GLOBAL CHANGE: RESPONSES AND MANAGEMENT STRATEGIES FOR SEMI-ARID RANGELANDS
Location: Rangeland Resources Research
Title: INTERACTIONS BETWEEN RESOURCES AND ENEMY RELEASE IN PLANT INVASION
Submitted to: Ecology Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 20, 2006
Publication Date: July 3, 2006
Citation: Blumenthal, D.M. 2006. Interactions between resources and enemy release in plant invasion. Ecology Letters. 9:887-895.
Interpretive Summary: In order to develop long-lasting solutions to invasive species problems, it is necessary to understand the mechanisms underlying invasion. This paper reviews evidence suggesting that two of the most important causes of invasion, release from natural enemies and increased resource availability, may interact. This interaction may occur because species adapted to habitats with high availability of plant resources, such as light, water or soil nutrients, tend to be strongly affected by enemies. Plants strongly effected by enemies in their native range stand to benefit from leaving those enemies behind (i.e., enemy release) when introduced to a new range. Consequently the same species that benefit from high-resource availability may benefit from enemy release. This hypothesis has a wide array of ramifications for how we understand and manage invasive species. Most importantly, however, it suggests that increasing plant resources through processes such as soil disturbance or nitrogen deposition, will promote invasion by exotic plant species. Furthermore, biological control, the introduction of an invasive species enemies from its native range, may be most effective against plant species from high resource habitats.
Understanding why some exotic species become invasive is essential to controlling their populations. This review discusses the possibility that two causes of invasion, release from natural enemies and increased resource availability, may interact. When plants invade new continents, they leave many herbivores and pathogens behind. Species most regulated by enemies in their native range have the most potential for enemy release, and enemy regulation may be strongest for high-resource species. High resource availability is associated with low defense investment, high nutritional value, high enemy damage, and consequently strong enemy regulation. Therefore, invasive plant species that benefit from high resource availability may also gain most from enemy release. Strong release of high-resource species would help to explain observed tendencies of exotic plants to have high-resource traits, and to succeed in high-resource environments. It would also predict that (a) increases in resource availability due to disturbance or eutrophication may increase the advantage of exotic over native species, (b) both enemy release and resources may underlie plant invasion, leading to potential interactions among control measures, and (c) although high-resource plants may experience strong enemy release in ecological time, well defended low-resource plants may have stronger evolutionary responses to the absence of enemies.