Relationships in Ecosystems

Relationships in Ecosystems

Middle School

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Learning Objectives

• Explain how populations grow and what factors limit their size.

• Describe the various factors that influence the carrying capacity of an ecosystem.

• Understand why the scale of an ecosystem is important when analyzing data.

Key Vocabulary

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Ecosystem

An ecosystem includes all living and nonliving components interacting together within a specifically defined area.

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Biotic Factors

Biotic factors are all of the living or once-living components of an ecosystem, such as plants and animals.

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Abiotic Factors

Abiotic factors are the nonliving chemical and physical parts of an ecosystem, including air, water, and soil.

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Community

A community consists of all the different populations of living organisms interacting with each other in an ecosystem.

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Population

A population is a group of organisms of the same species that are living in the same area.

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Predation

Predation is a biological interaction where one organism, the predator, hunts and consumes another organism, the prey.

Key Vocabulary

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Symbiosis

A close, long-term relationship between two different species where at least one of them benefits.

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Keystone Species

A species that has a very large effect on its entire ecosystem, much like a keystone.

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Carrying Capacity

The maximum population size of a species that an environment can support over a long period.

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Limiting Factors

Environmental conditions, like food or space, that limit the growth and size of a population.

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Invasive Species

A non-native species that is introduced to a new environment and causes harm to it.

What is an Ecosystem?

• An ecosystem has living and nonliving things in a specific area.

• Living parts are biotic, and nonliving parts are abiotic.

• Ecosystems have levels: organism, population, and community.

Multiple Choice

What is the definition of an ecosystem?

• A specific area containing only living things.

• A specific area containing only nonliving things.

• A specific area containing both living and nonliving things.

• A group of different populations living together.

Multiple Choice

What is the relationship between the biotic and abiotic parts of an ecosystem?

• Biotic parts are the nonliving components, while abiotic parts are the living components.

• Biotic parts are the living components, while abiotic parts are the nonliving components.

• Biotic and abiotic parts are both living components.

• Biotic and abiotic parts are both nonliving components.

Multiple Choice

A scientist observes a single fox, a group of foxes, and then all the different animals and plants in the same forest. Which list correctly shows the levels of organization the scientist observed, from simplest to most complex?

• Community, population, organism

• Population, organism, community

• Organism, population, community

• Community, organism, population

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Community Interactions

Competition

• Competition happens when organisms require the same limited resources, such as food or space.

• This can occur between members of the same species or different species.

• For instance, squirrels and chipmunks might compete for the same pile of acorns.

Predation

• Predation is an interaction where one organism, the predator, hunts and kills another.

• The organism that is hunted and consumed is known as the prey.

• This relationship helps to control population sizes and maintain a balanced ecosystem.

Multiple Choice

Which statement best defines competition?

• An interaction where organisms need the same limited resources.

• An interaction where one organism hunts and consumes another.

• An interaction where organisms work together to find food.

• An interaction where one organism lives on or inside another.

Multiple Choice

What is the primary function of predation in an ecosystem?

• It helps to control the population sizes of prey species.

• It increases the amount of food available in an ecosystem.

• It eliminates all competition between different animals.

• It forces predators to share resources with their prey.

Multiple Choice

In an area, foxes hunt both squirrels and chipmunks, which both rely on a limited supply of acorns. If all the foxes were removed from the area, what would be the most likely outcome?

• The amount of available acorns would increase.

• Competition between the squirrels and chipmunks would increase.

• The squirrel and chipmunk populations would stop growing.

• The squirrels and chipmunks would start hunting other animals.

Symbiotic Relationships

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Mutualism

• A relationship where both species benefit from interacting with each other.

• Bees get nectar from flowers and use it for their food.

• In the process, bees help the flowers to reproduce by pollination.

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Commensalism

• A relationship where one species benefits, but the other is unaffected.

• Cattle egrets eat insects that are stirred up by grazing cows.

• The cows are not helped or harmed by the egrets' presence.

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Parasitism

• One organism, the parasite, benefits by harming another, the host.

• The parasite lives on or inside the host's body for survival.

• Ticks are parasites that feed on the blood of their animal hosts.

Multiple Choice

Which term describes a relationship where both species benefit from the interaction?

• Mutualism

• Commensalism

• Parasitism

• Competition

Multiple Choice

Based on the definition of commensalism, what happens in the relationship between cattle egrets and cows?

• The egret gets food and the cow is unaffected.

• The cow gets cleaned and the egret gets food.

• The egret is harmed and the cow benefits.

• Both the egret and the cow are harmed.

Multiple Choice

Which statement best explains the difference in outcomes between a parasitic and a mutualistic relationship?

• In parasitism one organism is harmed, while in mutualism both benefit.

• In parasitism both organisms are harmed, while in mutualism one benefits.

• In parasitism one organism is unaffected, while in mutualism both are harmed.

• In parasitism both organisms benefit, while in mutualism one is unaffected.

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Population Growth and Keystone Species

Population Growth

• Population growth describes how the number of individuals in a certain area changes over time.

