Evolution

how and when the earth formed

• 4.5 billion years ago

• as mass of developing planet increased, heat generated by force of gravity and radioactive decay caused interior to melt

• produced dense metallic core surrounded by cooler, semi-solid mantle

• outside of that was crust - solidified to form continents and seafloor

conditions of early earth (and how it was formed)

• cooling of the crust caused gases from the hot interior to escape through volcanoes

• atmosphere contained hydrogen, water vapour, methane, ammonia, hydrogen sulfide

• lacked oxygen

cyanobacteria/stromatolite importance and overview

• cyanobacteria in rocks - oldest widely accepted fossils

• formed stromatolites - layers produced as CaCO3 precipitated over growing bacterial filaments

• released oxygen into the atmosphere by photosynthesis

processes necessary for life to begin on earth

• synthesis of simple organic molecules (e.g. amino acids) and ultimately synthesis of larger organic polymers (e.g. proteins)

• origin of molecules that can self-replicate

  • only molecules known to do this are RNA and DNA

• packaging of self-replicating molecules into membranes with internal environment different in composition from their surroundings. closed membrane vesicles form spontaneosuly from lipids, can maintian diff chemical compositions between intrace and extracellular environments

primordial soup theory

• life on earth started in ancient ocean/pond from mixture of simple chemicals

• lightning hit chemicals to form amino acids

• miller-urey experiment used to see if possible for simple inorganic substances to react and form complex organic molecules

• used water, methane, ammonia, hydrogen

• found 13/20 amino acids formed, high conc of adenine, 15% of carbon compounds were organic

meteor theory

• earth subjected to lengthy barrage of meteor showers and emissions from volcanoes

• caused atmosphere to contain precursors needed to make organic molecules

deep sea/hydrothermal vent theory

• vents warmed ocean water to temperatures conducive to life processes

• released hydrogen rich molecules and minerals to the water that early organisms could use for energy

to be considered living, an organism must…

• consist of cells

• control internal environment

• control exchange of materials

• remove waste

• respond to stimuli

• use energy

• grow and reproduce

ribozyme

• RNA molecule that can speed up specific chemical reactions in body

• self replicating

• catalyse range of reactions

• ability of RNA to be double helix or single strand allow them to self replicate and replicate other RNA molecules

RNA world hypothesis

• theory began due to discovery of ribozymes

• early life used RNA not DNA - first cells consisted of RNA molecule enclosed in vesicle (protocells)

• theorised because ribozymes self replicated and performed current role of proteins cayalyzing reactions

assumptions made in RNA world hypothesis

• genetic information was transmitted and stored by RNA in first cells

• same replication of RNA in first cells as modern

• metabolic reactions catalysed by RNA rather than enzymes in first cells

• RNA molecules with ability to catalyse reactions under certain circumstances - ribozymes

assumptions against primordial soup theory

• geochemists now believe that early atmosphere did not contain same proportions of gases as in miller-urey

• water breaks down protein chaincs in amino acids (or other constituents) - makes it v difficult to produce proteins/other polymers in soup

• amount of energy required is greater than likely energy generated by electrical storms

LUCA

• Last Universal Common Ancestor

• not a ref for first life on earth but ref to population from which all existing life derived from

prokaryotes existed before eukaryotes evidence - fossil record

• first cells existed 3.5 billion yrs ago - prokaryotes that didnt need O2 - cyanobacteria in stromatolites

• 2.3 billion yrs ago - photosynthetic prokaryotes - changed atmopsheric conditions by adding 02

• oldest eukaryotic fossil found 2.3 billion yrs ago - unicellular algae

• earliest multicellular eukaryotic fossil 1.6 billion yrs ago - red algae

prokaryotes existed before eukaryotes evidence - structural features

endosymbiotic theory

• proposes chloroplasts and mitochondria were once ‘free-living’ prokaryotic organisms that were engulfed by another cells by endocytosis

