The Biotic Resistance Hypothesis describes the chances of a invasive species to be succesful in introduced environments. It states that species diverse environments are more resistent to invasive species. This is because species rich environments are more able to use their resources more effectively then species poor environments (1). The two parts that determine species richness are the number of species, and the distribution of the species (2).
Hypothesis raised by Charles Elton (1958) he thought that communties were able to resist invasive species through a combination of predation, competition, parasitism, disease, and agression. However he thought that the biggest reason for resistance was found in the number of species found in the environment. to make his point he stated agricultural fields as areas of low species diversity and are easily invaded (3).
(1) Carlborg, E. (2014, January 15). Biotic resistence - Umeå University, Sweden. Retrieved April 14, 2015, from http://www.emg.umu.se/english/research/research-projects/biotic-resistence/
(2) Ecology/Invasive species. (2011, March 6). Retrieved April 14, 2015, from http://en.wikibooks.org/wiki/Ecology/Invasive_species#Invasive_Meltdown_Theory
(3) Simberloff, D. (2011). Elton Charles S. In Encyclopedia of biological invasions (p. 188). Berkeley, CA: University of California Press.