Organism Interactions in Ecosystems

Organism Interactions in Ecosystems

Middle School

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Learning Objectives

• Define biotic and abiotic factors and identify examples of each in an ecosystem.

• Explain how limiting factors determine the carrying capacity of a population.

• Describe how competition and an organism's niche influence survival and interactions between species.

• Analyze the cyclical relationship between predator and prey populations in an ecosystem.

Key Vocabulary

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Ecosystem

A community of living organisms interacting with their non-living physical environment.

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Biotic Factor

The living or once-living components of an ecosystem, such as plants and animals.

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Abiotic Factor

The non-living chemical and physical parts of the environment that affect living organisms.

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Limiting Factor

An environmental factor that restricts the size, growth, or distribution of a population.

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Carrying Capacity

The maximum population size of a species that the environment can sustain indefinitely.

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Niche

The specific role an organism plays within its ecosystem, including its diet and behavior.

Key Vocabulary

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Competition

The struggle between organisms to use the same limited resources, such as food or space.

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Interspecific Competition

Competition for the same limited resources that occurs between members of different species.

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Intraspecific Competition

Competition for the same limited resources that occurs between members of the same species.

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Predator

An organism that hunts and kills other organisms for its primary food source.

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Prey

An organism that is hunted and killed for food by another organism.

What Are Ecosystems?

• An ecosystem is a community of interacting organisms and their environment.

• Organisms depend on living (biotic) and non-living (abiotic) factors to survive.

• Ecosystems can be aquatic (water-based) or terrestrial (land-based).

Multiple Choice

What is the definition of an ecosystem?

• A community of interacting organisms and their environment

• A group of the same type of organisms

• The non-living things in a certain place

• A single animal or plant living alone

Multiple Choice

What is the relationship between the living (biotic) and non-living (abiotic) factors in an ecosystem?

• Living organisms depend on non-living factors to live.

• Non-living factors are created by living organisms.

• Living organisms are not affected by non-living factors.

• Non-living factors only exist in aquatic ecosystems.

Multiple Choice

A desert with lizards and cacti is a terrestrial ecosystem, while an ocean with fish and coral is an aquatic ecosystem. What must be true for both of these to be considered ecosystems?

• Both contain organisms that depend on their living and non-living environment.

• Both must be the same size to be considered ecosystems.

• Both are land-based types of ecosystems.

• Both have the same kinds of animals and plants.

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What Are Limiting Factors?

• A limiting factor is a resource that restricts how large a population can grow.

• Light is needed for photosynthesis, and water is essential for all living things.

• Shelter offers protection, while temperature must be within an organism's survival range.

• Soil type determines which plants can grow, which in turn supports local animals.

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Multiple Choice

Which of the following best defines a limiting factor?

• A resource that helps a population grow infinitely.

• A resource that only affects plants, not animals.

• A resource that is always abundant in every ecosystem.

• A resource that restricts how large a population can grow.

Multiple Choice

Why are resources like water, shelter, and a suitable temperature range considered limiting factors?

• They are only needed by plants for photosynthesis.

• They provide protection but do not affect population size.

• They are essential for survival, and their scarcity can prevent a population from growing.

• They determine the climate of an ecosystem.

Multiple Choice

If a region's soil type can only support a few kinds of plants, what is the most likely impact on the local animal populations?

• The animal population will be unaffected by the type of plants.

• The animal population will grow larger because there is less competition from plants.

• The animals will adapt to eat the soil directly.

• The animal population will be limited due to the restricted variety of plants.

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Carrying Capacity and Population Growth

• The limiting factors in an ecosystem determine its carrying capacity for a species.

• Carrying capacity is the maximum population that available resources can support long-term.

• Exponential growth (Curve A) occurs when there are no limits on the population.

• Logistic growth (Curve B) slows and levels off at the carrying capacity.

Multiple Choice

What does the 'carrying capacity' of an environment represent?

• The maximum population size that an environment can support over time.

• The initial number of individuals that start a new population.

• The speed at which a population increases when it has no limits.