• they evolved within host cell in symbiotic relationship

  • host took prokaryotic cell that may have capacity to photosynthesise (hence supply organic molecules) or perform aerobic respiration (provide energy for cells)

  • engulfed prokaryotes benefited by obtaining shelter and protection from predators

• other endosymbiotic events occured during evolution of eukaryotes (e.g. infolding of cell membrane to make ER and nucleus)

evidence for endosymbiotic theory

facts that both mitochondria and chloroplasts:

• have inner membranes resembling cell memrbranes of prokaryotes more than cell membrane of eukaryote they are found in

• divide by binary fission - new cant be produced as directed by genes in nucleus

  • however rely on nuclear proteins for division

• have circular DNA

• have own protein synthesis system (inc. ribosomes that are incidentally more similar in size and structure to prokaryotic than eukaryotic)

evidence for common ancestry of all living things

• universal presence of DNA

• suggests that early prokaryotes evolved on their own first, then eukaryotes appeared biollions of yrs later (approx 2.7)

mutations (general) - inhertiance, define, types

• permanent change in sequence of nucleotides of DNA

• random changes to DNA sequence of an organism - can be beneficial, harmful, or no effect

• sources of new forms of particular gene s(alleles) in population of species

• somatic cell mutations are not inherited, mutations in gametes or germline cells are

• are generally pt mutation to single gene, may or may not affect one protein only

mutations - evolution

• ultimate source of genetic variation in species

• if beneficial → adaptation, if harmful → genetic disease

• driving force of evolution - phenotypical features arise from them; beneficial mutations provide individuals with a greater survival chance and are passed through generations and become more abundant

• sources of new forms of particular gene s(alleles) in population of species

• accumulation of pt mutations to diff genes in diff populations, over long time period, contributes to array of differences between species

affect of population seperation on mutations

• If separated for long time, accumulate different mutations in DNA

• larger time separated, the more likely there is a greater difference

molecular clocks

• compares evolution of biological molecules (e.g., DNA and proteins) to estimate time in history when species diverged from a common ancestor

• differences in aa sequences for specific proteins in species are proportional to time since species diverged from CA

• all proteins have diff rates of change but occur at constant rate

• if constant rate is true for all species, diff in aa sequence between 2 species can be used to determine approx time of divergence

• molecular clock must be calibrated properly

  • generally use fossil record, geological evidence and species samples

  • more samples for clock, more precise calibration

phylogenics - definition and principle behind analysis

• phylogenics - finding evolutionary relationships among organisms

• DNA, RNA, and protein sequences analysed - greater similarity, fewer mutations required to convert one sequence to other ∴ more recently share common ancestor

phylogenetic tree

• common ancestor occurs at the ‘root’ of the tree

• each branching pt (node) indicates where species diverged

• longest separation means more differences through mutation (more time that mutations have to accumulate in DNA sequence

comparative genomics

• comparing complete genomes, genes or aa sequences of different species using a variety of tools

• requires use of computer-based analysis to locate differences in sequences and regions of similarity

• e.g. of program ‘Clustal Omega’ - global multiple sequence alignment program for DNA, RNA, proteins

benefits of comparative genomics

• major contributor to understanding organisms (inc. the human genome)

• Important in identifying genes that are essential to life and contributing to understanding of how gene signals control gene function across a range of species

• powerful tool for studying evolution and evolutionary relatedness between organisms and humans

• wide range of applications in agriculture and biology

DNA sequencing

• used to work out the sequence of bases in a specific gene/genome

• sample of DNA from species can be sequenced to compare evolutionary relationships

• more similar genetic code, more closely related species - less time for mutations to accumulate

• similarity therefore also indicates recent separation from common ancestor between species

