Evolution of Increased Competitive Ability (EICA) hypothesis

The evolution of increased competitive ability (EICA) hypothesis was developed in 1995 by Blossey and Nötzold to explain the success of invasive species particularly plants. It predicts that invasive plant species will be released from native specialist predators in their introduced habitat. They subsequently evolve with less investment in anti-herbivore defenses and allocate more resources to vegetative and reproductive growth relative to conspecifics. Scientists believe that a lack of native predators allows plants to reallocate resources from defense to growth and reproduction. It differs from similar ideas such s the predator release hypothesis in that it is believed invasives have lower fitness at the time of introduction and evolve to be more fit by the time it is considered invasive (Bossdorf, 2005).

This hypothesis has been supported by several studies. A study on Solidago gigantea observed the rate of herbivory by specialist and generalist insects found that plants in both invasive and native populations had similar levels of allelopathic chemicals. However, generalist caterpillars had higher growth rates on invasive populations suggesting partial agreement with the EICA hypothesis as some defense had been lost (Joshi, 2005). Another study on Senecio jacobaea measured levels of allelopathic chemicals in populations from North America, Australia and New Zealand. They similarly found that compounds involved in defense of specialist herbivores decreased. However an increase in compounds to deter generalist herbivores was observed. They concluded that in invasive populations there was a decrease in specialist defense and an increase in both growth and generalist herbivore defense (Hull-Sander, 2007).

Work Cited

Hull-Sanders, H. M., Clare, R., Johnson, R. H., & Meyer, G. A. (2007). Evaluation of the evolution of increased competitive ability (EICA) hypothesis: loss of defense against generalist but not specialist herbivores. Journal of chemical ecology, 33(4), 781-799.

Joshi, J., & Vrieling, K. (2005). The enemy release and EICA hypothesis revisited: incorporating the fundamental difference between specialist and generalist herbivores. Ecology Letters, 8(7), 704-714.

Bossdorf, O., Auge, H., Lafuma, L., Rogers, W. E., Siemann, E., & Prati, D. (2005). Phenotypic and genetic differentiation between native and introduced plant populations. Oecologia, 144(1), 1-11.