BIOL1020 Zanzot Bowling Unit 4
BIOL1020 Zanzot Bowling Unit 4 BIOL 1020
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Date Created: 05/03/16
Unit 4: Evolution and Ecology-Study Guide Chapter 22: A Darwinian View of Life Chapter 23: Evolution of Populations Chapter 24: The Origin of Species Chapter 53: Introduction to Ecology and Population Ecology Chapter 54: Community Ecology Chapter 22: A Darwinian View of Life 22.1 The Darwinian revolution challenged traditional views of a young Earth inhabited by unchanging species Darwin’s predecessors and contemporaries: Aristotle and the Old Testament claim that species are ﬁxed (unchanging). Linnaeus -taxonomy. Cuvier –paleontology and catastrophism. Hutton and Lyell –geology and uniformitarianism. Lamarck –evolution by means of acquired characteristics. Malthus –population growth in humans. A.R. Wallace –biogeography and similar ideas to Darwin. 22.2 Descent with modiﬁcation by natural selection explains the adaptations of organisms and the unity and diversity of life Darwin’s voyage on HMS Beagle inﬂuenced his ideas that would lead him to write “Origin”. His focus was on adaptation, or “descent with modiﬁcation”. Darwin’s theory explains: the unity of life, the diversity of life, and the match between organisms and their environment. Darwin viewed the history of life as a tree with the branches indicating shared common ancestry (“I think” ﬁgure, elephant phylogeny [family tree]) He also looked at artiﬁcial selection (human modiﬁcation of plant and animal species) Two observations lead Darwin to two inferences which are the crux of his theory. O1. Members of a population vary in their inherited traits. O2. All species are capable of producing more offspring than the environment can support, and most offspring fail to survive and reproduce. Therefore, I1. Individuals whose inherited traits give them a higher likelihood of surviving and reproducing will tend to leave more offspring than individuals lacking those heritable traits, and I2. Differential reproduction will lead to the accumulation of favorable traits over generations. 22.3 Evolution is supported by an overwhelming amount of scientiﬁc evidence DIRECT OBSERVATION OF EVOLUTIONARY CHANGE: MRSA (methicillin resistant Staphylococcus aureus) HOMOLOGY: Similarity in structure (anatomical, physiological, molecular, behavioral) resulting from shared common ancestry. E.g. forelimb structure in different mammals (cat, bat, whale, human). Comparative embryology reveals anatomical homologies and vestigial structures not seen in adults such as pharyngeal pouches and a post-anal tail. ANALOGY: Similarity in structure due to convergent evolution, NOT shared common ancestry. Analogy occurs when similar environments enforce similar adaptive constraints, e.g. ﬂying squirrels and sugar gliders in the US and Australia, or cactuses and euphorbs in deserts in N. America and Africa. FOSSILS: An extensive fossil record shows the origin of new groups, extinctions, and transitions within groups. E.g. the transition of cetaceans (whales and dolphins) from land to sea. BIOGEOGRAPHY: The geographic distribution of species provides evidence for evolution. E.g., the genus of oaks (Quercus) has radiated into 100s of oak species distributed throughout the northern hemisphere. Endemism occurs when a species is found only a certain area. E.g. the watercress darter (Etheostoma nuchale) is a ﬁsh that is endemic to the Black Warrior River of Alabama. Islands frequently have many endemic species. Chapter 23: Evolution of Populations The population is the smallest unit of evolution. Microevolution is the change in allele frequencies in a population over generations and it is driven by two random factors (genetic drift and gene ﬂow) and a non-random factor: natural selection. 23.1 Genetic variation makes evolution possible Genetic variation occurs due to changes in the nucleotide sequences in DNA. Variation can be discrete (all or none: purple/white) or quantitative (occurring along a spectrum: height). There are many ways to measure genetic variation in a population, such as average heterozygosity or nucleotide variability. New alleles for genes form via mutation (silent, missense, nonsense) or gene duplication. 23.2 The Hardy-Weinberg (HW) equation can be used to test whether a population is evolving The HW principle describes a situation where a population is NOT evolving and allele and genotypic frequencies DO NOT change from one generation to another. It is a NULL MODEL (meaning it is a useful way to describe a population that is NOT evolving). For a gene to be maintained at HW equilibrium, ﬁve conditions must be met: 1. No mutations 2. Random mating (no sexual selection) 3. No gene ﬂow (no immigration or emigration) 4. No genetic drift (large population size) 5. No natural selection 23.3 Natural selection, genetic drift, and gene ﬂow can alter allele frequencies in a population The three biggest contributors to shifts in allele frequencies (microevolution) are natural selection, genetic drift, and gene ﬂow. NATURAL SELECTION increases the frequency of beneﬁcial alleles, and diminishes the frequency of harmful