SImbio Prairie Patches

EATING Food consists of the larval host plant (though the larval stage is not specifically modeled). There’s no food in non-prairie. If a butterfly finds and eats food, it gains energy. Each week, some energy is subtracted from the butterfly’s energy store. If the butterfly runs out of energy, it dies. REPRODUCTION Butterflies can only mate in prairie habitat, only when their energy level exceeds a threshold, and only with other individuals that are nearby. They have two successful offspring per mating event, and each parent donates half its energy store to offspring. Parents can reproduce repeatedly until they die. DEATH Butterflies die one of three ways. They can starve to death. They can die randomly in non-prairie environments (death probability). They can die of old age. [6] Makeapredictionbasedonwhatyounowknowaboutthemodel. [6.1] Do you think the total number of butterflies supported by the two habitat configurations (Large Far and Small Near) should be the same or different? Explain. The two habitats should be different. The small near plot will be over crowded and unsustainable in contrast to the spread out butterflies in the large far plot. [ 7 ] To determine whether you were correct, you’ll need to collect some data. First click the RESET button in the Control Panel to return the simulation to its original settings. With the Large Far configuration selected. Click the STEP 100 button to advance the simulation 100 weeks. [7.1] When the simulation stops,recordthecurrentmovingaverageforthetotalpopulation size (i.e., the number in the right corner above the graph) in an excel spreadsheet. Then repeat the procedure two more times, entering your data into an excel spreadsheet. [ 7.2 ] What is the average population size of the three runs for the Large Far configuration? 62 [ 8 ] Repeat the steps above for the Small Near patch configuration. [ 8.1 ] Switch to the Small Near configuration and record your data for three runs as you did before. [8.2] What is the average population size of the three runs for the Small Near configuration? 60 [ 9 ] The average sizes for the two configurations were probably similar, although there likely was a good deal of variation between runs. Random variability is part of what adds to the realism of the simulation. (The real world is quite messy!) Because the simulated system includes random variability, when you collect data, it will be important to conduct replicate runs. To simplify this process, you will likely find the Automator tool (to the left of the Calculator tool) to be quite useful.

As a modeler, you may not know the actual probabilities for butterflies leaving prairie patches or changing direction when they fly outside their habitat. However, you can use the model to determine which parameters have the greatest influence over model outcomes. In this exercise, you will determine whether this modeled system is “sensitive” to certain parameters. The process you will use is called a sensitivity analysis , which is a very important tool to modelers—and to land managers who have access to models. You actually already conducted a sensitivity analysis, when you simulated prairies with and without fire. If you were to plot data from your simulations, it might look something like this: The graph above illustrates that the results from the simulation are sensitive to whether fire is included in the model. Moreover, the degree of sensitivity depends on the way butterfly habitat is configured— large far patches are more sensitive than small near patches. [ 1] Select Sense and Sensitivity from the SELECT AN EXERCISE button in the upper left- hand corner of the screen. Notice that the Parameters Panel now includes sliders for adjusting the Leave prairie probability and Turn probability (NP). « Note: “NP” stands for “non-prairie”; parameters with the NP designation only apply to butterflies when they are outside of prairie patches. If you see a P designation, it means the parameter only applies to butterflies when they are inside of prairie patches. [2] Make sure that the Turn probability parameter is set to its default value (0.2) and that the Periodic Fire Disturbance regime has been selected. [3] To begin, see whether under the Large Far patch configuration the model is sensitive to the Leave prairie probability parameter setting. That is, if Leave prairie probability is set to different values, does your model output (i.e., average butterfly count) change? To do this, select the Large Far patch configuration and set the Leave prairie probability parameter to 0.1. Launch the Automator tool, and change the Number of Runs to at least 30. (Do more runs if you have time.) Each run can go for 100 weeks. « Note: When doing a large number of runs, you can click Hide butterflies on the Automator window to disable prairie visuals and run the simulations faster. [3.1] Recordtheaveragebutterflycountinyourexcelspreadsheet.Setupyoursheetlikethetable below: [ 4] Repeat for Leave prairie probabilities of 0.5 and of 0.9, recording the average butterfly count for each probability in the appropriate cell in your spreadsheet. [5] Change the patch configuration to Small Near and use the Automator as above to conduct a sensitivity analysis of the Leave prairie probability parameter with the Small Near configuration. [ 5.1 ] Record your average butterfly counts in the appropriate cells of your spreadsheet. [6] Examine your data and consider whether your results at different parameter values are very different. Of course, there will always be some random variability in your data; it would be better to do 1,000 or

