Biology and anthropology of plant invasions - Invasive Plants: Ecological and Agricultural Aspects - page 214

phenotypes dominate their neighbors because the timing of their life history
optimizes their relative fitness and minimizes mortality. The character of these
opportunity spaces can be deduced by observing the new phenotypes adapted to
these new spaces, and what traits they possess allowing such ready invasion.

The plant invasion process

Given a plant species with certain life history traits and a vulnerable local
opportunity space, the invasion process consists of three component process-
es: dispersal of the species into that locality, followed by colonization and
enduring occupation of the habitat (Tab. 4). The invasion is successful only
when all these are accomplished. Most invading species probably fail to com-
plete all three steps, and there is little experimental information estimating the
failure rate.
Plant invasions are events in the ecology of community assembly and suc-
cession, as well as in the evolution of niche differentiation by speciation. There
is not a meaningful difference between the invasion process and these process-
es except the scale of attention humans bring to their observations. In all these
processes disturbance is a prime motivator of change. The scale of habitats in
time and space is continuous; and all communities are inter-related.

Dispersal
The first activity in invasion is successfully introducing propagules (seeds,
vegetative buds, etc.) into a candidate opportunity space. Dispersal is previ-

Table 4. The invasion matrix: the processes (invasion, colonization, enduring occupation), life histo-
ry activities (dispersal, recruitment, establishment including reproduction, and several modes of
enduring occupation) and examples

Invasion process Life history activity Example

Invasion Dispersal propagule (e.g., seed, vegetative

bud, spore, pollen) movement from
one continent (or locality) to
another and fails to reproduce

Colonization All events must occur: volunteer maize ( Zea mays L.)

a] recruitment lives for only one generation

b] establishment (F 2 ) in a field, failing to

c] reproduction colonize due to lack of dormancy

Enduring occupation Several modes possible: successful, long-term,

a] enduring presence for more agricultural weeds; e.g., North

than one generation America: Amarathus spp-gp.;

b] range expansion Setaria spp-gp

c] formation of soil propagule
(e.g., seed) pool