Exotic Brome-Grasses in Arid and Semiarid Ecosystems of the Western US

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Factor

Hypothesis

Basis/rationale

Independent variables

Comments based on analyses

6

Ploidy level

Polyploid chromosome counts are correlated with invasiveness

Polyploidy may result in more robust plants and provides greater opportunity for genetic variation

Ploidy level (diploid, polyploid, both)

Polyploid species and species with both diploid and polyploid individuals were more likely to be widely introduced and to be crop and ruderal weeds. This pattern was much weaker for annual species than for perennials

7

Human use

Use by humans for forage, hay, and revegetation is correlated with invasiveness

Species are introduced into new areas and grown in large quantities under conditions which encourage establishment

Human use (hay/forage/revegetation, no hay/forage/revegetation)

Use for hay/forage/revegetation was correlated with wide introduction and with weediness

8

Cultivar availability

Availability of cultivars is correlated with invasiveness

Cultivar development may promote increased genetic variation and allow plants to grow in more areas

Cultivar availability (cultivars, no cultivars)

Cultivar availability (having cultivars) was correlated with wide introduction and weediness

9

Climate

Ability to grow at both low and high temperatures is correlated with invasiveness

Ability to adapt to extreme environmental conditions may provide competitive advantages

Minimum temperature, Maximum temperature

Lower minimum temperature and higher maximum temperature were correlated with wide introduction and weediness

10

Climate

Ability to grow at a wide range of temperatures is correlated with invasiveness

Ability to adapt to extreme environmental conditions may provide competitive advantages

Temperature range

Wider temperature range was correlated with wide introduction and weediness

(continued)

6 Attributes That Confer Invasiveness and Impacts Across the Large Genus Bromus...