Niche partitioning and species coexistence worksheet answers

In this activity, you will make claims about different niche partitioning mechanisms based on scientific data. The activity begins by interpreting a graph about dietary niche partitioning by grazers on the African savanna. You will then watch two short videos (embedded at the end of this page), one on niche partitioning and the other on DNA metabolizing, and answer questions to apply what you have learned. I uploaded the questions in a docx. Please watch the videos and read the first page and briefly answer the 14 questions.INTRODUCTION In the African savanna ecosystem, many species of large herbivores share similar habitats. How do all these species coexist, or live together, without some species outcompeting the others? These species can coexist due to a mechanism called niche partitioning, which is when species partition, or divide up, resources by using their environment in different ways. (A species’ niche is its place and role in an ecosystem, including where it lives and how it gets the resources it needs to survive.) In this activity, you’ll use scientific data and videos to explore different examples of niche partitioning in the African savanna. The concepts you’ll learn can be applied to many other organisms and ecosystems, to help us better understand how species behave and interact. PART 1: Niche Partitioning by Time and Grass Height One type of niche partitioning in the savanna is shown in Figure 1. The resource partitioned in this example is a typical savanna grass called Panicum maximum. This grass’s growing season starts after the peak rain and continues for six months. When the grass is tall, it has lots of stems, which are relatively low-quality food for herbivores. The more nutritious parts of the grass are closer to the ground. If a grass-eating herbivore, or grazer, eats the top of the grass, the new parts of the grass that grow back are also more nutritious. Figure 1 shows three types of grazers — zebra, wildebeest, and Thomson’s gazelle — that graze, or eat, this grass over time. Zebras, the first grazers to use this resource, thrive when the grass is tall and abundant, even if it is less nutritious. The zebras have paired upper and lower teeth that help them bite off tall stems on the tops of the grass. Zebras can also digest food much more quickly than the other two grazers. This is because wildebeests and Thomson’s gazelles are ruminants, mammals with four-chambered stomachs that take longer to digest food. Sometimes ruminants must also regurgitate and rechew partly digested food before they can fully digest it. However, when the ruminants digest their food (via fermentation in the foregut), they take up more nutrients and proteins than when zebras digest food (via fermentation in the hindgut). So, a ruminant can extract more energy from a smaller amount of food if that food is more nutritious. Smaller ruminants, such as Thomson’s gazelles, need less energy than larger ruminants, such as wildebeests. Figure 1. The relative population densities of three different grazers — zebras, wildebeests, and Thomson’s gazelles — for six months after the peak rain in the African savanna. (All animals were counted in the same area, and the numbers were normalized to the maximum count for each species.) The images at the bottom show the relative heights of the P. maximum grass over this time period. Answer the following questions based on Figure 1 and the information above. 1. Describe how the relative zebra density changes over time. What characteristics of zebras could explain why zebra densities are greatest when the P. maximum grass is tallest and most abundant? 2. Describe how the relative wildebeest density changes over time. 3. Propose a reason or reasons why the relative wildebeest density spikes when it does. Support your idea with evidence from what you know about wildebeests and P. maximum grass. (Hint: Remember that the more nutritious parts of the grass are closer to the ground. The grasses continue to grow after being grazed, and the parts that grow back are also more nutritious.) 4. Describe how the relative Thomson’s gazelle density changes over time, in relation to the changes in the relative wildebeest density and in the grass height. Why do you think this is so? 5. Would you describe the interactions between zebras, wildebeests, and Thomson’s gazelles as competition or facilitation among species? Support your answer with data from Figure 1.