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Extinction, Conservation and Restoration Chap.19 Ecology 2000 目錄 • 19.1 Extinction is a natural process that expresses the failure of species to adapt. • 19.2 The risk of extinction is affected by population size, geographic range, age structure and spatial arrangement. • 19.3 Body size, longevity, and population size interact to affect the risk of extinction. 2 Chap.19 conservation & restoration 目錄 • 19.4 Patterns of distribution among and within islands suggest that extinction may result from a decrease in competitive ability. • 19.5 When conservation is no longer possible, restoration is sometimes an option. • 19.6 The metapopulation concept is central to conservation biology. 3 Chap.19 conservation & restoration 目錄 • 19.7 Recovery plans are based on the life history characteristics of the endangered species. • 19.8 Managing genetic diversity is an essential part of conservation and restoration. • 19.9 Restoration often involves the reintroduction of species. 4 Chap.19 conservation & restoration 19.1Extinction is a natural process that expresses the failure of species to adapt. • Extinction is a natural process that expresses the failure of species to adapt. • In 1810, the American ornithologist Alexander Wilson observed an immense flock of passenger pigeons in the Ohio river Valley. • Wilson estimated that there were more than 2 billion birds. • With its extinction on September 1, 1914, the passenger pigeon joined a growing list of species that have vanished from the Earth. 5 Chap.19 conservation & restoration Extinction • It has been estimated that 99.9% of all species that have ever lived are now extinct. • The several million species of plants and animals living today are derived from a small fraction of those alive at any time in the distant past. • At least three times in the past 570 million years the earth has experienced a series of extinction so devastating that 50% or more of the species on earth disappeared. 6 Chap.19 conservation & restoration The first mass extinction • The first occurred about 245 million years ago at the end of the Paleozoic era(Permian period), at a time coinciding with great geologic upheaval associated with the movement of continental landmasses. • It is estimated that about 90% of the earth's species were exterminated during this time. 7 Chap.19 conservation & restoration The second and the third mass extinction • The second occurred about 65 million years ago, at the end of the age of the dinosaurs, the Mesozoic era (Cretaceous period). • Over half of all the species on earth, including the dinosaurs, went extinct during this time. • A third mass extinction is now under way, one that is primarily the result of the activities of humankind. 8 Chap.19 conservation & restoration Types of Extinction • Background extinction reflects the fact that as ecosystems change, some species disappear and others take their places. This turnover of species, which occurs at a relatively low rate, appears to be a normal characteristic of the natural world. • Mass extinction refers to the dying off of large numbers of species as a result of natural catastrophes. 9 Chap.19 conservation & restoration Anthropogenic extinction • Anthropogenic extinction is extinction caused by humans. It is similar to mass extinction in the number of taxa affected and in its global dimensions and catastrophic nature. 10 Chap.19 conservation & restoration Psudo- vs. true extinction • Disappearances may occur in two ways. • (1) species may evolve sufficiently that individuals are no longer recognized as belonging to the same taxon as their ancestors and are given a different scientific name. This is referred to as pseudoextinctions. • (2) a species may cease to exist, in which case its disappearance from the fossil record is a case of true extinction. 11 Chap.19 conservation & restoration Causes of Extinction • 範例: heath hen (Tympanuchus cupido) • At the time of the arrival of Europeans in North America, the heath hen was distributed throughout much of the area of New England and south into Virginia. • It was fairly common and abundant throughout its range. • Hunting pressure and habitat alteration increased dramatically with the arrival of the Europeans, and by the early 1900s, the heath hen was restricted to one place, Martha's Vineyard. 12 Chap.19 conservation & restoration The extinction of heath hen • Concern about the survival of the species resulted in the establishment of a protected refuge in 1907, and the population began to increase. • A disastrous fire during the nesting season destroyed many nests, and a subsequent predation pressure, followed by an outbreak of disease, reduced the population to a handful of individuals by 1920. • The last individual died in 1932. 