BIOL1003
Molecular Genetics _________________________________________________________ 1
DNA and the Central Dogma ____________________________________________________ 1
Transcription – RNA Synthesis ___________________________________________________ 1
Translation ___________________________________________________________________ 2
DNA Replication _______________________________________________________________ 3
Mutation _____________________________________________________________________ 4
FOXP2 Gene __________________________________________________________________ 5
Ecology ___________________________________________________________________ 6
Lecture 1. _____________________________________________________________________ 6
Lecture 2. _____________________________________________________________________ 8
Lecture 3. ____________________________________________________________________ 14
Lecture 4. ____________________________________________________________________ 17
Lecture 5. ____________________________________________________________________ 20
Lecture 6. ____________________________________________________________________ 21
Lecture 7. ____________________________________________________________________ 27
Behavioural Ecology _______________________________________________________ 30
Ecology Review Questions ___________________________________________________ 31
Molecular Genetics
DNA and the Central Dogma
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Genetic information is carried by molecules
– The molecule is DNA
Biological information is carried in the sequence of monomers
– Information is digital
DNA is a double stranded helix
– nucleotides on one strand are linked by covalent bonds
– the two strands are linked by hydrogen bonds between the base pairs
Macromolecules are polymers made from similar monomer units
– Monomers are joined by identical covalent bonds but may have different
chemical groups attached (bases in DNA and RNA, amino acids in proteins)
The central dogma:
– The genotype is carried in the DNA, and proteins determine the phenotype.
RNA transfers information from DNA to proteins.
Transcription – RNA Synthesis
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Requires a DNA template
Occurs in one direction only, 5’ to 3’
Is catalysed by an enzyme: RNA polymerase II
Requires energy (provided by the monomers)
Initiation
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• RNA polymerase binds to a special DNA sequence called a promoter
Elongation
• Addition of complementary rNTPs
Termination
• Release of RNA polymerase and completed RNA from the DNA template at
the terminator
In eukaryotes, transcription takes place in the nucleus, translation in the cytosol and
cytosolic organelles.
In bacteria, both transcription and translation take place in the same cellular
compartment.
Viruses are weird. Covid-19 doesn’t even have DNA.
Translation
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Synthetic RNA was fed to a cell-free system (a cytoplasm extract).
The first synthetic RNA molecules were all made of just one kind of monomer:
poly-A, poly-T, poly-G, poly-C
• Poly-U mRNA yields a phenylalanine-only
protein.
• This also proved that RNA really was the
direct template for protein synthesis.
Features of the Genetic Code
• Universal (almost)
• Redundant, but unambiguous
• Non-overlapping
• Start and stop codons
Reading the Genetic Code
• Conversion of a base sequence to an amino acid sequence requires an adaptor
molecule.
– Bases and amino acids are not complementary
• The adapter molecule is a small RNA molecule called a transfer RNA (tRNA).
What is needed for translation
• mRNA: the template
• tRNA: adaptor molecules that convert a sequence of codons to a sequence of amino
acids
• rRNA: a component of the ribosome that makes the proteins.
