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BIOL 3500 Final: Final exam material

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BIOL 3500

Lecture 5 – Evolution Natural selection based on 3 assumptions: 1. Traits vary within a species 2. Variation is heritable 3. Non-random survivorship based on traits a. i.e. Individuals with traits better suited to their environment have better survivorship and thus pass their traits on (differential survival/success) i. These traits become more common Opportunities for competition (things for natural selection to act on) • Juvenile stage o Offspring need to survive and reach the age of reproductive maturity o Juveniles are often more susceptible to disease, parasites, predators, shortages of food, hostile weather conditions • Ornamental features o Offspring need to attract a mate or pollinate in order to produce their own offspring Genetics is the mechanism of evolution • Know basic genetic terms Evolution – genetically controlled changes in physiology, anatomy, and behaviour that occur in species over time Microevolution – the evolutionary change within species or populations (e.g. change in allele frequencies of a population over time) Macroevolution – the evolutionary change within larger taxonomic units, such as families (e.g. clades, tree of life) Microevolution: • New variation (alleles) arises from mutations • Allele frequencies can be altered by: o Genetic drift – variation in the frequency of different alleles in a population is due to random chance ▪ More common in small populations and can lead to a loss in diversity ▪ Bottleneck effect – loss of diversity due to a decrease in population size ▪ Founder effect – loss of diversity when a small number of indvls from a larger population form a new population (new population diversity doesn’t represent source population) Speciation – The development of two genetically differentiable species from a single common ancestor species • Speciation is a result of evolution, but evolution does not always lead to speciation • Requires some sort of reproductive barrier (reproductive isolation) o If two populations are separated for long enough, then reproductive barriers may develop which do not allow them to interbreed if they ever come in contact again (speciation has occurred) Isolating mechanisms Allopatric speciation – when divergence takes place in isolation of one another • Usually due to geographical barrier separating two populations • Often leads to adaptive radiation o Evolution of multiple species from a common ancestor to occupy all niches in the new environment • Islands are the best examples of allopatric speciation o E.g. Galapagos finches Sympatric speciation – when divergence takes place in the same geographical area • Changes in timing of life cycle (especially reproduction) occur • Behavioural changes occur (such as mate choice) Parapatric speciation – when divergence occurs in areas that narrowly overlap • Habitat differences in an area can lead to population divergence Clade – A group of species that includes a common ancestor and all of its descendants Vicariance Events – Geographical changes that isolate a species into two populations resulting in allopatric speciation • E.g. formation of mountain ranges, formation of islands (plate tectonics) E.g. Vicariance event is the island of Madagascar • Home to an enormous diversity of plants and animals, many of which are endemic • Result of vicariance events as well as dispersal and isolation events • Some resemble species of India and others to species of Africa because throughout its history, Madagascar was attached/close to both Phyletic Gradualism – changes in species are the result of slow and gradual small changes in the gene pool • Many intermediate forms Punctuated Equilibrium – changes in species are the result short periods of rapid and large changes in the gene pool, followed by long periods of no change • Few intermediate forms Lecture 6 – Island Biogeography Much of the ideas about evolution by Natural selection by Darwin and Wallace were established on islands • Speciation is very prevalent here because of isolation, making it ideal to study evolution Island biogeography looks at 4 fundamental processes: 1. Dispersal – Movement of organisms from a point of origin to a new location 2. Colonization – Organism reaches new location, survives, reproduces, and establishes new population 3. Extinction – Species is eliminated from a particular area a. species may survive elsewhere, and may re-colonize area where it went extinct. 4. Evolution – Surviving population in a particular area undergoes change in frequency of gene alleles; may result in altered phenotype, and, given sufficient time, possibly the formation of new species (= speciation). Types of Islands: • Those originally part of a nearby landmass, but becomes separated by rising sea levels (Newfoundland) or tectonic processes that split them (Madagascar) o These islands were colonized before separated, but may still receive new species via dispersal o The following two island types can only receive colonists via dispersal • Volcanic island arcs formed when oceanic crust subducts beneath other oceanic crust of the same plate • Those formed by hotspots where plumes of hot material rise from and form volcanoes. A chain of these types of islands can form as the plate above moves Colonization of Islands • Dispersal to islands is typically by a sweepstakes route o Sweepstakes meaning random chance plays a large role in determining which