Population evolution

Population evolutionPopulation evolution

Properties of PopulationProperties of Population

SizeDensityDispersion

Population sizePopulation size

Fundamental and important property of population but can be difficult to measure directly.◦Often too abundant, mobile, or widespread to

count.

Population DensityPopulation Density

Population density is the quantity of individuals living in a particular space.

Population DispersionPopulation Dispersion

Population ProfilePopulation ProfileAKA: Age StructureAKA: Age Structure

What would the data table for this look like?

Survivorship curvesSurvivorship curves

Type 1

Type 2

Type 3

Relative Age

What does each line

say about the

population?

Survivorship curveSurvivorship curve

Type 1: ex: humans: chances of death increase with age.

Type 2: ex: certain species of birds: probability of mortality does not change through out the lifespan.

Type 3: ex: sea turtles: chance of death is higher at younger ages. If they make it past this stage they stand a good chance to make it to old age.

Measuring PopulationsMeasuring Populations19.2

Population InfluencesPopulation Influences

Growth = births – deathsIncreased life expectancy: childhood

immunizations, vaccines, medications that prevent/maintain things like heart disease and diabetes, improved health care, etc.

This formula doesn’t take into account another factor of population growth: Immigration and emigration.

Mortality=death

Exponential Population Exponential Population GrowthGrowth

As long as births > deaths the population will grow• Even once births < deaths the population will take

time to level off or decrease because of the base number of individuals who are of reproductive age.

Population also grows faster if the start of reproduction is at earlier ages.

Once the environment reaches the maximum number of individuals it can support (K=carrying capacity)the population will level off.• Not true of human populations…they make choices

and can therefore change the dynamics of the graph.

Limiting factorLimiting factor

Any factor such as space which will limit the growth of an organism◦All populations are ultimately limited by their

environment.The logistic growth model is similar to the

exponential growth model except that it accounts for liming factors (carrying capacity=K)

Exponential growth with and Exponential growth with and without “K”without “K”

K

Logistic growth curve

Exponential growth curve

Limiting factor

Population FluctuationsPopulation Fluctuations• Predator populations follows close pattern to prey.

•If a new organism (for example another predator that is capable of eating the same prey) were artificially added the natural predator can be affected as can the prey population.•The new predator may eat more or less either dwindling the prey or causing it to “grow” out of control.

Density DependenceDensity Dependence

Density independent: Reduce the population by the same amount regardless of the size of the population◦Fire, flood, weather.

Density dependent: an individual’s chance of surviving or reproducing depends on the number of individuals in the area.◦Resources such as food, nesting space.

Perils of small populationsPerils of small populations

Small populations are more likely to be affected or even wiped out by such natural disasters as floods, fires, storms, or disease outbreaks.◦Can lead to too few individuals to maintain the

population.

California Condor

Human Population Human Population GrowthGrowth

19.3

Hunter/Gatherer PeriodHunter/Gatherer Period

What scientists learned from this time period:◦Small populations and high mortality rates lead

to slow growth.◦High infant and childhood mortality are

especially high factors in slowing population growth because they never make it to reproductive age.

Agricultural revolutionAgricultural revolution

What happened during this period?◦Agriculture greatly increased and stabilized

food supplies.◦Human populations began to grow faster.◦People had more children

Needed more hands to work the farm They weren’t as mobile so it made it easier to

have more children.

Industrial RevolutionIndustrial Revolution

After 1650:◦Sharp decline in death rates because of

improved sanitation, hygiene, control of disease, increased availability of food.

◦Birth rates remained high.

Environmental IssuesEnvironmental IssuesChapter 22 Section 2

Global WarmingGlobal Warming

What does this graph tell you?

•Shows a correlation between CO2 and global warming.

•Shows the concentration of CO2 in the atmosphere from 1880-2000.

Biological Biological MagnificationMagnification

EvolutionEvolutionLesson 15.1

LemarckLemarck

Supported the idea that populations changed over time, but thought that acquired changes would be carried to the next generation.◦Does a deer who looses an antler in a fight with

another deer pass that “lost antler” trait on to the next generation?

◦Lemarck thought it did.He also thought that individuals could acquire

traits within their lifetime due to experience or behavior.◦If you need fins, are you going to grow them?

DarwinDarwin

Proposed the theory of Natural selection◦Organisms may possess traits that make them

more suitable to their environment. Those individuals survive, pass on those traits to future generations. (survival of the fittest)

◦Requires genetic variation within a species.◦Is the process that leads to evolution (natural

selection over many generations)

Disruption of Genetic Disruption of Genetic EquilibriumEquilibrium

Lesson 16.2

Causes of evolutionCauses of evolution

Possible causes of disrupted genetic equilibrium:◦Mutation◦Immigration/emigration (migration)◦Genetic drift

Traits change as a result of random events or chance Happens more in smaller populations than in larger

ones.◦Artificial selection◦Nonrandom mating◦Small population size

Nonrandom MatingNonrandom Mating

Many times mate selection is determined by geographic proximity.◦May result in disorders caused by inbreeding.

Sometimes a mate is chosen because they possess similar traits: assortative mating.

Sexual Selection: In order to be selected by a mate, and leave offspring, an individual must possess extreme traits (like the plumage of a peacock)

Stabilizing SelectionStabilizing Selection

The “average” individual is best fit.Consider the hypothetical situation of the

lizard…Large ones may be more easily seen by predators, while small sized ones may be to slow to escaper predators…therefore it is the average sized individuals which may be best suited to the environment.

Disruptive SelectionDisruptive Selection

Individuals with the extreme variation of a trait have a greater chance of survival than the one with the average variation.◦Therefore individuals with short fat beaks and

those with long narrow beaks would survive, but those with average length beaks die out on an island with flowers and nuts.

Directional selectionDirectional selection

Individuals that display a more extreme form of a trait have greater fitness than an individual with an average trait.◦For example when anteaters feed, they push

their sticky tongue into the nest of termites. The longer the tongue the more fit the anteater.

Formation of SpeciesFormation of SpeciesLesson 16.3

SpeciationSpeciation

The process of species formation that results in closely related species.◦Some are very similar to their shared ancestor.

Biological Species ConceptBiological Species Concept

Proposed by Mayr, a species is an interbreeding population that cannot breed with other groups.

Isolation and SpeciationIsolation and Speciation

Geographic Isolation: Physical separation of members of a population.◦When the original habitat becomes physically

separated.Reproductive Isolation: May sometimes

arise through disruptive selection where the two extremes are selected for and as time passes, the two subpopulations can no longer interbreed.

Rates of SpeciationRates of SpeciationGradualism: speciation occurs at a

regular, gradual rate.Punctuated equilibrium: Speciation occurs

at a rapid pace.◦What is rapid in evolution?◦A few thousand years rather than a few million.

CoevolutionCoevolution

Two or more species become adapted to each other’s presence over a period of time

Divergent: one species becomes two separate subpopulations.◦Artificial selection has been used by humans to

speed up this process.

Convergent: two species develop similarities even though they come from two very different ancestors.