Progress review

So far I’ve been writing this blog for the Global Environmental Change module that I have studied as part of the MSc Climate Change course at UCL. Tomorrow the module unfortunately comes to an end, so it seems that today is an appropriate time to review my blog. As someone who had never blogged before, I was apprehensive when I started and was unsure as to how the blog would progress. Looking back at my blog archive, there are some key themes that run throughout the posts which have helped me form my current opinion on invasive species. Here goes an attempt to summarise my blog…

Historically invasive species were spread around the globe by human transportation, although natural environmental changes also led to the introduction of some invasives. These species are most commonly known for the negative effect that they have on ecological systems however, perhaps the neutral or positive impacts just aren’t headline material. As a result conservation efforts have focused on preventing and eradicating established invasives, such as the Himalayan balsam. Some people have even tried to eat them out of existence! Despite this established invaders are often very persistent and survive, so scientists have promoted citizen science to try and gain a clearer picture of just how widespread invasives really are. In the present day it appears that human induced climate change is the new driver of invasives and ecological communities now consist of species from all over the world. Climate change primarily leads to the spread of invasives by causing species to change their geographic distribution in order to survive physiological stress induced by increased temperature. Additionally, changes in the physical environment will soon enable humans to transport invasives as far as the North Pole. Perhaps it’s therefore time to change our opinion on invasive species when we strive to protect global biodiversity.

On a final note I would like to thank everyone for their comments and feedback. It has been very encouraging and has helped me direct my blog to relevant issues. I hope to continue blogging throughout the rest of the year however, I apologise in advance if the posts aren’t as regular as they have been to date!

Thanks again,

Elena

Positive potential

It's time to take a more optimistic approach, and look at the positive effects that invasive species can potentially have on ecosystems. I’ll start by proposing counter-arguments for the 3 problems described in ‘Why the bad press’. 

1. Predation
Let’s take a look at the European Green Crab, which was a successful invader to America at locations where the native predator (Blue Crab) had been removed as a result of human activity. Due to the local extinction of Blue Crabs, the population of an herbivorous crab species lower down the food chain dramatically increased. This herbivore was able to strip salt marshes of hundreds of hectors of vegetation, namely cordgrass, which resulted in salt marsh die-off and impacted negatively on the ecosystem. The invasion of the Green Crab is thought to have significantly reduced the population of the herbivorous crab via predation. Optimistically there was found to be a positive correlation with Green crab abundance and cordgrass recovery. (Bertness and Coverdale, 2013)

2. Competition

When an invasive species expands its geographic range, it competes for resources with pre-existing species. If some native individuals are able to survive, then invasives may drive the evolution of these native species and select for traits which increase fitness. Ferrero-Serrano et al., (2009) found this to be true for native grass populations. The authors demonstrated that as a consequence of previous competition imposed by invaders, evolved species were more likely to be able to tolerate new invaders. Importantly the authors argue that this knowledge may help advance the understanding and practice of restoration ecology. 

3. Disease

Ok so this one was a little bit harder….even after trawling the internet I have failed to come up with a valid argument! 

To compensate I have found a case study to share with you that I thought was particularly interesting. Pejchar and Mooney (2009) reviewed whether different ecosystem services in South Africa were positively or negatively impacted on by the invasion of woody plant species.

(Pejchar and Mooney, 2009)

This review by Pejchar and Mooney (2009) highlights just how many ecosystem services invasive species can affect. Moreover, there is only one ecosystem service where invasive species had a strictly positive influence. Whilst reading the literature in preparation for this blog post I found that this was often the case. As a result I am personally still not swayed; to me it seems evident that invasive species have a net negative effect.

Let me know what you think!

Elena