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What Limits Life?
Good morning Naturalists!
Welcome back! So far this week, we have learned about food webs, producers, and consumers. We've gotten to explore some of the fascinating ways that animals and plants are able to get what they need to survive, but we have not yet talked about why we aren't living in a world dominated by oak trees, squirrels, or caterpillars. Today we are going to be discovering what it is that controls how many living things can survive in a habitat. These are called limiting factors. Many of the limiting factors in any habitat are based on the resources that are available. Let's think back to some of the things that we said we needed in order to survive. Which of those are the easiest for you to get? Which are the most difficult?
When you are following the recipe for a yummy dessert, you need to have all the ingredients. Sunlight, water, carbon dioxide gas (CO2), soil, and space to grow are the “ingredients” plants need to survive.
Let’s use our imaginations and imagine that you and your family are going to plant trees in your front yard. You decide you want to plant 50 young trees in your front yard. If your yard is 500 square feet, and each baby tree needs 5 square feet to survive, how many trees can your yard support?
Here at ONSC's glade habitat, these young cedar trees are able to survive. As they get older, the taller ones shade out the smaller ones, killing them. It's a tough life!
As the trees get bigger, however, they need more resources. In this example, let's say an adult tree needs 25 square feet of space, how many of those original trees will survive? What will happen to the other trees? Make sure you do the math!
Why would that many trees not survive in your yard? There isn't enough space for them to all grow! In this case, space would be a limiting factor. The trees would begin to compete for the space, and some would do better than others. Even if the trees had all the soil, water, and air they needed to survive, if they are so tightly-packed that some do not have space to reach the sky, they will begin to die off. Only the trees that get what they need will be able to survive.
It may seem like a forest full of trees is a quiet peaceful place. What we don’t see is these trees are competing against each other like gladiators for what they need to live every day. In this case, some of these trees have been fighting for their lives for over 70 years.
It isn't just plants that are competing for resources, however. Animals also need to compete for resources. Let's take a look at that next!
If you have an outdoor space that you can use (or even a large enough room inside), this is a fun game to play with even just two people. The only thing you need for this activity is a handful or two of an item such as pasta, dried beans, or small beads. Something natural is better than man-made objects, as you may miss a few and we want to be as kind to our environment as possible! These items will represent resources that you need to survive. That being said, we recommend that you do not eat any of these supplies after using them and make sure to wash your hands thoroughly!
To begin, spread the items out in a space that will allow each person to have at least six feet of space to themselves. You will have fifteen seconds to collect as many pieces of food as possible. If you are able to collect at least 20% (1/5) of the total pieces, you survive the round.
Use this sheet to track your scores, or create your own!
Round 1: This is a free-for-all. You are a generalist species in this round, meaning you can eat a large variety of food rather than just one or two things. To represent this, your goal is to gather as much food as possible as quickly as possible (as long as you are being safe).
Round 2: Each player will sit on the ground, representing a small territory. The winner of a rock-paper-scissors game gets to choose their territory first. Otherwise the rules remain the same.
Round 3: This round is played similar to the last round, only instead of sitting, each player may stand to collect resources, and is allowed to move one foot to stretch farther. They must keep the other foot in the same spot! Otherwise, the rules remain the same.
Round 4: Some species are what we call specialists, meaning they only eat one specific thing in order to survive. In this round, you can only pick up one piece of food at a time, but are not forced into a single territory.
Other optional rounds:
If you have more than one type/color of bean/pasta/bead, pick up to three. Each one now represents a different resource. You must now collect 1/5 of every color to survive. Which were the easiest? Which were the hardest?
If you have more than one type/color of item, at the end of the round, pick one at random. That source of food has been replaced by plastic, which looks like food to many animals but does not help them survive. None of these pieces count towards your needs.
Change the size of your play area. What happens when the same amount of resources are spread in a larger area? In a smaller one?
Place an item such as a belt in the play area. You must go around that item to collect any resources. This belt represents a habitat boundary such as a road, mountain range, or large river.
What other challenges do animals face in gathering resources? How could you create a round of this game that would mimic those challenges?
If you have been following along with creating your own creature this week, think about some of the things that may limit your species' maximum population. Maybe your animal has a large territory (like bobcats), or needs to breed in small ponds to avoid being eaten by fish (like some frogs and salamanders), or maybe you created an animal that needs to eat a certain food to gain toxins that will protect it from predators (like monarch caterpillars). What can your animal do to survive if it cannot get enough of that resource?
One option is to adapt quickly to new environmental conditions. Have you ever seen a deer or a coyote in the middle of the city or town before? Deer and coyotes are examples of consumers that are able to adapt to live near people. If their habitats become too overcrowded they can adapt to living near people.
Sometimes an animal's habitat provides them with all the things it needs to live, but for only part of the year. Use your imagination and think of what it’s like near you during the winter, a difficult time to find food for many of our animals. Let's write down some of the things animals do to survive during the coldest months of the year.
There is not much food for this turtle to eat during the winter, so it spends a lot of its fall gorging itself on all the food it can find. When cold weather comes, it goes dormant and takes a big snooze until spring comes again.
Other animals think a little more distantly. When their habitat does not provide enough resources, they will travel long distances to get to a habitat that has what they need. This migration period is common for many species. What animals can you think of that migrate?
We've looked at several ways that species can survive times with limited resources. Go ahead and take some time to fill out the chart below. What do the species around you do? Which of these strategies do people use the most? Which ones would you want to do?
Some final thoughts: What are some disturbances that can affect large populations quickly?
A blaze like this may scorch many acres of habitat before it burns out. This will affect each species that lives here differently.
Let’s think about that forest fire in the picture above. The blaze will change the number of plants and animals can live in this habitat. What living things will decrease in numbers because of the fire? Are there any living things that will be able to increase in number after the burn?
Some things that rapidly change the limiting factors in a habitat are natural events or disasters. Others are actions taken by people that quickly alter the habitat. Take some time to list as many disturbances to a habitat as you can think of. Is each one caused entirely by nature, entirely by people, or is it a combination? In a few weeks, we'll be talking in more detail about ways that the forces of nature change the environment!
And now that it's Thursday, let's look at all of the resources WE use to get food to our table on this week's Food for Thought segment!
We hope you have had a great week exploring with us! Make sure you grab an early lunch and join us for Find Out Friday at our new time tomorrow (11:00AM CST), where we will be answering YOUR questions and sharing anything you've created! Feel free to send us your work on our Facebook page or at SocialMedia@onsc.us.
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