Habitat Loss, Exotic Species - Environmental Biology - Lecture Notes, Study notes of Biology

Download Habitat Loss, Exotic Species - Environmental Biology - Lecture Notes and more Study notes Biology in PDF only on Docsity! Environmental Biology Rev. 11/09 1 LECTURE 15 HABITAT LOSS & EXOTIC SPECIES The three greatest threats to the conservation of many ecosystems are 1) habitat loss 2) habitat fragmentation and 3) exotic species. I. Habitat Loss A. Trends in Extinctions 1. E. O Wilson of Harvard University estimates that between 1,000 and 50,000 species are going extinct each year. a. The natural ‘background rate of extinction is one out of every million species per year. 2. In the past 500 years, 816 species are know to have disappeared from the planet. a. In the United States, 526 species are listed as extinct or missing, never to be seen again. b. Birds are the group that has suffered the most extinctions (21 extinct bird species). c. Following close behind, however, are freshwater mussels (19 extinctions), d. Freshwater fishes (17 extinctions). e. Flowering plants (13 extinctions). 3. The Nature Conservancy reveals that approximately one-third of U.S. plant and animal species are at risk of extinction. a. The species with the greatest cause for concern are the animals that depend on freshwater ecosystems (e.g., mussels, crayfish, fish and amphibians) and flowering plants. B. Trends in Habitat Loss. 1. Habitat destruction is the leading cause of the current extinctions. a. Logging affects approximately 14-17 percent of listed species, b. Grazing impacts 19-22 percent, c. Water development affects 29-33 percent, d. Recreation affects 23-26 percent, e. Mining impacts 14-21 percent 2. Trends in species extinctions are estimated using the basic concept of species:area curves a. The number of species in a give area can be described using this technique. b. The number of species counted in an area is expected to increase as the size of the area searched is enlarged. c. For any given habitat, we can expect to find 90% of the species present after 50% of the area has been sampled. d. Based upon this relationship, some predictions can be made with regard to species extinction and the loss of habitat. i) If the size of the habitat were halved, 10% of the species would be lost. ii) Going further, if 90% of the habitat is lost, species extinction rates would be 50%. C. Habitat Fragmentation 1. Habitat can be destroyed or degraded in two basic ways: quantitative and qualitative losses. a. Quantitative losses, in principle, can be measured by looking at a previously mapped area and determining how much of the habitat area is no longer present. b. Qualitative changes involve a change or degradation in the structure, function, or composition of the habitat. Docsity.com Environmental Biology Rev. 11/09 2 2. Habitat fragmentation represents a qualitative change and has two parts. a. a decrease in the habitat type and b. the apportionment of the remaining habitat into smaller, more isolated pieces. 3. The problems that arise from habitat fragmentation include: a. smaller populations due to small amounts of habitat, b. isolation of populations in the fragmented parts, and c. potential increase in predators, competitors and parasites. 4. These problems can be summed up in once concept – increased edge effect. a. Fragmentation increases the amount of edge area, & the influence of the edge can extend 200–300 meters into the forest. b. Not only is the quality of the habitat changed for the interior species, c. But species that are adapted to open areas will be able to colonize the edges, providing competition for any interior species that remain. d. These edge species often have broader environmental tolerances (much like weeds). In fact, some of them are (exotics). 5. As a result, habitat fragmentation is one of the greatest threats to species and the ecosystems they rely upon for survival. II. Exotic Species 1. Of the 3,318 plant species in PA, 2,076 (62.5%) are native and 1,242 (37.4%) are non-native. a. These species may have been introduced from other states or other countries. Either way, they did not exist in this state prior to European settlement. 2. In the last 14 years, an additional 53 species have been added to the list of plant species in Pennsylvania. A. The damage they do - the basics 1. The three greatest threats to the conservation of many ecosystems are habitat loss habitat fragmentation and exotic species. a. Invasive species are second only to habitat destruction as a leading threat to the native species of the United States. 2. In the United States, more than 4,500 foreign species have gained a permanent foothold. a. If we consider cultivated species, like corn, wheat and rice and domesticated animals, the number of introduced species is over 30,000! 3. Exotic species have contributed to the decline of 42 percent of U.S. endangered and threatened species. 4. At least 3 of the 24 known extinctions of species listed under the Endangered Species Act were wholly or partially caused by hybridization between closely related exotic and native species. 5. It is estimated that non-indigenous species in the U.S. cost us more than $122 billion a year. B. Why are exotics so Successful? 1. The checks and balances of limiting resources, competition and carrying capacity are the result of a shared evolutionary history. Two closely related organisms are more likely to both persist if they avoid competition. 2. But, exotic species do not share the same evolutionary history. a. In their natural setting, the population of these introduced species is kept in check by their own competitors, parasites and disease. b. But in their new setting, they are able to side-step this evolutionary burden and enter a new realm, where the prey are defenseless, the plants are palatable and the parasites are fully engaged with your competitors. Docsity.com