default values using the RESTORE DEFAULT PARAMETERS button. In the next steps, you will practice using tools to create hypothetical reserves where prairie patches are connected using patch enlargement, corridors, or stepping stones. Start with a stepping stones configuration. [ 2 ] Select the ADD PRAIRIE tool from the Tools Panel (bottom of the screen) by clicking the “+” button immediately to the right of the BINOCULARS button. [3] Draw a small rectangle with your mouse in the middle of the prairie patch group. You will see the area turn green, indicating that it is a “stepping stone” of prairie habitat. [4] Continue making stepping stones wherever you like until the total Prairie Habitat Area is 85 hectares. At this point you’ve created 15 additional hectares of prairie. If you added too much prairie and need to remove some habitat, select the REMOVE PRAIRIE tool by clicking the “–” button in the Tool Panel and draw a rectangle around the chunk of prairie to remove. You will see it revert to non-prairie, turning brown. Be careful not to destroy any of the original prairie habitat with the REMOVE PRAIRIE tool! If you want to completely start over, click the blue RESTORE DEFAULT PATCHES button below your prairies. This will reload the original four patches in the study area. [5] Once you are satisfied with the stepping stone configuration, you can save it to experiment with later. Click the SAVE PATCHES button, name the patch configuration (for example, “Stepping Stones Config 1”) and then click OK. You will see this name appear under My Saved Patches. [ 6] Click RESTORE DEFAULT PATCHES to return to the original patches and then follow steps 2–5 to create and save two more prairie configurations; one representing patch enlargement and one representing corridor options. Each configuration should have a Prairie Habitat Area of 85 hectares. Remember, with corridors, the prairie habitat must be completely contiguous (i.e., touching) between patches. With patch enlargement, no new patches are created. [ 6.1 ] Which of your configurations (patch enlargement, corridors, or stepping stones) do you think will result in the largest, most stable population of Fender’s blue butterflies? Explain. I think the corridors would be the best since the butterflies would never have to fly outside of a patch. [ 7 ] Make sure parameters have their default settings and that Periodic Fires is unchecked (that is, fires are suppressed). Then conduct a quick experiment to see if your prediction was correct. [ 8 ] As before, use the Automator to collect butterfly population persistence data from the simulation for each of your three patch connection options. You will need to decide whether to focus on extinction rate or average butterfly count (or both) as a measure of persistence. You will also need to decide how many runs to conduct, and how long each run should be. [ 8.1 ] Briefly describe your experimental methods: We ran the automator 20 times for each configuration and recorded the extinction rate and Average butterfly count.

● Graphs of your data (such as those you made in Exercise 3: Sense and Sensitivity), where appropriate. ● Which parameters or fire regimes affected the optimal patch connection design (that is, which model parameters you designate as critical). ● A preliminary recommendation for optimal patch connection design, with justification, if one can be made. If you cannot recommend a specific design at this time, consider stating so and explaining why. ● The top priority (or priorities) for field research to be conducted. That is, what should be studied in order to recommend a specific habitat restoration plan for Fender’s blue butterflies? Graded Questions [ 1 ] Use the SELECT AN EXERCISE button in the upper left-hand corner of the screen to launch “ Graded Questions” . [ 2 ] Enter your answers for each of the questions and click the SUBMIT button. Wrap-up Habitat Fragmentation and the Need for Connectivity Habitat loss is the primary anthropogenic (human-induced) cause of loss of biodiversity. As we humans convert more and more natural habitat for our own uses, we not only reduce the amount of habitat suitable for other species, but we also subdivide remaining habitat into fragments. If individual fragments become too small and/or too isolated, a species may become vulnerable to extinction even if the total amount of its habitat appears sufficient. Such is the case with Fender’s blue butterfly and its larval host plant, Kincaid’s lupine. As an individual habitat fragment becomes smaller, organisms living in it face a number of challenges. Most obviously, smaller patches support smaller populations, which incur a higher risk of local extinction. Smaller populations are more likely to succumb to stochastic events such as severe storms, disease outbreaks, and droughts. Inbreeding and loss of genetic diversity can reduce fitness, further threatening species. Small habitat patches also have a relatively high ratio of edge to core habitat, increasing edge effects , as you saw in Exercise 1 (Virtual Blues). Depending on the nature of the core habitat and its surroundings, edge effects can include: increased sunlight, temperature, and aridity at the patch’s border; the establishment of predator and/or competitor populations that would otherwise not have access to core habitat; and invasion by exotic species. One way to mitigate the effects of habitat fragmentation is to facilitate dispersal for threatened species. Habitat patches can be connected in a few basic ways, all of which have been used in habitat restoration efforts. As a general rule, corridors are more restrictive. Land necessary to construct corridors is often unavailable for restoration, badly degraded, and/or expensive to restore. In addition, corridors carry risks: they facilitate movement not only of target organisms but