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Chapter 44 Unit Questions 1. Describe the five main interspecific interactions and how each affects the species positively, negatively, or neutrally. Competition (-/-) refers to the interaction in which two or more different species use the same resource. Interspecific competition can affect the population growth of a species negatively because it can result in extinction if the competing species uses up the resource. Consumer-resource interactions (+/-) are those in which organisms gain nutrition by eating other living organisms or are eaten themselves. This type of interaction is positive for the consumer but negative for the resource. Mutualism (+/+) is an interaction that benefits both species. Commensalism (+/0) is an interaction in which one species benefits while the other is unaffected. Amensalism (-/0) is when one species is harmed while the other is unaffected. 2. Define competition, and distinguish between interspecific and intraspecific competition. Competition is when two or more different species use the same resource. Interspecific competition refers to competition involving organisms of the same species (i.e. finding mating partners, territorial competition) while intraspecific competition involves different species (i.e. food, sunlight). 3. What is a limiting resource and summarize the concepts of resource partitioning and how it affects the habits and lifestyles of a species. A limiting resource is the resource that is in the shortest supply relative to demand. Resource partitioning, differences between competing species in resource use, is a mechanism that can cause intraspecific competition to be stronger than interspecific competition. For example, if finches and bees both eat nectar, but finches can also eat seeds, then finches will turn to seeds because there is less competition. Overtime, finches will evolve to eat only seeds rather than nectar. This shows how resource partitioning affects habits and lifestyles of different species. 4. Define predation or consumer-resource interactions, and describe the effects of natural selection on predator-prey relationships. Predation or consumer-resource interaction is when a predator/consumer consumes another organism, the prey/resource, for an energy source. Predator-prey relationships often result in an “evolutionary arms race” in which the prey evolves better defenses and the predator evolves better offenses; however, neither gains any significant advantage over the other. 5. Distinguish among mutualism, commensalism, amensalism, and parasitism, and give examples of each. Mutualism is an interaction between organisms of different species that benefits both species. An example of mutualism is the relationship between mycorrhizal fungi and plants, in which mycorrhizae expand a plant’s root surface, increasing the amount of soil the plant can explore for nutrients. In return, the fungus obtains the products of photosynthesis. Commensalism is an interaction in which one species benefits while the other is unaffected. An example is when cattle convert plants into dung, which dung beetles can use for nutrition. In this interaction, the cattle are neutrally affected while the beetles are positively affected. Amensalism is an interaction in which one species is harmed while the other is unaffected. An example is a herd of elephants or bison grazing the plains and crushing insects, plants, or other small animals. This is amensalism because the elephants or bison are unaffected while the organisms they crush are harmed. Parasitism is an interaction in which one species benefits from or lives off of another species, that is usually harmed. An example of this is fleas on a dog. 6. Read about the Kangaroo rats and explain their effect on grass growth. Highlight which aspects of their behavior had the greatest effect on grass. Kangaroo rats have a tendency to bury seeds in the ground for later use, if necessary. This aspect of their behavior causes a greater abundance of grass if it is a good year and the rats have more than enough seeds to eat, as the seeds buried in the ground germinate and grow during rainfall. 7. Explain how competition and resource partitioning leads to changes in population distribution and density. Resource partitioning causes species to evolve overtime, whereas competition can lead to extinction if one species beats out the other for resources. With resource partitioning, as species switch over to alternate resources to reduce competition, the species population shifts over to accommodate those new habits and traits. 8. **How does competition increase fitness of a species and can quickly lead to adaptation? Competition can help species to get rid of inferior traits but keep useful traits. For example, since small beaks can eat both big and tiny seeds, but the large beaks can only eat big seeds, the small-beaked birds have greater fitness. Over time, the small beaks would out-survive the big beaks, and there would be a greater small-beaked bird population (natural selection). 9. How does mimicry increase fitness? Mimicry gives advantage to prey by allowing them to mimic or disguise themselves as something the predator is trying to avoid. For example, zebra butterflies lay eggs on passionflower leaves for baby caterpillars to eat once they hatch, but they do not lay eggs on leaves that already have eggs. Over time, passionflower leaves have adapted to have yellow dots that mimic the butterfly eggs, so that butterflies avoid those leaves. This increases the leaves’ fitness because it allows them to not be eaten by baby caterpillars. 10. What kinds of attributes make a species invasive? Invasive species are generally non-natives to an area, reproduce rapidly, spread widely, and usually have negative effects on native species. An example of an invasive species is the purple loosestrife, which was introduced into North America in the early 1800s. The purple loosestrife now dominates many wetlands and has crowded out many native species such as cattails, affecting the life cycles of wetland organisms like waterfowl and amphibians.