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BILD 3 Midterm


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descent with modification
all organisms evolved from a common ancestor
Classification: hierarchical categories two part names
Paleontology: catastrophism, earth's biota has changed
Geology: Gradualism (big changes occur through gradual processes) Uniformitarianism (same geologic processes operated in the past as today)
Evolution: mechanism = inheritance of acquired characteristics; use disuse
Economics: population growth is faster than increase in food production -- lead to famine
adaptive radiation
rapid speciation of a single lineage to fill ecological niches (common for isolated ecosystems.. e.g. islands)
observed variation within and between species & described process of evolution by natural selection
**evolution is different from natural selection!**
genetic change over time
change in genetic composition (allele frequency) of a population over time
genetic change over time at the species level or higher
any trace of an organism that lived in the past ex: irish elk proved extinction
Law of Succession
fossils in one region are similar to extant oranisms in that same region
transitional forms ("missing link")
organisms have characteristics of both extinct and extant forms ex: tiktaalik (transition b/w aquatic & land dwelling). NOT NECESSARILY AN ANCESTOR OF MODERN FORM - can be on extinct side
vestigial organs
functionless or rudimentary organs in one species that are useful in another species. ex: blind cave tetra w/ eye ex2: flightless birds w/ wings ex3: goosebumps and wisdom teeth in humans
Structural Homology
similarity due to inheritance of traits from a common ancestor ex: mammalian forelimbs
Developmental Homology
similarities during development despite differences in adults ex: vertebrate embryos have tail remnants
Molecular Homology
similarities at the molecular level ex: genetic code - same codons specify same amino acids
characteristic of an organism due to both genes and the environment
genetic composition of the organism
natural selection
differential survival and reproduction of phenotypes
contribution an individual makes to the gene pool of the generation, relative to the contribution of other individuals
artificial selection
natural selection imposed by humans for a specific goal (e.g. breeding of crops or animals) ex: cauliflower from wild cabbage plant
change in genetic material of an organism.
sexual recombination
"reshuffles the deck" - creates new genetic combinations 1. crossing over 2. independent assortment (whether a gamete gets maternal or paternal copy of chromosome is random) 3. fertilization - combines genes from different individuals
sources of variation
mutation & sexual recombination
**mutation doesn't cause evolution but it is necessary**
How does evolution happen?
1. individuals vary 2. variation is heritable 3. individuals with certain traits survive longer and reproduce more (natural selection)
proportion of variation in a trait that is genetic heritability = genetic/phenotypic (b/w 0-1)
directional selection
the extreme phenotype is most fit. WILL change population mean will DECREASE variation ex: fishing for pink salmon
stablizing selection
intermediate phenotypes are most fit. will NOT change the population mean will DECREASE variation ex: humna birth weight ex2: female fly lays eggs on goldenrod & forms galls - large galls predated by birds, small galls by wasps
disruptive selection
two extreme phenotypes are more fit than intermediate phenotypes will NOT change population mean will INCREASE variation ex: seedcrackers are polymorphic for bill size - specialize on large or small seeds
frequency dependent selection
fitness of phenotype depends on the phenotype frequencies in the population
negative frequency dependent selection
fitness decreases with frequency. ex: cichlid fish - mouth twisted to left or right ex2: side blotched lizards/rock paper scissors ex3: evolution of sex ratio
positive frequency dependent selection
fitness increases with frequency. ex: yellow jackets' warning colors
group of individuals from the same species that live in the same area and have the potential to mate
formal study of the laws of chance (b/w 0-1)
Hardy Weinberg Equilibrium principle
Null model. 1. if allele frequencies are p & q, genotype frequencies are p2, 2pq, & q2 2. allele frequency will not change from generation to generation unless something changes them
HW equilibrium assumptions
1. no selection 2. mating is random 3. population is large enough that there are no chance events (genetic drift) 4. No gene flow from outside populations 5. No mutation
functional unit of heredity
alternative forms of a gene
location on a chromosome
same 2 alleles at a locus
different alleles at a locus
egg and sperm
fertilized egg
genetic drift
changes in the genetic composition of a population caused by chance events
genetic bottleneck
a reduction in population size to a low enough level for a long enough time that allele frequencies change randomly
founder effect
small number of individuals start a new population
gene flow
movement of alleles between populations ex: blue tits - island: nest in sync w/ tree leafing on poor host mainland: nest in sync on good host but out of sync on poor host b/c of gene flow
gene flow is a ________ force
evolutionary history of a group of species (Phylogenetic tree - picture of that history)
those who study the evoltionary relationships among organisms
**organisms that look alike aren't necessarily more closely related**
ex: birds and crocodiles are more closely related (share a more recent common ancestor) than crocodiles and lizards
branching point of a phylogenetic tree; represents a common ancestor
sister taxa
2 taxa tha derive from immediate common ancestor (each other's closest relative)
monophyletic (clade)
contains common ancestors and all descendents
contains common ancestor and some but not all descendants
taxa with different recent ancestor
group of taxa that are of interest, assumed to be monophyletic
one or more taxa assumed to be phylogenetically outside the ingroup
character shared between two or more species that was NOT present in common ancestor. due to convergent evolution
convergent evolution
independent evolution of the same character in 2 or more species -selection (enviroment) -random (ex: DNA sequences)
Homologies can be ______ or ________
ancestral (orginated in ancestor) OR derived (unique to clade)
shared derived homologies
outgroup comparisons
can distinguish between ancestral and derived character states
principle for developing phylogenies. tree with fewest evolutionary changes is correct
maximum likelihood
finds the most likely tree given a certain model of DNA change; assumes equal rates of DNA change
Phylogenies are useful because...