• Exponential growth is when a population grows at an accelerating rate due to unlimited resources.

• Logistic growth occurs when growth slows as it reaches the ecosystem's carrying capacity, or limit.

Keystone Species

• A keystone species is an organism that has a disproportionately large effect on its ecosystem.

• They are essential for maintaining the structure and health of the entire ecological community.

• For example, coral builds the reefs that provide homes for countless other ocean species.

Multiple Choice

What does the concept of population growth describe?

• How the number of individuals in a certain area changes over time.

• The maximum number of organisms an ecosystem can support.

• The role an organism plays in its environment.

• How a population grows at an accelerating rate.

Multiple Choice

What makes a keystone species different from other species in an ecosystem?

• It has a disproportionately large effect on its ecosystem.

• Its population grows at an accelerating, exponential rate.

• Its population size is limited by the carrying capacity.

• It is the most numerous species in the entire community.

Multiple Choice

Coral is a keystone species that builds reefs, providing homes for countless fish. If a disease eliminated the coral, what is the most likely impact on the fish populations?

• The fish populations would decrease because the ecosystem's carrying capacity would be reduced.

• The fish populations would experience exponential growth due to having more space.

• The fish populations would remain stable and be unaffected by the loss of coral.

• The fish populations would immediately find a new keystone species to build homes.

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What Are Limiting Factors?

Density-Dependent Factors

• These factors have a greater impact on larger, more crowded populations in an area.

• Examples include competition for resources, increased predation, and the spread of diseases and parasites.

• Invasive species can also increase competition for food and space in an ecosystem.

Density-Independent Factors

• These factors affect all populations, regardless of their size or how crowded they are.

• This category includes natural disasters such as destructive wildfires, floods, and severe storms.

• Human activities like pollution and habitat destruction also limit population growth in an ecosystem.

Multiple Choice

What is the primary role of a limiting factor in an ecosystem?

• To restrict the growth or size of a population

• To increase the number of resources in an ecosystem

• To help different species share the same food source

• To ensure all populations can grow without limits

Multiple Choice

What is the key difference between density-dependent and density-independent limiting factors?

• Whether the factor is caused by living or non-living things

• Whether the factor affects animals or plants

• Whether the factor's impact changes with population crowding

• Whether the factor is a result of human activity or not

Multiple Choice

A severe flood sweeps through a valley, affecting the local deer population. Which statement correctly classifies this event and explains why?

• The flood is a density-dependent factor because it will increase competition for the few resources left.

• The flood is a density-independent factor because it impacts the entire deer population, regardless of its size.

• The flood is a density-dependent factor because it will make it easier for predators to hunt the deer.

• The flood is a density-independent factor because it is a natural event and not caused by humans.

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Ecosystem Scale

10-Gallon Aquarium

• ​Small ecosystems are sensitive to minor changes, which can have a huge impact.

• ​​Adding a little chlorinated water can be deadly to the fish in a small aquarium.

• ​The harmful substance is concentrated in a small volume of water, increasing its effect.

165-Gallon Pond

• ​Large ecosystems are more resilient to small changes because of their greater size.

• ​​The same amount of chlorine has less impact because it is diluted in more water.

• ​Scientists monitor large ecosystems by sampling small sections to study population sizes.

Multiple Choice

What is the primary relationship between the size of an ecosystem and its ability to handle change?

• Larger ecosystems are more resilient to change than smaller ones.

• Smaller ecosystems have more types of fish than larger ones.

• Larger ecosystems are less affected by the amount of water they hold.

• Smaller ecosystems are monitored more frequently by scientists.

Multiple Choice

Why does a small amount of a harmful substance have a much greater effect on a small aquarium than on a large pond?

• The substance is more concentrated in the small volume of water.

• The fish in the aquarium are naturally weaker than pond fish.

• The water in the aquarium is warmer than the water in the pond.

• The substance evaporates more slowly in the smaller aquarium.

Multiple Choice

A scientist testing a large pond finds a high level of a harmful substance in one small sample of water. Based on how large ecosystems are monitored, what is the most logical conclusion?

• The substance will likely have no effect on the large pond.

• The health of the entire pond may be at risk from the substance.

• The substance will only affect the specific area that was sampled.

• The fish will adapt to the substance because the pond is large.

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Common Misconceptions

Misconception	Correction
An ecosystem can support unlimited growth.	Ecosystems have a carrying capacity that limits population sizes.
All interactions between species are negative or competitive.	Many species cooperate through symbiotic relationships like mutualism.
If two events happen together, one must cause the other.	Correlation does not equal causation; an underlying factor could be the cause.
Removing one species won't affect the whole system.	Removing a keystone species can drastically alter or collapse an ecosystem.

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Summary

• Ecosystems balance living (biotic) and non-living (abiotic) factors.

• Organisms interact through competition, predation, and symbiosis.

• Carrying capacity is the maximum population size an environment can support.

• Limiting factors can be density-dependent or density-independent.

• Keystone species are critical for an ecosystem’s health and structure.

• The scale of an ecosystem affects its response to change.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

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• 2

• 3

• 4