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Ecology 22.docx

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Department
Biology
Course
Biology 2483A
Professor
Mark Moscicki
Semester
Fall

Description
Ecology-Lecture 22 Nov 28, 2013 Introduction  As the human population has grown, and our use of resources has increased, we have destroyed the habitat of many species (outright destruction or through changes in the biological and physical properties).  A biodiversity crisis has developed. The World Conservation Union lists 16,913 species as threatened with extinction (1% of all species worldwide). This number is certainly an underestimate, as only the best studied taxonomic groups have been assessed for their conservation status. Conservation Biology  Conservation biology: This is the field of biology dedicated to reversing species declines. It can be defined as the scientific study of phenomena that affect the maintenance, loss, and restoration of biodiversity. Conservation biology is an integrative discipline that applies the principles of ecology to the protection of biodiversity.  Stabilization of populations requires expertise from several biological disciplines, as well as law, political science, and sociology (this integrative approach is characteristic of conservation biology).  Diversity protection is important for both practical and moral reasons. Humans rely on natures diversity. There are hundreds of domesticated species that sustain us (food, fuel, fiber). In addition, we harvest wild species for medicine, building materials, spices and decorative items. Beyond what we harvest, natural functioning of biological communities provides valuable services to humans via ecosystem services (water purification, soil maintenance, crop pollination, climate regulation, flood control). Natural communities and ecosystems are also important for our emotional health (providing place for solace). Many people also believe that we should protect species and their ecosystems for moral reasons (religious or spiritual beliefs that other species have a right to exist just as we do).  Conservation biology is a value-based discipline. The scientific method calls for objectivity (collection and interpretation of data without bias). However, science is not free of human values, and it takes place within a larger social context. Declining Biodiversity  Biodiversity is declining globally  Rates of extinction are difficult to measure because the number of species on Earth currently is unknown. Most studies have estimated that there are between 5-10 million eukaryotic species on earth, but there may actually be as few as 3 million or as many as 100 million.  Extinctions of barely known plant species continue throughout the tropics, despite our decades long recognition of the problem. Through greater efforts to explore earths ecosystems, ecologists are gaining knowledge of the worlds biota and tabulating new species at a faster rate, but threats to those species are keeping pace with such gains in our knowledge about them.  Many exploration voyages identified new endemic species (species that occur in a particular geographic region and nowhere else) at one time, to find them extinct a few years later (possibly as result of forest clearing)  Despite the uncertainty in species number, extinction rates can be estimated using several indirect measures.  Extinction rates determined from the fossil record are used as background rates. We can then compare current extinction rates to background extinction rates. For mammals and birds, the background rate is one species every 200 years. This is equivalent to an average species life span of 1 million to 10 million years. The current extinction rate for mammals and birds is one per year, equivalent to an average species life span of 10,000 years. Overall, the extinction rate in the twentieth century was 100 to 1,000 times higher than the background rate.  Today, we use the species area relationship to estimate current extinction rates. This involves the relationship between the number of endemic species and area. It allows us to estimate the number of species that would be driven to extinction by a given amount of habitat loss.  We also look at changes in the threat status of species (e.g., shift from endangered to critically endangered).  Finally, we look at rates of population decline or range contraction of common species (is the range in which they live declining?).  It is sometimes difficult to know when a species is definitely extinct. Many species are known from a single specimen or location; the logistics of relocating them may be insurmountable. However, declaring a species extinct can stimulate biologists’ search efforts.  A flora of Hawaiian plants (1990) listed many extinct species. 35 have since been relocated, though only a few individuals. These extremely small populations cannot serve the same ecological functions as larger populations.  Humans have always had a large impact on other species (although rapid increases in population over the last century have quickened and intensified the effects).  Bones found on Pacific islands reveal the prehistoric extinction of up to 8,000 species of birds following colonization by Polynesians. Most of the species were endemic. Some entire guilds (species with the same method of feeding) went extinct, which must have caused large community changes. Image (A) shows that prior to 3000 years ago, there were a large number of species. However, fossils records indicate that this number rapidly declined as soon a colonization began to occur. Figure (B) indicates the species decline, classified by the feeding guild found on the island. It shows an extinction of 50% or more of the frugivores (fruit feeding) and nectarivores (nectar feeding). This likely led to drastic changes in the islands plant communities (role in maintaining endemic tree populations).  Much research on extinction has focused on problems of small populations, which are vulnerable to genetic, demographic, and environmental events. This can reduce the population growth rate and increase the rate of extinction. As a result, a cyclic chain of events may ensue in which an already small population drops even further in size, thereby making it even more vulnerable to genetic, demographic, and environmental events.  