• The total area of the environment that a population lives in.

Multiple Choice

What causes a population to follow a logistic growth pattern instead of an exponential one?

• The presence of limiting factors, such as competition for resources.

• The absence of any limiting factors in the environment.

• A continuous increase in the population's growth rate.

• A pattern of growth represented by a steep, J-shaped curve.

Multiple Choice

A few deer are introduced to a large island with abundant food and no predators. Which statement best predicts the long-term growth of this deer population?

• The population will grow exponentially at first, then slow down as it approaches the environment's carrying capacity.

• The population will show a steady, constant rate of logistic growth from the beginning.

• The population will grow exponentially forever without ever slowing down.

• The population will immediately level off and stop growing.

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Biotic Interactions: Predator and Prey

• Biotic factors are the living parts of an ecosystem, like predators and prey.

• Predator and prey populations directly impact one another and follow a cyclic pattern.

• When more prey are available, the predator population can grow with more food.

• More predators lead to fewer prey, which in turn reduces the predator population.

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Multiple Choice

Which statement best describes the relationship between predators and prey in an ecosystem?

• They are living factors whose populations directly influence one another.

• They are non-living factors that have no effect on each other.

• One is a living factor and the other is a non-living factor.

• They are two species that cooperate to find the same food source.

Multiple Choice

What is the primary reason that a growing prey population can lead to an increase in the predator population?

• The availability of more prey provides more food for predators.

• A decrease in prey causes predators to reproduce more.

• Predators and prey compete for the same resources.

• Predators learn to hide from the increased number of prey.

Multiple Choice

If a large increase in the number of predators leads to a sharp decline in the prey population, what is the most likely long-term outcome for the predators?

• The predator population will eventually decrease due to a lack of food.

• The predator population will increase as they find other food sources.

• The predator population will remain stable indefinitely.

• The prey population will quickly recover and grow larger than before.

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Biotic Interactions: Competition and Niche

Interspecific Competition

• Competition between different species for the same limited resources is called interspecific competition.

• For instance, giraffes eat leaves high on trees, while zebras eat lower leaves and grasses.

• Each species occupies a specific niche, which helps them avoid direct competition with others.

Intraspecific Competition

• Competition that happens among members of the same species is called intraspecific competition.

• For example, male giraffes feed with their heads up while female giraffes feed down.

• Many animals also reduce competition by claiming and defending their own territories.

Multiple Choice

What is the main difference between interspecific and intraspecific competition?

• The types of species involved in the competition.

• The kind of resources being competed for.

• The time of day that the competition occurs.

• The environment where the competition takes place.

Multiple Choice

What is the main purpose of a species occupying a specific niche or an animal defending a territory?

• To attract more mates from different species.

• To increase the total amount of food available.

• To reduce competition for the same limited resources.

• To make it easier to move between different habitats.

Multiple Choice

If a drought caused all the lower leaves on trees to wither, leaving only leaves high up, what would be the most likely consequence for the giraffe population described?

• Interspecific competition between giraffes and zebras would decrease.

• Intraspecific competition between male and female giraffes would increase.

• Male and female giraffes would cooperate to find new food sources.

• Zebras would begin competing with giraffes for the high leaves.

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Common Misconceptions

Misconception	Correction
Ecosystems are only large areas like forests or deserts.	Ecosystems can be any size, from a large ocean to a small puddle.
Competition always results in a clear winner and a loser.	Often, both competing populations survive, but with reduced numbers.
An organism's niche is another word for its habitat.	A niche describes an organism's total role, including diet and behavior.
A population will always grow until it runs out of space.	Growth is limited by factors like food, water, and predators.

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Summary

• Ecosystems are communities where organisms interact with biotic and abiotic factors.

• A population's growth is restricted by limiting factors, determining carrying capacity.

• The relationship between predator and prey populations often follows a predictable cycle.

• Competition for resources occurs both within and between different species.

• An organism's unique role, or niche, helps to reduce the intensity of competition.

• Organisms reduce competition by partitioning resources or defending territories.

Poll

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

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