• Energy: in the form of GTP
• Ribosomal proteins: to make use of GTP
Ribosomes
• The A (amino acyl) site
– The next amino acid/tRNA waits for peptide bond formation
• The P (peptidyl) site
– Holds the growing protein attached to a tRNA
• The E (exit) site
– Releases the tRNA after it loses the peptide group
• The ribosome has two subunits
• Each subunit consists of proteins and RNA molecules (called ribosomal RNA, or
rRNA)
• Protein synthesis is catalysed by the ribosome
• Using information from a template mRNA
• Amino acids are linked by covalent bonds
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Protein grows in one direction only
• Amino acids added to C terminus
Protein Synthesis
• Initiation
– Assembly of the ribosome on the mRNA at the start codon
– The small ribosomal subunit interacts with mRNA, and the initiator tRNA
– When the large subunit attaches, the Met-tRNA is in the P site
• Elongation
– 3 step catalytic cycle involving addition of amino acids
– Entry of tRNA into the A site
– Formation of peptide bond
– Translocation (movement of the ribosome by one codon)
– The mRNA is translated 5' to 3'
• Termination
– Release of the completed protein at a stop codon
– Release factors catalyse release of the completed protein
Initiation of protein synthesis
• Identification of the AUG start codon
• Insertion of the initiator tRNA (Met)
• Assembly of the ribosome
Signal selection and amplification
• Transcription:
– Signal Selection:
• Promoter determines where, when and how many transcripts
– Signal Amplification:
• multiple mRNA molecules synthesised from one gene
• Translation:
– Signal Amplification
• Multiple protein molecules synthesised from one open reading frame
• Prokaryotes: No nucleus. Transcription and translation in the same compartment
(polysomes) in the cytosol
• Eukaryotes: Transcription in nucleus. Translation outside the nucleus: either on
membranes (RER), or freely in the cytosol (polysomes).
DNA Replication
DNA Synthesis
• Information transferred through complementary base pairing
– Hydrogen bonding between base on template strand and the correct dNTP
selects the right base ( A and T pair, G and C pair)
• Can only build 5’ to 3’
– Covalent bond formed between the
3’ end of the chain and the phosphate
group of the new dNTP
• Covalent bonds form to create a new sugar phosphate backbone
• Requires:
– A template strand – to copy
– dNTPs – energy AND building blocks
– Something to separate strands
– Something to initiate synthesis
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– Something to make it bidirectional
Limitations of DNA polymerase III
• DNA Pol III can catalyse DNA polymerisation in the 5' to 3' direction only.
• DNA polymerase can't unwind DNA strands.
• DNA polymerase can’t initiate DNA synthesis.
• But… DNA Pol III can “erase” in the 3’to 5’ direction.
Initiation of DNA replication
• DNA Helicase attaches to replication origins, and proceeds to separate the H-bonds
between the two DNA strands
• Primase (an RNA polymerase) produces an RNA primer complementary to a short
sequence of the template strand.
• DNA polymerase III can continue
from this.
• DNA Helicase unzips DNA from replication origins
• Primase produces a primer
• DNA polymerase III can continue from this.
• DNA polymerases can “back up” and remove the last nucleotide if it is incorrect.
• The removed nucleotide is then replaced by the normal 5'-3' DNA synthesis activity.
• 99% of incorrect bases are fixed this way
• DNA is antiparallel: as it is unwound, new single strand template becomes available
in the 3’->5’ direction on one strand, and 5’->3’ on the other.
• DNA polymerase can follow helicase on one strand (the leading strand), but not on
the other (the lagging strand).
• DNA polymerase III is the main replication polymerase for both the leading and
lagging strand.
• DNA polymerase I replaces RNA primers with DNA on the lagging strand only.
• Helicase - initiation
• Primase (RNA polymerase) - initiation
• DNA polymerase III - extension
• DNA polymerase I - fixing the lagging strand
• DNA ligase – fixing the lagging strand
• Helicase: separates DNA strands
• Primase : makes RNA primers
• DNA polymerase III : major polymerase
• DNA polymerase I : replaces primers with DNA
• Ligase : seals nicks between Okazaki fragments
Accuracy in DNA replication
• High accuracy is due to proof reading by DNA polymerases and DNA repair
mechanisms that happen after DNA replication
• Error rate in humans is still 3.0 × 10−8 mutations/nucleotide /generation
• Equivalent to 50-200 new mutations in humans each generation (official number is 64
for germ cells, human genome is ~3 billion base pairs)
• Most in non-coding DNA (1-2 mutations in coding DNA)
Mutation
Mutation rate balance
• Too many – most offspring are at a selective disadvantage (or dead).
• Too few – species are not able to adapt to change and might become extinct (not
enough variation).
• Mutation rate appears to be selected for over time.
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– Different species have different mutation rates
• E.g.: shorter vs. longer lived species can deal with different amounts of
mutation.
