Credit: Joe Lewandowski - Colorado Parks and Wildlife

Invasive Species or Overabundant Native Species? Which is a greater threat to ecosystems?

Key Vocabulary: species, range, ecosystem, biodiversity, local, native, invasive, wildlife, resources, predator, population, deciduous forest, herbivore, extinction, overabundant, cultivate

Next Generation Science Standards: 

  • MS-LS2-1. Analyze and interpret data to provide evidence for the effects of resource availability on organisms and populations of organisms in an ecosystem.
  • MS-LS2-4. Construct an argument supported by empirical evidence that changes to physical or biological components of an ecosystem affect populations.
  • MS-LS2-5Evaluate competing design solutions for maintaining biodiversity and ecosystem services.

One of the biggest issues facing local ecosystems comes from the introduction of invasive species. Invasive species are species that are found outside of their native geographical range and are introduced either by accident or on purpose. While the addition of species may seem beneficial for the ecosystem by increasing biodiversity, invasive species spread aggressively and cause many problems.

However, invasive species are not the only threat to local ecosystems. Native species over carrying capacity can also contribute to negative changes in ecosystems. The overabundance of native wildlife has negative consequences, such as over browsing, out-competing other native species, and depletion of resources. So poses a greater threat to local ecosystems: invasive species or overabundant native species?

Invasive Species

When invasive species are introduced to regions outside of their native ranges, they escape the predators and diseases that keep their population in check. This is known as the enemy release hypothesis and allows invasive species to spread rapidly and aggressively.

One example is the Amur honeysuckle, which is native to Northeast Asia.  The plant was brought to the United States for landscaping and wildlife, but escaped cultivation and has now become problematic. The plant is now a predominant invasive shrub found in Eastern deciduous forests in North America. Since the herbivores in North America forests are focused on eating native plants rather than invasive plants, the Amur honeysuckle is not only surviving but thriving. 

This has really hurt native plant populations. The honeysuckle exhibits what scientists call extended leaf phenology when leaves expand earlier in the spring and last longer in the fall than those of native plants. The early leaf expansion can give the invasive species a photosynthetic advantage over native plants. The costs of invasive species damages have been estimated to cost up to $120 billion per year.

Amur Honeysuckle in fruit
Credit: Ohio DNR

Overabundant Native Species:

Overabundant species are species that have population densities that are larger than normal. The large populations have negative consequences on the environment and can be a nuisance to the public. Overabundant wildlife increases through several processes, such as removal and/or extinction of top predators. The large population densities can damage agricultural crops, cause car collisions, and other economic costs.

A great example of this is the white-tailed deer, a native species to the Eastern and Midwestern United States, but their population densities have drastically increased from their pre-Columbian levels. While there is no one factor that is causing deer to be overabundant, the absence of native predators, such as gray wolves, have contributed to the problem.

White-tailed deer are generalist herbivores, which means they eat a variety of plants from agricultural crops to leaves of woody plants to acorns. This has led to overeating plants and as well as feeding on gardens and farms. These crops are generally higher in protein, which the deer need in the spring and summer for reproduction and growth.  

White-tailed deer browsing on an evergreen plant

Why this matters

This brings us back to the original issue of which threat is worse: invasive species or native overabundant wildlife. But perhaps we not asking the right question.  Instead, let’s ask how does the scientific community and public manage these issues without causing more harm to the environment.

Invasive species are costly to manage and remove and can invade habitats where most species would not thrive. This leaves researchers and land managers with the issue of how to remove them and not cause more harm to the environment. Invasive plants can be removed using herbicide, but spraying herbicide causes more harm than good. If the herbicide gets into the soil it could harm or kill native plants or wildlife. Land managers and researchers also have to struggle with which invasive species to remove and when. Is it worth removing an invasive species that will naturalize and not be harmful to the ecosystem versus an invasive species that will spread and be extremely costly and difficult to remove? These are the issues that scientists deal with when studying invasive species and when deciding what suggestions they should tell land managers in order to control invasive species.

However, overabundant wildlife can be just as difficult to manage and many scientists are struggling to find a solution. Populations have to be controlled either by natural causes (disease, storms, etc.) and/or by predators. If populations go above carrying capacity, issues can arise such as the population crashing or negative effects on other species.

Hunting is also important, particularly for limiting deer populations. Some have suggested removing restrictions on hunting in some parks so that hunters are not limited to one deer kill. However, that plan can be costly and some state parks do not agree with increasing deer hunting numbers. There is the issue of how many deer would have to be killed and if s there a more humane plan to control deer populations.

 Two birds with one stone?

Large-scale removal of honeysuckle in habitats where this invasive shrub is prevalent would be a more cost effective and humane way of reducing deer populations. Deer would then not have access to leafy twigs in early spring when there should not be any leaves available to deer. There are cost effective ways to remove honeysuckle without using pesticides, such as hand pulling and hand chainsaws. Some invasive councils, such as the Ohio Invasive Plant Council (OIPC), have local honeysuckle pulls where members and non-members unite to get the invasive shrubs out of the ground. Even schools could partner with Audubon societies and/or invasive species councils to do invasive plant removals.

White-tailed deer roaming fields

3 Comments Posted

  1. I believe that it would worse for an environment to take on an invasive species. Although invasive and overpopulated organisms pose many of the same problems, It would be easier to re introduce a natural predator for natural population control than it would be to dispose of a species such as the honeysuckle. It would take less time and energy also

  2. That is interesting that invasive species are species that are found outside their native geographical range that are introduced by accident or on purpose. I didn’t know that they could spread aggressively and cause many problems. That is pretty amazing that they could cause that many issues. Thank you for all the information!

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