Download Worksheet 6: Habitat and Niche

General Ecology (BIO 160) Worksheet #6 Dept. of Biological Sciences
Sacramento State University
Worksheet 6: Habitat and Niche 1. What is the definition of a habitat? Any place where an organism lives that meets the requirements for its survival and reproduction. 2. What is the difference between an environmental factor and a resource? An environmental factor influences the ability of a species to survive, grow and reproduce but is not actually used by the species. Across the range of conditions that a species experiences, there will be an optimal range of conditions (i.e., factors) over which the species can thrive (i.e., achieve adequate growth and reproduction). By contrast, a resource is a component of the environment that a species uses and that is necessary for its survival, growth and/or reproduction. For example, soil pH and nitrogen concentration both affect the growth, survival and reproduction of a species but pH is not consumed or used by the species, whereas nitrogen is. 3. Abiotic factors in the environment continually change from one location to another. We see this every place we look. For instance, mean annual temperature decreases with increasing altitude; the intensity of photosynthetic radiation declines with increasing water depth; soil moisture content tends to diminish with increasing distance from a water body; and so on. If you were to measure the performance of a species across the range of variation in any of these conditions you would tend to observe a characteristic ecological response curve of that species to that condition. (e.g., pg. 99, 112‐113) a. Using an abiotic condition of your choice, draw the ecological response curve you might expect for a species across the range of that condition. Example using tree nesting height. The example at right assumes that performance will drop off rapidly at the highest tree heights – since trees ec
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themselves reach a maximum height. Reproduction a
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would likely occur at higher nesting heights than r
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growth and survival due to competitive interactions P
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with other species at lower nesting heights. Survival
Tree nesting height
b. Indicate on your response curve the range of the condition over which you would expect greatest performance to occur in terms of each of the following: survival, growth and reproduction. See above. 4. The niche has variously been defined as “how an organism makes its living,” or “the way in which an organism fits into an ecological community or ecosystem.”1 (pgs. 246‐248) a. How does the concept of the niche differ from that of a habitat? Whereas a habitat is a physical place where a species lives, the niche is defined by a conceptual “space” (often depicted graphically) that a species occupies; it is defined by the resources it uses. 1
Note that your book defines the niche as follows: “Functional role of a species in the community, including activities and relationships.” Though this definition is not uncommon, I find that it is not very helpful in understanding the concept. Hence the definitions above. General Ecology (BIO 160) Worksheet #6 Dept. of Biological Sciences
Sacramento State University
b. Name some characteristics of a species that can be used to define its niche. Foraging location, food size, nesting location, seasonality, vegetation type, etc. c. Through the process of natural selection, a species’ niche is the evolutionary result of its morphological (morphology refers to an organism’s physical structure), physiological, and behavioral adaptations to its surroundings. What kinds of biotic interactions can affect the evolution of a species’ niche? Competition is an interaction between individuals of a species that limits the ability of each species to fully use a common limited resource. Predation is another interaction between individuals of a species that can limit the distribution of a species and thus limit its ability to use resources it otherwise might be able to use. If there is a long history of competition and/or predation pressure on a species, it will influence the evolution of the species’ niche through natural selection (most likely directional selection). d. The realized niche of a species can differ substantially from that of its fundamental niche. What is the difference between these niche spaces and how is each determined? The fundamental niche of an organism is defined by the full range of resources it can use to survive and reproduce without interference from other species. The realized niche is the actual observed niche a species occupies in the face of interactions with other species that limit its use of resources it might otherwise be able to use. The fundamental niche can only be measured by removing other species that are presumed to interfere with the focal species’ use of resources and then quantify the ranges of resources it uses without those interactions. The realized niche can be measured by quantifying the ranges of resources the species uses in the presence of interactions with other species. 5. Four species of chipmunk occur across different altitude ranges on the eastern slope of the Sierra Nevada in California (see pg 265‐266). Given the information provided in your textbook about their physiological tolerances to altitude, food requirements and aggressive behaviors, draw a diagram that illustrates the fundamental and realized niches of each species of chipmunk along this altitudinal gradient. Your exact drawing will differ, but should approximate the different niche ranges below. Keep in mind that the book did not provide all of the information to be exacting on the niche ranges. But it did provide enough to make a good guess and produce the drawing below. Alpine chipmunk
Lodgepole chipmunk
Yellow‐pine chipmunk
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Fundamental niche
Realized niche
Least chipmunk