alleles (see Ch. 22). GENETIC DRIFT (GD) is the result of a random decrease in population size, typically through founder effect or genetic bottleneck. The smaller a sample from a parent population, the greater the deviation in allele frequency. Alleles may be lost from a population. The founder effect occurs when a new small number of individuals leave a large population and start a new population in a new location, like an island. A genetic bottleneck may occur when populations become fragmented or a catastrophic event randomly destroys a large number of individuals in a population. GD is most signiﬁcant in small popualtions. GD causes random changes in allele frequency. GD can lead to loss of genetic diversity and allele ﬁxation (only one allele for a gene present in the population) GENE FLOW (GF) is the spread of alleles throughout a population and between populations. It can increase or decrease the ﬁtness of a population, but it is a random process. 23.4 Natural selection is the only mechanism that consistently causes adaptive evolution Mutation, GD and GF are random processes that contribute to changes in allele frequency in population. Natural selection is NOT RANDOM. NOTE: DARWIN did NOT coin the phrase “survival of the ﬁttest”. Survival and reproduction together comprise ﬁtness, so the term is circular, and implies a “high- bar” for ﬁtness. Survival of the ﬁt-enough also applies. Three modes of selection are typical when allele frequencies shift: directional, disruptive, and stabilizing. Know the differences. disruptive- tall or short, but not medium, polymorphic. directional-one extreme, giraffe necks only have long necks and not short. stabilizing- plants are medium height, not tall or short Sexual selection leads to mating success and can lead to sexual dimorphism (male and female appear different). Genetic variation can be preserved by diploidy or balancing selection. Chapter 24: The Origin of Species Speciation =origin of new species =divergence of old species 24.1 The biological species concept (BSC) emphasizes reproductive isolation A biological species is “is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; they do not breed successfully with other populations”. The key to species membership is GENE FLOW. Species are kept distinct by REPRODUCTIVE ISOLATION, though HYBRIDS may occur. Reproductive isolation is classiﬁed as PRE-ZYGOTIC or POST-ZYGOTIC. PRE-ZYGOTIC: Habitat isolation, temporal isolation, behavioral isolation, mechanical isolation, gametic isolation. POST-ZYGOTIC: Reduced hybrid viability, reduced hybrid fertility, hybrid breakdown BSC is limited in that it can’t resolve organisms that are asexual or extinct. Other species concepts include morphological species concept, ecological species concept, and phylogenetic species concept. 24.2 Speciation can take place with or without geographic separation Allopatric (other country) vs. sympatric (same country) speciation Allopatric speciation is much more common. Allopatric barriers not universal but depend on species Regions with more geographic barriers tend to be more biodiverse. Sympatric speciation may result from polyploidy (autopolyploidy or allopolyploidy), habitat differentiation, or sexual selection 24.3 Hybrid zones reveal factors that cause reproductive isolation When the ranges of different species overlap and mating occurs, hybrids may be produced. One of three outcomes is likely: reinforcement (of species boundaries), stabilization (of hybrid populations), or fusion (of the two species). 24.4 Speciation can occur rapidly or slowly and can result from changes in few or many genes Mass extinctions and large-scale radiation of new species are evident in the fossil record. Reproductive isolation may be as simple as a change in a single gene, but not typically. Chapter 53: Introduction to Ecology and Population Ecology Concept 53.0 Ecology is the scientiﬁc study of the interactions between organisms and the environment. Ecologists consider the factors that determine abundance and distribution at many scales and by observing and experimenting. 53.1 Biological processes inﬂuence population density, dispersion, and demographics Density = #individuals/area or volume Dispersion =pattern of spacing, clumped, uniform or random Demography is the study of how populations change in character based on births, deaths, immigration, emigration, and aging. The main focus is on birth and death rates. A life table tracks survival and reproduction from year to year in a population, and can be used to produce a survivorship curve. Survivorship curves generally fall into one of three categories. In Type I curves, the death rate is low at the beginning and middle of an organism’s life span and increases late in life (like human populations in the developed world). Type II curves are consistent over an organism’s life span, and type III curves have many offspring dying early on and long life for the few survivors. Demographers can also track births to determine whether all females are contributing equally to the next generation, or if few females produce most of the offspring in the next generation. 