Chapter 4 Student Notes (Part 1) 2017-2018
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Miami Dade College, Miami**We aren't endorsed by this school
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BSC 2010
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Biology
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Dec 20, 2024
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4
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Chapter 4: Biodiversity and Evolution Core Case Study: Why should we protect sharks? More than 400 species of sharks inhabit the world’s oceans. Due to widespread media coverage of attacks, the danger of sharks is greatly exaggerated. For every shark that injures or kills a person every year, people kill about 1.2 million sharks. •Sharks are caught for their fins, which are used in soup and for medicine. •They are killed for their meat, liver, skin, and jaws or simply out of fear. 32% of open-ocean shark species are threatened with extinction. Sharks are vulnerable to population declines because of their slow growth, late maturation, and low reproduction. Sharks are a keystone species that play a crucial role in maintaining food webs. •While feeding at the top of food webs, they remove sick and injured animals. •They also control the populations of their prey. Section 4-1: What Is Biodiversity and Why Is It Important? Biodiversityis the variety of earth’s species, the genesthey contain, the ecosystems in which they live, and the ecosystem processes of energy flow and nutrient recycling that sustain all life.•Species: set of individuals who can mate and produce fertile offspring •Estimates are that there are 8-100 million species on earth. The best guess is between 10-14 million. •1.9 million species have been identified •Almost 50% live in tropical rainforests that humans are rapidly clearing. These forests, along with oceans, are believed to hold most of the world’s unidentified species. Components of Biodiversity •Species diversity-the number and abundance of species present in different communities •Genetic diversity- the variety of genetic material within a species or a population •Ecosystem diversity (variety of terrestrial biomes and aquatic ecosystems) •Biomes: regions with distinct climates/species •Functional diversity- the processed needed for the survival of species, communities, and ecosystems. Section 4-2: How Does the Earth’s Life Change Over Time?Most of what we know about the history of life comes from the fossil record (the entire body of fossil evidence). •Fossils:mineralized or petrified replicas of skeletons, bones, teeth, shells, leaves, and seeds, or impressions of these items found in rocks. •The fossil record is uneven and incomplete. The fossils that have been found so far represent of 1% of all species that have ever lived on earth. Biological Evolution by Natural Selection Explains How Life Changes over Time •Biological evolution: how earth’s life changes over time through changes in the genetic characteristics of populations •According to the theory of evolution, all species descended from earlier, ancestral species. •In 1858 Charles Darwin and Alfred Russel Wallace independently proposed natural selection as the mechanism of evolution.
•Natural selectionoccurs when members of a population have certain genetic traits that improve their ability to survive and reproduce under a certain set of environmental conditions. For natural selection to work on a population, three steps occur: 1. The development of genetic variability, or variety of genetic makeup of individuals in a population. •This occurs through mutations, or random changes in the structure or number of DNA molecules in a cell. •Some mutations occur due to exposure to external agents like X-rays, mutagens, or radioactivity. Other mutations are a result of random errors in coded genetic information. 2. The environment favors individuals that possess heritable traits that give them an advantage over other individuals. •These adaptationsmay lead to differential reproduction, which enables organisms to produce more surviving offspring than other members of the population. 3. Populations are able to evolve so that they are better adapted to survive and reproduce under existing environmental conditions. There are two important limitations on adaptation through natural selection: 1. A change in environmental conditions can lead to an adaptation only for existing genes! The genetic traits must already present in a population’s gene pool or must result from mutations, which occur randomly. 2. Even if a beneficial heritable trait is present in a population, the population’s ability to adapt may be limited by reproductive capacity. •Species that reproduce rapidly and in large numbers often adapt in a short time (days to years). Ex: bacteria •Species that cannot produce large numbers quickly may take thousands or millions of years to adapt. Ex: humans Three Common Myths about Evolution through Natural Selection 1. Fitness is a measure of strength. FALSE •“Survival of the fittest” is not “survival of the strongest”•Fitness is a measure of reproductive success. The fittest individuals are those that leave the most descendents. 2. Organisms develop traits because they need them. FALSE 3. Evolution works according to some grand plan. FALSE •No plan or goal for genetic perfection has ever been identified in the evolutionary process. Section 4-3: How Do Geological Processes and Climate Change Affect Evolution? Processes such as the shifting of tectonic plates, volcanic eruptions, and earthquakes influence earth’s climate and in turn affect evolution by removing and/or isolating habitats and species. The fact that plates drift has two important effects on evolution and distribution of life. ➢Latitudes of continents and ocean basins affect earth’s climate and determine where plants and animals can live. ➢Movement of continents allows species to move, adapt to new environments, and form new species through natural selection. Geologic Processes Affect Natural Selection