• DNA replication is always very accurate.
Effects of point mutations on a protein
• Silent mutation: the base change does not result in a protein change
• Missense mutation: a single amino acid is changed.
• Nonsense mutation: an amino acid codon is changed to a stop codon
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Cystic fibrosis: most common is Phe508del: deletion of one codon (so it’s not a
frameshift), reduces function of the protein.
Huntington’s disease: insertion (up to 40x repeat) of an extra codon (so not a
frameshift) for C-terminal Gln causing abnormal function of the protein.
Achondroplastic dwarfism: Gly380Arg missense mutation causing protein to be more
active than normal
Colour blindness: deletion of
a whole gene
The function of globin (the protein component of haemoglobin) is the same in all
species
The sequences are NOT the same
Some mutations don’t affect function and phenotype
FOXP2 Gene
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Genetic speech disorder characterised in “KE” family in the UK
– Difficulty with writing, grammar and comprehension
– Difficulty with coordinating facial movements
Gene mapping revealed that all patients have a missense mutation in the FOXP2 gene
We might predict
– It would be present in all species that vocalise
– It would be different in humans than in non-vocalising close relatives
This can be tested by identifying and sequencing the FOXP2 gene from different
species
Evolved before the dinosaurs
- present in all vertebrates, not just vocalising ones
Highly conserved in mammals
– There is only one amino acid difference between mice and non-human
primates
• One change in 130 million years
Different in humans
– Two amino acid differences between humans and other primates
• Two changes in < 5 million years
• “Rapid” evolution implies new selection pressures
Loss of function mutation:
– Expect change in vocalization for the worse
Suggests that FOXP2 has roles in development and in learning to vocalise
Put human version of FOXP2 into mouse
– Humanized FOXP2 mice
• Have deeper squeaks
• Differences in brain structure
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• Learn faster in some tasks
Idea of ‘a language gene’ too simple
FOXP2 appears to be important for development of motor coordination
– Facial movements involved in speech are very complex
• Spoken language affected most by FOXP2 mutations
• May result from incorrect development of facial muscles or the part of
the brain that innervates them.
– Possible role in grammar, comprehension and learning as well?
DNA sequence data allows us to ask new questions about evolution
Both genotypic and phenotypic change can be examined
– Comparison between fossil evidence and genetic similarity
Molecular basis for evolutionary change can be examined and empirically tested
Ecology
Lecture 1.
The study of the interactions that determine the distribution and abundance of organisms.
Ecology considers interactions that can occur at different scales (organism > population >
community > ecosystem > biosphere.
Organismal Ecology – includes the subdisciplines of physiological, evolutionary, and
behavioural ecology, is concerned with how an organism’s structure, physiology, and
behaviour meet the challenges posed by its environment.
Population Ecology – a group of individuals of the same species living in an area. Analyses
factors that affect population size and how and why it changes through time.
Community Ecology – a group of populations of different species in an area. Examines how
interactions between species, such as predation and competition, affect community structure
and organisation.
Ecosystem Ecology – the community of organisms in an area and the physical factors with
which those organisms interact. Emphasises energy flow and chemical cycling between
organisms and the environment.
Landscape Ecology – (or seascape) a mosaic of connected ecosystems. Focuses on the factors
controlling exchanges of energy, materials, and organisms across multiple ecosystems.
Global Ecology – (biosphere is the global ecosystem) the sum of all the planet’s ecosystems
and landscapes. Examines how the regional exchange of energy and materials influences the
functioning and distribution of organisms across the biosphere.
Fundamental Ecological Questions:
Where do we find organisms (why are they there and how many)
- Biogeography
• distribution through space and time
- Biome
• E.g. tropical forests and woodlands of central Africa
- Habitat
• E.g. primary or secondary forests
What are they doing there (their role and what keeps them there)
Niche:
- What does the organism do?
- What role does it play?
