BIO101 Exam 4

ecology & evolution, microevolution,

microevolution

change in allele frequency from one generation to the next in a population

acts on phenotypes, requires change in genotype

mechanisms of microevolution

genetic drift: chance events lead to change in allele frequency unpredictably (founder effect, bottleneck effect, human action)

gene flow: genetic exchange due to migration between populations

mutation: a random change in DNA

natural selection

gene flow

genetic exchange due to the migration of fertile individuals/gametes between populations

DECREASES differences between populations and INCREASES genetic diversity within a population

can actually decrease fitness of receiving population in some cases (specific adaptations might not work in a diff environment) (or increase fitness)

can maintain alleles in a population, even if it’s disadvantageous and selected against

mutation

random change in nucleotide sequence of DNA in an individual - point mutation (change in single base pair)

causes: errors in replication, radiation exposure, certain chemicals

must be heritable to alter allele frequency and lead to evolution

more often bad than good, organisms are typically already well-suited to their environments

negative mutations often removed quickly by natural selection, positive ones may be selected for

rate of change depends on generation time (rapid in microbes and viruses, slower in animals)

neutral variation

no advantage of disadvantage for survival/reproduction; most mutations are neutral (happen in non-coding regions of DNA, don’t cause change in amino acid sequence)

natural selection

accumulates and maintains favorable genotypes in a population - eneds genetic variation

modes of natural selection

directional selection: favors individuals at one extreme of a phenotypic distribution (other extreme experience poor reproductive success)

disruptive selection: favors individuals with (both) extreme phenotypes (individuals w/ intermediate values of a trait have poor reproductive success)

stabilizing selection: favors individuals with intermediate phenotypes, leads to overall reduction of variation for the trait

balancing selectoin: maintains genetic diversity in a population

• frequency-dependent selection: fitness of a phenotype depends on how common it is in the population

• heterozygote advantage: individuals heterozygous for an allele have greater fitness than any homozygote (for example, sickle cell disease - those heterozygous for the allele are resistant to malaria

sexual selection: acts on traits that affect reporductive success; need to find a mate and reproduce successfully

• intrasexual: competition between same sex

• intersexual: help individuals on one sex be ‘chosen"‘ by other sex - leads to sexual dimorphism

speciation

bridge between microevolution and macroevolution

morphological species concept

WRONG: a group of individuals that are similar in appearance must be the same species - not always true

doesn’t account for gene flow between species

biological species concept

group of individuals that have the potential to interbreed and produce fertile offspring, does allow for the concept of gene flow

e.g. dogs don’t all look the same, but can all interbreed!

has some major limitations

limitations of biological species concept

can’t be applied to extinct forms of life - can’t tell who could reproduce

can’t be applied to species w/ asexual reproduction (many bacteria and other microorganisms, some plant species like dandelions, species of invertebrates)

what does potential to interbreed mean? what if the species are isolated in nature but COULD breed when put together

chronospecies

sequential development pattern of continual uniform changes from an extinct ancestral form

gradual change from one species to another - question of when it becomes a new species?

ring species

gene flow between neighboring populations, accrue differences over time, but at the ends of the “ring”

both new populations can reproduce with the original population, but not with each other

when to mark the point of speciation?

reproductive barriers

inhibit gene flow so that new species develop

reproductive isolation required - biological factors impede members of two species from interbreeding, limit the formation of hybrids, effectively isolate a species’ gene pool

two types: pre-zygotic and post-zygotic mating barriers

pre-zygotic reproductive barriers

prevents successful production of a zygote

no mating attempted types

temporal isolation - some aspect of reproductive cycle occur at different times (day/night, seasons, etc) between species

habitat isolation - different preferences in habitat or requirements for reproduction (one breeds in shallow puddles/creeks vs. in large pools/streams)

behavioral isolation - some behavior/behavioral preference prevents attraction/mating (unique mating calls only attract females of one species)

mating attempted, no zygote formed

mechanical isolation: morphological features (e.g. genetalia) physically prevent successful mating

gametic isolation: gametes do not unite (types of sea urchins release zygotes into water all at once, sperm and eggs have specific recognition molecules needed to form a zygote that are only present in the same species)

post-zygotic reproductive barriers

prevents viable offspring; mating and fertilizaiton occur and zygote forms

hybrid inviability: development of the hybrid zygote is impaired; hybrid is frail and doesn’t complete development

hybrid sterility: hybrid zygote develops, but cannot reproduce (mules are horse/donkey cross, ligers: can all develop fine but are infertile

hybrid breakdown: hybrid develops, can reproduce initially, but subsequent generations are weak or sterile, more common in plants (1st gen is fertile, 2nd gen is feeble or sterile)

process from speciating to distinct species

mechanisms of speciation

allopatric speciation: geographic separation, preventing gene flow

• natural selection and genetic drift → populations diverse

• reproductive isolation

means that regions w/ more geographic barriers will have more species - the reason endemic species are common on islands

sympatric speciation: without geographic isolation

• requires that a reproductive barrier evolves first

• polyploidy: one mechanism that can lead to sympatric speciation (uncommon in areas, common in plants): instant speciation event

how much genetic change needed for speciation?