• feasible using comparative genomics software

  • construct phylogenetic tree using DNA sequences

  • Clustal Omega produces multiple sequence alignments of divergent sequences, calculates best match for selected sequences

rRNA sequencing fixxx

• rRNA is component of ribosomes - found in all liing organisms

• prokaryotes - 16s rRNA gene codes for small ribosomal subunit

• eukaryotes - 18s rRNA gene codes for small ribosomal subunit

• cloesly related species (same genus) have similar rRNA sequences

  • info can be used to make phylogenetic trees using computer-based software

• can also be used as qualititative method to determine unknown species and diff types in sample

advantages of sequencing rRNA

• all living organisms need ribosomes to make proteins hence rRNA gene is in all species

• rRNA gene has highly conserved regions where few mutations occur - researchers can synthesise primers that will bind in complementary fashion so PCR can be done

• also consists of multiple highly variable regions where mutations occur more readily - researchers can distinguish between diff species

• can detect many species at once in comparison to DNA sequencing of individual species - useful since theres >billion prokaryote species

• DNA sequencing requires prokaryote species to be isolated and some cant be cultured and hence isolated easily

protein sequencng'/aa seuquncint

• if diff species produce proteins w/ v similar aa sequences, DNA is v similar, inherited from recent common ancestor

• proteins maintained through evolutionary history are identified (those crucial to survival)

  • e.g. cytochrome c - needed for aerobic respiration

  • protein varies from species to another - degree of similarity indicates closeness of evolutionary relationship

  • assumed that 1st organism had cytrochrome c, over billions of yrs mutations changed sequence of bases in gene coding for protein

DNA-DNA hybridisation process

1. particular gene sequence to be compared between species is isolated using gene probe and enzymes

2. DNA of 2 species is heated to 95 to seperate strands

3. strands are mixed togehter and allowed to cool - enables formation of hydrid DNA

4. strands are reheated to work out ‘melting pt’ of hybrid DNA. melting pt is defined as temp where 50% of DNA is single stranded, other half is double. higher melting pt, more bonding between DNA molecules, more in common 2 DNA sequences are

5. higher the melting point, the greater similarity between the DNA sequences and the more likely it is that they shared a more recent common ancestor

DNA DNA hybridisation general info

• heating solution containing DNA disrupts H bonding between 2 complementary strands (measured as boiling pt)

• when mixture is cooled, they recombine to form double helix again

• solutoin of DNA is heated from diff species is heated, allows hybrid DNA to form

• degree of H bonding between one species DNA and another gives measure of similarity of sequence of nucleotides, indicator of how closely related species are

principal groups for classifying organisms:

domain

kingdom

phylum

class

order

family

genus

species

naming species

• binomial nomenclature - first name of species is genus, second is species name

• genus name is capitalised

• both written in italics on typing, if handwritten underlined

biochemical similarities

• DNA is universal

• biochemical similarities of DNA and proteins can be used to determine between asequally reproducing species

• also other biochemical molecules that are v similar between soecies

  • cellular respiration, photosynthesis, transcription, translation are essential processes in organisms ∴ biomolecules involved in processes are similar

  • e.g. cytochrome c (cellular respiration)

  • similarity can be compared to determine evolutaionry relationships

population definition

group of individuals of the same species occupying the same space and interbreeding

gene pool

• sum of all genes (alleles) of all individuals in a population - form which guture generations of individuals will be created

• populations with large gene pools (large diersity of alleles) will be more robust, more likely to survive changing or harsh environmental conditions

• reduced genetic diversity means greater extinction risk

biological species concept

• most widely used, based on reproductive isolation

• members of one species are a population where members have similar characteristics (biochemical, morphological, and genetic) and capacity to interbreed and produce fertile offspring

• species consist of several populations that are geographically isolated

• even though physically isolated, still considered one species if contribute to gene pool by producing fertile offspring

limitations of biological species concept - asexually reproducing species

• doesnt apply to them (e.g. bacteria, hydra, sea stars)

• biochemical comparisons of DNA and proteins help establish relatedness in this circumstance

limitations of biological species concept - lack of data on breeding behaviour

• many speciies dont have extensive research conducted on breeding patterns and ability to produce fertile offspring w/other groups of organisms

limitations of biological species concept - fossils

• DNA of fossils has generally degraded for species that are long extinct - rules out ability to compare breeding behaviours and comparative genomics.

