go to this link: https://www.learner.org/wp-content/interactive/envsci/ecology/ecology.html Answer the following in the attachme

Online Ecology Lab – Simulating Ecosystem Interactions

In any given ecosystem, most organisms have carved out a niche for themselves where they can obtain all the resources necessary to survive. At first glance, it appears that many species in an ecosystem are similar and would require the same set of resources (water, light, soil minerals, food, nesting space). But it turns out that most species in an ecosystem cannot compete with each other directly. The reason for this is what we call the “competitive exclusion principle” (see chapter 17, section 11 in your book). What this principal predicts is that if two organisms need the same basic set of resources, i.e. they are competitors, then only one of them can win and the other one will be excluded from the ecosystem. The species won’t necessarily go extinct, because maybe it will win out in a different ecosystem or a different location. But it will not survive in that particular location.

However, certain species can live well together without direct competition – they do it symbiotically, parasitically, or by staying out of each other's way. For example, lichen and moss, often the first arrivals to a new ecosystem, tend to live fairly well in each other's vicinity because they have slightly different requirement sets in terms of resources. And many animal species have very similar food requirements, for example they all eat insects, but some have evolved to be nocturnal feeders and therefore they don’t compete with the species that feed during the day.

The Producers

Imagine an ecosystem is newly formed – the previous ecosystem was destroyed by fire or flood – and the first colonizers of the newly forming ecosystem are, of course, producers. In the first model, you will run the simulator using two “normal” green plants that are basically looking for the same resources: they are competitors. This should tip you off to the fact that the competitive exclusion principle will very likely show up in our simulation.

1. Open the simulator at this link:
   https://www.learner.org/wp-content/interactive/envsci/ecology/ecology.html
   [If you have trouble with the link, go to the Annenberg Learner web page at learner.org; click the Classroom Resources button and type in Ecology in the search field and submit the search; then open the link to “The Habitable Planet: A Systems Approach to Environmental Science”; in the list on the right side click the Ecology lab; then on the small link click Open Simulator.]

2. Make sure at the top of the simulator next to Lesson: it is set to The Producers.

3. You’ll notice that when you open the simulator, the two green plants are “chosen” and the ecosystem is populated with them already (there is no bare ground). You can click on the All Off button to see the bare ground scenario. Then click on Presets to reset the plants.

4. Using the visual of the simulator showing the “normal” plants colonizing the entire ecosystem (the two different colors) estimate the population percentage of each of the two species and multiply them each by 10,000, which is the total population estimate given on Day 0. Record your estimates in your data table as estimated starting populations.

5. Keeping in mind the competitive exclusion principle, estimate what you think will be the total population of both populations of plants at the end of 100 “days” (by the way, the “days” in the simulator don’t really equate to 24 hour days in real life, they are just a time step; they could be hours, days, weeks, months, seasons, even years, it will vary by ecosystem).

6. Now run the simulator (it is set automatically to run to 100 “days”). Grab the Day 1 populations from the graph by hovering your cursor over the lines on the graph at whatever time during the run you want. The day and actual population for that plant species will pop up on the screen. Get the ending populations from the graph by letting it run completely through 100 “days”. Record the populations of Plant A and Plant B in your data table.

7. Answer the questions on the data page under The Producers data table after you have run the simulation a few times through 100 days.

The Herbivore
Now you'll introduce an herbivore into the environment. In theory, an herbivore native to the ecosystem should feed mostly on the dominant species, because there would be more of that species, right? If so, then the herbivore may consume enough of the dominant species to give the non-dominant species a chance for growth and reproduction and survival. Basically, the herbivore will counteract the competitive exclusion principle.

1. Predict what will happen to the population numbers in the ecosystem when you add an herbivore such as a rabbit to the interactions. Fill in your data table with your predictions.

2. Click on herbivore A (the rabbit) and choose "eats plant A." Then, run the simulator for the full 100 “days” and record your results in the data table.
   Note: the number of “rabbits” on the screen is not representative of the actual population. Use the graph to retrieve the actual population numbers.

