Invasive Species, Endangered Species and Human Impacts on Biodiversity

AP Environmental Science · AP (Advanced Placement) · 5 min read · Updated: 7 Sept 2026

Welcome to Unit 9: Global Change!

In this final stretch of AP Environmental Science, we are looking at the big picture. We’ve already explored how the atmosphere is changing through ozone depletion and the greenhouse effect. Now, we are diving into the "living" part of global change: Invasive Species, Endangered Species, and Human Impacts on Biodiversity.

Don't worry if this seems like a lot of information—most of these concepts build on things you learned back in Unit \( 2 \) (Biodiversity) and Unit \( 3 \) (Populations). We’re just putting them into the context of a rapidly changing world.

9.8 Invasive Species

Think of an invasive species as an uninvited guest who shows up to a party, eats all the food, takes over the couch, and kicks the original guests out. These are species that are not native to a specific area and cause harm to the environment, the economy, or human health.

Why are they so successful?

Invasive species usually share certain traits that help them take over. Think back to Unit \( 3 \). Most invasive species are:

• Generalists: They can eat almost anything and live in many different climates.
• r-selected species: They have high reproductive rates, grow quickly, and reach sexual maturity early.
• Lack of Natural Predators: Because they are in a new environment, the local predators don't know how to hunt them yet. This allows their population to grow unchecked.

Environmental Impact

Invasive species outcompete native species for resources like food, water, and space. This leads to a decrease in biodiversity and can push native species toward extinction. For example, an invasive vine might grow over a forest canopy, blocking sunlight for the native plants below.

Quick Review: Invasive species = Generalists + r-selected + No natural predators = Big trouble for biodiversity.

9.9 Endangered Species

While invasive species are winning the "survival game," endangered species are on the verge of losing it. A species is considered endangered when its population has dwindled to the point where it is at risk of extinction.

What makes a species vulnerable?

Unlike invasive species, endangered species are often:

• Specialists: They have a very narrow ecological niche (e.g., they only eat one type of food or live in one specific temperature range).
• K-selected species: They reproduce slowly, have few offspring, and provide lots of parental care. This makes it hard for their populations to recover if they take a hit.
• Small Population Size: They have less genetic diversity, making them more vulnerable to diseases or environmental changes.

How do we protect them?

The AP exam requires you to know two specific pieces of legislation that help protect biodiversity:

1. CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora): This is an international treaty. Its goal is to ensure that the international trade of wild animals and plants does not threaten their survival. If you see a question about stopping the illegal ivory trade or exotic pet smuggling, think CITES.

2. Endangered Species Act (ESA): This is a United States law. It provides a program for the conservation of threatened and endangered plants and animals and the habitats in which they are found. It forbids the government and citizens from taking actions that harm these species or their "critical habitat."

Key Takeaway: Factors like being a specialist or having a low reproductive rate make a species more likely to become endangered when their environment changes.

9.10 Human Impacts on Biodiversity

Humans are the primary drivers of the current "biodiversity crisis." To remember the main ways humans decrease biodiversity, use the acronym HIPPCO. (Note: While the acronym is a great tool, the exam will ask you to explain these concepts in detail).

The HIPPCO Acronym

H — Habitat Destruction: This is the number one cause of species extinction. Activities like deforestation, agriculture, and urbanization destroy the homes of wildlife. This also includes habitat fragmentation, where a large habitat is broken into smaller, isolated "islands" (like building a highway through a forest).

I — Invasive Species: As discussed in \( 9.8 \), these species outcompete natives.

P — Population Growth (Human): As the human population grows, we require more space and more resources (\( food, water, energy \)), which puts pressure on all other species.

P — Pollution: Toxic chemicals, plastic waste, and nutrient runoff (like nitrogen and phosphorus) can kill organisms or disrupt their reproduction. Think back to bioaccumulation and biomagnification from Unit \( 8 \)!

C — Climate Change: Rapid changes in temperature and precipitation patterns can happen faster than species can adapt or migrate. This is especially dangerous for specialists.

O — Overexploitation: This is harvesting species from the wild faster than they can recover. Examples include overfishing and poaching.

What can we do? (Environmental Solutions)

The AP exam focuses heavily on Practice \( 7 \): Proposing and justifying solutions. Some ways to mitigate (reduce) human impacts include:

• Creating Protected Areas: Establishing national parks or wildlife refuges.
• Habitat Corridors: Connecting fragmented habitats with "green bridges" so animals can move safely between patches.
• Sustainable Land Use: Using selective cutting in forestry or practicing conservation agriculture.
• Restoration Ecology: Replanting native vegetation or removing invasive species to restore an ecosystem to its original state.

Exam Tips and Common Mistakes

• Don't confuse "Non-native" with "Invasive": Many species in our yards are non-native (like tomatoes or tulips), but they aren't "invasive" unless they cause ecological or economic harm.

• The "Habitat" Priority: If an FRQ asks for the best way to save a species, protecting the habitat is almost always a stronger answer than "captive breeding" or "zoos."

• Know your Laws: Remember that CITES is for international trade, while the Endangered Species Act is for domestic (U.S.) protection.

• Calculations: While this chapter is conceptual, remember that Question \( 3 \) of the FRQ section involves math. You might be asked to calculate the percentage change in a population or use the Rule of \( 70 \) if given a growth rate. Always show your work and include units!

You've got this! Understanding how we impact the planet is the first step toward finding solutions to protect it.

Quick check

Can you answer these now?

Open each question to check the key ideas from this chapter.

What is an invasive species and why is it problematic for ecosystems?

An invasive species is a non-native organism that causes harm to the environment, economy, or human health by outcompeting native species for resources.

What biological traits typically allow invasive species to dominate a new environment?

Invasive species are often r-selected generalists with high reproductive rates and a lack of natural predators in their new environment.

What biological characteristics make a species more vulnerable to becoming endangered?

Species that are K-selected, specialists with narrow niches, or have small population sizes are highly vulnerable to extinction.

How does CITES protect endangered species differently than the Endangered Species Act (ESA)?

CITES is an international treaty focusing on preventing illegal trade of species, whereas the ESA is a domestic U.S. law protecting species and their critical habitats.

What does the acronym HIPPCO represent in environmental science?

HIPPCO stands for Habitat destruction, Invasive species, Population growth (human), Pollution, Climate change, and Overexploitation.

What is habitat fragmentation and how does it affect wildlife?

Habitat fragmentation occurs when large habitats are broken into smaller, isolated patches, often by human infrastructure like roads or agriculture.

How can habitat corridors help mitigate the effects of habitat fragmentation?

Habitat corridors are "green bridges" or protected strips of land that connect isolated habitat patches, allowing animals to move safely between them.

Why is protecting habitat generally considered more effective than captive breeding for saving species?

Protecting habitat preserves the entire ecosystem and the species' natural niche, which is more sustainable and cost-effective than managing a species in captivity.

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