Species Interaction

A biological community is made up of many different species. Some of these species interact directly with each other. The most common type of direct interaction is the relationship is represented by the lines on a food web: one species eating another. These can be herbivore/plant interactions, predator/prey interactions, scavenger/detritus interactions, etc. There are also other, less obvious types of direct interactions: one species might rely on another for survival or reproduction (think about plants and their pollinators, for example). There can also be indirect interactions between species. In this case, species A and species B might not interact directly, but if they both interact with species C, then changes in species A can affect species C, which can in turn affect species B. Competition is a common example of an indirect interaction – when two species rely on the same third species, an increase in the population of one of the two species can have indirect effects on the population of the other species, mediated by its effect on their shared resource. In this activity, we’re asking you to think about some of these direct and indirect species interactions and how they scale up to shape the overall structure and function of ecological communities. Question 1: Think of an organism you’ve encountered in the wild (perhaps during your Module 12 Eukaryotes assignment?), and decide on 4 additional species with which this focal organism interacts, either directly or indirectly. Your five species can be terrestrial or aquatic, but should all be species within a single community, and should include organisms at several different trophic levels.  (NOTE: You should select species that have not already been used as examples in this course.  So no sea otters / kelp forests, or Isle Royale wolves / moose, etc.) Draw these the interactions between your focal species and the 4 interacting species, using solid lines for direct interactions and dotted lines for indirect interactions. For each species you include, identify its trophic level, and make sure to identify which of the five species is your focal species. You can draw this by hand and take a picture/scan it, or you can use the drawing tools in MS Office. If you draw it by hand, please make sure to write your name on the paper.  If you use images that you did not create in your submission, please make sure to cite the sources they came from. Question 2: In full sentences/paragraphs, describe the qualitative nature of the interactions between your focal species and each of the other four species you chose. For which species is each interaction beneficial? Harmful? Neutral? Which relationships are cases of competition? Predation/parasitism? Mutualism? Commensalism? Question 3: Next, imagine that the ecosystem where your focal species lives undergoes one of the following changes: Strange and unseasonable weather strikes your ecosystem: higher air temperatures reduce soil moisture levels and raise water temperatures (if you are thinking of an aquatic system); OR An exotic herbivorous invertebrate is accidentally introduced to the ecosystem through the mass transit system. Choose one environmental change and describe in full sentences/paragraphs how it might directly affect your focal species. Question 4: Now, predict how the environmental change may indirectly affect your focal organism by affecting each of the four interacting species you drew. Hint: Write down a short prediction for the overall effect of the environmental change on each of the four interacting organisms and then, based on the type of species interaction you drew between it and the focal organism, predict the indirect effect on the focal organism. Question 5: How might the changes you described in questions 3 & 4 affect humans? These effects can be ecological, social and/or economic in nature. Question 6: Imagine you’re a land manager whose job it is to protect the ecological community of Yellowstone National Park. You’ve been asked to allow people to acquire permits that would let them hunt wolves from the reestablished population in and around the park. What would the direct consequences of allowing this hunting be? What would the indirect consequences be? What factors would be important to consider in making the decision of whether or not to allow hunting? Why do you think decisions of this sort often have unexpected or unintended consequences?

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