• also no evidence regarding interbreeding and behaviour of fossilised organisms.

• can still show structural (morphological) featers, which can be compared

limitations of biological species concept - overlap of populations and hybrids

• difficult yo examine extent of interbreeding

• overlap in distribution areas and presence of hybrids exists

• if diff give rise to intermediate forms, considered one species

• may classify into seperate subspecies

morphological species concept

• groups species according to structural features that are unique to particualr group of organisms

• can be applied to any group, mainly useful for fossils

limiation of morphological species concept

• different species have similar structural features

• thus, only used when biological species concept cant be used

• species w/ similar features due to convergent evolution is example of the limit

fossils

• DNA in fossils generally degraded for species that are extinct for long time - cant compare breeding or comparative genomics, no evidence of interbreeding

• can still show structural features - thus morphological species concept used

reproductive isolation

• members of separate species cannot interbreed and have fertile offspring

• achieved through pre and post zygotic mechanisms

• pre - occur before zygote formed (before fertilisation)

• post - occur after zygote formed, prevent from developing into viable, fertile adult hybrid

pre-zygotic mechanism - temporal (time) isolation

• breeding cycles/time of fertility differs between one population of species to the next

• e.g. plants flower at different seasons, some animals are nocturnal and others arent

pre-zygotic mechanism - behavioural isolation

• development in populations of highly specific calls or rituals detected and responded only by other members of particular populatoin

• e.g. mating calls, mating dances

pre-zygotic mechanism - mechanical (morphological) isolation

• incompatible sexual organs, whereby significant anatomical differences act as powerful mecahnism to ensure different populations remain reproductively isolated

• eg. of plants - use different populations

pre-zygotic mechanism - gamete isolation

• incompatibility of sperm and eggs from populations of different species

• range of mechanisms and chemicals in species ensuring sperm can fertilise and fuse with egg from member of same species only

• isolating mechanisms operating here include:

  • sperm does not respond to chemical signals from egg

  • sperm cannot penetrate egg

post-zygotic mechanisms - hybrid inviability

• hybrid is weak and compete poorly for resoruces

• unlikely to reach reproductive age and contribute to gene pool

post-zygotic mechanisms - hybrid sterility

• extension of hybrid inviability

• hybrid formed is sterise, hence cannot contribute to gene pool

• chromosome number of 2 parents differs, hence do not have complete set of homologous pairs and meitoci division cannot occur in normal fashion

dominant and recessive, hetero and homozygous explained

• zygote inherits ½ genetic material from each parent

• genes act in various ways - some according to dominant and recessive patern of inheritence

• homozygous (2 dominant or 2 recessible

• heterozygous (1 dominant 1 recessive)

• dominant - alleles that are expressed when at least one dominant gene is in genotype

• recessive - 2 copies required to be expressed

cystic fibrosis and type of mutation

• caused by faulty recessive allele of a gene

• normal (C) is dominant over recessive mutant allele ©

• CC - normal, does not carry CF allele

• Cc - normal, carries one CF ellele

• cc - CF sufferer, has 2 CF alleles

• lethal mutation

sickle-cell anaemia caused how and homo and heterozygous

• change in one base, leads to protein with one aa changed

• A is changed to T in substitution mutation in codon for 2th aa in beta chain; codon changes from GAG to GTG

  • causes glutamic acid to be replaced by valine

• normal haemoglobin HbA and mutatn HbS alelles therefore:

  • homozygous can be HbA HbA or HbS HbS

  • heterozygous is HbA HbS

sickle cell anaemia sufferers how does it work (and codominance)

• HbA and HbS exhibit form of co-dominance (or incomplete dominance) - heterzygous form exhibits features from both alleles (normal and abnormal haemoglobin made)

