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Chapter 55

BIOLOGY 1M03 Chapter 55: Biology Chapter 55

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Ben Evans

1 Biology Chapter 55: Biodiversity and Conservation Biology What is Biodiversity  Perhaps simplest way to think about biodiversity is in terms of tree of life, the phylogenetic tree of all organisms  When biodiversity, increases, branches and tips are added and tree of life gets fuller and bushier  When extinctions occur, tips and perhaps branches are removed, the tree of life becomes thinner and sparser  Biodiversity Can be Measured and Analyzed at Several Levels o To get a complete understanding of the diversity of life, biologist recognize and analyze biodiversity on three levels ▪ Genetic diversity is the total genetic information contained within all individuals of a species and is measured as the number and relative frequency of all alleles present in a species • Because no two members of the same species are genetically identical, each species is the repository of an immense array of alleles ▪ Species diversity is based on the variety of species on Earth • Measured by quantifying the number and relative frequency of species in a particular region • Additional aspect of species diversity called taxonomic diversity and is documented by estimating phylogenies ▪ Ecosystem diversity is the variety of biotic communities in a region along with abiotic components such as soil, water and nutrients • More difficult to define and measure than first two because ecosystems do not have sharp boundaries • Attempts to measure ecosystem diversity focus on capturing array of biotic communities in a region, along with variation in the physical conditions present • Ex. Areas around estuaries tend to have high ecosystem diversity due to combination of stream, wetland, intertidal, neritic and upland habitats • When an estuary is dredged or filled, biodiversity is affected at all three levels o Genetic and species diversity change due to different numbers and types of individuals present o Ecosystem diversity is altered due to change in abiotic conditions o Biodiversity is dynamic ▪ Mutations that create new alleles increase genetic diversity 2 ▪ Natural selection, genetic drift and gene flow can increase or decrease overall genetic diversity ▪ Speciation, extinction increases and decreases species diversity ▪ Changes in climate or other physical conditions can result in formation of new ecosystems  How Many Species are Living Today o Approximately 1.5 M species catalogued to date represent a tiny fraction of number actually present o Given that only a fraction of organisms alive have been discovered to date, how can biologists go about estimating the total number of species on Earth o Two general approaches have been used o One is based on intensive surveys of species-rich groups at small sites o A second is based on attempts to identify all of the species present in a particular region o Taxon-Specific Surveys ▪ Researchers began by estimating number of insect species that live in the canopy of a single tropical forest ▪ After using an insecticidal fog to knock down insects from top of a luehea seemannii tree, they identified over 900 species of beetles among individuals that fell ▪ Most were new to science ▪ Researchers used the following logic • Based on earlier work, estimated that 160 out of 900 beetle species live only on L. seemannii • Worldwide, beetles represent about 40% of all known arthropods • Reasonable to suggest that 400 species of arthropods live only in canopy of L. seemannii • By adding estimate of arthropods specializing on trunk and roots of the tree, researchers projected that it is host to 600 specialist arthropods • If each of the 50,000 species of tropical trees harbours the same number of arthropod specialists, then the world total of arthropod species exceeds 30M • Based on such studies, biologists estimate that at least 10M and possible as many as 100M species of all types exist today ▪ More recent single-taxon surveys have sampled larger geographic areas o All-Taxa Surveys ▪ First effort to find and catalogue all of the species present in a large area is now under way ▪ To date, survey has discovered over 650 species that are new to science and over 4650 species that had never been found in the park Where Is Biodiversity Highest? 