Ecology

Geology/Geography/Oceanography/Atmospheric Sciences

Quiz 21 :

Landscape Ecology

Quiz 21 :

Landscape Ecology

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Analyses such as Milne's comparison (1993) of bald eagles and barnacles demonstrate that organisms of different sizes interact with the environment at very different spatial scales. With this in mind consider the experiments of Diffendorfer and colleagues (1995) on the influence of habitat fragmentation on movement patterns of small mammals. Think about the size of their experimental study area (see fig. 21.10). How might a manipulation of this size have affected the movements of prairie birds? How would their manipulation have affected the movements of ground-dwelling beetles?
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Milne has carried out the studies on measurement of landscape from the point of view of organisms of different sizes such as the bald eagles and the barnacles. He suggested that the organisms differing in size perceive the environment at different scales.
Diffendorfer and colleagues have studied the effect of habitat fragmentation on the movement of the small mammals. They divided the prairie habitat into small, medium and large patches. They observed that the fragmentation caused the organisms to move farther in search of resources.
However, the number of individuals moving out of the patch was less. Thus, fragmentation was shown to decrease the movement of the organisms.
In other words organisms in medium and large patches showed more movement as compared to the smaller patches.
The patch size is small, medium or large with respect to the size of the organism under study.
In case of small mammals, the territory of an individual mammal can be considered as a unit for measurement of patch size.
A patch that can accommodate few individuals is considered small for the mammal and a patch that can accommodate large number of members is considered large for the mammal.
The patch sizes created for the small mammals may be perceived differently by organisms greater or smaller in size than the small mammals. Hence, the beetles that are smaller than the mammals, may perceive all the patches of the mammals to be large. Their movement might not have been significantly affected.
For a species larger than the mammals such as the prairie birds, the manipulation of the prairie habitat might have affected significantly. The birds might have experienced severe fragmentation of habitat with decrease in patch size. This would have caused farther movement of a small population of birds.

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How do the activities of animals affect landscape heterogeneity? You might use either beaver or human activity as your model. What parallels can you think of between the influence of animal activity on landscape heterogeneity and the intermediate disturbance hypothesis? Which is concerned with the effect of disturbance on species diversity?
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Organisms causing changes in the landscape structure are called ecosystem engineers. These include the plants, animals, and the humans.
Animals such as the beaver have been studied extensively for its effect on the landscape structure.
The beaver influences the landscape structure even on a large scale. The beaver affecting the landscape structure in following ways:
• Cutting of trees for food and wood for building dams affects the patches of trees
• Building dams across streams or rivers to support their homes called lodges, for protection from predators and to stock food for winter affect the landscape structure
• The dams lead to flooding of adjoining areas and create wetlands
• Their activity creates different ecosystems such as ponds, meadows, and wetlands
Thus, the beavers increase the diversity or heterogeneity of the landscape.
The intermediate disturbance hypothesis proposed by Joseph Connell states that moderate amount and level of disturbance leads to increase in species diversity.
Thus, animal activity can increase the landscape diversity and moderate disturbance can affect species diversity. Too high or low levels of activity of animals or of disturbance do not create optimum diversity.
The intermediate disturbance hypothesis is concerned with the species diversity. However animal activity, especially humans or predation by animals can act as a type of biotic disturbance and influence species diversity.
Hence, both animal activity and the intermediate disturbance hypothesis are related to the effect of disturbance on species diversity.

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How do the positions of patches in a landscape affect the movement of individuals among habitat patches and among portions of a metapopulation? Again, consider the hypothetical landscapes shown in question 5. Which of the two landscapes would promote the highest rate of movement of individuals between forest patches? Can you think of any circumstances in which it might be desirable to reduce the movement of individuals across a landscape? (Hint: Think of the potential threat of pathogens that are spread mainly by direct contact between individuals within a population.)
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The metapopulations are subpopulations of species separated by a distance. The organisms show movement between the subpopulations. This movement is affected by the location of the habitat patches.
As the distance between the habitats patches increases and they become more isolated, the movement of the organisms between the habitats decreases. This increases the risk of extinction of the local subpopulations.
The landscapes are illustrated as follows:
img The forest patches in landscape 3 are elongated and appear to be close to each other. The forest patches in landscape 4 appear to be more geographically separated and isolated. Hence, landscape 3 will promote highest rate of movement of individuals across the forest patches.
The movement of individuals between the habitats patches helps in increasing the population size and density of the species.
However, it also promotes the transmission of diseases and predators from one patch to another. Hence, reduced movement of organisms is desirable to check the spread of diseases between the habitat patches.

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How does landscape ecology differ from ecosystem and community ecology? What questions might an ecosystem ecologist ask about a forest? What questions might a community ecologist ask about the same forest? Now, what kinds of questions would a landscape ecologist ask about a forested landscape?
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Can we conclude from this study that streams draining deciduous versus coniferous forest patches contain different amounts of detritus?
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How does the concept of metapopulations differ from the perspective of populations that we discussed in Section III? (Hint: Think of the spatial contexts of these two views of populations.)
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How should the area of forest patches in an agricultural landscape affect the proportion of bird species in a community that are associated with forest edge habitats? How should patch area affect the presence of birds associated with forest interiors?
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How might the shapes of forest patches in a landscape affect the proportion of birds in the community associated with forest edge habitat? How might patch shape affect the presence of birds associated with forest interior?
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Consider the following options for preserving patches of riverside forest. Again, the two landscapes contain the same total area of forest but the patches in the two landscapes differ in shape. Which of the two would be most dominated by forest edge species?
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Use fractal geometry and the niche concept (see chapters 13 and 16) to explain why the canopy of a forest should accommodate more species of predaceous insects than insectivorous birds. Assume that the numbers of bird and predaceous insect species are limited by competition. (Milne's study [1993] of barnacles and bald eagles on Admiralty Island should provide a beginning for your argument.)
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The green areas represent forest fragments surrounded by agriculture. Landscapes 1 and 2 contain the same total forest area. Will landscape 1 or 2 contain more forest interior species? Explain.
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