species become successful ▪ Those who by chance arrive earlier may establish first and succeed • The dispersing organisms share adaptations that allow them to reach the island, rather than adaptations allowing them to live there once they reach it. o This is one factor that restricts the diversity of life on islands. • In order to reach and survive on an island, you must have traits that allow you to reach it and then survive on it Islands often contain a smaller number of species than equivalent sized mainland areas because: • Small, isolated – no refuge when conditions deteriorate • Re-introduction is difficult if a species goes extinct (no reliable source of immigrants) • Colonists are often not adapted to the environment – mainland conditions are very different • Genetic diversity of colonists is often low (founder principle, small population size) Adaption and evolution of island species • Many lose their anti-predator defenses due to the lack of predation • They may lose the traits which allowed them to disperse there in the first place (e.g. wings for penguins) • Island species tend to be larger than their mainland relatives (less energy put towards traits which aid in competition and predation) • The reverse can also be true – an island may be able to support a larger population of a species if the size of each individual is reduced (insular dwarfism) Much of our understanding of island biogeography began with the publishing of The Theory of Island Biogeography by Robert H. MacArthur (1930-1972) and Edward O. Wilson (b. 1929) Patterns of Island biogeography: • The Island Rule – There is a tendency for small island species to be larger and large island species to be smaller than their mainland relatives • Area of island pattern o Larger islands have a greater species richness than smaller islands o Because of more resources, niches, greater environmental stability, etc. • Island isolation (distance from mainland) o Islands closer to the mainland have a greater species richness than those further from the mainland o Because more species have the dispersal ability to overcome a smaller distance from the mainland • Islands tend to have a high amount of endemic species • Communities on islands tend to resemble subsets of those on the nearby mainland • Sea-dispersed plant spp.  Wind-dispersed  Animal-dispersed o is the order in which islands tend to be colonized by plants o animals establish after plants Classic Equilibrium theory of biogeography On a new island • Rate of colonization will start off high as species capable of dispersal reach it o It will gradually decrease as the species which can reach the island have already done so • Rate of extinction will start off low and gradually increase as the number of species increases o Because competition, predation increase Rescue Effect • Classic model assumes islands near mainland will have greater colonization rates and thus greater extinction rates • However, some islands have been shown to have lower extinction rates due to the rescue effect o Rescue effect – endangered populations on an island are rescued by new colonizers of the same species Target Area Effect • Classic model assumes rates of colonization are only effected by distance from mainland • However, island area plays a role o the larger the island, the greater the chance a dispersing organism has of colonizing it ▪ i.e. the bigger the target for the dispersing organism Habitat fragmentation creates many smaller isolated areas which may behave similarly to islands Lecture 7 – Geologic Time The Geologic Time Scale – the internal standard by which time is divided • Geologic time is based on the identification and dating of different layers of rock called strata, which have very unique fossils and composition • The geologic time scale extends over 4 billion years and is divided into a hierarchy of eons, eras, periods and epochs • Each unit of geologic time is defined by the organisms that were alive on (and dominated) the planet The Law of Superimposition – the assumption that lower strata are older than higher strata The Law of Uniformitarianism – the assumption that the processes that occur today are the same in the past We are in the: • Phanerozoic eon  beginning with Cambrian explosion • Cenozoic Era  dominance by mammals • Quaternary period  retreating and advancing of ice sheets • Holocene epoch  last 10,000 yrs, latest interglacial period soon to be split into Anthropocene epoch • Anthropocene epoch  a potentially new epoch for the last 50-150 yrs Precambrian eon • Earliest period of earth’s history • Spans 4.6 billion yrs ago  Cambrian period 541 million yrs ago Cambrian period • Defined by the Cambrian explosion which saw rapid diversification of life, and where more complex animals first appeared Ordovician period • Experienced the highest sea levels of the Paleozoic era Silurian period • Diversification of jawed and bony fish • Multicellular life begins to inhabit land Devonian period “Age of Fish” • First significant adaptive radiation (rapid diversification) of animals on land Carboniferous period • Much carbon was produced during this time in form of coal beds • Amphibians and Arthropods were dominant on land Permian period • Diversification of amniotes (egg-bearing animals) Mesozoic era “Age of Reptiles (dinosaurs)” “Age of Conifers” • Includes Triassic, Jurassic, and Cretaceous periods • Pangea began to split into separate landmasses via plate tectonics • Mammals and birds appeared Cenozoic era “Age of Mammals”  Current era • Includes