Alien Vs. Native: The Sequel You Have All been Waiting For

With all this talk about the impact of travel on energy use and CO₂ emissions, I have neglected other environmental impacts. Way back in my second post I mentioned many ways in which the impact of travel could be measured, and therefore today, I’m going to talk a little about the extinction of species via species invasion, before looking at habitat fragmentation a little later.

For as long as humans have been trading and moving around the globe, they have transported species, and created aliens, a species occurring outside its natural range. While some have little impact, many have become invasive and have had huge effects on native populations causing extinctions through multiple means such as…



Water Vole

Predation: Water voles are now under threat by the Mink. 

Resource competition: This is very common and is often owing to an invasive species’ ability to reproduce and grow quickly.   

Muntjac Deer

Habitat alteration: This is very common and is often owing to an invasive species’, such as the munjac deer's, ability to reproduce and grow quickly.

Signal Crayfish

and even through the Spreading of new diseases: The signal crayfish has caused a mass extinction of the White Clawed Crayfish population through spreading the crayfish plague.

According to Preston et. al (2004) the spread of invasive species as a result of human movement can be traced back to the 1500s, a period when colonialisation was born, there was great exploration and the Europeans discovered America. Not all academics agree with this thought and some suggest it can be traced back further, an idea touched on by the video at the bottom. Either way, it is important to note that the level of invasive species at that point in time was low, see fig 1, and it was not until the industrial revolution that the number really began to grow rapidly Hulme (2009).

Figure 1. A clear representation of how invasive species of plants, invertebrates and mammals have grown rapidly since 1800. Although this post is perhaps focussing on mammals, the increase of invertabrates between 1975 and 2000, could perhaps be the geratest cause for concern (Hulme, 2009).

The continued growth over the last 2 centuries has in fact prompted Hulme (2009: 11) to suggest we have now entered the “3^rd age of biological invasions: the era of globalisation”. While there seems to be little literature to contest this, there are plenty of studies that highlight the impact globalisation has had, often highlighting different factors:

1.)    The growth of invasive species is regularly linked to the increase in trade and the emergence of new markets and products especially at particular nodes across the globe (McNeely, 2006; Meyerson and Mooney, 2007) In their 2007 article that focusses on North America, Meyeson and Mooney are able to explain the impact through a comparison between California and Chile, as despite their similar climates, the authors suggest the former has seen a considerably greater influx of invasive species as a result of the worldwide networks it belongs to.

2.)    increases in transport efficiency too are often cited as a contributing factor in the growth of invasive species (Hulme, 2009; McCullough et. al, 2006). As global travel becomes faster, more affordable and more available, more people and cargo are traveling than ever before. Containerisation and the speed at which ships can travel have provided the foundation a 4x increase in global imports since the 1970s (UNCTAD, 2007). This has in turn lead to an increase in the number of ports across all continents, and as the number of ports increase, so does the difficulty in locating stowaway species and pests.

3.)    Links are also made to disturbances. Although these can be at a local scale, such as road and rail tracks, they can also be seen on a global scale with climate change as a result of transport emissions. As climates change, the abiotic frame of species’ does not. This therefore requires many to shift their range, another idea touched upon by the video below, changing local biodiversity’s, and causing species to invade areas they could once not survive in.     

It is evident that the impact of human travel on invasive species and subsequent extinctions, although present from at least the middle ages, is now greater than ever. It seems globalisation has been the main driver in recent years, and from looking at fig. 1, if we do not do something to halt this trend we could be heading for an ecological crisis. But how…

Just a quick video to reiterate what I was saying regarding the damage that invasive species can do. This video is based in North East America, but many of the ideas are transferable.