnik et al., 2009),
several hypotheses have been proposed to explain why some
environments are more susceptible to establishment than others
(Davis et al., 2000). This section aims to examine the important of
key biotic and abiotic factors in affecting the invasibility of
environments.
2. What is the environment?Within the context of this report, it
is of importance to outline what constitutes the environment.
Environments are highly heterogeneous in space
3. Assumptions
4. Key factors4.1. Resource availabilityThe availability of
unused resources within an environment is widely accepted to
influence invasibility (Davis et al., 2000). As new organisms
require access to available resources (e.g. light, water and
nutrients), the theory postulates that environments with an
abundance of unused resources will be more susceptible to
establishment than that of one with few available resources. This
is attributed to the fact that community competition intensity is
generally inversely correlated with the amount of unused resources
(Davis et al., 2000).
4.2. DisturbanceDisturbance is often regarded as a key mechanism
that permits an alien species to invade, as it reduces population
density in the native community, potentially allowing the invaders
to establish. copied!Invasion success of exotic in natural
ecosystems: the role of disturbance, plant attributes and freedom
from herbivores Plant traits and temporal scale: evidence from a
5-year invasion experiment using native species
5. ConclusionsThough the aforementioned factors are generally
accepted to simultaneously affect invasibility of environments,
studies considering inter-factor interactions are rare and are
often conflicting and ambiguous (Davis et al., 2000; Olyarnik et
al., 2009)Also, in nature we often just observe species that were
able to persist while introduced species that fail to establish go
mostly unnoticed. Only experiments allow a causal manipulation of
factors, replication and the recording of failed invasions.
However, intentional invasion experiments in the wild are
unethical.
