What is an Invasive Species?
Just as they dominate the ecosystems to which they are introduced, invasive species now dominate the discourse surrounding conservation. In fact, invasive species have been classed as one of the most serious environmental threats of the 21st century. Considering all of the other dumb crap we put the environment through, this is a pretty big deal. In order to raise awareness about the threat they pose, I’m releasing a series of blogs examining the impact of specific invasive species across the globe. Today, I’m going to start by explaining what exactly makes a species ‘invasive’.
An invasive species is defined as a non-native species that threatens ecosystems, habitats or species in its introduced range. Basically, they turn up to parties uninvited and spoil the fun for everyone. Invasions can occur when an organism is transported—either intentionally or accidentally—beyond its native range, resulting in its introduction into a novel habitat. Once introduced, these species can become established and rapidly reproduce.
In any given habitat, the native species which reside there have co-evolved alongside one another. In essence, this means that they have developed ways to co-exist in relative harmony… that is, until an uninvited guest shows up.
When a species becomes introduced beyond its native range, the organisms in its introduced habitat do not have the ability to defend or compete against the invader. This is exacerbated by the ability of invasive species to rapidly “get it on”, unchecked by the limitations which would curtail population size within their native range (e.g. predators and resource availability).
As their numbers increase, invasive species can cause harm in a huge number of ways: they can predate or outcompete native species, decimate or replace native food sources, and spread diseases and parasites. Native species begin to suffer and become displaced by the invaders, which can even result in their extinction. This, in turn, results in the reshuffling or degradation of entire ecosystems. Thanks invasive species.
Although invasive species are not a novel problem, globalisation has accelerated the processes by which they become introduced. We benefit massively from tourism, migration and trade—but they all have the unfortunate side effect of facilitating the movement of species between habitats. The chart on the right outlines just a handful of the potential pathways for introduction.
Why Should we Worry?
Invasive species present a huge threat to wild and agricultural systems. This means that even if you don’t particularly care about biodiversity, you should be worried about invasive species—unless eating isn’t your thing.
Sidenote: if you don’t care about biodiversity, meet me in the car park after dark. I just wanna talk.
Unless your Tesco visit coincides with some underpaid teenager bringing out the ‘reduced’ stickers, you’ve probably never had to fight for your food at the supermarket. That’s because we have a fairly high level of food security: a continuous stream of access to enough safe and nutritious food in order to maintain a good standard of living.
Invasive species everywhere cackle in the face of food security.
Invaders present a huge threat to agricultural ecosystems. They are a major cause of crop loss, and have the ability to negatively affect food security on a global scale. Invasive species can mechanically damage and contaminate crops, either through feeding or by creating cosy little homes within them. As a result, in the United States alone, invasive species are estimated to cost $137 billion annually.
Invasive insects can also affect agriculture indirectly—for example, through predation on honeybees which are vital for insect-pollinated crops. As a result, it’s incredibly difficult to estimate the true scale of the threat posed by invasive species.
…But invasive species don’t stop there. Not content with their ability to damage agriculture on a global scale, invaders also wreak havoc in wild ecosystems. Globally, invasive species are regarded as one of the greatest threats to biological diversity. They can also prevent the delivery of ‘ecosystem services’—valuable services which the environment provides, such as climate regulation and fuel provision.
In this mini-series, I’m going to examine four different invasive insects. The first, Anoplolepis gracilipes, largely affects wild ecosystems; the second, Aphis glycines, predominantly affects agricultural ecosystems; and the final two species, Anoplophora glabripennis and Vespa velutina have a double-whammy of effects which damage both types of ecosystem.
Why insects? Well…
In Europe, 87% of a recorded 2,500 non-native terrestrial invertebrates are insects. Social insects in particular are hugely successful as invasive species; despite only representing about 2% of insect species globally, more than 24% of the invasive insect species which cause environmental harm are social. Insects therefore have huge potential to influence ecosystems beyond their native range.
If you’d like to learn more about invasive species, make sure to keep an eye out for my next few blogs. Although they’re a pain in the… ecosystem, invasive species are really interesting, so keep your eyes peeled.