Figure 1.
Plant origin does not predict native caterpillar preference for extracted chemistry.
Preference of caterpillars for secondary chemistry extracted from 21 native (open bars) and 19 exotic (filled bars) plant species. Bars represent mean (±1 SE) fraction of extract eaten relative to total amount of diet eaten. Phylogenetic relationships are shown without branch lengths for clarity, although branch lengths were used in statistical analysis of phylogenetic influence (see text). Asterisks beside bars denote significantly (P<0.05, paired t-tests) deterrent or stimulatory extracts from individual plant species. Inset: overall mean (±1 SE) fraction eaten by species origin (ANCOVA with caterpillar mass as covariate; origin effect P = 0.76).
Figure 2.
Local abundance, but not time since introduction, predicts native herbivore preference for extracted exotic plant chemistry.
Relationship between leaf extract consumption and (A) date of introduction and (B) local plant abundance. There was no relationship between the earliest recorded date of introduction and extract deterrence to a native herbivore (A). However, plant species with deterrent secondary chemistry were the least abundant species in forest understory communities (B), a pattern that held across both native and exotic species (non-significant origin*abundance interaction). Filled circles represent exotic species; open circles represent native species.
Figure 3.
Native and exotic plant species occupy similar leaf trait space.
Principal components biplot of native (open circles) and exotic (filled circles) species and their measured traits. PCA axis 1 (carbon-growth) explains 29% of trait variation across 19 exotic and 21 native species; PCA axis 2 (defense-nutrition) explains 19% of the remaining variation. All trait vectors are significantly associated with species PCA position according to randomization tests. Units for traits are given in Table 1.
Table 1.
Mean (± SE) values for nine measured traits of 19 exotic and 21 native species co-occurring in forest understory communities.