Does the evolution of increased competitive ability hypothesis explain invasion? Comparing native and non-native populations of Plantago lanceolata

Izzadora Dean

Abstract


1. The evolution of increased competitive ability (EICA) hypothesis proposes that release from enemy regulation in new ranges results in changes in selective pressure, producing poorly defended, rapidly growing phenotypes. Plantago lanceolata is not exposed to intense mollusc herbivory in its non-native North American range, therefore post-invasive evolutionary change may be observed in these populations.
2. Seeds from eight populations, four invasive and four native, were collected and grown in glasshouses. Seedling acceptability to the mollusc Helix aspersa was measured, along with recovery after artificial cotyledon removal, seed mass and seedling mass at 14d old.
3. No difference in acceptability was found, and recovery from cotyledon damage missed statistical significance. The results do not support the EICA hypothesis, with variation between populations likely to be due to factors such as differing selective pressures or founder effects.
4. No link between acceptability and recovery was evident, suggesting no trade-off occurs between these two traits.
5. Seed and seedling mass was smaller in invasive provenance populations (P < 0.01, P = 0.053). This may indicate the different environmental pressures in each provenance, resulting in different life history strategies. A correlation between the two exists (P < 0.05). In seedling and seed mass, the main contribution to the smaller invasive provenance populations came from the reduced sizes of the Carson population. However, no links between seed mass and acceptability or recovery were found.
6. Synthesis. To develop an understanding of the mechanisms underlying botanical invasions, the assimilation of hypotheses must occur, to gain insight as to the relative importance of disturbance, competition, plant traits and enemy release.

Key-words: EICA, enemy release, Helix aspersa, herbivory, invasive species, palatability, plant defence, post-invasion evolution, seed mass, trade-offs

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