By: Lauren Ash
Now, after reading the title and before you start thinking ‘I’m quite certain this isn’t a science fiction blog,’ let me assure you, I am not talking about these kinds of invasions:
The invasions I am speaking of are subtler. The danger of these invasions is indirect and is a threat to ecosystems, native species, biodiversity, and the economy. I am speaking of invasive non-native species.
What are invasive species?
Firstly, non-native species are species found outside their present or past natural ecosystems. Historically, species have been translocated for as long as humans have been moving, mostly through ships. It is important to note that not all non-native species are bad because not all non-native species are invasive. Invasive species are usually defined as non-native species that cause economic, environmental and/or human harm. They usually become so successful with a few shared characteristics, including tolerating and adapting to a variety of new environments, growing and reproducing quickly, competing aggressively for resources, and not having any natural predators in this new habitat. This often causes the invasive population to explode, grow rapidly, and outcompete similar native species, often disrupting the entire ecosystem. Two examples of this can be found in the Florida Everglades and the Great Lakes.
The exotic Burmese pythons (Python bivittatus) have been released by fickle pet owners since the 1980’s, and since then, the population has flourished. As seen in the image on the right, the largest Burmese python ever recorded, measured at 5.7 meters, was caught in south Florida in May 2013. Because Florida biologists are unsure of how many pythons are currently terrorizing the Everglades, it is hard to determine their impact. Nevertheless, it is assumed that they are eating native mammals, reptiles, and birds, as well as outcompeting other native wildlife for food.
The exotic zebra mussel (Dreissena polymorpha) is currently threatening the Great Lakes in the northern United States. This freshwater mussel first appeared 20 years ago in North America, through ship ballasts, and actually drove out the native mussel species entirely within the first 10 years. As many as 700,000 mussels have been found in just one square yard of surface area on boats, pilings, and pipes. The zebra mussel is efficient at filtering large amounts of water so has contributed to the explosive and detrimental algal bloom occurring in nearby fresh bodies of water. It has also outcompeted more energy-rich and nutritional species, leaving the native fish with fewer food options.
From these two examples, we can conclude that understanding invasion ecology is very important to many ecosystems, but with the changing environment, it may be very difficult to study.
Climate change and invasive species
The impacts that invasive species can have on native wildlife and ecosystems, in addition to the economic effects, have been studied extensively. Unfortunately, what hasn’t been studied extensively is the relationship between the growing issue of climate change and these biological invaders. I had originally intended to write about how, with the ever-warming climate and with the extremely adaptable characteristics of invasive species, invasives will be on the rise. However, I quickly found that this is certainly not the case for all species, and perhaps, the reason this issue has not been extensively studied yet is due to the murkiness of the topic.
Climate change helping invasives
The Asian needle ant (Pachycondyla chinensis) is an invasive species that was introduced to the USA from Asia and is quickly spreading into a variety of habitats. Recently, to predict its potential to spread to new regions, species distribution maps were made to determine suitable areas under the present climatic conditions as well as in 2020, 2050, and 2080.  Using a consensus model, with 5 different modeling techniques (3 Global Circulation Models and 2 CO2 emission scenarios), suitable world maps with climatic conditions for the different years were created. The results of the study showed an increase of range suitability due to climate change “by 64.9% worldwide, with large increases in Europe (+210.1%), Oceania (75.1%), North America (+74.9%) and Asia (+62.7%)” and can be seen in Figure 1. 
Climate change deterring invasives
In a similar experiment to the one just described, the big-headed ant’s (Pheidole megacephala) invasive potential was mapped for the years 2020, 2050, and 2080 using ecological niche models and the same 5 modeling techniques.  However, the results are quite different. Currently, 18.5% of landmass has suitable climatic conditions for the big-headed ant. Not only was it predicted that P. megacephala would be unlikely to benefit from climate change, it was predicted that the species would suffer from it. A decline in invasive potential was seen as early as 2020 with a global decrease in favorable climate of 19.4% by the time it reached 2080. 
Climate change helping and deterring invasives
In a very recent study, using ensemble forecasts from species distribution models, future suitable habitat for the 100 of the world’s worst invasive species was projected.  Climate and land use change was modeled, and it’s predicted that species range distributions will shift drastically. However, the findings amongst species were not consistent. These scenarios show a consistent shrinking in potential range distributions for “invasive amphibians and birds, while for aquatic and terrestrial invertebrates distributions are projected to substantially increase in most cases” as seen in Figure 3. 
These varying results show how complex the relationship between invasive and climate change ecology can be. To better understand how species will react to future change, further research should be done on a greater number of species and should probably take into consideration the new species interactions that would result. This could tell us which native species have the potential to be negatively impacted and could help with preventative conservation measures. Although this field is quite multifaceted, climate change is occurring and currently impacting species in many ways, so it will be in our best interest to put a great effort into realizing its consequences.
*Cover photo: Asian needle ant killing the eastern subterranean termite (Reticulitermes flavipes) Credit: Alex Wild
 Courchamp, F. (2013). Climate Change May Boost the Invasion of the Asian Needle Ant, 8(10), 2–9. doi:10.1371/Citation
 Bertelsmeier, C., Luque, G. M., & Courchamp, F. (2012). Global warming may freeze the invasion of big-headed ants. Biological Invasions, 15(7), 1561–1572. doi:10.1007/s10530-012-0390-y
 Bellard, C., Thuiller, W., Leroy, B., Genovesi, P., Bakkenes, M., & Courchamp, F. (2013). Will climate change promote future invasions? Global change biology, 3740–3748. doi:10.1111/gcb.12344