Summary: Bennett et. al 2011

Through my own research and readings I find that plants are often an easy way to demonstrate the potential effects invasive species can have on native species.  There appears to be an abundance of information in regards to invasive vegetation but I also find the studies interesting because they appear to an easier way of studying the effects within a short time scale compared to various other species whose effects may not be apparent for multiple generations to come.  With that said, here is a brief summary of a study conducted in California examining the ways in which non-native species can impact the local communities

The success of invasive species is due to a combination of factors such as “enemies, disturbance, allelopathy” (Bennett et. al 2011).  Allelopathy is when the presence of one plant effects the success of another (Ferguson et. al 2013).

Invasive species are not only known for out-competing native species but can also effect the local communities on a smaller scale as well.  For example, they can alter soil types which in return impacts the ability for local plant species to successfully grow.  Invasive species can also impact decomposers, such as fungi, which have an important role in the communities which also adds to the changing soil types by altering “soil nutrient cycles” (Bennett et. al 2011).

Other factors to consider when examining the success of an invasive species is “moisture availability and elevation” (Bennett et. al 2011).  As pointed out by Bennett et. al, H. Lanatus, a perennial grass, provides a good example of how an introduced species can be successful as a result of a combination of these factors (2011).

According to Bennett et. al (2011) by conducting a study on H. Lanatus four “potential mechanisms” for how an invasive species can alter the local communities was proposed. 

The first mechanism is referred to as “direct competition” (Bennett et. al 2011) which is where the introduced species directly competes with the native species for natural resources and generally stands a better chance at winning the game due to the lack of natural predators.

The second mechanism proposed is “changes in the soil community abundance and diversity” (Bennett et. al 2011).  Bennett et. al (2011) refers to a study conducted by Bodega Marine Reserve (BMR) to illustrate a measured increase in “bacteria to fungi ratio”.  This increased ratio alters the nutrient cycling and availability within a soil which then results the successive growth of the native vegetation.

“Indirect competition via herbivore effects” is the third mechanism outlined by Bennett et. al (2011).  An herbivore refers to an animal which feeds on vegetation.  Native herbivore specie to an area are likely to prefer a diet consisting of the native vegetation, although it is worthwhile to note this is not always the case.  However, in cases in which this is true, in addition to the already present direct competition and altered habitat, the native vegetation (Bennett et. al 2011).  

The final mechanism proposed is “interference competition via allelopathy” (Bennett et. al 2011).  Allelepathy again is when one plant alters the success rate of another (Ferguson et. Al, 2013) and the presence of these circumstances can ultimately effect the reproductive success of the native plants (Bennett et al 2011).

According to Bennett et. al (2011) along with the study conducted on H. Lanatus, examining the four mechanisms in more depth, they found that survival was more related to the presence of direct competition while the “growth rate” was a function of herbivory.

References:

Bennett A. 2011, ‘Multiple mechanisms enable invasive species to suppress native species’, American Journal of Botany, Vol. 98, no. 7, pp. 1086-1094.

James J. Ferguson et. Al 2013, Allelopathy: how plants suppress other plants, University of Florida IFAS Extension, Florida, viewed 20 April 2014, http://edis.ifas.ufl.edu/hs186