Deck 21: Landscape Ecology

Question 1

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?

Answer 1

The relationship between patch perimeter and patch area influences the patch structure in a landscape.
Long perimeter and a small area is a characteristic of an elongated patch. Such patches have a longer edge compared to the interiors.
Similarly, increase in patch area increases the patch interiors decreasing the edge.
The edges of habitats with different ecosystems on either side have been referred to as ecotones.
The proportion of species living in the ecotones depends on the area of the habitat patch enclosed by the ecotones.
A smaller area with a large perimeter leads to longer ecotones thus increasing the proportion of inhabitant species such as birds.
Thus elongated habitats possess more ecotones compared to a circular patch.
A habitat patch with a larger area has a large interior and comparatively less edge.
Hence such areas have more species of birds associated with forest interiors.

Question 2

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.

Answer 2

The species living in the interiors of a habitat are called the interior species. The abundance of an interior species depends on the area of the habitat available for these species. The fragmentation of the habitat has been shown by ecologists to decrease the area of an individual habitat patch.
Landscapes 1 and 2 have been illustrated below: Landscape 1 and landscape 2 possess the same total forest area.
However, the landscape 2 is more fragmented. Hence, landscape 2 has more edge habitat than the interior habitat.
Landscape 1 is less fragmented. Hence it has more interior habitat than the edge habitat.
Therefore, out of landscape 1 and 2, landscape 1 will contain more forest interior species.

Question 3

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?

Answer 3

The structure of a landscape consists of the number, size, and shape of the habitat patch.
The shape of the habitat patch depends on the perimeter and area of the patch.
A forest patch with a longer perimeter relative to area is found to have an elongated shape. A patch with more area relative to the perimeter is found to be nearly circular. The shape of the forest patch also decides the abundance of species living within it.
The elongated patches have more edge and show more edge species. Hence, an elongated patch of a forest will have abundant species of birds living at the edge of the habitat.
Roughly spherical patches with more area have more interior species. Hence, a roughly circular forest patch will show abundant species of birds living in the interiors.
Thus, the shape of forest patch can affect the abundance of birds living at the edge and the interiors.

Question 4

Consider the options for preserving patches of riverside forest shown in landscapes 3 and 4. 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?

Question 5

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.)

Question 6

Use fractal geometry and the niche concept (see chapters 9, 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.)

Question 7

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?
Figure 21.10 Experimental landscape for the study of small mammal movements (data from Diffendorfer, Gaines, and Holt 1995).

Question 8

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?

Question 9

In the landscapes shown in figure 21.4, what is patch and what is matrix?
Figure 21.4 Forest fragments, shown as dark green, in six landscapes in Ohio (data from Bowen and Burgess 1981).

Question 10

The populations of many forest bird species in eastern North America have declined following deforestation and fragmentation of forest habitat (see fig. 21.4), while many birds associated with open grassland habitats have thrived. From a landscape perspective, how could forest succession (chapter 20) change this situation?
Figure 21.4 Forest fragments, shown as dark green, in six landscapes in Ohio (data from Bowen and Burgess 1981).

Question 11

What do the patterns shown in figure 21.11 suggest about the relative impact of fragmentation of prairie habitat on populations of Sigmodon, Microtus, and Peromyscus ?
Figure 21.11 Influence of patch size on small mammal movements within experimental landscapes (means, 1 standard error) (data from Diffendorfer, Gaines, and Holt 1995).

Question 12

Habitat corridors are widely recommended for conser­vation of species whose populations are restricted to isolated patches of habitat. Why?

Question 13

Are there any potential risks associated with increasing the exchange of individuals between habitat patches through the creation of habitat corridors?

Question 14

How are "landscape engineers" similar to keystone species? How are they different?

Question 15

Can we conclude from this study that streams draining deciduous versus coniferous forest patches contain different amounts of detritus?

Question 16

Can a dominant species of tree in a forest or coral on a coral reef (see fig. 17.17) be an ecosystem engineer?

Question 17

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?

Question 18

The patterns shown in figure 21.28 support Minnich's hypothesis that fire protection in southern California would produce a difference in median burn area. How­ever, do these results show conclusively that the dif­ferences in burn area in the two regions are the result of different fire management practices?
Figure 21.28 Characteristics of fires in the Mediterranean landscapes of southern and Baja California from 1972 to 1980 (data from Minnich 1983).