53.2 The exponential model describes population growth in an idealized, unlimited environment In the absence of signiﬁcant immigration and emigration, a population’s growth can be modeled if the birth and death rates are known over a period of time. Zero population growth occurs when the birth and death rates are equal. Under ideal conditions (no limiting resources), population growth may be exponential, with a J- shaped curve over time. Exponential growth curves cannot be sustained indeﬁnitely, but may be observed if conditions change (as with elephants in Kruger National Park, South Africa). The exponential model is represented by the expression: Which means the change in a population over a period of time is indicated by the growth rate times the initial population. 53.3 The logistic model describes how a population grows more slowly as it nears its carrying capacity Resources such as food, light, space, etc are typically limited, and most population growth reﬂects this by slowing down as resources become limited around the carrying capacity (K), which is the maximum population size a habitat may support. The logistic model is sigmoid (S-shaped), and can be expressed as: This expression says that as the population reaches the carrying capacity, K, the rate of growth of the population slows down to approach zero, or no more growth of the population may occur when the carrying capacity is reached. Population growth is similar to exponential growth until half the carrying capacity is reached (K/2), then the rate of growth slows down. Some populations overshoot K and show a negative growth (die-off) until the population size reaches K. If resources ﬂuctuate, K will also ﬂuctuate. The Allee effect occurs when a population is too small to effectively survive and reproduce. This may occur in threatened and endangered populations. 53.4 Life history traits are products of natural selection Life history reﬂects the age of ﬁrst reproduction, the number of times an organism reproduces, and how many offspring are produced each time it reproduces. Semelparous species reproduce only once and usually produce lots of progeny (e.g. salmon) and occur in highly unpredictable environments. Iteroparous species reproduce several times and usually produce few progeny each time they reproduce (e.g. humans) and typically occur in more stable environments. Organisms only have ﬁnite access to resources, so survival and reproduction may be trade-offs. In other words, some organisms may not survive as long, but produce lots of progeny, and vice versa. Some organisms produce fewer, larger progeny, others produce many, smaller progeny. K-selection is density dependent, and favors fewer, larger progeny r-selection is density independent, and favors many, smaller progeny 53.5 Many factors that regulate population growth are density dependent Factors that increase the death rate or decrease the birth rate near K are density dependent factors. These include: disease, predation, territoriality, competition for limited resources, toxic wastes, and intrinsic factors (like hormones). 53.6 The human population is no longer growing exponentially but is still increasing rapidly The global human population is currently 7.2 billion people, with over 300 million people living in the United States. The rate of growth is slowing down, but the population did exhibit exponential growth with the industrial revolution. The rate of growth is not consistent between countries, with some still increasing exponentially and others with negative growth (a declining population). Chapter 54: Community Ecology Populations of species co-exist in a habitat, and different species can and do interact. 54.1 Community interactions are classiﬁed by whether they help, harm, or have no effect on the species involved Competition (-/-) Competitive exclusion: two species competing for the same limited resource cannot coexist in the same habitat Niche: the sum of a species’ use of biotic and abiotic resources, or a species’ “occupation” Resource partitioning: differentiation of ecological niches such that similar species may coexist in a community Fundamental (potential) vs. realized (actual) niche Character displacement: a tendency for characteristics to be more divergent in sympatric populations of two species than in allopatric populations of the same two species Predation (+/-): One species (predator,+) kills and eats the other (prey,-). Predators have numerous adaptations to gather prey (claws, fangs, venom, crypsis), and prey species have many adaptations to avoid predation (behavioral, morphological, physiological, mechanical, chemical) Batesian (harmless species mimics harmful species) and Mullerian mimicry (two harmful species mimic each other) Herbivory (+/-): A heterotroph(+) eats an autotroph(-). Many autotrophs such as plants have mechanical (thorns, prickles, toughened leaves) and chemical (toxic secondary compounds) defenses against herbivory Symbiosis: an intimate, direct contact between two or more species. Includes: parasitism (+/-), mutualism (+/+), commensalism (0/+) and facilitation (+/+ or 0/+)
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