Real-world examples of the role of keystone species in ecosystems

Teachers and judges don’t just want definitions; they want examples of the role of keystone species that you can actually investigate. When you pick a keystone species case study, you’re basically choosing a natural experiment that scientists have already been watching for decades.

Some of the best examples include:

• Large predators that control herbivores
• Small predators that control grazers
• Herbivores that reshape habitats
• Ecosystem engineers that physically change the environment
• Mutualists that connect multiple species (like pollinators or seed dispersers)

Below, we’ll walk through real examples that show how removing or reintroducing a species changed an entire community. These are the kinds of systems you can turn into models, simulations, or data-analysis projects for a strong zoology science fair entry.

Yellowstone wolves: a classic example of the role of keystone species

One of the best-known examples of the role of keystone species is the gray wolf in Yellowstone National Park.

For most of the 20th century, wolves were removed from Yellowstone. Without wolves, elk populations soared. Elk overgrazed young willow, aspen, and cottonwood along rivers. The result: fewer trees, eroding riverbanks, and less habitat for birds and beavers.

When wolves were reintroduced in the mid-1990s, everything shifted:

• Elk changed where and how long they grazed.
• Willow and aspen stands recovered in many areas.
• Beaver colonies expanded, building dams that created ponds and wetlands.
• Songbirds, amphibians, and fish benefited from better habitat.

Ecologists call this a trophic cascade: predators indirectly help plants and other species by controlling herbivores. For a science fair project, you can:

• Build a food web model showing elk, wolves, plants, and beavers.
• Use publicly available data on wolf and elk numbers over time from the National Park Service.
• Simulate what happens to plant biomass if wolf numbers go up or down.

This Yellowstone case is often cited in ecology textbooks and is still being studied in 2024, making it a reliable example of how a keystone predator can reshape an ecosystem.

Sea otters and kelp forests: marine examples of the role of keystone species

If you’re more interested in ocean systems, sea otters are one of the best examples of the role of keystone species in marine ecology.

Here’s the chain of interactions:

• Sea otters eat sea urchins.
• Sea urchins eat kelp.
• Kelp forests provide habitat and food for fish, invertebrates, and marine mammals.

Where sea otters are present, urchin populations stay in check and kelp forests thrive. Where otters are removed (through hunting, pollution, or orca predation), urchins explode in number and mow down kelp, creating “urchin barrens.”

Real examples include coastal ecosystems in Alaska and the Pacific Northwest, where scientists have documented sharp switches between kelp-dominated and urchin-dominated states. Research from institutions like the University of California system and NOAA has tracked these changes for decades.

For a science fair project, you might:

• Build a tank or virtual simulation with “otter,” “urchin,” and “kelp” roles.
• Model how different predation rates affect kelp coverage.
• Analyze case studies from NOAA’s National Marine Fisheries Service on kelp forest health.

This is a clean, easy-to-explain example of how a single predator can stabilize an entire habitat.

Sea stars and mussel beds: small predators with big impacts

Another marine case that shows examples of examples of the role of keystone species is the ochre sea star along rocky Pacific coasts.

Ecologist Robert Paine’s classic experiments in the 1960s and 1970s showed that when sea stars were removed from intertidal zones, mussels took over, crowding out many other invertebrates and algae. With sea stars present, mussel numbers stayed lower, and overall species diversity was higher.

This system became a textbook example of a keystone predator:

• Sea stars prefer mussels but also eat other invertebrates.
• By limiting mussels, they keep space open for barnacles, algae, and other species.
• Remove sea stars, and you get a simpler, less diverse community.

In the 2010s, a disease called sea star wasting syndrome caused massive die-offs along the West Coast. Scientists observed real-world versions of Paine’s experiments as mussel populations expanded in some areas. Current research (still ongoing in 2024) continues to monitor recovery.

For a project, consider:

• Building a model rocky shore community.
• Using published data from universities or agencies like USGS to track sea star declines and community changes.

African lions and wild dogs: savanna examples of the role of keystone species

African savannas offer multiple examples of the role of keystone species, especially large carnivores like lions, leopards, and African wild dogs.

In many protected areas, when top predators decline due to poaching or habitat loss, herbivores like zebra, wildebeest, and antelope can increase or change behavior. That can lead to:

• Heavier grazing in certain areas
• Shifts in fire patterns due to changes in grass cover
• Impacts on tree regeneration and bird communities

Some real examples include parts of East and Southern Africa where predator reintroduction or better protection has led to more balanced herbivore populations and improved vegetation structure.

For a science fair angle, you can:

• Analyze long-term data from organizations like the Smithsonian or national park reports.
• Model how changes in predator density affect herbivore numbers and plant cover.

While these systems are more complex than the Yellowstone story, they give you additional examples of how keystone predators influence entire landscapes.

Beavers: ecosystem engineers as keystone species

Not all keystone species are top predators. Beavers are a strong example of the role of keystone species as ecosystem engineers.

By building dams, beavers:

• Slow down water flow and create ponds and wetlands.
• Increase groundwater recharge.
• Provide habitat for fish, amphibians, waterfowl, and invertebrates.
• Change plant communities along streams and floodplains.

Remove beavers, and streams often become narrower, faster, and less structurally complex. Biodiversity can drop as habitats shrink.

