5.03 Carrying Capacity

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Objectives

• interpret the relationship between resource availability and carrying capacity

• compare and contrast exponential growth and logistic growth

• analyze the lag phase and exponential growth phase, and their relationship to carrying capacity

• compare and contrast K-selected species and r-selected species and relate them back to population growth

interpret the relationship between resource availability and carrying capacity

Resource Availability and Carrying Capacity

Resource availability refers to how much food, water, shelter, and space are available for living things in an environment.

Carrying capacity is the maximum number of individuals a habitat can support based on the resources available.

--> When resources are plentiful, the carrying capacity is higher, allowing more organisms to survive and grow.

--> If resources become scarce, the carrying capacity decreases, and the population size may shrink due to competition for limited resources.

--> If a population exceeds the carrying capacity, it can lead to resource depletion and a sharp population decline.

compare and contrast exponential growth and logistic growth

Exponential Growth

What is Exponential Growth?

• Exponential growth refers to the rapid increase in a population over time.

• The population grows faster with each generation.

Key Features of Exponential Growth

• Occurs when resources are abundant (e.g., food, space).

• Each generation grows faster than the previous one.

• The growth follows a J-shaped curve.

Why is Exponential Growth Unsustainable?

• Exponential growth assumes unlimited resources.

• In reality, resources are limited, leading to problems like overcrowding and scarcity.

Examples in Animal Populations

• Rabbits in an Ideal Environment

Scenario: If rabbits are introduced to a new area with no predators and abundant food, their population will grow exponentially.

• Invasive Species

Scenario: When a non-native species (such as the zebra mussel or the cane toad) is introduced into an environment with no natural predators, it can multiply rapidly.

• Algae Blooms (Phytoplankton)

Scenario: Algae can reproduce rapidly when conditions are right, such as during nutrient-rich waters or warm temperatures.

Multiple Choice

The graph shows an exponential growth curve.

Which of the following conditions could cause this type of population growth?

• polluted water supplies

• unlimited resource availability

• lack of shelter

• increased predator population

Multiple Choice

Why is it not possible for populations to experience exponential growth for an indefinite period of time?

• because reproductive rates will eventually decrease

• because there will be an imbalance in the ratio of males and females

• because resources are not never-ending

• because it would lead to high death rates among infants

Overshoot

• If a population goes above its carrying capacity, it results in an overshoot.

• An overshoot is a phenomenon that occurs when demand exceeds the regenerative capacity of a natural ecosystem.

• Overshoots lead to dieback events, bringing the population back below the carrying capacity.

Multiple Choice

Which of the following best describes what happens when a population experiences overshoot and exceeds carrying capacity?

• 
  It continues to grow exponentially, but at a slow rate.

• 
  It experiences dieback, sending the population numbers below carrying capacity again.

• 
  It is able to adapt to the new population size with no change in growth rate.

• 
  It continues to grow exponentially at an elevated rate.

Logistical Growth

What is Logistic Growth?

• Logistic growth occurs when a population's growth rate slows down as it approaches a maximum size due to limited resources.

• The population grows rapidly at first, but as resources become scarce, the growth slows down

Key Features of Logistic Growth:

• Starts with rapid growth when resources are abundant.

• Growth slows down as resources become limited.

• The population reaches a stable size called the carrying capacity.

Logistical Growth

Why is Logistic Growth Realistic?

• Unlike exponential growth, which assumes unlimited resources, logistic growth accounts for environmental limits, such as: Food, Space, Competition

Example of Logistic Growth:

• Deer in a forest: Initially, the population increases rapidly, but as food and space become limited, the growth slows and stabilizes at the forest’s carrying capacity.

Multiple Choice

What best describes logistic growth in a population?

• The population grows exponentially without any limits.

• The population grows rapidly at first, then slows as it reaches the carrying capacity of the environment.

• The population stops growing completely after a short period.

• The population grows steadily at a constant rate, regardless of environmental conditions.

analyze the lag phase and exponential growth phase, and their relationship to carrying capacity

​Lag phases occur when a population remains low for a number of years. The population is growing at this time, but at a very slow rate.

​The exponential phase occurs when populations grow exceedingly faster and larger due to resource availability. This growth cannot be sustained forever as resources are limited.

Multiple Choice

What happens during the exponential growth phase of a population?

• The population size stays constant because resources are limited.

• The population grows very slowly as the organisms adjust to their environment.

• The population grows rapidly because resources are abundant and reproduction is at its maximum rate.

• The population stops growing completely due to overcrowding.

​The stationary phase occurs when populations sit just below carrying capacity and remain stable. This is called the stationary phase because population levels remain relatively stable.

compare and contrast K-selected species and r-selected species and relate them back to population growth

K-selected species

K-selected species have low birth rates and slow population growth.

Key Features:

• Low Birth Rate

• Long Gestation (Pregnancy) Period

• One Offspring Per Pregnancy

• Parental Care

Examples:

• Chimpanzees

• Elephants

r-selected species

r-selected species reproduce quickly and have larger populations.

Key Features:

• Short gestation periods (quick pregnancies).

• Often have multiple offspring at once.

• Little to no parental care.

Examples:

• Rabbits

• Insects

• Fish

Categorize

Options (4)

reproduce infrequently

variable population size

provide parental care to offspring

produce many offspring at once

Categorize the following traits as those exhibited by K-selected or r-selected species.

K-selected

r-selected

Multiple Choice

Why would an r-selected species experience overshoot sooner than a K-selected species?

• 
  because r-selected species have faster growing populations

• 
  because r-selected species do not raise their young

• 
  because r-selected species have a shorter lifespan

• because r-selected species are larger and require more food and water

Open Ended

Based on reproductive patterns, are humans a K-selected or an r-selected species? Explain.

optional sentence starter: Humans are ______species because....

Summary

• resource availability impacts a population‘s carrying capacity;

• exponential population growth would occur in the presence of unlimited resources, while logistic growth occurs when resources are limited

• If a population goes above its carrying capacity, it results in an overshoot which leads to a dieback event

• K-selected species have low birth rates and slow population growth while r-selected species reproduce quickly and have larger populations.

Open Ended

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