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E.g. primary consumer, herbivore, competitor, mutualist, prey
How is it that they are a success (life histories and why they have fitness)
Population Ecology: life history
- Live to 20 years
- One offspring per year after maturity at ~6 years
- Undisturbed populations are maintaining numbers/increasing
- Decreasing where hunted for bush food
LEADS TO PREDICTING THE FUTURE AND UNDERSTANDING THE PAST
Why is ecology an important field?
Ecology studies both the biotic and abiotic interactions that determine distribution and
abundance.
What is it good for?
- Solving problems of DISTRIBUTION
• Why are some organisms not found where they should be expected?
• Why are some organisms found where they shouldn’t be?
- Solving problems of ABUNDANCE
• Why are some organisms more abundant than they should be?
• Why are some organisms less abundant than they should be?
Distribution and Abundance:
Includes environmental influences on population density and distribution, age structure, and
variations in population size.
Range: population versus species range
(What’s a metapopulation?)
- Dispersion verses dispersal (PATTERNS. PROCESSES)
• Randomly spaced
• Individual has equal probability of occurring anywhere in an area
• Neutral interactions between individuals, and between individuals and local
environment.
• Uniformly spaced
• Individuals are uniformly spaced through the environment
• Antagonistic interactions between individuals or local depletion of resources
• Clumped
• Individuals live in areas of high local abundance, separated by areas of low
abundance
• Attraction between individuals or attraction of individuals to a common resource
How does the topic of ecology directly relate to human welfare, population health and
medicine?
“Ecological epidemiology is the study of the ecology of infectious diseases. It includes
population and community level studies of the interactions between hosts and their pathogens
and parasites, and covers diseases of both humans and wildlife.” Nature: International Journal
of Science
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“The U.S. Environmental Protection Agency (EPA) supports research on the linkages
between ecology and human health to facilitate sustainable and healthy communities.” 2016
“Natural features can modify adverse effects of noise, heat and pollution, and promote
healthful behaviours including physical activity and social interactions.”
Problems of Distribution and Abundance:
More widespread diseases that can diversify into different strains and can affect livestock etc.
Introduction of predator-proof electric fence made a wallaby population jump from 5 to 39
due to the introduction of the zone.
Lecture 2.
Biomes
Major life zones:
- Terrestrial biomes are most often characterised by the main vegetation type
• Climate is a major determinant
- Aquatic biomes by physical environment
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Biogeography
Abundance and diversity of organisms depends on available resources:
- Energy (light, temperature)
- Nutrients
• Water & Air – Sugars and fatty acids
• N, P – DNA, proteins
• K, Na – electrolytes
• S – proteins
• Mg – chlorophyll
• Ca – electrolytes and skeletal
• Micronutrients (Cl, Fe, B, Mn, I, Cu, Zn, Ni)
*what are limitations for biota in terrestrial ecosystems?
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Climate
Temperature, sunlight, wind and precipitation.
- Macroclimate – patterns on the global, ecosystem, and landscape levels
- Microclimate – finer scale patterns, e.g. community of organisms on a tree trunk
Distribution of Water
Major components of climate = temperature, sunlight, wind and precipitation
All four components affect the distribution and abundance of organisms in terrestrial
environments, but the availability of WATER is most important.
Movement of air determines the distribution of water on land (e.g. rain, snow, fog)
Movement of air follow some “simple” physical principals.
1. Hot air carries more water than cold air
a. When water is breathed out from 37*C to much lower temps – it precipitates
(from gas to water droplets)
2. Hot air moves up and cold air moves down
a. Cold air is more dense (molecules closer together) than hot air
b. What heats air? Energy radiating from a surface
3. Hopkins’ bioclimatic law: air cools as it rises
a. 180m higher = 100km closer to pole
b. E.g. climbing Telstra tower versus moving south towards pole
4. Coriolis effect: Longitudinal movement on a rotating object results in apparent
latitudinal drift
a. Deflection of air due to earth’s spin
b. It is warmer closer to the equator, because sunshine (heat energy) acts directly
rather than obliquely
c. Results in higher surface temps at equator compared to poles
Climate determines distribution
Major components of climate = temperature, sunlight, wind and precipitation
Long-term prevailing weather constitutes climate.
