Thread by @AlexPetrovnia

I’m sure you’ve heard plenty of alarms about invasive species, maybe even about specific invasive species in your area. But I bet no one has taken the time to explain what it means for a species to be “invasive”. 🧵

To understand what makes a species "invasive", we must first understand the opposite. This is usually described as what makes a species "native", but as this term is co-opted from indigenous people, I will use the term "endemic" for this thread.

What makes a species "endemic" is that this species has existed in a specific area for a long period of time. How long? Well, that depends.

In order for a species to be endemic, a species must have existed in an area for long enough that other species in the area have adapted to their presence.

To explain this concept, let's look at a hypothetical example. Let's say there's an ecosystem of rabbits and hawks. The rabbits eat plants, and the hawks eat rabbits. So the rabbits must reproduce at a high enough rate to replace the rabbits that get eaten.

But let's say that foxes move into the area! Then the rabbits have to deal with being preyed upon by both hawks AND foxes.
The foxes would be considered endemic to the area when enough time has passed that the rabbits have evolved or adapted to have a stable population again.

Until that point, the foxes would be considered a foreign species, and not endemic to that region. In the meantime, this would also pose a serious threat to the rabbit population in that area.

If they couldn't adapt fast enough, the combined pressure of the foxes and hawks might eat all the rabbits, and prevent them from existing in this area. This is one way in which invasive species can cause problems for endemic species.

Another way can be through competition for food. In our rabbit example, let's say instead of foxes moving into the area, that mice do. If the mice were to become populous enough, they would be in direct competition with the rabbits for a limited food supply.

If the mice are more successful at reproducing more quickly, or accessing the food more successfully, they may outcompete all the rabbits in the area and eventually replace them.

This causes problems for the entire ecosystem. Remember our hawks from earlier? If they evolved specifically to hunt rabbits, they are going to have a much more difficult time hunting mice. If they cannot adapt to this change in the ecosystem, their population may also collapse.

The basic premise of why invasive species are a threat is this; organisms are not interchangeable, and all ecosystems are very delicate balances that have been honed over millennia. Even a slight destabilization of one species can have catastrophic consequences.

Not every foreign species in an area is going to be invasive. What makes a species specifically invasive is this; if it is more successful at finding food, surviving or reproducing than an endemic species.

Keep this in mind as well, many foreign species have unfair advantages compared to endemic species. Predators may not prey on foreign species as easily as on endemic species, and prey species may not be as successful at avoiding predation by foreign species.

When species have coexisted in a specific region for a long period of time, they often adapt to specifically occupy different "niches". This means they adapt to have different food, shelter and reproductive strategies so they do not need to compete with other species in the area.

For an example of this, let's go back to our rabbits. Rabbits nest in burrows that they dig into the ground. Squirrels, which often share areas with rabbits, nest in holes in trees. The hawks we mentioned before nest in the branches of trees.

By having different nesting environments, they can all successfully nest in the same area without having to fight over a more limited number of suitable locations. The same principle applies to food sources, micro-habitats, and much, much more.

The longer an ecosystem has gone without being disturbed, the more species in it have found very specific niches to occupy, and often the more species it can support. This principle is why a greater variety of species exist in regions that have been undisturbed longer.

One trait that nearly all invasive species possess is that of being generalists. A generalist is a species that is very versatile in the food sources it can utilize, the places it can reproduce, and the habitats it can occupy successfully.

So, when moving into a new environment, generalist species are much more likely to thrive, and displace existing populations.
Invasive species in general also reproduce quickly, allowing them to disrupt the existing balance even more rapidly.

So what can we do about invasive species? Well, the number one strategy to managing invasive species is to prevent them from invading in the first place. Invasive species are introduced to new environments by human activities, and human carelessness.

Firstly, never ever release pets into the wild. This includes everything from cats to snakes to hermit crabs to goldfish. These species can be catastrophic when introduced to environments where they are often invasive and highly successful at displacing endemic species.

Secondly, be mindful of hitchhiking species! If you are travelling between habitats, make sure to prevent species travelling with you. This can be everything from plants to larva that can live in water bodies to rats on ships and more. Think about who is travelling with you!

Thirdly, be very careful about ornamental and houseplants! While keeping plants is a lovely hobby, it is important to make sure that kept plants cannot reproduce uncontrolled in the wild. Keep any outdoor plants in safe pots and plant endemic plants whenever possible!

Fourthly, learn and pay attention to what species are invasive in your area! And if you see them, kill them if at all possible. It may seem harsh, but invasive species have the potential to destabilize and wipe out whole ecosystems without intervention!