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05 PopulationsMolles, 4th edition (2007): Chapters 8 & 9= 5th edition (2009): Chapters 4 & 9
LSM2251Ecology & the Environment
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Lecture 05 – Populations
Topics
1. What is a population?2. The process of natural selection
3. Population genetics and Natural Selection[Molles 4th Edn - Chapter 8; 5th Edn - Chapter 9]
Part I - Populations & Natural Selection
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Lecture 05 – Populations
Topics
4. What is a population?
5. Environmental limits to species distribution
6. Distribution patterns
7. Applications to conservation
Part II - Population distribution and
abundance [Molles 4/5th Edn - Chapter 9]
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PART I.
POPULATIONSAND NATURAL
SELECTION
1. What is a population?
2. The process of natural selection3. Population genetics and Natural
Selection
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1. What is a population?
De f ini t ions
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1. What is a population?
• a group of individuals,
• of a single species,
• inhabiting a specific area,
• defined by natural or artificial boundaries.
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“Population” – definitions• Population ecology - a group of individuals
of the same species inhabiting the same
area
• Genetics - a group of interbreedingindividuals of the same species, which is
isolated from other groups• Human demography - a set of humans in a
given area
1. What is apopulation
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2. The process of
natural selection
De f ini t ions
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Charles Robert Darwin• English naturalist
• “On the origin of species,”1859 amongst others
• Theory of natural selection
• Modern evolutionarysynthesis
• Post-synthesis
• LSM3252 Evolution andComparative Genomics
2. The process of natural selection
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http://darwin-online.org.uk/2. The process of natural selection
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•Mechanism of Inheritance?
• Darwin (1859) has no idea what the mechanism of inheritance was.
• Regarding mathematics - “the work was repugnant to
me”
• He regretted this later, “for men thus endowed seem to have an extra sense”
•Mendel was a schoolboy when Darwin was exploring
the Galápagos Islands.
• His university education emphasisedexperimentation and provided a solidfoundation in mathematics.
2. The process of natural selection
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Mechanism of Inheritance?
• Gregor Mendel (1822-1884) worked with plants, mostfamously the garden pea, Pisum sativum.
• Domestic varieties showed great physical variation as aresult of underlying genetic variation .
• Use of manageable characteristics - seed form, stemlength, flower positions, etc.
• Discovered alleles - dominant, recessive forms.
Mendel’s failed to studyinheritance with bees.
His work was onlydiscovered later and
adopted in 1900
2. The process of natural selection
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Points to reflect on
• Observation
• Experimentation
• The right study subject
• A systematic approach
• Role of mathematics
• Collaboration
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http://evolution.berkeley.edu/
2. The process of natural selection
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http://evolution.berkeley.edu/
2. The process of natural selection
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Evolution
• Biological evolution = “descent withmodification” - is a change in gene frequencywithin a population over time.
• Small-scale evolution - changes in genefrequency in a population from one generationto the next.
• Large-scale evolution - the descent of differentspecies from a common ancestor over manygenerations.
2. The process of natural selection
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Natural selection?
• It is a key mechanism of evolution.
• The process by which heritable traits thatare likely to improve an organism’s chancesof survival and successfully reproduce
become more common in a populationover successive generations.
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VIST:
1. Variation
2. Inheritance
3. Selection
4. Time
2. The process of
natural selection
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VIST:
1. Variation - genetic variation upon which selectionworks [source: mutations, gene transfer between populations or
species (prokaryotes) and genetic drift]
2. Inheritance - genetic traits inherited fromparents and passed to offspring.
3. Selection - organisms with favourable traits
survive and pass genes on to the next generation.4. Time - evolution happens over generations [small-
scale], but speciation can take much longer [large-scale].
2. The process of natural selection
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Adaptation
• A feature (e.g. your molars are adapted to chewing)or a process
• The evolutionary process by which a population becomes
better suited to its habitat.
• Environmental pressure acting on variation amongstindividuals in populations results in adaptations.These are:
• changes in anatomy, physiology and behaviour
• improving the ability of members of a population
• to live in a particular environment.
