Effects of community diversity and resource availability on invasion in marine fouling communities

Community diversity and resource availability are commonly used to explain the mechanisms driving successful invasion of non-native species. The diversity resistance hypothesis predicts that high diversity should lead to community resistance to invasion. In contrast, the fluctuating resources theory states that resource availability, disturbance, and environmental fluctuations affect community invasibility. Conflicting observational and experimental results make it difficult to discern what drives community resistance to invasion and what mechanisms ensure invasion success. Manipulative experiments examining the combined effect of community diversity and resource availability on invasion success were conducted using marine fouling communities. Treatments included communities of varying levels of species richness and varying levels of bare substrate. Initial results suggest that two weeks after treatments have been established, a significant increase in invasive recruit abundance is seen as resources increase (F= 4.65, P=0.03) and a significant decrease is seen as diversity level increases (F= 4.89, P=0.01). When diversity increased from the lowest treatment levels, the average number of recruits fell by nearly half. Currently, there appears to be no difference in abundance of recruits between the higher diversity treatments and there does not seem to be a strong effect of resource availability at higher diversity levels. Similar trends are seen on a species-specific level. In higher diversity treatments, recruitment is lower overall but does not change with resource availability. These results suggest that recruitment of invaders into the community is affected by diversity, but that the relationships between recruitment, space availability and diversity are not straightforward.