13 Chap.19 conservation & restoration Anthropogenic climate changes • Anthropogenic climate changes may raise temperatures between 2oC and 6oC sometime during the 21st century. • This is equal to the warming of the earth's climate since the last glaciation, only it is happening 50 times faster. • It is likely to cause the worldwide extinction of many species, particularly plants. 14 Chap.19 conservation & restoration Introduced organisms • Introduced organisms often wreak havoc on local, native species. • 範例: – Nile perch引入 Lake Victoria – brown tree snake意外引入關島,造成許多本土鳥類 滅絕。 – 夏威夷的外來種入侵,許多特有鳥類和蝸牛滅絕。 連帶造成一些植物滅絕。 15 Chap.19 conservation & restoration Habitat loss • Habitat loss may cause extinction by wiping out suitable places to live. 16 Chap.19 conservation & restoration Economic pressure • Economic pressures may accelerate the natural process of extinction. • (Fig 19-1) 17 Chap.19 conservation & restoration Fig. 19-2 The amount of ivory harvested from African elephants increased dramatically in the 1970s and 1980s, contributing to the decline of elephant populations during the same time period 18 Chap.19 conservation & restoration 19.2 The risk of extinction is affected by population size, geographic range, age structure and spatial arrangement. Fig. 19-3 Probability of extinction per year as a function of population size for 39 populations of birds of the British Isles. As population size increases, the probability of extinction decreases. 19 Chap.19 conservation & restoration Fig. 19-4 Percentage of species going extinct through time(millions of years) among late Cretaceous bivalves and gastropods having geographic distributions of three different 20 Chap.19 conservation & restoration sizes. Probability of extinction • When a population is at equilibrium, the probability of extinction at a particular time, P0(t), may be given as • P0(t) = [ bt / (1 + bt) ] , N – where b is the birth rate and N is the population size. • At equilibrium, the birth rate and the death rate, d, are equal, b=d, and the rate of change of the population, dN/dt = 0. 21 Chap.19 conservation & restoration P0(t) = [ bt / (1 + bt) ] , 族群愈小,滅 絕機率愈大。 22 Fig. 19-5 Changes in the probability of extinction with increasing population size, N, for three Chap.19 conservation & restoration different time periods N persistence time • We may think of extinction in terms of the time to extinction or persistence time, which is generally taken to be the time that elapses between the colonization of a site and extinction. • The average time to extinction, T • T= 2/Vc [ (K c - a)/c - lnK ] – where c = 2r/V - 1 and V is the variance in the intrinsic rate of increase, r. 23 Chap.19 conservation & restoration The parameter c decreases as the variance increases with respect to r. Fig. 19-6 Relationship between the c = 2r/V - 1 and the variance, V. (r = 0.2) 24 Chap.19 conservation & restoration A small population with carrying capacity K1 and a low V, indicating low environmental stochasticity, may have a longer time to extinction. Fig. 19-7 Lande's model of time to extinction for r > V (upper line) and r < V (lower line). 25 Chap.19 conservation & restoration Age and spatial structure • Populations of similar size are likely to differ in demographic characteristics such as age structure and sex ratio. These characteristics can influence the probability of extinction. • The spatial structure of a population can also influence the likelihood of extinction. • Both age and spatial population structure could buffer a population from extinction. 26 Chap.19 conservation & restoration 19.3 Body size, longevity, and population size interact to affect the risk of extinction. • The rate at which the population returns to its equilibrium is referred t as the resilience of the population. • Pimm (1991) Longevity and body size – In cases in which population are small, all else being equal, large, long-lived animals may be exposed to less risk of extinction than small, short-lived species. – In situations in which population are large, small, short-lived species should be at an advantage owing to their greater resilience. 27 Chap.19 conservation & restoration 19.4 Patterns of distribution among and within islands suggest that extinction may result from a decrease in competitive ability. • Immigrants to islands appear to be excellent competitors initially. • Species that colonize islands are usually abundant and widespread on the mainland; these qualities make good colonizers. • After an immigrant population becomes established on an island, however, its competitive ability appears to wane; its distribution among habitats becomes restricted, and local population densities decrease. These trends eventually can lead to extinction. Taxon cycle 28 Chap.19 conservation & restoration The Shiny cowbird expanded its range in the islands (stage I), the house wren has become extinct (E) on several island (stage III). 