yr 11 bio mod 3

selection pressures

external agents which affect an organism’s ability to survive in a given environment

• may not remain constant - leads to changes in what constitutes a beneficial adaptation

distribution of a species

describes where it is found

abundance of a species

determines how many individuals of that species live throughout the ecosystem

examples of abiotic selection pressures (in terrestrial environments)

• temperature

• light

• water availability

examples of abiotic selection pressures (in aquatic environments)

• salinity

• availability/concentration of dissolved gases

• pH of water

examples of biotic selection pressures

• availability of food

• number of competitors

• number to mates

• number of predators

• number / variety of disease-causing organisms

where are cane toads originally from and why were they introduced to australia?

• native to south/central america

• introduced to australia in 1935 to control greyback cane beetle in sugar cane plantations

structural/behavioural adaptations cane toads have, enabling them to thrive in australian environment

• feed at night

• ground dwellers

• eat anything

• absorb water through their skin

• no known predators

• breed all year round

  • females lay up to 30 000 eggs at a time which hatch in 2-3 days

• contain toxins killing many native animals trying to eat them

does the cane toad toxin affect all members of a population in the same way?

• no

• some individuals are more tolerant of the toad’s poison than others

• some individuals are more reluctant to eat toads

are toads considered a selection pressure in australia and why?

• yes

• predators w/ characteristics such as vulnerability to bufotoxin / increased preference to eat cane toads are removed from population

• predators w/ increased resistance to bufotoxin / reluctant to eat cane toads will survive + reproduce

example of selection pressures: cane toads effect of red bellied black snakes

• snakes w/ larger heads tended to eat larger cane toads containing grater doses of toxin + died

• smaller headed snakes were unable to open their jaws wide enough to eat larger cane toads and survived

how did prickly pears come to australia?

introduced in 1800s from americas to start a cochineal dye industry

what structural adaptation does the prickly pear have which helps it reproduce?

the parent plant contains branches which easily detach and distribute the plant (and its seeds)

what biotic factor did the prickly pear have to its benefit?

no natural predators in australia

what were some early (but ineffective) control methods to control prickly pear?

burning, crushing, herbicides

what was used to successfully in control the prickly pear?

cactoblastis moth restored 3 million previously infected hectares of land by 1932

how did introducing the cactoblastis moth provide selection pressure to the prickly pear?

provided strong selection pressure and it worked on a lack of diversity in the population + quickly reduced the number of prickly pears

biological control

use of natural predator to control numbers of a pest organism

adaptations

• characteristics organisms have inherited that make it suited to its environment

• result of a change or variation that randomly arises

steps for natural selection

• variation within a population/species

• selection pressures making certain characteristics beneficial for survival

• organisms w/ beneficial characteristics will survive + pass characteristic onto offspring

• over many generations there will be an increase in organisms with this characteristic

structural adaptations

how the organism is built/structured + how this aids their survival in their natural habitat

how does the structural adaptation of a eucalyptus’ leaves hanging vertically help the plant survive?

• prevents water pooling on top of the leaf

  • prevents potential pathogens from reproducing/entering plant via stomata in leaf

how does the structural adaptation of a eucalyptus’ having both top and bottom sides of the leaves contain palisade cells help the plant survive?

• significant amount of chloroplasts (containing chlorophyll) in the palisade cells

  • allow the eucalypt to be able to capture maximum sunlight in the morning and late afternoon, and not need to open its stomates in the middle of the day (when the sun is shining directly above and is the hottest)

    • helps it conserve water

  • chloroplasts also help the eucalypt photosynthesise efficiently

how does the structural adaptation of a wombat having a rear opening pouch help it survive?

• adaptation in response to wombat’s prolific digging behaviour

• ensures joey will be protected from dirt that would otherwise fill the pouch

  • assists survival of species as it ensures offspring is protected from threat until it can survive on its own

how does the structural adaptation of a wombat having 24 rootless teeth that grow continuously help it survive?