3. Answer the questions after you run the simulation with the rabbit that eats Plant A; the rabbit does not eat Plant B!

The competitive exclusion principle occurs only where resources are limited. That applies to almost any natural ecosystem. But what usually happens is an herbivore or omnivore is around to feed on the dominant plant and keep that plant’s population under control, which allows the other species to survive.

Food Webs – A Simple Food Chain

Now you will take the idea of succession, where the primary producers give way to secondary producers and consumers begin to settle in as well, eventually creating a stable ecosystem; and competitive exclusion, which creates different sets of species interactions; and combine them into the ideas of food chains and food webs.

A food chain is a very simple way to imagine relationships among producers and consumers in ecosystems. The problem is that food chains are not very realistic. Ecosystems are extremely complicated, and there is rarely just one type of primary producer or one type of secondary consumer and so forth. But food chains do give us a good conceptual start, and then we can move on to the food web from there. So you will use the simulator to run several scenarios and compare the simulator outcomes with your predicted outcomes.

1. Choose only one organism from each trophic level and make sure that the food chain goes in a straight line from one trophic level to the next. For example: Herbivore A eats Plant A, Omnivore A eats Herbivore A, and the Top Predator eats Omnivore A. Let Plant B go without a consumer in this food chain.

2. Predict whether each species in your chain will survive, and whether it will increase or decrease in number, as well as whether Plant B will survive to the end. Record your predictions in the data table. Use the symbols X for "die out," ↑ for "increase in numbers," and ↓ for "decrease in numbers" as it shows on the table.

3. Run the simulation and record the results. You can retrieve the actual numbers from the graphs by hovering over the graph lines with your cursor.

4. Run another simulation using a different food chain this time. Again, leave Plant B without a consumer. Record the data for this simulation in the table.

5. Answer the questions in the Food Webs – A Simple Food Chain section.

Food Webs – A Food Web

We’ll finish off with a little bit more realistic simulation of an ecosystem, called a food web. In this case, we have multiple interactions at the same time, with multiple species at each level of producer, herbivore, and consumer.

1. Click the All On button. The model that is created by the simulator shows who eats whom and the paths by which energy is transferred. And this is a pretty simple one!

2. Predict which populations will die out, increase in numbers, or decrease in numbers and record your predictions in the data table using the symbols we set up in the previous simulation. These are just estimates, you don’t have to calculate actual numbers.

3. Run the simulation twice and record the results (remember you can get the actual data by hovering over the graph lines with your cursor). Compare the results with your predictions and see how you did. Note that the two simulator runs may give very different results.

4. Now, try to change the interactions within the food web in order to ensure that all species survive to the end of the simulation run. It may take you several tries to achieve “total survival” in your ecosystem. Keep trying! When you achieve survival, record those modifications in your data table. You only need to record the data for the successful run.

5. Answer the questions below the Food Web table.
   

That’s it! Make sure you have the data tables filled in, and your questions filled in as well.
Scan or take a picture of the data table pages, and send them to me in the Online Ecology lab assignment.

Ecology Simulator Data Tables and Questions

1. Which plant was dominant?
   

2. Why might one plant be dominant over another in a real ecosystem?

1. Does adding the herbivore that eats Plant A establish a more equal competition between the two original colonizing plants A and B during the simulation?
   

2. What about the total population sizes? Are they about the same or different? I am talking about the total number of plants of both species combined at the end of the simulation with the herbivore, compared to the total number of plants combined at the end of the simulation we did in the first activity The Producers: which one ends with more individual plants overall, regardless of the which species they are? Why do you think that is?
   

1. Was your prediction correct? How did you arrive at your prediction?
   

2. In this simulated (and very simple) ecosystem, which populations would benefit the most from the presence of decomposers breaking down dead and decaying material in the soil and water?
   

1. Were your predictions correct? How did you arrive at your predictions? What differences were there between your predictions and the simulation?
   

2. Were you able to modify the parameters so that each species survived? What were the key changes you had to make, in your opinion?
   

3. Which way does energy flow in an ecosystem? With that in mind, why are there always so few top predators in an ecosystem compared to the primary producers, both in numbers and in biomass?