29 階段 I 絕跡 亞種 階段 II 階段 III Fig. 19-8 Distribution patterns and taxonomic differentiation of several birds in the Lesser Antilles, illustrating Chap.19 restoration progressive stages of theconservation taxon&cycle. 30 Chap.19 conservation & restoration 31 Fig. 19-9 Relative indices of population density and ecological distribution of songbirds in the Chap.19 conservation & restoration West Indies as a function of stage of taxon cycle. 32 Chap.19 conservation & restoration New species and new cycle • A large number of existing species can evolve faster than the new species can adapt to meet their evolutionary challenge. • On the other side, the species may again increase and begin a new cycle of expansion throughout the island. • This has occurred many times in the birds populations within the West Indies. 33 Chap.19 conservation & restoration 19.5 When conservation is no longer possible, restoration is sometimes an option. • Restoration involves not only scientific work, but also organization, communication, and the necessity of working within the relevant political and social establishment. • Restoration ecology should focuses on restoring whole habitats and their consituent biological communities, rather than on single populations. 34 Chap.19 conservation & restoration 19.6 The metapopulation concept is central to conservation biology. • Habitat fragmentation related to human development and expansion is a major reason for the decline of many endangered species. • Thus one of the most daunting challenges of conservation efforts is to understand the dynamics of spatially structured populations. 35 Chap.19 conservation & restoration Conservation biology • The metapopulation and landscape concepts have helped shaped the approach to this challenge in recent years. • Theory of island biogeography (chap. 29) • One aspect of the dynamics of wildlife reserves that has received considerable attention is the concept of habitat corridors, which are often in strips or narrow lanes that connect patches. 36 Chap.19 conservation & restoration 19.7 Recovery plans are based on the life history characteristics of the endangered species. • The Endangered Species Act of the United Sates requires that a recovery plan be developed for each species placed on the endangered species list. • Typically, these plans are prepared by teams of ecologists and others, such as representative of industry or governmental agencies. 37 Chap.19 conservation & restoration Recovery plan • The recovery plan includes an analysis of the predicament of the species and proposes strategies for its recovery. • The plan also usually includes an analysis of the costs and benefits of the preservation of the species. • The scientific foundation of the plan is based on the natural history of the species. 38 Chap.19 conservation & restoration Fig. 19-10 The woodland caribou (Rangifer tarandus caribou) 39 Chap.19 conservation & restoration The dashed line indicates the southern extent of the main range of the species. 殘餘 再引入 Fig. 19-11 Distribution of the woodland caribou in southern Ontario, Canada. 40 Chap.19 conservation & restoration 經費足夠 棲息地有無 可以再引入 Fig. 19-12 Flowchart of the planning process involved in the reintroduction of the woodland caribou. 41 Chap.19 conservation & restoration 19.8 Managing genetic diversity is an essential part of conservation and restoration. 範例 • The lakeside daisy is found in only three small populations, two in Ontario and one in northern Ohio near Lake Erie (Fig. 19-13) • The Illinois populations had disappeared by the early 1970s. No viable seeds were produced by these plants during 1970s, and some of the plants were moved to gardens for preservation and study. 42 Chap.19 conservation & restoration 尚存的 過期的 A few remaining living individuals in Illinois populations, but they cannot produce seeds, their population is essentially extinct. Fig. 19-13 Distribution of populations of the rare and threatened lakeside daisy. 43 Chap.19 conservation & restoration Restoration plan of daisy • The restoration plan for the lakeside daisy called for the establishment of two populations, each having a minimum viable population size of about 1,000 plants, a number determined by population viability analysis and life history study. • It was estimated that this population size would buffer the plats against loss of genetic variation. 