impossible to generalize - speciation can be caused by cumulative divergence of many genes or just one or two changes

macroevolution

development of many new species over geological time - modern biodiversity

changes in diversity of life causes

intrinsic properties of the species

large-scale changes in climate or environment

can compare the fossil record to paleoclimate to see trends of climate events and loss of biodiversity events

“gap” in fossil record

often can’t see all the fossil record due to erosion - hard to tell how fast speciation occurs

gradualism

slow and steady change, mechanism by which speciation occurs

how most species develop

supported by studies of microevolution, population genetics

punctuated equilibrium

other theory of how speciation occurs

less common than gradualism, but happens!

periods of little change interrupted by short periods of rapid change

supported by polyploidy, antibiotic resistance

adaptive radiation

periods of rapid speciation, amny new species arive

often when there’s an ecological niche to fill

• release from competition, predation

  • after a mass extinction

• evolution of a key adaptation (hard body parts like jaws, shells), ability to breathe air and survive on land, flowers

and subsequent specialization

most involve exploitation of changes in environments not occupied by competitors

• using key innovations via microevolution

adaptive radiation of mammals

after the extinction of dinosaurs, left ecological niche

mass extinctions

high rate of extinction compared to background rate, triggered by environmental change

5 major mass extinctions (6th now)

3. Permian-Triassic Extinction

largest mass extinction

changes in climate due to rapid increase of CO2 and CH4 (believed to be caused by volcanic activity) → heating and acidic oceans

96% of all life perished

5. Cretaceous-Paleogene Extinction

dinosaurs

(start of 01)

evolution

unifying concept of all biology, needed to understand: origin and diversification of life, disease, behavior

heritable change in a population across many generations

ecology

biology on the scale of interactions between organisms and their environments

microevolution

small-scale evolution causes change in a single gene and leads to the existence of different traits in a population

macroevolution

large-scale evolution causes change above the species level and leads to different species

evolution of evolutionary thought

First was Divine Creation: species are permanent and life is unchanging

• Plato: every organism was perfect essence created by God, unchanging

• Aristotle: Scala Naturae (a species hierarchy from imperfect to perfect, starting with inanimate matter and then “lower plants”, humans on top, without room for movement)

fossils provided evidence for change over time; best explanation for them is evolution

catastrophism

major disturbances cause change

Georges Cuvier

uniformitarianism

school of thought on evolution where gradual change over time due to natural processes

Charles Lyell

Jean-Baptiste De Lamarck

first to propose a mechanism for how life changes over time: inheritance of acquired characteristics (INCORRECT)

Charles Darwin

evidence: observations of thousands of species on sea voyages, fossil resembling living S American organisms, greater similarity within continents than within climates, deposits of marine shells found far above sea level (related slow changes in the Earth w/ slow changes in animals, diversity of life (bill shapes of finches on Galapagos Islands were adapted to their specific diet and means of gathering food)

extant

modern-day, currently living

endemic

species unique to a defined geographic location

Alfred Russell Wallace

independently developed theory of natural selection at same time as Darwin

Descent with modification

species present today descended from ancestral species

natural selection

mechanism responsible for change in a species over time

sources of genetic variation

mutation (creates new alleles), sexual reproduction (new combinations of alleles)

fitness

probability of surviving and reproducing in a given environment

• surviving, finding mate, reproducing

inherited traits contribute to this, individuals with higher fitness tend to have more offspring

evolution

increasing frequency of favored traits in a population

natural selection

differential survival and reproduction of individuals due to differences in traits

leads to evolution

evidence for evolutionary change

artificial selection: shows how change occurs

homology

analogous structures

biogeography

fossil record

artificial selection (selective breeding)

purposeful selection for traits - pugs, Darwin’s pigeons (he argued that selection for their traits was analogous to what happens in nature)

homologous structure

some ancient structure becomes modified in different ways depending on lifestyle/environment → functionally different features with similar construction due to common ancestry

human arms, cat legs, whale fins, and bat wings all have the same types of bones

vestigial structures

anatomical features without function, resemble structures of presumed ancestors

human appendix, wisdom teeth, body hair, tiny femurs of whales and snakes

molecular homologies

similar molecular composition of proteins, DNA

embryonic homologies

similarities in embryonic life stage across species

due in part to molecular homologies

analogous structures

like an analogy - similar but no common ancestor

evolved independently for the same purpose, same or similar function

eg. bird, bat, bug winds

result of convergent evolution Isimilar structures in distant organisms with similar environments)

eg. carcinization (evolution of a crab-like body, has happened at least 5 separate times)

biogeography

geographic distribution of species

similarities between species separated by huge distances or impassable borders like an ocean indicate a common ancestor when land masses were together

species on ocean islands

resemble species of nearest mainland, wven if environment is different, don’t resemble species on island with similar environments in different parts of the world

fossil record

similarities between extinct and extant species with notable differences like size

Snider-Pellegrini-Wegener fossil map

shows plant and animal distributions across Pangea, explains how similar fossils are found across oceans

what are the units of evolution?

