Species traits as predictors for setting biosecurity priorities

A number of species have invaded widely separated places on the planet (e.g. the shrub Lantana camara (Figure 7.8), the starling Sturnus vulgaris and the rat Rattus rattus) prompting the question of whether successful invaders share traits that raise the odds of successful invasion (Mack et al., 2000). Were it possible to produce a list of traits associated with invasion success, managers would be in a good position to assess the risks of establishment, and thus to prioritize potential invaders and devise appropriate biosecurity

... to set priorities for dealing with invasive species...

Table 7.3 Ecological traits of forbs that showed a significant relationship with plant performance in years 1-4 after sowing in grassland restoration experiments. The sign shows whether the relationship was positive or negative. (After Pywell et al., 2003.)

Trait

n

Year 1

Year 2

Year 3

Year 4

Ruderality (colonization ability)

39

+ *

NS

NS

NS

Fall germination

42

+ *

NS

NS

NS

Germination (%)

43

+ **

+*

+*

NS

Seedling growth rate

21

NS

+*

+ **

+*

Competitive ability

39

+*

+ **

+ ***

+ ***

Vegetative growth

36

+ **

+*

+*

+*

Seed bank longevity

44

+*

+*

+*

+*

Stress tolerance

39

_ **

_ **

_ ***

_ ***

Generalist habitat

45

+ **

+ **

+ **

+ **

*, P< 0.05; **, P< 0.01; ***, P< 0.001; n, number of species in analysis; NS, not significant.

*, P< 0.05; **, P< 0.01; ***, P< 0.001; n, number of species in analysis; NS, not significant.

Figure 7.8 The shrub Lantana camara, an example of a very successful invader, was deliberately transported from its native range (shaded area) to widely dispersed subtropical and tropical locations where it spread and increased to pest proportions. (After Cronk & Fuller, 1995.)

procedures (Wittenberg & Cock, 2001). The success of some invasive taxa has an element of predictability. Of 100 or so introduced pine species in the USA, for example, the handful that have successfully encroached into native habitats are characterized by small seeds, a short interval between successive large seed crops and a short juvenile period (Rejmanek & Richardson, 1996). In New Zealand there is a similarly precise record of successes and failures of attempted bird introductions. Sol and Lefebvre (2000) found that invasion success increased with introduction effort (number of attempts and number of individuals since European colonization), which is not surprising. Invasion success was also higher for nidifugous species whose young are not fed by their parents (such as game birds), species that do not migrate and, in particular, birds with relatively large brains. The relationship with brain size was partly a consequence of nidifugous species having large brains but probably also reflects greater behavioral flexibility; the successful invaders have more reports in the international literature of adopting novel food or feeding techniques (mean for 28 species 1.96, SD 3.21) than the unsuccessful species (mean for 48 species 0.58, SD 1.01).

Despite indications of predictability of invasion success for some taxa, related to high fecundity (e.g. pine seed production) and broad niches (e.g. bird behavioral flexibility), exceptions to the 'rules' are common and there are many more cases where no relationships have been found, prompting Williamson (1999) to wonder whether invasions are any more predictable than earthquakes. The best predictor of invasion success is previous success as an invader elsewhere. However, even this provides invasion managers with useful pointers for prioritizing potential invaders to their regions.

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