• wombat’s herbivorous diet of coarse native plants constantly wears their teeth down

  • teeth are adapted to cope with their diet by continuously growing to balance the natural grinding down of their teeth from eating fibrous material

physiological adaptations

adaptations related to how organisms function that increase the organisms’ chances of survival in their natural environment

how does the physiological adaptation of a deciduous beech losing its leaves in autumn help it survive?

• loses leaves in response to shortening of days (when days are getting colder)

• allows trees to survive extremely low temperatures and conserve water (as leaves are the main site for water loss)

• also allows trees to survive lower sunlight availability

how does the physiological adaptation of pigface increasing water content in large vacuoles help it survive in its saline environment?

• minimises salt toxicity

  • as the accumulation of extra salt (from its saline environment) is balanced w/ additional water drawn into cells

halophytes

plants adapted to saline environments

how does the physiological adaptation of the spinifex hopping mouse excreting extremely concentrated urine and using water produced as a by-product of cellular resp. help it survive in its desert environment?

• extremely concentrated urine - reduces water loss as it can reabsorb most of the water they drink back into their bloodstream

• these adaptations allow the mouse to conserve maximum water and allow it to produce enough metabolic water to supply its needs

how does the physiological adaptation of penguins having countercurrent heat exchange help it survive in its antarctic environment?

• blood travelling through arteries to the feet warms the blood returning to the body in the adjacent veins

• because the gradient of temperature difference between the feet and surroundings is reduced, less heat is lost

behavioural adaptations

refer to those actions performed by an organism in response to a stimulus that improve its chances of survival

how does the behavioural adaptation of the venus flytrap being carnivorous help it survive in its nitrogen-poor environment?

• part of the plant is able to snap shut when an insect touches delicate sensory hairs

  • insect becomes trapped and plant secretes digestive enzymes onto insect + nutrients (including nitrogen) are absorbed by plant

how does the behavioural adaptation of the central netted dragon lying in the sun/retreating to shade help it survive in its desert environment?

• ectotherm (must rely on environment to regulate its temperature)

• able to withstand variations in body temp. from 13*C - 44*C

• in lower temperatures, dragon will lie in the sun + alter its body position to expose more of its body SA to sun (to conserve heat)

• in higher temps, dragon will retreat to shade + reduce its activity (to avoid overheating)

how does the behavioural adaptation of meerkats living in large social communities help it survive in its desert environment?

• meerkats are burrowing carnivores that spend a lot of time w/ heads in the ground searching for food

  • makes them vulnerable to attack by predators

• meerkat communities have one meerkat posted as a sentry, and if a threat is imminent the sentry produces distinctive calls warning all meerkats to be alert

(finches in galapagos islands) who did charles darwin present his specimens of finches to and what did that person say about them?

• John Gould (famous English ornithologist)

• he classified them as 14 different species, 12 of which were new

• Gould also noted the birds were similar to those found in South America

what did darwin notice about the finches (structural adaptation) and what did he theorise about it?

• he noticed they had different beak sizes

• he theorised all finches on Galapagos islands could have descended from an original population from the mainland (South America)

explain (using the language of evolution by natural selection) how the finches evolved to have different beak sizes

• a few south american finches arrived on one of the remote islands + had naturally occurring variations

• descendants of these birds gradually populated other islands with different environments

• depending which island they lived on, some birds thrived and reproduced

• those that weren’t adapted to the conditions on the island died

what evidence did the finches on galapagos provide to darwin?

provided evidence to him that species could split from a common ancestor + might exist at the same time in the same geographical area (divergent evolution)

(darwin + native flora + fauna in Australia) what observations did darwin make in his trip to bathurst?

