CHAPTER 8: CHANGES IN SPECIES OVER TIME

Question 1

what is mass extinction

Answer 1

• mass extinction is when a larger-than-normal number of groups become extinct
  
  • regional and global scale
  • evolutionary opportunity for other species to thrive and diversify

Question 2

evidence for evolution

Answer 2

• fossils
• biogeographical distribution
• comparative
  
  • anatomy - structural morphology
  • embryology - developmental biology
  • molecular homology - DNA and amino acid sequences

Question 3

conditions that favour fossilisation

Answer 3

• rapidly buried
• protected from scavengers
• prevented from decomposition by low oxygen levels and low tempratures
• organisms having hard structures (won’t decompose as rapidly)

Question 4

process of fossilisation

Answer 4

• an organism dies and is rapidly buried
• protected from scavengers
• prevented from decomposition by
  
  • low oxygen levels
  • low temperatures
• continued deposits of sediments bury it more and more deeply
• over time the molecules in the organism (usually the hard parts) are replaced by minerals from groundwater
• gradually, the weight of the overlying sediments compresses the original sediment layer so that it becomes rock
• over time the rock is eroded, uplifted through the movement of tectonic plates or excavated
• Fossilization: undergo mineral exchange with the surrounding rock.
• preservation which as a process does not involve mineral exchange.

Question 5

timeline of life on earth

Answer 5

• prokaryotes
• first photosynthetic bacteria
• first aerobic microbes
• first unicellular eukaryotes
• first multicellular eukaryotes
• first vertebraes (jawless fish)
• first insects
• first land plants
• first amphibians
• first ferns
• first reptiles
• first conifers
• first dinosaurs
• birds
• first mammals
• first flowering plants
• primates
• humans

from single cellular forms to structurally complex multicellular forms

Question 6

mineralised/petrified fossils

Answer 6

organic material of a structure replaced by minerals

Question 7

mold fossils

Answer 7

• form when a mineralised/petrified fossil dissolves and leave an impression of the original
• these can be filled in to make cast fossils

Question 8

trace fossils

Answer 8

• form when traces of activity are buried before they are erased and turn into rock
  
  • eg footprints, teeth marks, scats (faeces)

Question 9

purpose of fossil record

Answer 9

• the fossil record reveals that over time changes have occurred in the types of organisms living on this planet
• provides evidence in support of the prediction that ancestral species will appear before the species that descend from them

Question 10

fossil/faunal succession

Answer 10

• fossilised fauna and flora in sedimentary rock strata (layers) are arranged vertically in a specific order
• fossils are used to identify rocks of the same age - fossils found in the same layer as rock formed at the same time
• different kinds of organisms do not occur randomly in the fossil record but are found only in rocks of particular ages and appear in a consistent order (in an order of fossil succesion)
• can find relative dates of appearance of species

Question 11

relative dating

Answer 11

• sedimentary rocks form in layers (strata)
• newer layers are at the top and the older layers are at the bottom
• can determine relative age from that (as in newer or older - not the specific time)

Question 12

index fossils

Answer 12

• index fossils can be used to determine the relative ages of rock strata anywhere in the world
• presence of index fossils in rock strata in widely separated regions of the world can identify these rocks as having the same age.

Question 13

transitional fossils

Answer 13

• can tell us about major changes - evidence of evolution
• is the fossilised remains of a life form that exhibits traits common to both an ancestral group and its derived descendant group

Question 14

absolute dating techniques

Answer 14

• radiometric dating is the most common way to find the actual age of a fossil (rock)
• measure the relative amounts (decay) of radioactive materials (parent) and their daughter products
• the radioactive isotopes (parents) spontaneously decay or break down over time to form stable daughter products
• the rate of the decay is specific for each radioactive isotope

Question 15

relative vs absolute dating

Answer 15

relative age provides a comparative age whereas absolute age provides a more precise numerical age

Question 16

half-life

Answer 16

half life → the time taken for half of the original radioactive isotope to decay

Question 17

carbon dating

Answer 17

• carbon 14 will decay into nitrogen 14 (half-life of 5700 years)
• living things take in C14 when they eat
• living things stop taking in C14 when they die
• by comparing the amount of C14 and N14, the time since death can be determined
• limitation of carbon dating: can’t be used to date fossils older than around 50000 - 60000 years
• because there are very small amounts of carbon 14 left in the organic matter

Question 18

what is speciation

Answer 18

the formation of a new species

Question 19

process of speciation

Answer 19

• variation of characteristics is present in the population
• breeding population becomes isolated
• different selective pressures applied to isolated populations, random genetic drift, mutations
• b/c of natural selection, some characteristics are favoured over others
• those best suited to the environment survive
• survivors reproduce and pass on favourable genes + traits to offspring
• frequency of genes for new traits increases
• overtime, differences and mutations accumulate resulting in speciation

Question 20

definition of species

Answer 20

organisms that can breed and produce fertile and viable offspring

Question 21

allopatric speciation

Answer 21

• populations are geographically separated
• one species may diverge to give rise to new species when
  
  • there is no gene flow between the two daughter populations
  • mutations (may) arise in each population (randomly) and or
  • different selection pressure operates in each population
  • over generations, phenotypes are selected by natural selection or genetic drift
  • two distinct gene pools and different species
• may evolve to become so different that if individuals from the daughter population meet they would no longer mate or produce fertile offspring

Initially a population (or populations) of the same species becomes isolated by a geographical
barrier.
Over time the isolated population(s) is exposed to different selective pressures and accumulates
sufficient differences to the original population so that it forms a new species.