• people with mutant gene and mutant heamoglobin dont have normal bi-concave TBC - become sickle-shaped

  • often causes death in homoxygous individiuals

types of mutations:

• lethal

• disadvantageous

• neutral

• beneficial

disadvantageous mutation e.g. osteoporosis

• cause disease in those with mutant gene but is not fatal

• e.g. osteoporosis

  • sufferers have brittle bones

  • low-density lipoprotein receptor related protein 5 (LRP5) involved in bone density and mutations in gene can cause osteoporosis

  • bones of affected individuals lose/’leak’ minerals (e.g. calcium) into blood

neutral mutations

• no affect on either appearence (phenotype) or its function

• majority of mutations are neutral

  • some scientists argue they are still mutations - change genotype and will be passed to guture generations (if germline cells)

  • changes to introns of DNA, may cause unknown changes to function

sickle cell anaemia

• homozygous individuals have LETHAL mutation

• heterozygous individuals (HbA, HbS) have some HbS-derived haemoglobin but more normal haemoglobin - suffer form mild anaebia

• if in malaria infested area, protists that cause disease cannot reproduce in RBC with haemoglobin made from HbS allele

  • have reduced chance of getting malaria

sexual reproduction on evolution (and evolution in asexually reproducing)

• introduces variety into offspring so they dont look the same as parents

• variation expresses itself as diff genotypes (pairs of alleles of genes) and thus different phenotypes (appearance)

• mutations are only source of new alleles in genes, sexual reproduction reshuffles alleles of genes in parents to give new combos

• popultions of sexually reproducing species show variation between individual members of population

• asexual - reproduction happens quickly if there is a favourable mutation

how variation introduced in meiosis

• crossing over - introduces new combo of alleles of maternal and paternal genes

• independent assortment of chromosomes - gives rise to new combos of maternal and paternal chromosomes in gamets through random alignment of homologous chromosomes on opposite side of equator of cell (meiosis 1)

how variation introduced in fertilisation

• random fusion of an ovum and sperm, each w/ unique collection of chromosomes and alleles

allele frequency

• relative proportion of particular allele in population

• usually expressed as fraction or percentage

changes in gene pool bought on by:

• mutations

• gene flow

• genetic drift

changes in gene pool - gene flow

• movement of alleles between diff populations of same species

• occur when individuals move in and out of populations, or migrate - change frequency of alleles found in gene pool

• inc. flow of alleles of genes between populations reduces diff between populations

• limited gene flow leads to populations evolving and developing in own environment

changes in gene pool - genetic drift

• random changes in frequency of alleles, more pronounced effects on small populations

• if any individuals dont contribute their alleles to next gen, major impact of gene pool

• seen in populations where effects (e.g. bottlneck) occur

• reduced population size reduces variation in gene pool → reduced genetic biodiversity

bottleneck affect

• impact of random factors (e.g. bushfires) on population

• changes allele frequency - removes certain alleles due to random cahnce

natural selection and darwins hypothesis

• for each population, more individuals were born and survived to reproduce, and environmental factors hold all populations in check

• natural selection - nature/the environment selected individuals who were best adapted -

• variation between individuals gave reproductive advantages, enable organisms to have more offfspring to survive next gen

• life evolved from common acnester, and due to natural slection, populations were modifed over time according to diff environments and diff selective pressures they were exposed to

darwins finches

• have diff beak shapes - provide unique adaptation for type of food predominantly found in particular environment of diff islands

natural selection def and selective pressures

• natural selection - nature/the environment selected individuals who were best adapted

• selective pressures act on phenotypes of individuals in the population, leading to changes in in allele frequency

  • certain alleles are favoured, otehrs are selected against

• ‘survival of the fittest’ - alleles of favoured traits in population of gene pool inc in frequency over time