Extinction vortex: A small population declines even further and becomes ever more vulnerable to processes that lead to extinction. There is a need to determine the causes of population declines, to identify actions that could counteract problems before the extinction vortex takes hold (otherwise, this pattern can doom a population to extinction).  Research has also been focused on a spatial approach that tracks changes in species’ ranges. A decline often moves through a population as a wave, retreating from all edges of a population into its center (may be due to invasive species spreading through)  A study of 173 declining mammal species worldwide showed that, collectively, these species had lost half of their range area over the past 100-200 years.  Example: The cheetah occupies only 56% of the land it once did.  When populations are lost from a community, there are consequences for that species’ predators, prey, or mutualistic partners (not just declining species).  The resulting changes at the community level may bring about secondary extinctions and ultimately affect ecosystem function.  While food webs can be resistant to species removal, the deletion of certain species can trigger a cascade of secondary extinctions. Generally, the stronger a species’ interactions in the food web, the greater the impact of its removal.  In a study of plant–pollinator interaction webs, the effect of removing pollinators depended on whether they were specialists or generalists. If generalist pollinators (those that visited the most plant species) were removed first, there was a more rapid reduction of pollinator visits to plants than if the removal started with the most specialized pollinators.  The movement and introduction of species to all parts of the globe has increased greatly over the last century (largely as a result of human expansion).The range expansion of some species has coincided with range contraction of many native species (native species are going extinct as non native take over).  These three images show that the number of species that have become established in the U.S has increased about five fold over the past century. Image (A) shows that plant pathogens and terrestrial vertebrates have increased, posing a threat to the native species (American Elm tree). Image (B) shows as increase in the number of mollusks and fishes, largely from ballast water. For example, the Round Goby was introduced into the N.A Great Lakes by ballast water, and it has outcompeted native fish species causing their populations to decline. Image (C) show that there has been an increase in non native plants and insects, such as the Mediterranean fruit fly which causes extensive damage to a wide range of fruits and vegetables.  The greatest “losers” among native species tend to be specialists with adaptations that resulted from evolution in a particular place (small ranges).  The “winners” tend to be generalists with less stringent habitat requirements (can live in a wide variety of areas, so may leave if invasive species invade their habitat).  The spread of introduced species and native generalists, and the decline of native specialists, is leading to taxonomic homogenization of Earth’s biota.Taxonomic homogenization is common in terrestrial areas, but also in fresh waters.  Homogenization has been observed among the fresh water fishes of the U.S, largely as a result of widespread introductions of game fishes.  A study quantified the homogenization of U.S fish faunas by examining the change in the number of species shared between all possible pairs of the 48 states. On average, pairs of states share 15 more species than they did at the time of European colonization.  The below graph shows that the average increase in the number of shared species was 15. Historically, Arizona and Montana had no species in common, but they now share 35.  Genetic homogenization is also occurring through hybridization between native and non-native species (on genetic level).  Example: The California tiger salamander, a threatened endemic, has hybridized with another species of tiger salamander introduced from the Midwest 50 years ago as fish bait. The California tiger species is at risk of extinction through genetic swamping by the introduced species. Threats to Biodiversity  Primary threats to biodiversity include habitat loss, invasive species, overexploitation, pollution, disease, and climate change.  Understanding the causes of biodiversity loss is the first step toward reversing them.  Multiple factors are likely to contribute to decline and extinction of a species.  The Pyrenean ibex was endemic to the Pyrenees. Its decline was due to hunting, climate change, disease, and competition with domestic livestock and non-native ungulates such as chamois. The last one was killed in 2000 by a falling tree.  Multiple causes of biodiversity loss are also apparent in higher taxonomic groups.  Over 1,100 mammal species are currently threatened with extinction.  Primary threats facing mammals are loss of habitat, hunting, accidental mortality, and pollution. Some mammals are threatened by additional factors such as disease. However, the relative importance of these factors differs between terrestrial and marine mammals. Habitat Loss & Degradation=Largest Threats  The source of the biodiversity crisis is the scale of human impact on the planet. Earth has been modified across 60% of its land surface and all marine ecosystems have been affected by humans. There are areas of extreme influence (agricultural regions and coastal waters) and areas of little influence (deserts and polar areas) but everywhere has been affected to some extent.  Addressing the degradation, fragmentation, and loss of habitat is central to conservation work.  Habitat loss: conversion of an ecosystem to another use (urban development or agriculture).  Habitat fragmentation: breaking up of once continuous habitat into a series of habitat patches amid a human-dominated landscape.  Habitat degradation: changes that reduce quality of the habitat for many, but not all, species.
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