44 Chap.19 conservation & restoration Captive breeding in animals • The Florida panther (豹), for examples, is now represented by fewer than 50 cats in southern Florida. • The black-booted ferret(貂) , California condor(兀鷹) , and red wolf(狼) are other such examples. • Only hope for the preservation of such species is through captive breeding programs. 45 Chap.19 conservation & restoration Captive breeding program • The success of a captive breeding program depends on the preservation of all aspects of behavior and physiology that are unique to the species. • One of the most challenging goals is to maintain, even enhance genetic variation in the population. 46 Chap.19 conservation & restoration The antelopes as a example • When antelopes(羚羊)are started in the wild, they turn quickly away from the disturbance and sprint in the opposite direction for some distance, then stop and reexamine the situation. • The behavior is not adaptive in the confinement of a zoo, however, where an antelope may sprint directly into a fence or wall and suffer great injury. 47 Chap.19 conservation & restoration Captive vs natural evolution • In zoos, there will be a consequent evolution of the antelope herd away from the natural behavior. • If reintroduced into the wild, these animals would be expected to fare poorly. • Considerable effort has been expended to develop techniques to minimize such nonadaptive genetic change. 48 Chap.19 conservation & restoration 19.9 Restoration often involves the reintroduction of species. 範例:reintroduction of the swift fox(狐狸) to Canadian prairies • The fox disappeared from Canada in the early 1930s, and its range has retreated southward since that time, owing primarily to the destruction of the prairie ecosystem resulting from agriculture and development. • Currently distribution (Fig. 19-14) 49 Chap.19 conservation & restoration Fig. 19-14 Ranges of the swift fox and kit fox. Candidate reintroduction sites are number 1 through 4. 50 Chap.19 conservation & restoration Soft vs hard release Two types of release strategies were used. • Animals were transported the release site and placed in pens constructed in the prairie. The foxes were held in the pens for several months until they bred, after which the adults and young were released into the wild. • This type of release strategy is called a soft release. 51 Chap.19 conservation & restoration Hard release • Foxes were simply transported from the captive breeding area or from source populations to the reintroduction site, where they were released. • This strategy is known as a hard release. • There appeared to by no difference in survival between the two release methods. 52 Chap.19 conservation & restoration No difference One of the major concerns of those interested in conservation is the maintenance of biodiversity. The principles of ecological diversity will be discussed in detail in Part 6 as part of our discussion of community ecology. 53 Chap.19 conservation & restoration Suggested readings (I) • Burney, D. A. 1993. Recent animal extinctions: Recipes for disaster. American Scientist 81:240-251. • Caro, T. M., and M. K. Laurenson. 1994. Ecological and genetic factors in conservation: A cautionary tale. Science 263:485-486. • Ceballos, G., and J. H. Brown. 1995. Global patterns of mammalian diversity, endemism, and endangerment. Conservation Biology 9:559-568. • Eisner, T., J. Lubchenco, E. O. Wilson, D. S. Wilcove, and M. J. Bean. 1995. Building a scientifically sound policy for protecting endangered species. Science 268:1231-1232. • Glen, W. 1990. What killed the dinosaurs? American Scientist 78:354-370. 54 Chap.19 conservation & restoration Suggested readings (II) • Hansen, A. J., T. A. Spies, F. J. Swanson, and J. L. Ohmann. 1991. Conserving biodiversity in managed forests. BioScience 41:382-392. • Mills, L. S., M. E. Soule, and D. F. Doak. 1993. The keystone-species concept in ecology and conservation. BioScience 43:219-224. • Myers, J. P., et al. 1987. Conservation strategy for migratory species. American Scientist 75:18-26. • Redford, K. H. 1992. The empty forest. BioScience 42:412422. • Robinson, S. K., et al. 1995. Regional forest fragmentation and the nesting success of migratory birds. Science 267:1987-1990. 55 Chap.19 conservation & restoration Suggested readings (III) • Rolston, H., III. 1985. Duties to endangered species. BioScience 35:718-726. • Simons, T., S. K. Sherrod, M. W. Collopy, and M. A. Jenkins. 1988. Restoring the bald eagle. American Scientist 76:252-260. • Soule, M. E. 1985. What is conservation biology? BioScience 35:727-734. • Timan, D., and J. A. Downing. 1994. Biodiversity and stability in grasslands. Nature 367:363-365. • Westman, W. E. 1990. Managing for biodiversity. BioScience 40L26-33. 56 Chap.19 conservation & restoration 問題與討論 請提出問題! 57 Chap.19 conservation & restoration