Name: sea stars, wolves, and ecosystem balance
Uploaded: 2026-06-01T06:28:04.059Z
Duration: 1 min 39 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

NC K-12 Science Standard Course of Study

9-12

Biology

ecosystems-interactions-energy-and-dynamics

Ecosystems- Interactions, Energy, and Dynamics

LS.Bio.5.1

Keystone Species

In architecture, a keystone is the central stone in an arch that holds the other stones in place. If the keystone is removed, the structure collapses.A keystone species plays a key role in the structure of an ecological community by influencing the number and variety of species through ecological interactions, including predation, competition, and habitat modification.Relative to its abundance in the community, a keystone species has a disproportionately large effect on community structure.If the keystone species is removed, the community structure can change dramatically, often leading to major shifts in species composition.For example, in kelp forest ecosystems along the Pacific coast, sea otters are a keystone species.These otters consume large quantities of sea urchins, which mainly graze on kelp. Without predation by sea otters, the sea urchin population increases dramatically and can destroy the kelp forests.Species such as fish, crabs, and clams that depend on kelp forests decline significantly, resulting in the formation of urchin barrens.Biodiversity describes the variety of life in a community and is often discussed in terms of species richness, which is the number of species present, and evenness, which is their relative abundance.Sea otters promote biodiversity by reducing the sea urchin population. They are the primary predator in the kelp forest and help regulate this population.So, many species that live in kelp forests rely on sea otters to protect their habitat.

keystone species

Measures of species biodiversity, such as richness (i.e., the number of species present) and evenness (i.e., their relative abundance), describe an ecological community&#x2019;s structure. Many factors affect community structure, including abiotic factors (e.g., sunlight and nutrients), disturbances (e.g., fire or flood), species interactions (e.g., predation or competition), and chance events (e.g., foreign species invasion). Certain species&#x2014;such as keystone species&#x2014;also play a pivotal role in the structure of a community.Relative to their abundance, keystone species have a disproportionately large impact on community structure. Keystone species exert top-down control over lower trophic level organisms and reduce those organisms&#x2019; exploitation of the ecosystem&#x2019;s resources. The intertidal sea star (Pisaster ochraceus) is a keystone species that influences the biodiversity of the Pacific coast&#x2019;s kelp forest ecosystem. If the sea star is removed, the population of their prey species (mussels) increases. Left unchecked, mussels overrun the community and displace other organisms&#x2014;changing the community&#x2019;s species composition and reducing biodiversity.Recognizing keystone species is important for the maintenance and restoration of ecosystems. The North American gray wolf is a keystone species that affects the biodiversity of the Greater Yellowstone Ecosystem (GYE). In the early 1900s, humans hunted the gray wolf into near extinction because ranchers feared the wolf would also target livestock. Since humans eliminated the elk&#x2019;s primary predator, its population soared. Overgrazing led to the destruction of other organisms&#x2019; habitats and altered abiotic factors, such as stream bank stability and nutrient cycling. When gray wolves were reintroduced into the GYE, the ecosystem largely recovered.Keystone species preserve the balance and often safeguard the existence of a community. However, other ecological roles exist that also impact community structure. For example, foundation species (e.g., kelp) are habitat-forming organisms that support an ecosystem, while dominant species (e.g., mussels) are the most abundant organisms in a community. Ecologists&#x2019; knowledge of the roles of the various organisms in an ecosystem allows for more effective conservation and restoration efforts.

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Education

JoVE Core

Ecology

Population and Community Ecology

KEY TERMS AND CONCEPTS

sea stars, wolves, and ecosystem balance

Keystone species help keep ecosystems balanced. In ecology, biodiversity is often described by species richness, which is the number of species present, and evenness, which is how evenly those species are represented. Community structure can also be shaped by abiotic factors such as sunlight and nutrients, disturbances such as fire or flood, species interactions such as predation or competition, and chance events such as the invasion of a foreign species.

A keystone species has a much larger effect on its community than its numbers might suggest. These species create top-down control over organisms at lower trophic levels and limit how much those organisms use the ecosystem’s resources. Because of that role, a keystone species can influence which other species survive and how diverse the community stays.

