The paper “Ecological and Evolutionary consequences of Coastal Invasions,” by Edwin Grosholz presented a review of the literature regarding invasive species in estuarine and marine environments. He begins with an introduction of how these environments are among the most invaded habitats and yet had not been as well studied with regards to the consequences of invasions as terrestrial or freshwater ecosystems. However, research in this area is beginning to increase (especially since the time of publication) since the effects like hybridization, impacts on species and ecosystems, cryptic species invasions and extensive geographical spread of the invaders suggests that the consequences might be worse than realized.
Grosholz begins by examining the ecological consequences of invasions looking at different levels. First he looks at species-level consequences between the invader and a single species. He uses studies of invasive snails and their impact on native snails to illustrate this point. Next he looks at community-level consequences by the Asian mussel introduced into mudflat communities in San Diego. The study found that the mussels provided byssal thread habitats and therefore a novel community structure. However the cascading effects on higher trophic levels were not addressed because they were not yet known for the discussed environments. Next were ecosystem-level consequences and how a species of Asian clam changed the food web in San Francisco Bay by inhibiting the spring phytoplankton blooms.
In order to provide a well-rounded view of invasive species Grosholz provided information about the effects on the invaders themselves as well. These include suffering higher predation, as in the case of the Asian mussel, native species resisting exotic species, and the debated theory that more diverse communities are less easily invaded. Native communities can affect the geographical spread of invaders as well. Coastal invasions showed greater variation in the rate of spread and a more extensive range expansive over a short amount of time. Finally Grosholz also mentioned the more frequent transportation of pathogens and parasites in harbors which could have profound effects.
There are also many evolutionary consequences to the introduction of invasive species which are outlined with examples from literature. First is the tracing of invasion pathways using microsatellite DNA (which is NOT abbreviated: mtDNA). But this technology will hopefully aid in predicting impacts of invasions, preventing future invasions and seeing the invasion pathways. Cryptic invasions are also a problem with misidentification of native and invasive species. Native genotypes can be lost through hybridization and introgression and invasive species can also affect phenotypic plasticity and population structure. The thickening of snail shells as a result of crab invasions depicts changes in phenotypic plasticity and variation among subpopulations of clams was used to demonstrate changes in population structure. The final evolutionary consequence was physiological adaptation or the selection and physiological evolution influencing success in invading populations. The example for this was the multiple invasions by genetically distinct copepods in different areas of the world.
Grosholz ended his review with some final conclusions about the gaps in the knowledge we have as well as future directions of study to fill in these gaps. Overall it was a good review of the literature and applicable to any environment that has invasive species. The paper brought up several points of discussion however. First it raised the question of what constitutes a “naturalized” species. It seems that there isn’t a clearly defined answer at this time, although these species seem to be ones that do not have harmful effects on the environment they have invaded and over some period of time have become “normal.” We all seemed to agree that for science to move forward it is important to integrate ecology and evolution but it was also important that we distinguish the two. Despite the interconnectedness, the two areas do have their differences; the largest component seems to be time. Ecology is the study of relationships in an environment at the present time while evolution is change over time. Both are necessary to understanding biology and, while it is not always possible, integrating the two provides a more complete understanding for the future.