2. The process of natural selection
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Question
What is:
• the introduction and elimination of inheritedtraits of a population of organisms throughsuccessive generations as a result of genes
and the environment
2. The process of natural selection
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3. Population genetics
and Natural Selection
Molle s Chap t e r 8 (4 t h Edn) ; Ch 4 (5 t h Edn)
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1. Variation within populations
2. The Hardy-Weinberg equilibrium
3. Natural selection
4. Evolution by natural selection5. Random processes
3. Population genetics
and Natural Selection
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1. Variation withinpopulations
Phenotypic variation among individuals in apopulation results from the combined effects of
genes and the environment.
3. PopulationGenetics and
Natural Selection
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Phenotypic and genetic variation inPotentilla glandulosa
Clausen, Keck & Hiersey, 1940
Tom Hiltonhttp://www.flickr.com/photos/
tomhilton/2710780978/
Grows from 0 - 3,000m asl
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• Grew clones of lowland, mid-elevation andalpine plants in three experimental
gardens: 30m, 1,400m and 3,050m asl.
Phenotypic and genetic variation inPotentilla glandulosa
Clausen, Keck & Hiersey, 1940
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Null hypothesis - there are no genetic differencesbetween populations, all plants would grow equally well.
Phenotypic and genetic variation inPotentilla glandulosa
Clausen, Keck & Hiersey, 1940
The plants did not grow equally well(height, flowering)
There were genetic differences (variation)between o ulations.
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Ph i d i i i i
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In alpine conditions,
• Lowland plants mostly died or fruits didnot mature.
• Mid-elevations populations survived poorlyand fruits did not mature.
Phenotypic and genetic variation inPotentilla glandulosaClausen, Keck & Hiersey, 1940
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Ph i d i i i i
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Ecotype
• Each ecotype performed best under conditions most
closely resembling its natural habitat.
• Each ecotype is genetically distinctive and is best
adapted to an optimal habitat (natural environment).
• Clausen postulated in 1951 that more than 100 genes
determine the morphological and physiological
differences allowing Potentilla glandulosa to adapt to its
respective environmental conditions.
Phenotypic and genetic variation inPotentilla glandulosaClausen, Keck & Hiersey, 1940
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Predict the outcome of populationsas a result of global warming
• What happens to the populations of lowland, mid-elevation and alpinespecies?
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3 P l ti
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4. Evolution by Natural Selection
The extent to which phenotypic variation
is due to genetic variation determines thepotential for evolution by natural
selection.
- for natural selection to produce evolutionary change, traits must be heritable
3. PopulationGenetics and
Natural Selection
Covered inLSM1102Molecular
Genetics
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Ada ti e chan e in Br n
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Adaptive change in Brownanole Anolis sagrei
Losos, Warheit & Schoener (1997)
Carla Kishinamihttp://www.flickr.com/photos/kishlc/
3721231192/
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Adaptive change in Brown
anole Anolis sagrei Losos, Warheit & Schoener (1997)
• Anolis lizards:
•Hind limb length long - run faster
• Hind limb length short - move efficientlyon narrow branches
• Source population: 5-10 lizards to 11 smallislands with no lizards and shortervegetation than source; 10-14 year waitbefore remeasure.
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Ad i h i B l A li i
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Adaptive change in Brown anole Anolis sagrei Losos, Warheit & Schoener (1997)
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Colonising populations adapt rapidly!
Adaptive change in Brown anole Anolis sagrei Losos, Warheit & Schoener (1997)
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Significance?
• Some species can adapt rapidly to newenvironments.
• Remind of you of any movies?
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3 Population
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Random processes, such as genetic drift, can
change gene frequencies in populations, especially
in small populations.
5. Change Due to Chance
3. PopulationGenetics and
Natural Selection
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Genetic variation in Island populationsFrankham (1997)
• Historically, extinction rates have beenmuch higher for island populations
•Did island populations have lower genetic variationcompared to mainland populations?
• Do endemic island populations have lower genetic
variation than non-endemic mainland populations?
• Literature:
• 202 comparisons of island vs mainland geneticdiversity; 38 endemic species studies
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Genetic variation in Island populations
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Genetic variation in Island populations
• Generally, genetic variation is lower insmaller, isolated islands
•Saccheri et al., 1998 working on Melitaea
cinxia butterflies showed:
• Highest inbred populations (lowheterozygosity) had the highest
probability of extinction.
