POP: Lesson - Carrying Capacity (Topic 3.4) đź“–

⏳ Estimated Reading/Listening Time: 7 - 9 minutes

Learning Objective

Describe carrying capacity and how populations adjust to an environment's carrying capacity.

 

Carrying Capacity

A graph showing population size changing over time. The vertical axis measures population size, and the horizontal axis measures time. Slow Growth Phase: Population increases slowly due to low birth rates or high death rates. Fast Growth Phase: Population increases rapidly due to high birth rates or low death rates. Stable Equilibrium Phase: Population remains constant as birth and death rates balance, approaching the environment's carrying capacity. The carrying capacity, the maximum number of individuals the environment can support, is marked by a dotted orange line.
The orange line is the carrying capacity. Population growth levels off at this point because of limited resources. This makes an S-curve, which is logistic growth. (More on this next lesson)

The carrying capacity of a population is the maximum population of a species that a given habitat can support without being degraded over time.  Carrying capacity is usually represented by a capital letter K.  The carrying capacity of a population represents a sustainable population size.  The biotic potential and environmental resistance of a population determine the carrying capacity of a population.  It is important to remember that each environment has a different carrying capacity because each environment has a different biotic potential and environmental resistance.

However, fast-growing populations can overshoot their carrying capacity. This means that they grow so fast, the population doesn't realize their resources are almost depleted until it is too late.

 

Essential Knowledge

When a population exceeds its carrying capacity (carrying capacity can be denoted as K), overshoot occurs. There are environmental impacts of population overshoot, including resource depletion.

 

A graph shows population size changes over time relative to carrying capacity. The x-axis is time, and the y-axis is population size. An orange dashed line labeled "K" represents carrying capacity. A blue curve shows population growth, overshoot (exceeding K), and die-off (sharp decline below K). Labels mark "overshoot" and "die-off," illustrating how exceeding carrying capacity leads to population collapse.
Can you spot where the population overshoots the carrying capacity? What are some of the consequences of overshooting the population's carrying capacity?

Sometimes, a population consumes too many resources and eats up more than the environment can handle. That’s when a population overshoots its carrying capacity, the maximum number of individuals that an environment can support. When this happens, the population goes through a series of booms and busts, where it grows too big and then crashes down, over and over again, until it settles around the carrying capacity.

Overshoot can to population decline, as individuals face hunger, sickness, and/or fighting. This decline is called dieback, and it can be very harsh and fast, causing a population crash. It’s like a roller coaster ride, but not the fun kind. Sometimes, however, dieback can alter both the population and the ecosystem, as it changes the balance of living and non-living factors. For example, increased nutrients in aquatic ecosystems can start a process called eutrophication, which can cause fish die-off due to low oxygen levels.

 

The short (3 minutes) podcast episode below is an interview with Dr. Suzanne Bricker, a scientist from the National Centers for Coastal Ocean Science explains how eutrophication occurs and how it can reduce the carrying capacity of the ecosystem. (click here to access the transcript - NOAA Ocean Shorts: Eutrophication) Links to an external site.

 

 

 

 

Eventually, this process can lead to reduced oxygen availability in the water (known as a "dead zone"), permanently degrading the habitat and further reducing the carrying capacity of the habitat.

an image of the Gulf of Mexico dead zone, with the worst areas (less than 2 mg/L oxygen) depicted in red

In 2017, the Gulf of Mexico dead zone was about the size of New Jersey! Can spot the dead zone? It’s the area in re, where the dissolved oxygen level is less than 2 mg/L.

 

 

 

Essential Knowledge

A major ecological effect of population overshoot is dieback of the population (often severe to catastrophic) because of the lack of available resources leads to famine, disease, and/or conflict.

 

Biological Dispersal Patterns

There are three main ways that organisms are usually found in nature.  We call these dispersal patterns.

Take a moment to explore the Dispersal Patterns below. Can you think of other examples from each category?

Clumped 

a white box with blue dots clumped together. There are 5 total clumps. 

Clumped distributions are the most common type of dispersal in nature. This is because resources are not uniformly or randomly distributed. For example, living organisms need water to survive. In an area with very little water, you will see most of the plants and animals located near water because this is the best location for survival. 

Additionally, many plants have seeds that fall very close to the parent plant, or they are colonial, and their “offspring” grow out from the original plant. This creates many of the same plant in the same area. Bamboo and banana plants are like this. When plants grow clumpy like this, the organisms that feed on them tend to clump around the clumps of plants. And the animals that feed on those herbivores tend to clump around the herbivores and so on.

 

 

[CC BY-NC-SA 4.0 Links to an external site.] UNLESS OTHERWISE NOTED | IMAGES: LICENSED AND USED ACCORDING TO TERMS OF SUBSCRIPTION - INTENDED ONLY FOR USE WITHIN LESSON.