Habitat Fragmentation

Transcription

1 Habitat Fragmentation

2 Habitat Fragmentation Habitat fragmentation is the process by which habitat loss results in the division of large, continuous habitats into smaller, more isolated remnants.

3 Many times, natural habitats show a patchy distribution. This affects the organisms that live there.

4 The effects of man-made habitat fragmentation are much more significant Organisms in these habitats are not adapted for fragmentation

5 Activities such as clearcutting have created a mosaic of forested and deforested areas in many regions that were once completely covered with forests.

6

7 With the growth of human population and the increasing removal of natural habitat, the remaining wild areas begin to take the form of habitat islands surrounded by relatively uninhabitable areas. This habitat fragmentation is an increasingly serious problem in biological conservation.

8 The most noteworthy effects of the fragmentation of natural habitats are: 1. The formation of isolated patches of habitat. 2. The increasing significance of edge effects.

9 What does this mean? It means that, when we reduce the size of a habitat we can expect to lose species.

10 National Parks are habitat islands, and often show damage to animal populations. This is often most pronounced in the smaller parks. Mount Rainier National Park in Washington has seen a reduction in the number of mammals found there from 68 to 37 species.

11 The study of these dynamics has introduced modeling into conservation biology. Spatially explicit models combine population models with landscape maps to make mathematical predictions.

12 Species-area curves (special computer models) can be used to predict how large a reserve must be to preserve its biological diversity. For the Australian wheat-belt region, estimates are that a reserve of 43,000 hectares would be necessary to preserve all 25 species, and a reserve ¾ that large to preserve 90% of them. The largest current reserve is 5,119 hectares. What are the problems with estimates like these?

13 5000 square kilometers has been adopted as a rough minimum size for major tropical forest preserve in the Amazon Basin. Based on very speculative reasoning, it is thought that this might reduce extinction rates to less than 1%.

14 Edge Effects The creation of habitat patches from formerly continuous woodlands modifies the microclimate of the forest, resulting in increased edge effects. Environmental conditions around edges are different from those in the interior. This results in differences in the types of trees, the understory, and even the animals.

15 One effect is the ability of predators from open habitats to penetrate forest edges and prey on the animals there. Striped skunk Blue jay Common crow

16 The brown-headed cowbird is a nest parasite that frequents edge habitats.

17 A study in California looked at the number of chaparral bird species in isolated canyons in an urban setting. The number of bird species declined as the size of the canyon decreased. Interesting, canyons visited by coyotes had more bird species than those that were not. The coyotes apparently helped control the abundance of bird predators, like skunks and domestic cats.

18 Estimates are that the Mkomazi Game Reserve in Tanzania will lose 17 of its 39 species of large mammals if it is separated from surrounding reserves.

19 Biological Dynamics of Forest Fragments Project Near Manaus, Brazil, forest patches have been created. They are made of individual sections of: 1, 10, 100, 1000, and hectares. Observed prior to isolation, and will be studied for at least 20 years.

20 Habitat Fragmentation What are the key issues habitat fragmentation creates? Limits access to food, water, mates Creates edge effects Limits escape for prey and hunting range for predators Isolates organisms genetically Reduces overall habitat size

21 Habitat Fragmentation What causes habitat fragmentation in the following biomes? Rainforest Tundra Grasslands Desert

22 Habitat Fragmentation What can we do to help stop it?