• diff selection pressures can lead to divergent evolution or adaptive radiation

biotic selection factors

• predators

• disease-causing organisms

• competition from members of the same or different species

• symbiotic relationships with other organisms

• human activities

abiotic selection factors

• rainfall

• temperature

• nutrient levels

• light intensity

• medical drugs (e.g. antibiotics)

• chemicals (e.g. pesticides)

industrial melanism in peppered moths

• before industrial revolution, trees moths lived in were covered in offwhite lichen

• moths were light (light work) and speckled - camouflaged from predation by birds

  • occasionally black (dark form) would grow - high visibility, high chance of being eaten before reproducing

• due to coal based industry, trees covered in black soot - white moths were easily spotten and eaten

  • black (melanic) variant became predominant by 1850 - phenomenon called industrial melanism

• reduction of coal use in later 20th century made trees green (algae) - now both moth forms are common - balanced polymorphism

summary of evolution by natural selection

• individuals in populations show phenotypic variation - result of environment and differences in genotype (inherited by next gen)

• struggle for suvial between individuals of population due to biotic or abiotic selection pressures

• organisms best adapted to environmental conditions are more likely to survive to reproductive age and pass favourable alleles of genes to next gen

• over many gens, populations may evolve (showing changes in gene pool)

  • effects of natural selection can be measured by changes in frequency of alleles in gene pool - evidence of evolution occuring

  • populations/species that evolve, not individual organismsm

• environmental elective pressures determine reproductive success of population, population does not adapt to conditions

process of evolutino suggests

• all life forms evolved from single, simple common ancestor (LUCA)

• species change through time

• evolution in a species can be recognised by changing frequency of alleles in population

founder effect

• small group of individuals separate/move away from original population

• founding populations have a very different genotype from the original

• changes allele frequency in populations

speciation

• process that gives rise to new species

  • gene flow between 2 populations has stopped and reproductive isolation occurs

  • causes change in allele frequency in each population at differen rates

  • cumulative change in allele frequency over time means populations cant meet biological species def

• 2 types: allopatric and sympatric

allopatric speciation

• Members of the original population are separated by a geographical barrier - gene flow between them is prevented

• each population is subjected to different biotic and abiotic factors - selective factors and natural selection acts diff in each new location

• genetic diff accumulate in isolated populations

• if gene pools are separated and no gene flow occurs for long enough, geographical isolation evolves to reproductive isolation

  • speciation has occurred by divergent evolution

• adaptive radiation can occur

adaptive radiation

• A single ancestral species rapidly diversifies into new forms to fill different ecological niches

• divergent evolutoin of related species from common ancestor

• 
  

sympatric speciation

• one population gives rise to two or more new species while inhabiting the same region (no geographical isolation)

• gene flow must be prevented/reduced - reproductive isolatino must ultimately arise

• occurs via:

  • occupying different microhabitats

  • polyploidy

sympatric speciation - occupying different microhabitats

• particular members of one population occupy specific niche or microhabitat

• creates ecological isolation within same geographical area

  • diff microhabitats impose contrasting environmental pressures - favour traits for each speficic niche

  • habitat based mating

  • causes gene flow restriction into the subpopulations

sympatric speciation - polyploidy

• organisms possess more than two sets of chromosomes

• occurs commonly in plants and certain groups of fish and amphibians

• result of malfunction during meiosis - chromosomes fail to separate properly (nondisjunction)

• example of instantaneous speciation - polyploid organism can’t interbreed with organism with a normal diploid number; gene flow is stopped

• major role in flowering plant evolution

convergent evolution

• different species of roganisms develop similar (analogous) features with similar functions

• different groups of organisms (often in similar habitats w/similar selective pressure) have v similar structures/behavoiurs

• occurs when analogous features evolve independently in unrelated groups or seperate species

analogous features

• evolved separately in different lines of evolution

• similar functoins, different anatomy

• formed by convergent evolution

convergent evolution - wings and eyes

wings:

• birds, bats, and butterflies (unrelated) all have wings for flight - invovled independently of each other

eyes:

• an ancestral master gene ‘Pax6’ - og gene responsible for development of collections of simple light-sensitive cells

• found across diverse set of organimss

• probably part of genome of very early comon ancestor lived approx 500mil yrs ago

• cephalopods and vertebrate have camera eye

divergent evolution

• evolution of species from common ancestor

• groups separate by speciation - accumulation of diff in geome by mutation

• subjected to diff selective pressures therefore no gene flow - reproductively isolated

• have homologous features

homologous features

• share a common ancestor, have physical features with common evolution that have different functions

• e.g., pentadactyl limb

divergent vs convergent evolution comparison

succession

• gradual process where the species composition of a community changes and is brought about by the modification of the habitat caused by organisms that live there

• leads to significant change that whole ecosystem changes to favour new mix of species - caused by long term change due to colonisation or natural disasters

ways organisms modify ecosystems

• provide food or shelter for others

• changing soil structure, causing breakdown of rock or increasing organic matter in soil

• decomposing dead organic material, making nutrients available to other organisms

primary succession

• unidirectional process - lifeless ecosystems are colonised by progressively more stable communities of living things

• 1st stage - colonisation of bare land by pioneer species

  • carry out life processes (inc chemical reactions weathering rock over time)

  • transform material to soil

  • death and decay, increasing nutrient content in soil

• intermediate species sprout from seeds blown from nearby areas or insects and birds

• area is colonised by plants that become communities dominant vegetation - climax community produce

adaptations that improve survival of pioneer species

• autotrophic nutrition

• ability to reproduce quickly

• ability to tolerate harsh environmetal conditions

secondary succession

• occur in mature ecosystems following natural disaster or major human impact (e.g. forest clearing)

• e.g. woodland ecosystems destroyed by wildfires

  • fire stimulates germination of seeds; growth is more rapid than with primary succession - soils are warm, high nutrient content, can retain water better

  • new mix of plants and animal populations is quickly established

  • competition between colonising species populations and returning and new species influences new community and how it compares to og

• different selective pressures can lead to divergent evolutoin or adaptive radiation as species exploit new niches

characterisits of mature or late sucession in communities and ecosystems

• usually more species

• number of heterotrophs increases more than number of autotrophs

• recycling of nutrients is more efficient

• organisms are more specialised

importance of species diveristy

• species w/ reduced gene pool have higher risk of extinction - greater risk of becoming extinct due to greater susceptibility to environmental pressures

affect of human population growht on biodiversity

• exponential growth of global human population

• unsustainable - huge demands on resources needed by humans - jeopardises biodiversity

introduced/invasive/exotic species

• foreign species brought to australia from other countries - move intentionally or accidentallyform native location to new geographic area

• those who cause harm are invasive

• compete with native species for habitat or resources or directly feed on them

• if they have virtually no natural predators, spread across huge areas and reduce biodiversity

introduced species eg. - cane toads and rabbits

cane toads:

• native to Central and south america

• introduced to QLD to act is biological control agents of cane beetles

• have virtually no natural predators - spread over huge area of Australia

• Predators die after ingesting the toad due to poison glands on their backs - reduce biodiversity

rabbits:

• destroy native vegetation, compete with native animals for resources

• take over burrows from burrowing Australian species (eg. bandicoots, bilby)

serious threats of pollution

• chemical pesticides affect higher order consumers through biomagnification (DDT, insecticides)

• oil spills from ships at sea

• accumulation of plastic waste in waterways and oceans

  • kills animals

  • degradation into microplastics - enter food chain through biomagnification

• acid rain and photochemical smog - product of emission of SO2 and NOx into atmosphere from fossil fuel combustion

• ineffective or insufficient sewage treating and disposal

• production, transport, and storage of radioactive waste

• impact of chlorofluorocarbons (CFCs) used in aerosols and fridges - destroys ozone layer