lsm2251-05 populations i

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05 PopulationsMolles, 4th edition (2007): Chapters 8 & 9= 5th edition (2009): Chapters 4 & 9

LSM2251Ecology & the Environment

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

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]

PART I.

POPULATIONSAND NATURAL

SELECTION

2. The process of natural selection3. Population genetics and Natural

Selection

De f ini t ions

• a group of individuals,

• of a single species,

• inhabiting a specific area,

• defined by natural or artificial boundaries.

“Population” – definitions• Population ecology - a group of individuals

of the same species inhabiting the same

• 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

2. The process of

natural selection

De f ini t ions

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

http://darwin-online.org.uk/2. The process of natural selection

•Mechanism of Inheritance?

• Darwin (1859) has no idea what the mechanism of inheritance was.

• Regarding mathematics - “the work was repugnant to

• 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.

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

Points to reflect on

• Observation

• Experimentation

• The right study subject

• A systematic approach

• Role of mathematics

• Collaboration

http://evolution.berkeley.edu/

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.

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.

1. Variation

2. Inheritance

3. Selection

4. Time

2. The process of

natural selection

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].

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.

Question

What is:

• the introduction and elimination of inheritedtraits of a population of organisms throughsuccessive generations as a result of genes

and the environment

3. Population genetics

and Natural Selection

Molle s Chap t e r 8 (4 t h Edn) ; Ch 4 (5 t h Edn)

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

1. Variation withinpopulations

Phenotypic variation among individuals in apopulation results from the combined effects of

genes and the environment.

3. PopulationGenetics and

Natural Selection

Phenotypic and genetic variation inPotentilla glandulosa

Clausen, Keck & Hiersey, 1940

Tom Hiltonhttp://www.flickr.com/photos/

tomhilton/2710780978/

Grows from 0 - 3,000m asl

• Grew clones of lowland, mid-elevation andalpine plants in three experimental

gardens: 30m, 1,400m and 3,050m asl.

Null hypothesis - there are no genetic differencesbetween populations, all plants would grow equally well.

The plants did not grow equally well(height, flowering)

There were genetic differences (variation)between o ulations.

Ph i d i i i i

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

Ph i d i i i i

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

Predict the outcome of populationsas a result of global warming

• What happens to the populations of lowland, mid-elevation and alpinespecies?

3 P l ti

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

Natural Selection

Covered inLSM1102Molecular

Genetics

Ada ti e chan e in Br n

Adaptive change in Brownanole Anolis sagrei

Losos, Warheit & Schoener (1997)

Carla Kishinamihttp://www.flickr.com/photos/kishlc/

3721231192/

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.

Ad i h i B l A li i

Adaptive change in Brown anole Anolis sagrei Losos, Warheit & Schoener (1997)

Colonising populations adapt rapidly!

Adaptive change in Brown anole Anolis sagrei Losos, Warheit & Schoener (1997)

Significance?

• Some species can adapt rapidly to newenvironments.

• Remind of you of any movies?

3 Population

Random processes, such as genetic drift, can

change gene frequencies in populations, especially

in small populations.

5. Change Due to Chance

Natural Selection

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

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.

Speciation in widelydispersed populations

Photo by AmandaFl b P l i

yTan, Pulau Ubin jetty,

04 Sep 2010Flower crab, Portunus pelagicusDistribution: Indo-west pacific

Portunus pelagicus is now four species (Lai et al 2010)

Portunus pelagicus is now four species (Lai et al ,, 2010)

WesternIndian Ocean

Bay of Bengal Australia

East & SouthEast Asia

Indian Ocean

WestPacificBay of

Bengal

East Asia

Southeast

Australia

SoutheastAsia

Portunus pelagicus is now four species (Lai et al,, 2010)

Portunus pelagicus is now four species (Lai et al ,, 2010)

WesternIndian Ocean

Bay of Bengal Australia

East & SouthEast Asia

PART II. POPULATIONDISTRIBUTION AND

ABUNDANCE

Applications in:

biogeography,conservation and management of

endangered species,aliens, pests and disease vectors,

climate change issues

Popula t ion dis t r ibu t ion and abundance

What is a population?

• a group of individuals,

• of a single species,

• inhabiting a specific area,

• defined by natural or artificial boundaries.

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.

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.

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.

Oriental pied hornbill on Pulau Ubin

Photo by eawtan, ClubSnap

http://www.clubsnap.com/forums/showthread.php?p=912250

Is the Oriental pied hornbill on Pulau

Is the Oriental pied hornbill on PulauUbin a metapopulation?

Are mangrove species at

Are mangrove species atMandai mangrove a subpopulation?

Ch i i f

Characteristic of a

population

• Distribution - let’s examine this now• Density

• Age distribution, rates of birth and death,immigration, emigration, growth etc

5. Environmental limits

to species distribution Limits imposed by physiology,behaviour and morphology

Popula t ion dis t r ibu t ion and abundance

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!

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.

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.

Aedes (Stegomyia) albopictus

The Asian tiger mosquito or forest day mosquito

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.

Distribution across a gradient:

Distribution across a gradient:rocky shore barnacles (Conell, 1961)

Calm seas,warm weather

Factors

• Optimal habitat - physical

• Competition - biological

IVLE: Weblinks

Local species of barnacles

IVLE: Weblinks

(Recess week)Consultation

IM: sivasothi@live.com

Email for appointments: sivasothi@nus.edu.sg

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