• observed platypus was similar to water rat in England

• observed rat kangaroo was similar to rabbit in both appearance and behaviour

what did these observations lead him to conclude?

led him to the idea organisms living in similar environments (in different geographical areas) could evolve to have similar adaptations

• because they face similar environmental selection pressures

(convergent evolution)

step 1 for evolution by natural selection

overpopulation - most species produce more offspring than can survive as they don’t have the resources to sustain them

step 2 for evolution by natural selection

variation

within every population of a species, there is phenotypic variation between individuals in the population

step 3 for evolution by natural selection

selection pressure is introduced

e.g physical, chemical, disease, competition for resources/food

step 4 for evolution by natural selection

survival of the fittest

• individuals who are not negatively impacted by selection pressure survive + reproduce, passing their favourable characteristic onto offspring

• individuals negatively impacted will die + not pass on unfavourable trait onto offspring

step 5 for evolution by natural selection

evolution of a population/species

• over generations, the population will show a greater proportion of individuals expressing the favourable characteristic

• individuals with unfavourable characteristic will be fewer in no. or completely removed

step 6 for evolution by natural selection (only for divergent evolution)

• if populations of a species become physically isolated, the process of NS will occur over generations

• + there could be such diversification of traits between 2 population that 2 new species are created

what is endosymbiosis

• theory to explain how eukaryotes evolved

• proposes that organelles found in eukaryotes were once prokaryotes that were engulfed + living in a larger host cell, and both cells mutually benefit from this

how is the theory of endosymbiosis evident in mitochondria?

• mitochondrion was once a free-living bacterium engulfed by another cell

• host cell benefited from chemical energy mitochondria produced + mitochondria benefited from protected, nutrient-rich environment surrounding it

• mutual symbiotic relationship

evidence for endosymbiosis

• membranes - e.g mitochondria and chloroplasts have their own membranes (like prokaryotes)

• DNA - e.g each mitochondria has its own DNA genome (like a bacterium’s genome)

  • DNA is passed from a mitochondrion to its offspring + separated from host cell’s genome in nucleus

genetic diversity

total no. of genetic characteristics in genetic make up of a species

why is low genetic diversity bad for a species long term?

• without a rich pool of genetic variation within a population, it has a higher risk of extinction

  • because a selection pressure is introduced and there isn’t enough variation many members of the population might die

species diversity

measure of diversity of different species in an ecological community

ecosystem diversity

variation of different ecosystems found in a region

what causes speciation?

• allopatric speciation - when members are physically isolated and get exposed to different environmental pressures

• sympatric - same physical location but due to ecological/behavioural separation

evolution

a change in a species over time

macroevolution

a change in a species over millions of years, usually resulting in the creation of new species

microevolution

change in a species over some generations (shorter period of time), often resulting in changes within populations (e.g dog breeds)

how did a horse’s teeth evolve?

as horses faced the selection pressure of having to eat tough and fibrous vegetation,

their teeth evolved to have long “reserve crows” inside their jaw bone that continuously erupt

to account for the constant grinding of their teeth due to their diet

also their eyes moved out of the way for their longer teeth to take more space in their skulls

how did a horse’s hooves evolve?

as horses faced the selection pressure of living in a grasslands biome (compared to the forest where their ancestors lived), their toes evolved into one hoof (due to natural selection) as they had to walk on a harder ground and become better at absorbing high-impact running stress

what does DNA evidence about the platypus conclude?

• it has many genes in common w/ reptiles, birds + fish

• its ancestors must have split off from ancestors of other mammals ~165 Myr BP

• was present during Mesozoic (dinosaur) era (fossil record)

• confirms platypus’ line of evolution is very ancient + different compared to other mammals

divergent evolution

when one common ancestor splits into 2 or more different species due to facing new/different selection pressures as they moved into different habitats (due to NS)

what conditions are essential for divergent evolution?

• physical isolation - leads to new species over time

• the organisms in the different species have homologous structure

  • similar structure which has evolved to have a different function

  • e.g pentadactyl limb is a leg in a horse and a wing in a bat

convergent evolution

when distantly related species independently evolve (due to NS) to have similar traits as they face similar selection pressures

what conditions are essential for convergent evolution?

• no common ancestor

• similar ecological roles/environments

• similar selection pressures result in distantly related organisms having similar traits

• analogous structure - structures w/ similar function but from different evolutionary origins

  • e.g wings of an insect and a bird