population

population

localized group of individuals that can interbreed, produce fertile offspring

microevolution

generation-to-generation change in allele frequencies in a population

changes in gene pool (sum of alleles in a population)

genetic drift

chance events cause allel frequencies to fluctuate unpredictably from one generation to the next

most important in small population, can greatly reduce or even eliminate alleles

fixed allele

when only one allele remains in a population

no variation → no natural selection

founder effect

individuals are isolated from the main population (can have loss of alleles, increase of frequency of rare alleles)

bottleneck effect

population goes through period of size decrease - loss of lots of individuals and their alleles

population later increases, but genetic diversity is low

ecological hierarchy

organismal, population, community, ecosystem, landscape, biosphere/global

organismal ecology

how physiology and behavior meet the challenges of an organism’s environment

landscape ecology

controls on the exchange of energy, materials, organisms across a mosaic of connected ecosystems

abiotic factors

non-living factors that determine where a population/species is found: environmental or climatic, can be geological, physical, etc

for terrestrial organisms: climate has strongest effect

• temperature and precipitation

for aquatic organisms: light and nutrient availability

biotic factors

living factors that affect where a population lives

competition, predation, pathogens

a species’ potential range is determined by

tolerance to abiotic factors; wide for some species, narrow for others

a species’ distribution is determined by

a combo of biotic and abiotic factors; populations may not be found in some suitable areas because of predation, etc

abiotic factors limit ___ and biotic factors limit ___

the potential range of organisms; the actual distribution of organisms within those ranges

population ecology

dynamics of species populations and how they interact w/ the environment

population

group of indiv. of the same species that live in the same area

characteristics: density, dispersion, population structure (make-up of individuals: age and sex distribution), population rates

sex ratio

primary: at fertilization

secondary: birth/hatching

tertiary: later stage (adult)

becomes more skewed over time

hypotheses for skewed tertiary sex ratio

reproduction-related stresses (battles for reproduction, care for offspring)

dispersal (leaving the nest increases risk of predation)

intraspecific competition for dominance status, energetic requirements

age structure diagrams

predict future growth trend in humans, highlight future socio-economic conditions

pyramid (growing), bell (dome) shaped (stable), urn shaped (declining)

population rates

birth rate (b) (# births/population)

death rate (d)

fecundity (# of offspring/time per female), generally limited by # of gametes

generation time: time period from birth of individuals to birth of their offspring

generation time relation to body size

smaller body size trends with shorter ge

survivorship

tracks changes in # of individuals in a cohort over time

life table

summarizes the survival and reproduction rates of individuals in specific age groups, follows a cohort of individuals from birth til death

for sexually reproducing species, only the females are often followed/studied (they produce the offspring)

used to construct a survivorship curve

survivorship curve

proportion of individuals alive at each age

generally one of three types

differences are based on death rates during different life stages

Type 1 survivorship curve

late loss; high survival of offspring, high mortality later in life, females produce few offspring, high parental investment in care, many large mammal species

Type 2 survivorship curve

constant loss: mortality relatively constant across all ages (constant proportion dying at each age), common in rodents, invertebrates, lizards, annual plants

Type 3 survivorship curve

early loss: low survival of offspring, low mortality of adults, females produce many offspring, often no parental investment in care, common in long-lived plants, marine invertebrates, fish, sea turtles

r-strategists

live fast, die young

many small offspring, no parental care, fast growth rate, young at first reproduction

Type III, pyramid shapes, fast/exponential growth rate

K-strategists

slow and steady

few big offspring, lots of parental care, slow growth rate, delayed first reproduction

Type I, bell/urn shaped, slow/logistic growth rate

examples in between extremes of r and K strategists

trees and turtles (many small offspring, no parental care, slow growth, late reproduction)

change in population size

births + immigrants - deaths - emigrants

births - deaths

convert to instant in time … r = change in population

• different between populations

exponential growth

resources are abundant (ideal conditions) and no limits to pop growth —> free to reproduce at physiological capacity

r is the intrinsic rate of increase: per capita rate at which an exponentially growing population increases in size at each instant in time

• small if there’s a high death/low birth rates

• larger r, faster the population grows

N = # individuals in pop at given time

• the larger N is, the faster the population grows

density-dependent population limiting factors

effect on population growth depends on population density

biotic factors - resource availability, predation, competition, infectious disease, etc

can be related to abiotic/independent: larger population density increases ability to resist environmental stress

density-independent population limiting factors

density not important; proportional effects

effect on population size is unpredictable

abiotic factors: weather/climate, disturbances, natural disasters, soil pH, etc

effects on populations when limits set in

possibly crash (risk esp. on islands)

can stabilize

logistic population growth model

idealized population growth that is slowed by population limiting factors as the population size increases

growth with constraint

• slows as population size reaches carrying capacity

growth rate small when population is large or small, highest when population is at intermediate level relative to K

population grows exponentially at low population

carrying capacity (K)

maximum population size a particular environment can sustain

changes w resources → varies over space and time

community

all populations of organisms living close enough together for potential interaction

interspecific interactions

predation, symbiosis (mutualism, commensalism, parasitism), competition

exploitation

(+ / -)

predation and herbivory