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Convection of air is determined by the incidence of sunlight. In general:
- At the equator and at 60* latitude ascending air releases water, resulting in an
abundance of vegetation
- At the poles and at 30* latitude, descending air sucks water away, resulting in deserts
Equator hotter than poles showing expected convections of air.
Equator hotter than poles showing realised driven convections of air.
Rotation from west to east drives winds (40000km/day at equator c.f. poles).
The direction of wind is determined by the Coriolis force.
- At the equator land rotates at 40,075km per day (1670 km/h)
- At the poles, the speed is ~0
- Winds are easterly in the tropics (trade winds)
- Winds are westerly in the temperate zones
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Intertropical Convergence Zone
Belt of low air pressure
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Since water has a higher heat capacity than land, the ITCZ propagates poleward more
prominently over land than over water, and over the Northern Hemisphere than over the
Southern Hemisphere.
What causes rain shadows?
Mountains obstructing the prevailing winds force air to move up. Air cools down as it moves
up, and loses its water content in the form of precipitation (rain, snow).
Air cools. Carrying capacity decreases.
Air warms again. Carrying capacity increases.
Bringing it all together
A few simple laws of physics result in the complex patterns of distribution and abundance
observed today.
Valid mainly for terrestrial ecosystems.
Lecture 3.
Use of energy
- Phototrophs
- Chemotrophs
- Radiotrophs
Energy Transfer
Photosynthesis
Cellular Respiration
The availability of biochemical energy (ATP) depends on air, water and sunlight.
Limits to primary production
On land, water, sunlight, and temperatures are the main limits to production.
In deep aquatic environments, what main limitations are there?
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Primary Production
Net production = Gross production – Respiration
Productivity is a measure of Ecosystems
Trophic levels: food chains
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Ecological Efficiency
Production efficiency = percentage of energy from a food source that is used for growth and
reproduction.
Waste
- Unassimilated energy
- Highest in herbivores
- Over 50% food consumed is not utilised
Growth
- Energy assimilated as biomass/reproduction
Cellular respiration
- Energy used to maintain life
- Cellular respiration is wasteful
- Highest in homeotherms
90% of energy is lost between trophic levels.
Ecological efficiency determines abundance
Pyramid of organism abundance
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Pyramid of biomass
Biomass
Rare, but if primary production has a high rate of replenishment (i.e. reproductivity or
growth), the biomass of consumers can be larger than that of producers.
Nutrients: Biogeochemical cycles
Energy flows through the biosphere
- But is lost at each tropic level
Nutrients cycle between trophic levels
- Gross availability =/ biological availability
Lecture 4.
Bioaccumulation/Biomagnification
Accumulating chemicals that
1. The body cannot eliminate (e.g. Pb, Hg)
OR
2. The body actively retains (by mistake)
Toxicity can be influenced by the number of trophic levels involved.
“Internal exposure to Sr-90 is linked to bone cancer, cancer of the soft tissue near the bone,
and leukemia” EPA
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Bioaccumulation of heavy metals.
Effects of Lead Poisoning:
- Brain or nerve damage
- Hearing problems
- Digestive issues
- Stunted growth
Resources drive abundance
The availability of energy and resources determines primary productivity.
The abundance of organisms depends on primary productivity in their ecosystem, their own
role and their ecological efficiency.
Primary production is the ultimate limiting factor on abundance at the ecosystem scale.
Factors that drive biodiversity:
- Island biogeography
- Competition
- Competitive exclusion
- Disturbance
Interactions drive diversity
Biodiversity is primarily defined as the number of species present.
The number of species is limited by the number of available niches.
Niches are limited by interactions with the environment and other species (e.g. realised
niche).
