CHANGING POPULATION SIZESCHANGING POPULATION SIZES• Four Rates Determine Population Four Rates Determine Population

SizeSizeSize of a population changes through

timeoThere are 4 factors that determine population Natality = births Mortality = deathsImmigration = moving INEmigration = moving OUT

If a biologist counts 700 ponderosa pines in a If a biologist counts 700 ponderosa pines in a hill in Colorado in 1990, but counts 500 in hill in Colorado in 1990, but counts 500 in 2000, there was a 2000, there was a decreasedecrease in the population in the population Change can be expressed as a rate (rate = Change can be expressed as a rate (rate =

amount divided by certain amount of time)amount divided by certain amount of time) Ex: - 200 trees Ex: - 200 trees 10 years = - 20 trees per 10 years = - 20 trees per

yearyear Decrease may be due to fire, cutting, or Decrease may be due to fire, cutting, or

other meansother meansEither way, decrease represents Either way, decrease represents death death rate rate ((mortality ratemortality rate) of pine tree ) of pine tree populationpopulation

Mortality rateMortality rate: death in population : death in population per unit of timeper unit of time

Population of Ponderosa PinesPopulation of Ponderosa Pines

1990 2000(200 less)

Even though some trees die, some Even though some trees die, some are starting to grow from a seed, so are starting to grow from a seed, so it will increase the populationit will increase the populationIncrease represents reproduction Increase represents reproduction

increase called increase called birthratebirthrate or or natalitynatalityNatality rateNatality rate: birth in : birth in population per unit of timepopulation per unit of time

Death or birth rate is not only way Death or birth rate is not only way population can changepopulation can change ImmigrationImmigration – organisms moving INTO – organisms moving INTO

ecosystemecosystem EmigrationEmigration – organisms EXITING – organisms EXITING

ecosystemecosystem If no immigration or emigration is If no immigration or emigration is

allowed, it’s called a allowed, it’s called a closed populationclosed population If immigration and emigration are

allowed, it’s called an open populationopen population

Open SystemOpen Systemex: Pacific Ocean(organisms are free to immigrate and emigrate to other oceans)

Closed SystemClosed Systemex: aquarium

(organisms are not allowed to immigrate or emigrate [unless

owner intervenes])

if add all population limiting factors if add all population limiting factors together, get together, get growth rategrowth rate mortality rate + natality rate +

immigration + emigration = growth rate ex: studying number of frogs in Balboa Lake over 1 year’s timemortality rate = - 17natality rate = + 26immigration = + 7 (from people

dumping them off)emigration = - 6 (from people

catching them)

growth rate = (- 17) + (+26) + (+7) + (- 6) = +10Means we get 10 more frogs in

Balboa Lake each year, which means over 10 years, 100 more frogs will be there!

Balboa Lake

Population Density May FluctuatePopulation Density May Fluctuate In all populations, only certain amount of In all populations, only certain amount of

organisms that it can holdorganisms that it can holdo Balboa Lake can’t hold 10,000,000 frogs! Balboa Lake can’t hold 10,000,000 frogs!

There wouldn’t be enough food or water to There wouldn’t be enough food or water to sustain them allsustain them all How many frogs can it hold?How many frogs can it hold?

This is called This is called carrying capacitycarrying capacity, or amount , or amount of individuals an ecosystem can hold before of individuals an ecosystem can hold before it crashesit crashes

Like carrying books in your backpack, it Like carrying books in your backpack, it can only carry so many before it breakscan only carry so many before it breaks

o Sometimes population fluctuations occur Sometimes population fluctuations occur regularly with little knowledge of why they regularly with little knowledge of why they fluctuatefluctuate LemmingsLemmings (like big hamsters) increase (like big hamsters) increase

1,000 fold every 3 - 4 years1,000 fold every 3 - 4 years During big spikes in population, During big spikes in population,

lemmings frequently emigrate to other lemmings frequently emigrate to other areas where they can find food and areas where they can find food and shelter for survivalshelter for survival

SuccessionSuccession If certain ecosystem or environment If certain ecosystem or environment

gets destroyed by fire or flood or gets destroyed by fire or flood or something else, will it ever get back to something else, will it ever get back to its original form?its original form?o Yes, but it takes many years and it Yes, but it takes many years and it

happens in specific orderhappens in specific order Process of re-growth that follows Process of re-growth that follows environmental change is called environmental change is called successionsuccession

Two types of succession:Two types of succession:1. Primary succession1. Primary succession: occurs in : occurs in

area where no communities ever area where no communities ever existed beforeexisted beforeAfter volcano spreads lava, the area After volcano spreads lava, the area is barren and has no growthis barren and has no growth

After glacier recedes (melts away), After glacier recedes (melts away), land also is barren and has never land also is barren and has never had growthhad growth Both have Both have NO SOILNO SOIL, so must make soil , so must make soil

before land can grow anything. It can before land can grow anything. It can take years to make soil BEFORE take years to make soil BEFORE anything can growanything can grow

Causes of Primary SuccessionCauses of Primary Succession

< Glacier retreats (melts)

^ Volcanic eruption

2. Secondary succession2. Secondary succession: occurs : occurs following destruction of a communityfollowing destruction of a communityAfter fire, is still soil to support After fire, is still soil to support

growth, so re-growth doesn’t take growth, so re-growth doesn’t take very longvery long

Communities that grow after Communities that grow after succession happens in specific ordersuccession happens in specific order 1. 1. pioneer communitypioneer community

First plants to grow which are small shrubs and ferns that can tolerate lots of sun (no shade around) high temperatures

2. 2. seral stagesseral stages In between communities which are medium

shrubs, some trees3. 3. climax communityclimax community

Final stage which are lots of trees, shrubs, ferns, animals

Primary SuccessionPrimary Succession

a.No soil, barren land

b.Making soil

c.Lichens

d.Some shrubs

e.Some trees

f. Lots of trees

Pictures show growth after glacier has retreated

Lichens (white) with Moss (green) Fern

Shrub

Primary SuccessionPrimary Succession

Secondary SuccessionSecondary Succession

Notice that there is soil on the ground for seeds to take hold and grow

Secondary SuccessionSecondary Succession