The intertidal sea star, Pisaster ochraceus, is a classic example in the Pacific coast kelp forest ecosystem. When the sea star is removed, mussel prey increase quickly. If mussels are left unchecked, they spread through the community, displace other organisms, change species composition, and reduce biodiversity.

The gray wolf shows the same idea in the Greater Yellowstone Ecosystem. In the early 1900s, humans hunted gray wolves to near extinction because ranchers feared they would also take livestock. Without the elk’s main predator, elk numbers rose, and overgrazing damaged other habitats and changed abiotic factors such as stream bank stability and nutrient cycling.

When gray wolves were reintroduced to Yellowstone, the ecosystem largely recovered. Keystone species often help preserve balance and can protect the existence of a community. Ecologists also recognize other important roles, including foundation species, which are habitat-forming organisms like kelp, and dominant species, which are the most abundant organisms in a community, such as mussels. Knowing these roles helps scientists plan better conservation and restoration efforts.

Sea Stars, Wolves, and Ecosystem Balance

what are populations and communities?

Population Size, Density, and Community Roles

Populations, metapopulations, and communities are key parts of ecology. Ecology is the study of how organisms interact with each other and with their environment. A population is a group of individuals of the same species that live in the same general area. A community includes multiple populations of different species that coexist and interact in one habitat. Populations are dynamic because they respond to biotic and abiotic factors. Biotic factors are living influences, and abiotic factors...

distribution and dispersion

Species Range and Spacing Patterns

Ecology looks at how organisms interact with each other and with their environment. It also examines where species live and how individuals are arranged within those areas. The geographic range of a species is the total area where its members are found. Dispersion is the pattern of spacing among individuals inside that range. Within a species’ geographic range, dispersion can follow three main patterns: uniform, random, or clumped. These patterns depend on environmental conditions and on...

life histories

Life History Strategies and Survivorship

Life history strategies show how organisms balance survival and reproduction across a lifetime. An organism’s life history includes birth, growth, sexual maturation, reproduction, and death. These patterns reflect trade-offs in how much energy and resources go to making offspring and caring for them. R-strategists and K-strategists show two common reproductive strategies. R-strategists, with r standing for rate, have high fecundity, or reproductive potential. They produce many offspring that...

energy budgets and reproductive strategies

Reproductive Trade-Offs in Life Cycles

Organisms must divide limited energy between growth, maintenance, and reproduction. These energy budgets create trade-offs. Energy used for reproduction cannot be used for survival or growth, so species follow different reproductive patterns. Semelparity and iteroparity are two main strategies on this continuum. Semelparous species reproduce only once in their lifetime. They usually put most or all available resources into that single reproductive event and then die. This approach often...

population growth

Population Growth Curves and Carrying Capacity

Population growth changes with births, deaths, immigration, and emigration. When birth rates and immigration are higher than death rates and emigration, a population increases. When deaths and emigration are higher, the population decreases. These changes can be shown on a graph of population size over time. Under ideal conditions with unlimited resources, populations can grow exponentially. This produces a J-shaped growth curve. Such rapid growth is seen in newly introduced invasive species...

ecological niches

How Species Share Ecological Niches

Ecological niches describe how species fit into an ecosystem. A niche includes the living and nonliving factors that shape where an organism can live. Food resources, climate, and terrain are all part of that role. Two species cannot occupy the exact same niche in the same habitat for long. When their niches overlap too much, the competitive exclusion principle applies. One species will outcompete the other, and the weaker species must adapt or disappear. Similar species can still coexist...

symbiosis

Symbiosis and Species Interactions

Symbiosis and other close species interactions shape how organisms live together in a community. These long-term relationships can affect the distribution and abundance of the species involved. They also often lead to co-evolution, where species change in response to one another. Mutualism is a symbiotic relationship that benefits both species. A common example is ants and aphids. Aphids feed on phloem in plant stems with piercing mouthparts and release a sugary fluid. Ants feed on this fluid,...

competition

How Limited Resources Shape Competition

Competition happens when organisms need the same limited resources in an environment. It is a net-negative interaction because both competitors lose fitness when neither has full access to the resource. This can happen even without direct contact between the competing individuals or populations. Competition within a species is called intraspecific competition. It often helps control population size because rapid growth can lead to crowding and fewer available resources. Stronger individuals...

predator-prey interactions

Predator and Prey Evolution

Predator and prey evolution shapes how animals survive and reproduce. Predators gain energy by eating prey, while prey that avoid being eaten improve their fitness. Over time, both sides develop traits that help them win this struggle. Predators often evolve tools for attack, such as claws, teeth, and speed. Prey evolve defenses that help them escape or stay hidden. These defenses can include crypsis, or blending in with the background, aposematism, or warning coloration, and mimicry, which is...