Evolutionary consequences of competitive interactions can be:
One species becomes extinct OR
Division of niche takes place
Island Equilibrium theory of Biogeography
Species diversity on “islands” will represent a dynamic balance between the probability of
successful colonisation by new immigrant species, and extinction of existing resident
species.
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Von
Humbolt: species area curve
Design of conservation reserves: the SLOSS debate
Single Large or Several Small?
Based on island biogeography theory
Why might some of these ideas be
contentious?
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Lecture 5.
Specialists v generalists
Specialists are ecologically more efficient than generalists at the cost of having a more
restricted fundamental niche.
When ample resources are available, specialists will usually out-compete generalists.
Specialists tend to be spaced more evenly along axes of resource distribution.
Specialists are less resilient to change (disturbance) than generalists.
Evolutionary time and competition is required for specialisation.
Specialists are ecologically more efficient than generalists, at the cost of having a more
restricted fundamental niche. E.g. Sanderlings versus Avocets, Curlews, Spoonbills, Wrybills
Fundamental versus realised niches
Specialists are less resilient to disturbance than generalists because of their restricted
fundamental niche.
Competitive exclusion
A competitive advantage, will eventuate in success … and extinction of the other species
(can be on a local scale). E.g. barnacles in different areas/heights of a rock during low tide.
Coping with disturbance
Disturbance limits the availability of resources.
Specialists are less resilient to disturbance than generalists because of their more restricted
fundamental niche.
No disturbance – Great Barrier Reef perfectly healthy
Maximal disturbance – Great Barrier Reef corals all dead/bleached/dredging etc.
Intermediate disturbance hypothesis
Diversity will be highest when interference prevents competitive exclusion, but is of low
enough intensity or frequency to allow many species to prosper.
The disturbance may be due to interaction with the environment (abiotic) or other species
(biotic).
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Predation can be disturbance
Chitons, limpets, mussels, acorn barnacles, gooseneck barnacles.
Starfish can eat muscles. Muscles can be outcompeted by barnacles.
*review slide e.g. placentals v marsupials – Wallace linie etc.
Lecture 6.
Community Ecology
So far we have covered:
- Island biogeography
- Specialists v generalists
- Competitive exclusion
- Disturbance
Next:
- Keystone species
- Red Queen Hypothesis
- Symbiotic interactions
- Hot spots of biodiversity
What drives Biodiversity?
Keystone species
Defined by having the largest number of interactions within an ecosystem.
Keystones can tip the balance.
Have a disproportionate effect on other organisms.
Can be at any level of the food chain.
Are considered vital in maintaining the diversity of ecosystems.
E.g. Prairie dogs
“Provide some unique functions not duplicated by any other species and that continued
decline of prairie dogs may lead to a substantial erosion of biological diversity and landscape
heterogeneity. A total of 117 species may have some relationship with prairie dogs. 208
species listed in the literature.”
E.g. maple trees
“In addition to its importance to the maple syrup industry… sugar maple is a keystone
species in the forests of the north-eastern and midwestern United States and eastern
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Canada. The decline in the health and numbers of sugar maples appears to be altering the
local ecology of those areas affected.”
Interactions drive diversity
Interspecific (= between species)
Can be positive (+), negative (-), or have no effect (O).
E.g.
Predation (+/- interaction)
Herbivory (+/- interaction)
Red Queen Hypothesis
An evolutionary arms race of survival
“It takes all the running you can do to keep in the same place” the Red Queen
E.g.
Gazelle running from cheetah
HIV
• “The vertebrate adaptive immune system provides a flexible and diverse set of
molecules to neutralise pathogens. Yet, viruses such as HIV can cause chronic
infections by evolving as quickly as the adaptive immune system, forming an
evolutionary arms race.”
Bacterial resistance
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Symbiosis
+/- Parasitism
+/+ Mutualism
+/O Commensalism
Biodiversity hot spots
On a global scale:
- >1500 species of endemic vascular plants
- Lost 70% of their original habitat
- 34 on the planet
Biodiversity
Are diverse communities better?
- Are they more resilient?
