Biology and anthropology of plant invasions - Invasive Plants: Ecological and Agricultural Aspects - page 208

jecture is that species succeeding in occupying a locality must be perceived by
humans as being problematic. Without the occurrence of all three processes, a
plant species is not labeled invasive.
If this is a valid conjecture, then a broad perspective is required of everyone
involved in the dialogue of invasive species. Those interested and involved in
invasion biology are a very diverse range of humans, including citizens, bio-
logical and social scientists, and those with governmental, environmental or
public policy roles. The terminology used by those interested in invasion biol-
ogy is often defined somewhat differently by these respective groups (see
Chapter 1). As such, to avoid confusion herein essential terminology is defined
to ensure clarity in the presentation of this conjecture. Where differences may
occur, alternative forms of those definitions are provided.
The biology of plant invasion
A successful plant invasion may result from the presence of a particular spe-
cies possessing life history traits suitable to exploit an opportunity space in a
particular locality. The presence of that species may be dependent on its abil-
ity to disperse into the locality, or disturbance at that locality creating oppor-
tunity, or both.
Local opportunity: space and time
Plants will fill any available and habitable growing space; therefore the primary
resource limiting plant growth is habitable space. Available and habitable space
to an invading plant is opportunity space at a particular time. Opportunity space
for plant invasion is a consequence of disturbance, a change in local conditions,
and the first selection pressure on invasive populations.
Disturbance
Competitive exclusion by extant individuals within a plant community puts
invading species at a disadvantage in establishment. The reasons invasions occur
when confronted with existing plant communities is based on an appreciation of
the role disturbance plays in creating space for new individuals to grow in.
Disturbance is defined as i) the act of disturbing or the state of being dis-
turbed [2, 3], ii) an interruption or intrusion [2, 3], or iii) destruction of biomass
by any natural or human agency [4]. Disturbance herein is defined as interrup-
tion or intrusion with direct and indirect spatial, temporal, biological, or abio-
logical effects that alters or destroys a biological individual or community.
Dimensionality of disturbance
Disturbance is more than the direct cause of damage or mortality to a plant. It
also includes the indirect effects of the abiotic environment, and the biological