- Position‹3 of 3
- Invasive species help ecosystems
- Argument‹2 of 2
Invasive species are a new food source
Invasive species can provide a new food source to the surrounding native animals and plants. For example, new types of pests could be eaten by predators if a native species starts to run out.
The argument
The usual account of invasive species treats their arrival as a subtraction from an ecosystem. This argument proposes a different reading: an introduced species is also biomass that was not there before, and biomass is food. Invasive species can be a new source of food for their surrounding ecosystem, and on this view that contribution is part of what their arrival does. The point is said to hold for plants and animals alike. Among plants, the dandelion can be fit for human consumption if prepared correctly, which shows that an introduced species need not be merely tolerated but can be used directly. Among animals, even invasive pests can become food for predatory animals: the brown rat, which has invaded European countries and North America, is hunted by birds and snakes. In each case the arriving species is absorbed into the food web rather than sitting outside it, and the predators that take it gain a resource they did not previously have. The general claim rests on what this does to an ecosystem's resilience. A system with a narrow set of nutrition sources is vulnerable to any one of them failing, because the organisms that depend on it have nowhere else to turn. Additional sources reduce that exposure, giving predators and consumers alternatives when a familiar prey or plant becomes scarce. On this reasoning an ecosystem will never die while an availability of different nutrition sources remains, and an introduced species adds to that stock rather than depleting it. Because invasive species become a new food source in the systems they enter, on this view they can help those ecosystems rather than only harming them.
Premises
Counter-arguments
Invasive species could eat other animals or plants that need to exist within the ecosystem. The cane toad eats small native rodent species while killing native predators. With the cane toad as the top of the food chain, the ecosystem’s health will decline. Invasive species could potentially do more harm than good.
Rejecting the premises
[Rejecting P1] Invasive species could hurt the ecosystem.