- Are they more productive?
Generally have more niches available, and so over evolutionary time, tend to be more
resilient to change – less likely to lose species in the long term.
‘As part of our National Cooperative Drug Discovery Group (NCDDG) research project,
numerous compounds from tropical rainforest plant species with potential anticancer
activity have been identified. Our group has also isolated several compounds, mainly from
edible plant species or plants used as dietary supplements, that may act as
chemopreventive agents.’ Life Science
CONCEPTS TO KNOW
- Island biogeography
- Competition: competitive exclusion, resource partitioning, character displacement
- Intermediate disturbance events
- Keystone species
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Red Queen Hypothesis
Symbiotic interactions
What are hot spots
Population Ecology
- Growth rates
• Exponential
• Logistic
- Carrying capacity
• Factors that influence population growth
The size of a population is determined by four parameters.
Sources of increase:
Birth
Immigration
Sources of decrease:
Death
Emigration
Growth rate / Population Growth
Growth rate (r) is determined by birth rates (b) and mortality rates (m).
b–m=r
If
r = 0 : no growth
r > 0 : population increase
r < 0 : population decrease
Intrinsic rate of growth (rmax) is the rate of growth with no extrinsic (limiting) factors
- rmax is characteristic of the species
Is exponential population growth sustainable
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Change in population size during a time interval
Number of births (B) – Number of deaths (D)
Change in N / Change in t = B-D
Where:
N = population size
t = time
Change in N / Change in t = bN – mN
B = bN
D = mN
Where:
b = offspring in a given time/indiv. In popn.
If N is 100 and there are 5 births (B); b = 0.05
Or if we know that “birth rate” per capita (b) = 0.05, then B = 5
So if:
r < 0 : decreasing
r = 0 : zero population growth
r > 0 : increasing
Exponential Growth
rmax = Intrinsic rate of growth
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rmax is expressed as per capita growth per year
K = the carrying capacity of the environment
At any time K – N individuals can be accommodated
So (K – N)/K individuals is the fraction of K that is still available for population growth
Logistic Growth
When N is smaller in value to K, per capita growth approaches 1 (high rate)
When N is large and resources are limiting, r max approaches 0 (low rate)
Logistic growth is sometimes a good model.
Density dependence
Density independent is when abundance is low e.g. rapid reproduction. - Exponential
Density dependent is when abundance is approaching K e.g. dependant on the density of
population. – Logistic
Summary
Populations cannot increase without limit: they are expected to converge on a carrying
capacity (K).
Understanding population regulation requires recognition of both intrinsic and extrinsic
factors. Consideration of:
- rmax
- Exponential and logistic growth
- K
- Fundamental niche and realised niche
K is determined by interactions with the environment and other species.
Rmax is determined by intrinsic factors such as vital rates.
Carrying capacity can be dynamic
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Lecture 7.
Life History Traits
Reflect evolutionary adaptations of:
- Reproduction strategies
• Number of offspring (e.g. compare pigs with beluga)
• Level of investment (e.g. compare kangaroo with kiwi)
- Age-specific distribution of reproduction and mortality
• Age of sexual maturity
• Senescence and death
Reproductive Strategies
- Number of offspring (chances?)
- Size of young (investment?)
Three types of survivorship
Type I survival – mortality accelerates with age
Type II survival – mostly constant mortality rate
Type III survival – mortality decelerates over typical life span
Optimising reproduction
1. When resources are limited, an increase in reproductive effort (and output) leads to
somatic costs (a reduction in investment in growth).
2. These somatic costs reduce future fecundity (the probability of surviving to breed
again).
3. There is a trade-off between current reproduction and residual reproductive value.
4. This trade-off is optimised by natural selection.
You cannot put all your resources into both reproduction and growth at the same time.
Trade-offs and Natural Selection
Life history traits: essentially depend on costs of reproduction
Every breeding episode results in costs – REPRODUCTION HAS COSTS
Is the investment worth the effort?
Impacts …?
Fitness.