In the western United States, beaver reintroduction and “beaver mimicry” projects (using structures that imitate dams) are being used as low-cost tools for stream restoration and climate resilience. These efforts are still expanding in 2024–2025, and agencies like the U.S. Fish & Wildlife Service publish updates and case studies.

For a project, you might:

• Compare biodiversity in beaver ponds vs. nearby streams without beavers.
• Use satellite images or maps to measure how water surfaces change over time.

This is one of the best examples for showing how a single mammal can reshape physical habitat and influence many other species.

Pisaster, pollinators, and fig wasps: less obvious examples of the role of keystone species

Some of the best examples of the role of keystone species are not charismatic mammals but tiny invertebrates or mutualists.

Fig trees and fig wasps

In many tropical forests, certain fig tree species fruit during times when few other plants do. They become critical food sources for birds, bats, and primates. Each fig species typically relies on a single fig wasp species for pollination.

If the fig wasp disappears:

• The fig tree may fail to reproduce.
• Animals that depend on figs lose a key food source.
• Other plants and animals that depend on those fruit-eaters are indirectly affected.

This nested dependency makes fig–fig wasp pairs classic examples of mutualistic keystone interactions.

Pollinators as potential keystone species

In some systems, specific pollinators or seed dispersers act as keystone mutualists. For instance, certain bat or bird species in tropical regions pollinate or disperse seeds of many plant species. Their loss can dramatically change forest composition over decades.

You can draw on research from universities and organizations like the Smithsonian Tropical Research Institute for 2020s-era studies showing how losing key mutualists reshapes forests.

Sea turtles, sharks, and other 2024–2025 relevant examples

Recent conservation work gives more real examples of the role of keystone species that are very current and science-fair-friendly.

Green sea turtles and seagrass beds

Green sea turtles graze on seagrass. In some areas, moderate grazing keeps seagrass beds healthy by promoting new growth and preventing overaccumulation of old leaves. Where turtle numbers are too low due to overharvesting or bycatch, seagrass beds can become overgrown and less productive; where turtle numbers spike unnaturally (for example, in protected areas without natural predators), overgrazing can damage seagrass.

This makes green turtles a nuanced example of a species that may act as a keystone herbivore in some locations, depending on density and predator presence.

Sharks as apex predators

In several coastal ecosystems, shark declines have been linked to increases in mid-level predators and shifts in fish communities. For instance, some studies in the western Atlantic have connected large shark declines to increases in rays, which then heavily graze shellfish like scallops.

These systems are more complex and sometimes debated, but they offer good examples of how removing apex predators can send ripples through food webs. Agencies like NOAA and academic groups continue to update shark population and ecosystem impact data into 2024 and beyond.

For a project, you could:

• Use open fisheries data to track shark catch trends.
• Model how changes in shark numbers affect lower trophic levels.

Turning these examples into science fair projects

Now that you’ve seen multiple examples of examples of the role of keystone species, how do you turn them into a strong zoology project?

You don’t need to visit Yellowstone or scuba dive in a kelp forest. Instead, you can:

• Build food web models: Use software or poster diagrams to show how a keystone species connects to others. Then simulate removal or reintroduction.
• Analyze existing data: Many government and university sites share open datasets. For example, the National Park Service and USGS host data you can graph and interpret.
• Create microcosms or analogs: Use small-scale systems (like algae–snail–fish setups in aquariums or predator–prey insect systems in terrariums) as analog models of larger keystone dynamics.
• Compare biodiversity: If you can safely access local ponds, streams, or forests, compare areas with and without a suspected local “keystone-like” species (for example, a dominant tree that provides most of the shade or fruit).

The key is to clearly show cause-and-effect: when the keystone species changes, the community changes.

FAQ: common questions about examples of the role of keystone species

What are some of the best examples of the role of keystone species for students?

Some of the best examples for student projects include Yellowstone wolves and elk, sea otters and kelp forests, ochre sea stars and mussel beds, beavers as ecosystem engineers, and fig trees with their fig wasps. These systems are well-studied, well-documented, and rich in publicly available data.

Can plants be keystone species, or are they always animals?

Plants can absolutely be keystone species. For instance, certain fig trees in tropical forests provide fruit during food-scarce seasons, supporting many animals. Some dominant tree species in temperate forests also structure habitat and food availability for dozens of other species, making them strong examples of plant keystones.

How do I know if a species is really a keystone or just important?

A species is considered keystone if its impact on the ecosystem is disproportionately large compared to its abundance or biomass. In other words, if removing that species causes big, cascading changes in many other species or in ecosystem structure, it’s a strong example of a keystone. Ecologists often test this through long-term observations, experiments, or models.

Are humans keystone species?

Humans influence virtually every ecosystem on Earth, but ecologists usually describe us as ecosystem engineers or global drivers rather than classic keystone species. That said, in some local contexts (like traditional land management systems), human practices can resemble keystone effects by shaping fire regimes, plant communities, and animal populations.

What is an easy, data-based project using examples of keystone species?

One accessible project idea is to pick a well-known keystone example—such as Yellowstone wolves or sea otters and kelp—and gather population and habitat data from government or university websites. You can graph changes over time and explain how those trends match the idea of a keystone species, using your graphs as part of your science fair display.

By grounding your project in these real examples of the role of keystone species, you’re not just repeating a definition—you’re showing how ecology works in the real world. That’s the kind of work that stands out on a science fair table.