Question 22

galapagos finches

Answer 22

• Galapagos islands are made of 13 main volcanic islands
• have a variety of habitats - arid regions and mountainous regions
• Darwin finches are a group of 13 species of bird
• differing environmental selection pressures on each of the islands based on food availability (main environmental pressure)
  
  • caused change in beak shape bc of diff food source
• after the finches had arrived on an island → became geographically isolated due to the surrounding ocean
  
  • don’t tend to fly between the islands
  • over time allopatric speciation occurred
• despite significant beak shape, they are closely related
• evolved rapidly by allopatric speciation - a process known as adaptive radiation

Question 23

sympatric speciation

Answer 23

• occurs when members of a population living in the same area diverge sufficiently to become 2 different species
  
  • no geographical barrier
• evolution of a new species from a surviving ancestral species while both continue to inhabit the same geographic region
• common in plants (can be polyploidy) + disruptive selection in animals
• non-geographic barrier isolates populations from each other (eg. active day/night
  
  • would have some gene flow
• isolated populations are subject to different selection pressures → different phenotypes are favoured
• over generations, genetic divergence occurs
  
  • responds to diff environmental pressures → different phenotypes and isolated populations change
• when the population come together again - can no longer interbreed - two separate species (2 distinct gene pools and different species)

Question 24

lord howe island palms

Answer 24

• both species of Howea palm share the same ancestor
• both are found in the same location
• barrier: the dirt they grow in
  
  • volcanic soil has more nutrients than calcareous soil
  • plants in volcanic soil can grow more quickly → flower earlier
  • different flowering times results in pre-zygotic isolation
    
    • cannot mate
• curly palm grew in nutrient-rich volcanic soil
• kentia palm grows in nutrient-poor calcarenite soils
• shift in nutrient content caused a shift in flowering times
• variation in which they live
• flowering time difference reduces mating and promotes species divergence (speciation)
• only some of the palms in volcanic soil can mate with those in calcareous soil → some overlap in flowering time.
• speciation is followed by further phenotypic, physiological genetic divergence
• over time further differences accumulate in the two species → resulting in completely diff flowering times

Question 25

transitional fossil example

Answer 25

• archaopteryx
  
  • transitional fossil of dinosaur and modern birds
  • feathers
  • wishbone
  • however it shows some reptilian features now lost in modern birds
  • teeth in its beak
  • claws on its wings
  • unfused (free) bones in its hand
  • long bony tail
  • also not capable of long flight of modern birds

Question 26

why is sympatric speciation rare?

Answer 26

• gene flow can still occur in sympatric speciation
• genetic drift has less of an impact
• less likely to be isolated
• as it requires reproductive isolation
• there is usually gene flow between populations in the same area, this limits this isolation occurring
• natural selection would need to be strong to favour specific traits that then lead to a divergence and a new species evolving

Question 27

What evidence do vestigial structures provide for evolution?

Answer 27

• they indicate the relatedness between species
• the structures are similar, indicating that species share and have evolved over time from a common ancestor.

Question 28

what is a common ancestor

Answer 28

• is a species that existed earlier in the fossil record
• subsequently evolved into two or more different species
• an ancestor shared by later species: one from which two or more species evolved.

Question 29

conditions to be an index fossil

Answer 29

• index fossils must be
  
  • abundant
  • distributed worldwide
  • existed for only a short period of time
• index fossils are of organisms that were common throughout the world for a limited geological time
• fossils of geographically short-lived (found in only one layer) species that are widely distributed
• found in a restricted depth of rock strata
• abundant during their lifetime but not able to survive changes in environmental conditions
• majority of index fossils are marine organisms because they are universal to the ocean and can be covered by the ocean floor sediment

Question 30

pre-zygotic/post zygotic isolation

Answer 30

• Pre-zygotic isolation mechanisms are barriers that prevent an organism from finding and securing a mate
  - Temporal isolation → nocturnal and diurnal species are unlikely to meet
  - Geographical isolation → species who live on mountain tops are unlikely to meet those in valleys
• Post-zygotic isolation mechanisms are barriers that prevent fertile offspring from developing after mating
  - Incompatibility of gametes → sperm cannot succesfully penetrate the egg, thus, fertilisation does not occur
  - Zygote mortality → fertilisation occurs but the zygote (fertilised egg) fails to develop

Question 31

how does faunal succession provide a record of evidence of evolutionary past

Answer 31

• based on the premise that strata accumalates in chronological order
• fossils in lower strata are older than fossils closer to the surface
• fossils in lower strata are less complex than strata closer to surface