Keystone species help keep ecosystems balanced. In ecology, biodiversity is often described by species richness, which is the number of species present, and evenness, which is how evenly those species are represented. Community structure can also be shaped by abiotic factors such as sunlight and nutrients, disturbances such as fire or flood, species interactions such as predation or competition, and chance events such as the invasion of a foreign species. A keystone species has a much larger...

ecological disturbance

Disturbance Patterns and Biodiversity

Ecological disturbance is a temporary disruption in an environment that can change an ecosystem in a major way. It may come from abiotic, biotic, or human-caused factors. The size of the impact depends on the disturbance’s intensity, how often it happens, and how widely it spreads. Disturbances can be very small or very large. Trampling underbrush is one example of a small disturbance. Forest fires and floods are larger examples. Natural events such as volcanoes and hurricanes can also disturb...

ecological succession

How Succession Shapes Ecosystem Recovery

Ecological succession is shaped by facilitation, inhibition, and toleration. These processes explain how one community changes into the next after a disturbance or a new surface becomes available. Early species can either help, block, or simply coexist with later species. Facilitation happens when pioneer species make conditions better for later species. They may increase nutrients, water, or light. In inhibition, early species make conditions worse by limiting resources. In some cases, later...

key terms and concepts

Learn how sea stars and gray wolves act as keystone species that shape biodiversity, control prey populations, and support ecosystem recovery.

Sea Stars, Wolves, and Ecosystem Balance | JoVE K12

JoVE Core series brings biology to life through over 300 concise and easy-to-understand animated video lessons that explain key concepts in biology, plus more than 150 scientist-in-action videos that show actual research experiments conducted in today’s laboratories.

biology

Pennsylvania State Academic Standards

Life Science

interdependent-relationships-in-ecosystems

Interdependent Relationships in Ecosystems

3.1.9-12.I

3.1.9-12.L

Louisiana Student Standards for Science

High School

Life Sciences

Ecosystems: Interactions, Energy And Dynamics

HS-LS2-1

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Diversity And Interdependence Of Life

Biodiversity

Tennessee Academic Standards

Ecosystems: Interactions, Energy, and Dynamics

BIO1.LS2.5

Virginia  Standards of Learning

HIgh School

BIO.7

BIO.7.b

BIO.8

BIO.8.c

LS.6

LS.6.a

LS.6.d

LS.9

LS.9.b

Alabama Course of Study Science

Environmental Science

Unity and Diversity

9-12.EVS.2.3.a

Next Generation Science Standards

HS-LS2-6

HS-LS2-7

heredity-inheritance-and-variation-of-traits

Heredity: Inheritance and Variation of Traits

HS-LS4-5

Texas Essential Knowledge and Skills

BIO.13

BIO.13.A

south-carolina-college-and-career-ready-science-standards

South Carolina College and Career Ready Science Standards

B-LS2-1.

B-LS2-2.

B-LS2-6.

Biological Evolution: Unity and Diversity

B-LS4-3.

B-LS4-4.

Earth and Space Science (ESS)

Earth and Human Activity

E-ESS3-1.

E-ESS3-2.

Georgia Standards of Excellence

SEV2.

SEV2.a

Entomology

SEN1.

SEN1.a

SEC3.

SEC3.c

What are Biogeochemical Cycles?

The most common elements in organic molecules, carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorus, are only available in the ecosystem in limited ...

The Water Cycle

The Earth&rsquo;s hydrosphere includes all of the areas where the storage and movement of water occurs. Since water is the basis of all living processes, ...

The Carbon Cycle

Carbon is the basis of all organic matter on Earth, and is recycled through the ecosystem in two primary processes: one in which carbon is exchanged among ...