Paleogene, Neogene, and Quaternary periods • Continents settled into current positions Quaternary period • Defined by alterations between cold and warm conditions resulting in long glacial periods (ice ages) followed by shorter interglacial periods Long glacial periods had devastating effects on many species in many areas, but there were certain places unaffected by ice ages called Glacial refugia • These allowed flora and fauna to survive the ice ages and then recognize the world post-ice age What caused large-scale glaciation to begin in the Quaternary period when little evidence of glaciation occurred in the two other periods of the Cenozoic era? • Plate tectonics were the reason why glaciation could occur, but didn’t explain interglacial periods • Milankovitch orbital theory of glaciation explains the alterations between glacial and interglacial periods o Three natural and periodic variations in the geometry of the Earth’s orbit result in changes in the seasonal and latitudinal distribution of incoming solar radiation 1. The eccentricity of the of the earth’s orbit around the sun a. i.e. the degree to which the orbit differs from a perfect circle 2. The obliquity/tilt of the Earth’s axis 3. The precession of the equinoxes (times when closest to sun and farthest from sun) o These factors lead to cool summers where the winter snow and ice don’t melt  ice age Stratigraphy – a branch of science which studies strata and stratification • Any archive that builds up over time based on the law of superposition is a stratigraphic record • The relative abundances of Isotopes in different strata are often used as markers o Different isotopes have different properties e.g. some are heavier or lighter o Common isotopic elements are H, C, O • Lake sediments, ice sheets, rocks are all good stratigraphic records Younger Dryas • The short cold period which interrupted the current interglacial period • I.e. Last glacial period (ice age) ended and climate became warmer (interglacial period) before being interrupted by a short cold period before returning back to the current interglacial period Lecture 8 – The Fossil Record Fossils – the preserved traces or remains of animals, plants, and other organisms from the past Paleontology – the study of prehistoric life. It is heavily based on the study of the fossil record Paleoecology – the study of the relationship between fossil organisms and their environment Taphonomy – the study of changes to fossils after the death of the organism. Types of fossils: • Body Fossils – a fossil preserving the body of an organisms o Normally, it is the calcified or hard parts that are preserved ▪ E.g. bones, teeth, nails • Trace Fossils – fossil evidence of some behavioural activity of an organism o E.g. footprints, burrows How are fossils preserved? 1. Petrification – replacement of organic matter by minerals 2. Casts, molds, imprints – fossil is dissolved leaving by imprints/molds of organism 3. Carbonization – only the residual carbon of the organism remains usually due to extreme heat or pressure 4. Encasement – organism protected in an encasement e.g. amber, permafrost, tar Factors enhancing likelihood of fossilization: 1. Hard body parts 2. Rapid burial 3. If species was abundant Fossils are often poorly preserved, incomplete and must be pieced together (why taphonomy is important) Palynology – the study of pollen grains and spores to track shifts in vegetation • Extremely important in biogeography • Can often be preserved in lake sediments which can be dated and then you will have an idea of what the vegetation was like during that time period Two types of sediment coring: 1. Surface sediment gravity coring a. For more recent sediments 2. Surface sediment gravity coring a. For much older sediments Other biogeographical archives: • Bat and bird guano as they become stratigraphic • Packrat middens o Packrats live in the desert ▪ Here there are no/few lake sediments to look at the past environment o Their urine is very viscous in order to preserve water o Packrats are hoarders which create garbage piles called middens ▪ They urinate on these piles to mark their territory ▪ The urine is like a glue when it crystallizes which helps fossilizes the midden o Fossil middens provide information on past environments because they contain plant and animal remains of those periods o Even fecal pellets in the midden are important because the size of the packrat can be estimated which can give insight into the air temperature during the time, and thus other climate conditions ▪ Bergmann’s Rule – body size of vertebrates is proportional to avg air temp. of region Extinction • Extinction – the loss of all individuals of a species, genus, etc. • Local extinction – loss of all individuals in defined areas • Global extinction – loss of all individuals across the entire world • Phyletic extinction – the extinction of a taxon because it evolved into a new species, genus, etc. Extinctions of certain species (e.g. keystone spp.) may have repercussions down the trophic cascade • E.g. If a highly-specialized predator’s food source goes extinct, there is a high chance the predator goes extinct o E.g. Extinction of mammoth may have resulted in extinction of smilodon (sabretooth tiger) and California condors (large scavenging birds) Factors which influence extinction • Lack of genetic diversity • Chance events (especially the destruction of habitat for an endemic taxon) • Evolution of a pathogen • Competition • Env
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