•When continents join together, populations can disperse to new areas and adapt to new environmental conditions. •When continents separate and when islands are formed, populations must evolve under isolated conditions. •Earthquakes resulting from plate movements can cause fissure’s in earth’s crust that can separate and isolate species. •Volcanic eruptions that occur along plate boundaries can destroy habitats and reduce or wipe out populations of species. Climate Change and Catastrophes Affect Natural Selection Throughout its history, earth’s climate has changed drastically, including alternating periods of cooling and warming. These climate changes have affected evolution by determining where different types of plants and animals can survive and thrive, and by changing the locations of different types of ecosystems. Catastrophic events, such as asteroid and meteorite collisions have cause environmental stress and mass extinctions. They have also caused shifts in locations of ecosystems and created opportunities for the evolution of new species. Section 4-4: How Do Speciation, Extinction, and Human Activities Affect Biodiversity? Under certain circumstances, natural selection can lead to an entirely new species. In speciation, one species splits into two or more different species. A new species forms when one population of the species had evolved to the point where its members can no longer breed and produce fertile offspring with members of a population that did not change or that evolved differently. The most common way in which speciation occurs is when a barrier or distant migrations prevents the flow of genes between two or more populations of a species. This happens in two phases: 1. Geographic isolation 2. Reproductive isolation Geographic isolationoccurs when different groups of the same population of a species become physically isolated from one another for a long period of time. Inreproductive isolation, mutation and change by natural selection operate independently in the gene pools of geographically isolated populations. This leads to the inability to produce viable offspring if they are rejoined and attempt to interbreed. Extinction When population members cannot adapt to changing environmental conditions, the species becomes extinct. •Biological extinctionmeans the entire species ceases to exist•Local extinctionmeans a population has become extinct over a large region, but not globally.Species that are found in only one area are called endemic species. These organisms are especially vulnerable.
When local environmental conditions change, species face 3 possible futures: adapt through natural selection, move to an area with more favorable conditions, orbecome extinct. This leads to species disappearing at a low rate, called background extinction. A mass extinctionis a significant rise in extinction rates, where 25-95% of species are wiped out worldwide in a few million years or less. Earth has experienced 5 in its history. •Each mass extinction has been followed by an increase in species diversity as new species arise to occupy new habitats or exploit newly available resources. •The millions of species that exist today means that speciation has kept ahead of extinction (allowing species diversity to increase over time). •There is new evidence that the rate if extinction is currently higher than at any other time during the past 65 million years due to human activities. Section 4-5: What Is Species Diversity and Why Is It Important? Species diversityis the number of species in a given area (species richness) combined with their relative abundance (species evenness).The species diversity of communities varies with geographical location. Species diversity (primarily species richness) is highest in the tropics and declines as we move from the equator to the poles. The most species-rich environments are: •Tropical rainforests •Coral reefs •Large tropical lakes •Ocean-bottom zones Species richness increases productivity and stability of an ecosystem. Species Richness on Islands In the 1960s, Robert MacArthur and Edward Wilson began studying communities on islands to discover why large islands tend to have more species than small islands. Their research led to the theory of island biogeography. Two features of an island affect the immigration and extinction rates of species (and thus its diversity): 1. Smaller islands are smaller targets for potential colonizers, so they have lower immigration rates than larger islands. In addition, a small island should have a higher extinction rate because it usually has fewer resources and less diverse habitats for its species. 2. Islands closer to the mainland are easier for potential colonizers to reach. The farther a potential colonizing species has to travel, the less likely it is to reach the island. So species richness is greatest on large islands closer to the mainland!