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Speciation in widelydispersed populations
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Photo by AmandaFl b P l i
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yTan, Pulau Ubin jetty,
04 Sep 2010Flower crab, Portunus pelagicusDistribution: Indo-west pacific
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Portunus pelagicus is now four species (Lai et al 2010)
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Portunus pelagicus is now four species (Lai et al ,, 2010)
WesternIndian Ocean
Bay of Bengal Australia
East & SouthEast Asia
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Indian Ocean
WestPacificBay of
Bengal
East Asia
Southeast
Asia
Australia
SoutheastAsia
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Portunus pelagicus is now four species (Lai et al,, 2010)
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Portunus pelagicus is now four species (Lai et al ,, 2010)
WesternIndian Ocean
Bay of Bengal Australia
East & SouthEast Asia
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PART II. POPULATIONDISTRIBUTION AND
ABUNDANCE
Applications in:
biogeography,conservation and management of
endangered species,aliens, pests and disease vectors,
climate change issues
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4. What is a population?
Popula t ion dis t r ibu t ion and abundance
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What is a population?
• a group of individuals,
• of a single species,
• inhabiting a specific area,
• defined by natural or artificial boundaries.
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Ch f
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Characteristic of a
population
• Distribution - size, shape, location of
occupied area.
• Density - spacing of individuals/abundance.
• Age distribution, rates of birth and death,
immigration, emigration, growth etc.
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What is a subpopulation?[Molles, Chapter 10.2]
• A population may not occur as a singlecontinuously distributed population.
• It may instead occur in spatially isolatedpatches with significant exchange of indivduals among patches.
• Each patch is occupied by a subpopulation.
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What is a metapopulation?[Molles, Chapter 10.2]
• A group of subpopulations living onspatially isolated patches but exchangingindividuals through immigration or emigration collectively form a metapopulation.
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Oriental pied hornbill on Pulau Ubin
Photo by eawtan, ClubSnap
http://www.clubsnap.com/forums/showthread.php?p=912250
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Is the Oriental pied hornbill on Pulau
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Is the Oriental pied hornbill on PulauUbin a metapopulation?
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Are mangrove species at
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Are mangrove species atMandai mangrove a subpopulation?
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Ch i i f
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Characteristic of a
population
• Distribution - let’s examine this now• Density
• Age distribution, rates of birth and death,immigration, emigration, growth etc
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5. Environmental limits
to species distribution Limits imposed by physiology,behaviour and morphology
Popula t ion dis t r ibu t ion and abundance
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Eastern greykangaroo,
uniformly wet
Western greykangaroo,
wet winters
Red kangaroo,hot and dry
North:
Too hot!
North: Too
hot, winters
too dry!
North:Too wet!
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Global distribution (Robinson projection) of dominant orpotentially important malaria vectors. From Kiszewski et al., 2004.American Journal of Tropical Medicine and Hygiene 70(5):486-498.
Anopheles: 430 spp., about 40 spp. are vectors.
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Global distribution (Robinson projection) of dominant orpotentially important malaria vectors. From Kiszewski et al., 2004.American Journal of Tropical Medicine and Hygiene 70(5):486-498.
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Aedes (Stegomyia) albopictus
The Asian tiger mosquito or forest day mosquito
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Historicaldistribution of
AnophelesPredicted Australasian range map of Ae. albopictus.
From: Benedict, M. Q., R. S. Levine, W. A. Hawley & L. P. Lounibos, 2007. Spread of the Tiger: Global
Risk of Invasion by the Mosquito Aedes albopictus. Vector Borne Zoonotic Diseases, 7(1): 76–85.
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Distribution across a gradient:
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Distribution across a gradient:rocky shore barnacles (Conell, 1961)
Calm seas,warm weather
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Factors
• Optimal habitat - physical
• Competition - biological
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IVLE: Weblinks
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Local species of barnacles
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IVLE: Weblinks
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(Recess week)Consultation
Email for appointments: [email protected]