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Levels of parental care differ
Precocial – birds e.g. ducks, chickens
Altricial – birds e.g. passerines (perching birds)
Think of it in terms of the level of dependency of the young: the more dependent the young,
the greater the parental investment required.
Optimising reproduction
General trends:
- Larger organisms tend to be slower to reach reproductive age
- E.coli ~ 20 minutes
- Elephant or human ~ 10-14 years
When might future reproduction be favoured over current reproduction?
When might current reproduction be favoured at the expense of future survival and
reproduction?
- When growing big is risky e.g. fish and mice
- When there is no going back e.g. long finned eels
Iteroparity vs. semelparity
Iteroparity – living to reproduce repeatedly such as with humans
Semelparity – plant and animal species that have life histories characterised by death after
first reproduction.
It is no coincidence that our three major seed plant crops breed and then die.
Extreme investment can be required for success
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Demographic Transition
Human societies change predictably from high birth and death rates to low birth and death
rates.
Birth rate equals death rate in stable populations.
What causes the Demographic Transition?
- Contraception?
- Cost of reproduction?
- Death rates decline first!
- Increasing wealth, health and education
- More competition for resources
- Reproductive success
Demographic Transition and population pyramids
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Population demography
1. Ecology and evolution interact to produce suites of life history traits (life history
strategies)
2. These influence age structure and growth of populations
3. Humans are not exempt from these influences
Life History Traits Summary
You cannot put all of your resources into both reproduction and growth at the same time
i.e. reproduction has consequences and costs
Some of those costs include:
- Parental care (many aspects), predation risk, physiological risk of damage, energetic,
etc.
Ecology and food biosecurity
1080 poison – sodium fluoroacetate – NaFC2H2O2
Knowing K (carrying capacity) is key to sustainability
Ecology in Medicine
Geographic distribution of Ebola virus disease outbreaks in humans and animals.
Natural medicines
Behavioural Ecology
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Ecology Review Questions
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The study of ecology is. …
Some examples of the applications of ecology
How can the study of ecology help you
Abiotic versus biotic
Distribution versus abundance
Landscape Ecology, Ecosystems, Community Ecology, Population Ecology,
Organismal ecology
By what general criteria are biomes usually identified?
What biomes are not present in Australia and where are they found globally?
Define organic versus inorganic resources, giving examples for each.
Give at least five examples of abiotic factors that affect distribution and/or
abundance of living organisms?
What main factors of climate contribute to distribution and abundance?
What constitutes precipitation?
Define the Coriolis affect.
Describe the main physical principles that contribute to the Coriolis affect
Why are deserts biomes more commonly found at around 30 degrees north or south
latitudes than anywhere else?
Why are many coastal areas often wetter than inland areas?
What is a primary producer and give some examples of how different organisms can
achieve that production.
Why are food chains often limited to no more than 5 levels?
How does energy transfer decline through food chains and why?
What does the measure of ecological efficiency refer to? How would this be a useful
concept for managers of agriculture? Consider both plant and animal farming.
Under what circumstances would current reproduction be preferential at the
expense of future survival and reproduction? Give examples
When would it be a good idea to put reproduction off for now? Give examples
Give an example of a reproductive trade-off.
Why is retaining natural biodiversity important to the medical fraternity?
Describe the difference(s) between exponential and logistic growth curves.
Populations cannot increase without limit: they are expected to converge on a
carrying capacity (K)
Understanding population regulation requires recognition of both intrinsic and
extrinsic factors
Consideration of : • rmax
o Exponential and logistic growth
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o K
o fundamental niche and realised niche
ECOLOGY MODULE
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Campbell’s Biology 11th
Edition:
Chapters 52-56
1258-1259 1275-1282
pp1265-1268; Section 54.4: island biogeography
pp1248-1250: competitive exclusion p1260: dominant and keystone spp
pp1262-1263; Section 54.3: disturbance
pp1249 -1255
pp 1220-1222 pp 1226-1229 pp 1236-1239
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