Lesson Plan - Get It!
Have you ever been to the ocean and seen or even felt the sharp stab of huge clusters of barnacles under your feet? They seem to be everywhere — especially on rocky beaches. The fact is, barnacles can live in almost any environment. Knowing that, why do you think they haven’t just taken over the entire shoreline or even the entire ocean?
Barnacles are found on shorelines, on rocks, on boats, attached to shells, and even riding on whales!
That is because they have a need to attach to things in order to live.
This need to attach limits the ability of barnacles to take over because there are only so many surfaces available. Space, therefore, is defined as a limiting factor for barnacles. Every population of organisms is limited by certain aspects of their environment. These factors prevent too many of the organisms from exploiting the area of natural resources.
Barnacles are just one of many different organisms that can appear in great numbers. However, just like space is a limiting factor for barnacles, every population is limited by certain aspects of their environment.
There are two types of limiting factors: density dependent and density independent.
Think about what the term "density" broadly means: the amount of material in a given volume or area. For populations of organisms, density can be defined as the number of living things in a given area, like the number of white-tailed deer in a meadow or the number of great white sharks in a particular region of the ocean.
- Can you identify some variables that might influence the number of hawks living in a five-mile radius?
You may have mentioned things like the number of mice or squirrels living in the local area, or the number of trees that are available for nesting sites. These are all factors that limit the number of hawks and would be considered density dependent limiting factors because they depend on the number of hawks competing for the same resources.
Density dependent limiting factors can include food resources, the availability of shelter, local water sources, number of predators, and the spread of infectious diseases.
Image by MasterOfHisOwnDomain, via Wikimedia Commons, is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.
Density independent limiting factors impact the entire population regardless of the number of organisms in the area.
- Can you think of some events that might be considered density independent limiting factors in an ecosystem?
By Fredlyfish4 [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], from Wikimedia Commons
Things like forest fires, floods, and ocean acidification, are all examples of density independent limiting factors. When a forest fire occurs in an environment, it eliminates members of the population based on their location, not the density. Small-scale climate changes, like an increase or decrease in average temperature or rainfall, can also impact the number of organisms in an area.
Attribution 3.0 [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)], from Wikimedia Commons
Density independent and density dependent limiting factors keep local populations regulated. This balance is important in creation because it prevents the destruction of local areas due to overpopulation.
- How might these limiting factors influence your environment?
- How does the size of a fish tank limit the number of fish that can live there?
- Do you think different fish need different space?
- How would you find out what you need to know in order to ensure that your fish can live in the space you provide?
List a few density dependent and density independent factors that would influence the success of plants in a garden.
In the Got It? section, you will practice sorting images and statements into density independent and density dependent limiting factors based on key ideas from this section!