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.
As far as “invasive” versus “naturalized” species are concerned, I think it’s like Nicole said in class: “It’s like a subspecies.” I know it’s something we joke about, but the question still stands. Is there even a difference between the two concepts? And if there is, how do you definitively differentiate them? Every “naturalized” species was once an invasive. Is there a way to determine when an invasive crosses the boundary between “outsider” and “member” species in an environment? Every species in every environment operates according to a different set of criteria, taking a different amount of time to become ingrained in the ecosystem it was introduced into, so the defining factor can’t be a set measure of time.
Looking at it another way, I’ll give an example illustrated in another of my classes. If I hadn’t attended a guest speaker’s lecture, I would never have known that the alewife fish was invasive to Lake Michigan, or that many of the lake’s endemic species had been driven to extinction by the alewife and other invasives like it. It altered the lake environment so much that people now will never know what the ecosystem was, and even if such an endeavor were possible, no restoration could ever reset that environment back to the way it used to be. So, the question remains: can you consider the alewife a naturalized species? When was the point it stopped being “invasive” and people began accepting it as “belonging” to the lake ecosystem? When no one around could remember a time before it was found in the environment it was introduced into? Naturalization seems like a false concept to me. Once an invasive, always an invasive, especially since these species have the power to change the environments they end up in beyond recognition.
I think that a lot of terminology for invasive species is defined by the local people. One definition for a naturalized species that I’ve found refers to any non-native species that moves into a new area and is able to reproduce enough to maintain a population. The species remains classified as non-native, but has naturalized. The tricky part to this definition is that people have to remember that the non-native hasn’t always belonged in the new area. Lindsay, although you may disagree with the concept of naturalization, the alewife invasion you mentioned is a great example of it (at least by this definition). Many people don’t know that alewife aren’t originally from the Great Lakes and on top of that, that Coho and Chinook salmon were introduced by state Natural Resource agencies to maintain alewife population from getting out of control. The alewife are non-native to this area, but are able to reproduce to such great numbers that they begin to effect their new ecosystem.
Another complicated example that comes to mind are wild mustang horses in the western US. Fossils show that prehistoric horses lived in North America, but it is estimated that they went extinct about 12,000 years ago. Spanish explorers brought over horses who’s descendants have become the wild mustang horses we know today. They technically aren’t native, but mustangs have become a symbol of the wild west and people want to keep them around (remember the movie Hidalgo?). The horses maintain a reproducing population and we can call them naturalized, but they are still non-native.
The thing I found most interesting about this article was how the research group looked at the different levels of the coral reef. I felt like this was very interesting because many of the ecological papers that I have read have only focused on a particular region or one how an invasive species only affects a certain population. This may have been done because the ecosystem of a coral reef is very delicate and every species can impact the coral reef ecosystem. Now it would be interesting to see if how the different protection practices of coral reefs are impacting the rate at which invasive species can successfully populate the coral reef. I feel like this would be a worthy study because every country has a different rules regarding the fishery management and habitat protection. I am sure that those countries that have a more strict restrictions have a reduced impact of invasive species in those coral reefs.
What I find more interesting is the impact that alien seaweed has on coral reefs. The spread of alien seaweed I feel have a much greater impact on coral reefs due to the fact that the can not be eaten by the native species, spread very easily, destroy native habitats, and out compete the native species fairly easily. These alien seaweeds are not as well studied and not easily distinguished from native seaweed species. The reason that I feel alien seaweed provides a greater chance to destroying a coral reef is that it can be spread by almost anything that goes in the water.
I really liked this paper and I think it provided a nice framework for future scientists that are looking to take an ecological and evolutionary approach to biology (not just coastal invasions). One aspect in particular that I found interesting is the concept of phenotypic plasticity as an aspect of evolutionary consequences. Invaders are often refered to as “plastic” and this term has come up a couple of times in our class discussions. Whitman and Agrawal wrote a nice chapter on the phenotypic plasticity of insects. They state that: “Phenotypic plasticity, the capacity of a single genotype to exhibit variable phenotypes in different environments… All plasticity is
physiological, but can manifest as changes in biochemistry, physiology,
morphology, behavior, or life history. Phenotypic plasticity can be passive,
anticipatory, instantaneous, delayed, continuous, discrete, permanent,
reversible, beneficial, harmful, adaptive or non-adaptive, and generational.
Virtually any abiotic or biotic factor can serve to induce plasticity, and
resulting changes vary from harmful susceptibilities to highly integrated and
adaptive alternative phenotypes. Numerous physiological mechanisms
accomplish plasticity, including transcription, translation, enzyme, and
hormonal regulation, producing local or systemic responses. The timing,
specificity, and speed of plastic responses are critical to their adaptive value.
Understanding plasticity requires knowing the environment, physiological
mechanisms, and fitness outcomes. Plasticity is thought to be evolutionarily
favored under specific conditions, yet many theoretical predictions about
benefits, costs, and selection on plasticity remain untested. The ecological
consequences of plasticity range from simple environmental susceptibilities
to mediating interspecific interactions, and extend to structuring of ecological
communities, often through indirect effects. Phenotypic plasticity, through
its ecological effects, can facilitate evolutionary change and speciation.”
Plasticity, therefore, is pretty all encompassing. It is not just variation within a population, but the ability of an individual to vary. Plasticity is an important concept to understand invasion biology and ecological and evolutionary biology.
I enjoyed this paper, and agree with Alex, it was nice to see a study that looked at different levels. Most invasive studies concentrate on a specific population and how the invasive is negatively impacting it. Very rarely do they address the entire habitat and the adaptations experienced from both native and invasive populations. As we all know impacts caused by invasive populations occur at all levels of the food web and therefore impact the entire habitat.
The comment of keeping ecology and evolution separate on some level reminds me of many debates on management. Throughout the year we have all experienced the challenge of keeping idealistic approaches and studies separate from realistic (in the sense of time, money and community). Management practices are concerned about the areas in their jurisdiction, they aim for them to be in good health, self-sustaining, and usable for profit. This means looking at it from a ecological stand point, aka a shorter time period. While our papers this year have focused on the natural habitat (what populations have historically been found in the area, what the food web was, what genetics were in the area) and how the natural habitat has changed usually due to anthropogenic influence. Bringing this back to natural vs. invasive, I agree with Mike. Communities will consider a population natural when it is a self-sustaining population and of course not tearing down the food web. Looking at the alewife, it was considered invasive when they consumed all the phytoplankton; causing local cisco and perch populations to decrease. Although with the introduction of salmon, this population is now under control. In the ecological sense, the population has become naturalized but evolutionary it will never be considered naturalized since historically their genes were never found here.