Biology Reference
In-Depth Information
specific , evaluation of biological characters , evaluation of habitat compatibility , and
experimentation .
The stochastic approach focuses on initial plant population size and number and
timing of introductions as factors that increase the probability of invasion success.
For example, a significant correlation can usually be demonstrated between the
total number of known localities of an invasive plant species and the years since the
first observation of the species was recorded (Rejmánek 2000). An e mpirical-taxon
specific management approach is based on information about the invasiveness of a
species elsewhere. Knowing the experiences of others helps land managers make
decisions about control and/or eradication of invasive plants. Williams et al. (2000)
indicate that 80% of the exotic weed species in New Zealand are also described as
invasive outside that country. These two approaches form the basis for a commonly
used management tactic of many land management agencies in the USA, i.e., early
detection and rapid response (EDRR). The shortcoming of the approaches, how-
ever, is that they tell little about the real impact of the species or the environmental
and biological factors necessary to manage them (Mashadi and Radosevich 2003).
Rappoort (1991) e valuated the biological characters of invasive plants and
reported that 10% of the estimated 260,000 vascular plant species on earth are poten-
tial invaders. Only 15% of these potential invaders have actually invaded an area
outside their native range. The traits that make some plants more invasive than others
have been extensively studied since Baker (1965) conceived the concept of an “ideal
weed.” Statistical tools such as discriminate analysis, multiple logistic regression,
and classification and regression trees can be used to assess biological characters
responsible for invasiveness (Endress et al. 2007). However, adaptive change
induced by selection plays a central role in plant speciation and in molding traits of
weeds and invasive plants. During biological invasions, significant genetic change
can occur in species that are no longer limited by their native environment (Gray
et al. 1986). It is unlikely, therefore, that studies of the shared attributes of successful
weeds or invasive plants will provide the adequate information to assess biological
characters responsible for invasiveness. Studies also should focus on information
regarding the genetic changes that plants undergo during colonization and the factors
controlling these evolutionary changes. Adaptability of a species may be more
important than its tolerance or plasticity to environmental change. There are many
examples of differentiation among plant populations that occur across short spatial
distances and over relatively short time periods. The importance of evolutionary
adaptation is well known for both agricultural weeds (Dekker 2003) and invasive
plants (Ellstrand and Schierenbeck 2000), making a strong case for natural and
human-induced selection (Radosevich et al. 2007). Unfortunately, few studies evalu-
ate invasiveness by combining the stochastic approach with particular traits that
control the adaptability of a species, i.e., successive introductions and the probability
of generating adaptive variability through hybridization (Gray et al. 1986).
The fourth approach indicated by Rejmánek (2000) for management of invasive
plants is the e valuation of habitat compatibility (invasibility) to determine whether
a particular species can invade a particular habitat type. This approach assumes that
climate is the overriding factor that determines the suitability of a site for an inva-
sive species (Woodward 1987; Panetta and Mitchell 1991; Mack 1996). Several
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