Megastigmus wasp damage to seeds of Schinus molle, Peruvian pepper tree, across a rainfall gradient in South Africa: implications for invasiveness

摘要

Biological invasions pose one of the biggest threats to biodiversity worldwide (Williamson 1999). Invasive species have caused economic or ecological problems that are difficult and sometimes impossible to control. Understanding the reasons why some alien species become invasive may help to identify appropriate management strategies. One hypothesis often cited to explain invasion success is the enemy release hypothesis (Williams 1954; Elton 1958; Blumenthal 2006), which attributes the success of alien species to the fact that they are freed from the limiting biotic mortality factors (e.g. diseases, herbivores and pathogens) when introduced to a new habitat. Escape from natural enemies, it is argued, may give alien species a competitive advantage over native species and lead to a demographic increase of their populations, possibly leading to invasion (Blumenthal 2006).