The Nitrogen Cycle

Nitrogen atoms, present in all proteins and DNA, are recycled between abiotic and biotic components of the ecosystem. However, the primary form of ...

The Phosphorus Cycle

Unlike carbon, water, and nitrogen, phosphorus is not present in the atmosphere as a gas. Instead, most phosphorus in the ecosystem exists as compounds, ...

The Sulfur Cycle

Sulfur, an important element in the chemical makeup of proteins, is recycled through the atmosphere and aquatic and terrestrial environments. Found in the ...

Use models to illustrate how processes in organisms contribute to the flow of energy and the cycling of matter within an ecosystem.

LS.Bio.4.1

What are Populations and Communities?

Populations are groups of individuals of the same species that inhabit a shared environment. Communities include multiple co-existing, interacting ...

Distribution and Dispersion

Ecology is the study of how organisms interact with their environment and with one another. An important aspect of ecology is understanding where species ...

Life Histories

Constrained by limited energy and resources, organisms must compromise between offspring quantity and parental investment. This trade-off is represented ...

Energy Budgets and Reproductive Strategies

Organisms must balance energy intake with the energy required for growth, maintenance, and reproduction. These trade-offs result in a variety of ...

Population Growth

Population size is dynamic, increasing with birth rates and immigration, and decreasing with death rates and emigration. In ideal conditions with ...

Use models to explain the relationship between the flow of energy and cycling of matter among organisms in an ecosystem.

LS.Bio.4.2

Ecological Niches

All organisms have a position within an ecosystem. The complete set of living and nonliving factors&#x2014;including food resources, climate, and ...

Ecological Succession

Ecological succession is influenced by the processes of facilitation, inhibition, and toleration. Facilitation occurs when early successional species ...

Measures of species biodiversity, such as richness (i.e., the number of species present) and evenness (i.e., their relative abundance), describe an ...

Symbiosis

Symbiotic relationships are long-term, close interactions between individuals of different species that affect the distribution and abundance of those ...

Competition

When organisms require the same limited resources within an environment, they may have to compete for them. Competition is a net-negative interaction. ...

Predator-Prey Interactions

Predators consume prey for energy. Predators that acquire prey and prey that avoid predation both increase their chances of survival and reproduction ...

Ecological Disturbance

An ecological disturbance is a temporary disruption in the environment resulting from abiotic, biotic, or anthropogenic factors, causing a pronounced ...

Use mathematics and computational thinking to explain how interactions between organisms (predator/prey, competition) affect carrying capacity and maintain stability in an ecosystem.

What is Biodiversity?

Biodiversity describes the variety of living things at multiple organizational levels: genetic, species and ecosystem diversity. Species diversity ...

Threats to Biodiversity

There have been five major extinction events throughout geological history, resulting in the elimination of biodiversity, followed by a rebound of species ...

Biodiversity and Human Values

Human civilization relies on biodiversity in many ways. Sudden changes in species biodiversity result in environmental changes that can modify weather ...

What is Conservation Biology?

Conservation biology is a scientific field that focuses on the preservation of biodiversity in order to protect ecosystems while meeting the needs of the ...

Sustainable Development

As the human population continues to grow and use resources, we must be mindful of our planet&rsquo;s natural limits. Sustainable development provides a ...

Conservation of Small Populations

Small population sizes put a species at extreme risk of extinction due to a lack of variation, and a consequent decrease in adaptability. This weakens ...

What is Weather?

Overview

Weather refers to the current state of atmospheric conditions at a specific time and place. Weather is temporary and is influenced by the ...

Global Climate Change

Throughout its ~4.5 billion year history, the Earth has experienced periods of warming and cooling. However, the current drastic increase in global ...

Conservation of Declining Populations

Conservation of declining population focuses on ways of detecting, diagnosing, and halting a population decline. The approach uses methods to prevent ...

Habitat Fragmentation

Habitat fragmentation describes the division of a more extensive, continuous habitat into smaller, discontinuous areas. Human activities such as land ...

Engage in argument from evidence to evaluate various solutions to reduce the impact of human activities on biodiversity and ecosystem health.

LS.Bio.5.2

Analyze the relationships between matter and energy within ecosystems.

Sea Stars, Wolves, and Ecosystem Balance

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