1. Shows how an ecologically important trait has evolved 2. solves crime
molecular clock
way of estimating absolute age of evolutionary change - species divergence
divergence of lineage to create new species
size is proportional to the number of described species in the higher taxon it represents
biological species concept
species is a group whose members have the potential to interbreed in nature and produce viable, fertile offspring
what unites a species?
gene flow
reproductive isolation
barriers that prevent different species from producing viable offspring
prezygotic barriers
individuals never mate ex: 2 species of green lacewings that are morphologically indistinguishable but sing different songs
postzygotic barriers
mating occurs but offspring not viable or fertile ex: donkey + horse = mule (sterile)
morphospecies concept
species defined by morphological traits -used by paleontologists to define fossils
phylogenetic species concept
set of organisms with unique genetic history
problems with biological species concept
1. mating/lack of mating can be hard to see 2. ability to mate vs likelihood of mating 3. cannot be applied to fossils 4. cannot be applied to asexual organisms
problem with morphospecies concept
cryptic species (morphologically identical but genetically distinct)
allopatric speciation
reproductive isolation occurs because populations are geographically separated
2 types of allopatric speciation
1. vicariance: divergence of one population to two 2. dispersal: divergence of a small population away from a large ancestral population
sympatric speciation
speciation in geographically overlapping populations
2 types of sympatric speciation
1. Habitat differentiation (ex: apple maggot fly has strong association with host plant) 2. polyploid (organism with >2 copies of chromosomes)
reproductive isolation as a byproduct
ex: beetles look like caterpillar frass
reproductive isolation as an adaptation (reinforcement)
to prevent unfit hybrids
the study of the interactions between organisms and their environment
population density
the number of individuals per unit area
how to measure population density
1. count 2. count then extrapolate 3. proxy (nest, damage, droppings) 4. mark-recapture
clumped dispersion
individuals aggregate in patches ex:wolves
uniform dispersion
individuals are evenly distributed ex: penguins
random dispersion
position of each individual is independent of other organisms
study of population growth
life tables
age specific summary of the survival pattern of a population
survivorship curves
way to express survival information graphically
type I survivorship curve
survivorship is high for young/middle aged; low for old ex: humans
type II survivorship curve
equal rate of survivorship ex: squirrels
type III survivorship curve
survivorship is low for young/middle aged ex: oysters
life histories
pattern of age specific survival and reproduction of an organism
"big bang" reproduction produce many offspring once and die offspring not well provisioned
repeated reproduction produce fewer well provisioned offspring & do so repeatedly over time
factors that favor semelparity
-unpredictable environments -low probability that any one offspring will survive -low probability that adults will live to reproduce again
factors that favor iteroparity
-dependable environment -high probability of offspring survival
**all organisms face _______ in how to allocate finite resources***
populations can change in size through
birth death emigration immigration
population growth equations
dN/dt = (b-d)N = rN Nt=Noert
logistic growth equation
dN/dt= rmaxN(K-N)/K
carrying capacity (K)
the maximum population size the environment can support
density independent factors
affect population independent of its density ex: disturbance, landslide, fire, etc
density dependent factors
birth and or death rates change with density
types of density dependent population regulation
1. intraspecific competition for resources - as density increases, individual reproduction decreases 2. density dependent predation - ex: trout preferentially prey on most abundant insect in stream 3. territoriality - ex: cheetahs 4. density dependent disease spread - ex: TB spreads in densely populated aread 5. Wastes - ex: wine: alcohol byproduct of yeast fermentation. 6. Intrinsic factors - ex: mice decrease reproductive rates in crowded pop... aggressive interactions
groups of populations linked by immigration and emigration (can be a buffer against extinction of populations)
age structure
the relativ number of individuals at each age -affects a country's future growth
mark-recapture assumptions
1. marked & unmarked individuals have the same probability of being captured 2. marked organisms mix completely back into the population 3. no individuals are born, die, immigrate, or emigrate during the re-sampling interval

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