3  In most taxonomic groups, species richness is highest in the tropics and declines toward the poles  Tropical rain forests are particularly species rich  Data indicates that some areas of the tropics are much more species rich than others  Biologists use the term hotspot to capture this point  In terms of bird species richness, the Andes mountains, the Amazon River basin, portions of East African and Southwest China are important hotspots  Researchers also want to understand which regions of the world have a high proportion of endemic species, meaning species that are found in an area and nowhere else  Mapping species richness hotspots and centres of endemism can inspire interesting questions, mainly, efforts to understand why certain regions contain many species or a high proportion of endemic taxa  In addition, biologists are studying the geographic distribution of biodiversity as a way of focusing conservation efforts Threats to Biodiversity  Today, species are vanishing faster than at virtually any other time in Earth’s history  Modern rates of extinction are 100 to 1000 times greater than the average rate recorded in the fossil record over the past 550 M years  Humans Have Affected Biodiversity Throughout History o Recent research on fossil bids found on islands of South Pacific suggests that about 2000 bird species were wiped out as people colonized this area o Many of these extinctions occurred due to predation by humans or rats, pigs and other animals introduced by humans o Historically, humans have a poor record of conserving resources and protecting species, as well as preserving species they depend on for survival o Ex. Easter Island ▪ When European explorers arrived there in 1722, about 1000 people lived there ▪ Island was treeless and dotted with gigantic stone statues ▪ Researchers who analyzed buried pollen samples taken from swamps discovered that island had once been covered with lush forest dominated by palm trees ▪ A rapid decline in tree pollen coincided with arrival of first human settlers ▪ Fossil digs confirmed that fauna of island underwent drastic changes at the same time  Current Threats to Biodiversity o Most extinctions that have occurred over the past 1000 years took place on islands and were caused by overhunting or the introduction of exotic species, which are non-native competitors, diseases or predators o Endangered species, which are almost certain to go extinct unless effective conservation programs are put in place, are now more likely to live on continents than islands 4 o Habitat destruction has replaced overhunting and species introductions as a primary threat to such species o Results of a recent analysis on causes of endangerment show some patterns ▪ Virtually all of the endangered species are affected by more than one factor • Important because it means that conservation biologists may have to solve more than one problem for any given species to recover ▪ Habitat loss is the most important factor in the decline of these species ▪ Overharvestation is the dominant problem for marine species, while pollution plays a large role for freshwater species ▪ Factors beyond human control can be important • Include predation or competition with native species, natural disturbances or the fact that some species have narrow niches and have historically been rare o Most analyses completed to date are broadly consistent with Canadian data o Habitat Destruction ▪ Humans cause habitat destruction by logging and burning forests, damming rivers, dredging or filling estuaries and wetlands etc. ▪ On a global scale, one of the most important types of habitat destruction is deforestation, especially the conversion of primary forests to agricultural fields and human settlements o Habitat Fragmentation ▪ In addition to destroying natural areas outright, human activities fragment large, contiguous areas of natural habitats into small, isolated fragments ▪ Habitat fragmentation concerns biologists for several reasons • It can reduce habitats to size that is too small to support some species o Especially true for keystone predators such as mountain lions, grizzly bears, which need vast natural spaces in which to feed, find mates and reproduce successfully • By creating islands of habitat in a sea of human-dominated landscapes, fragmentation reduces the ability of individuals to disperse from one habitat to another o Forcing many species into metapopulation structure, which makes them more likely to be wiped out by catastrophic events o Can also suffer from inbreeding depression and random loss of alleles due to genetic drift • Fragmentation creates large amounts of “edge” habitat o Edges of intact habitats are subject to invasion by weedy species and are exposed to more intense sunlight and wind, creating difficult conditions for plants 5 ▪ Decline in habitat quality caused by fragmentation is being documented in a long-term experiment in a tropical wet forest ▪ In an area near Manaus, Brazil, a research group set up 66 square, 1 ha experimental plots that remained uncut ▪ 39 of these study plots were located in fragments designed to contain 1, 10 or 100 ha of intact forest ▪ 27 of the plots were set up nearby, in continuous wet forest ▪ Distribution of study plots allowed research team to monitor changes inside forest fragments of different sizes and to compare these changes with conditions in unfragmented forest ▪ When research group surveyed plots at least 10 years after initial cut, they recorded two
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