CarryingCapacityandHumanPopulationGrowth

8/7/2019 CarryingCapacityandHumanPopulationGrowth

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Imagine our planet as a global bus

Suppose thata bus has

enough seats

for fiftypassengers

We would all agree that we could crowd a few extrapersons on board in an emergency


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C learly atsome point a

critical systemwould fail

The engine would overheatThe tires would blowThe axles would break The transmission would fail orThe engine would blow a gasket


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Why should we suppose that earths biologicaland ecological machinery is invulnerable?


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The number of members of a population an ecosystem cansupport over a long period of timewithout suffering severe or irreparable damage.

B iologists employ the term

wh ich is defined as follows


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Since ecosystemsare finite in sizeand resources,

each has an upperlimit to the

population that itcan support

Each also has an upper limit to its ability to providefood, resources, ecological services, maintain itself,

resist damage, and to accept, cleanse, and recycle wastes


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There are a variety of limiting factors

that play a role in regulating the ultimatesize of a population


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Limiting Factors

can be defined as: Those thingswhich preventa populationfrom growinginfinitely large.


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F ood supplies

are not always themost importantlimiting factors

Elephants, when confined, knock down trees,strip them of vegetation, and trample grasses and groundcover

Sometimes it is physicaldamage to the environment


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A n explodingpopulation of yeastcells in grape juice

generatepoisonous wastes

in the form of ethanol

Sometimes wastes are the mostimportant limiting factor


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A populationexplosion of algae ina pond can quicklydeplete the water of

its dissolved O 2

catastrophically changing the entire environmentto ano x ic conditions that kill most other life forms

eutrophication


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Population explosions of marine dinoflagellates canproduce deadly red-tides and fish-kills

Each dinoflagellatereleases tiny amounts of a poisonous neurotoxic

waste into theenvironment

A t some point, t h e environments capacity to dissipate,cleanse, and recycle t h e poisonous wastes is e x ceeded


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H uman body wastes are unlikelyto affect our entire planet


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B ut the collective impacts of all

our industrial and societal wastes,

S uc h as

represent significant c h allengesto eart h s ecological systems

C hlorofluorocarbonsH eavy metalsA cid rainNuclear wastes and R ising levels of greenhouse gases


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Today ourpopulation isalmost seven

billion


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A re there any Warning L amps beginning to light up on the global das h board ?

Oz one depletionGreenhouse gasesMelting iceAcid precipitationHunger and starvationDeforestationDisappearing wildernessCollapsing fisheries/dead z onesDesertificationMass extinctions of wild plants and animals


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D ead zone in Gulf of Mexico

The large region of lowoxygen, high nitrogenwater often referred to asthe 'Gulf D ead Zone,'shown here, crossesnearly 5,800 squaremiles of the Gulf of Mexico


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I f all these stresses are occurring now,

what will happen as we add three or moreadditional billions over the next half century?


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F inally, we arenot alone on our

global bus


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Other passengers (species)occupy much of the available seating


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Today, as more and more human passengersclimb aboard, these other speciesare being displaced at an accelerating rate


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S o just how fast has our speciesbeen growing?


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S o what does this look like?


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8000 BC 5 Million000 1 AD 250 Million1650 AD 500 Million1831 AD 00 1 B illion

1930 AD 00 2 B illion1960 AD 00 3 B illion1975 AD 00 4 B illion1987 AD 00 5 B illion1999 AD 00 6 B illion

Approximate

World PopulationYear

000 1 - 1650 = D oubled in 1650 yrs1650 - 1830 = D oubled in 0 180 yrs1830 - 1930 = D oubled in 0 100 yrs1960 - 2 000 = D oubled in 00 40 yrs


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H istorical D emographics

8000 BC 5 Million000 1 AD 250 Million1650 AD 500 Million1831 AD 00 1 B illion


Approximate

World PopulationYear

D o you see any patterns here?H ow long does it take for our numbers to double?


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N otice t h at it took all of h uman h istory until

1830 for us to reac h our first billion

A nd just 30 years toadd our third billion

Just 100 years to reachour second billion

8000 BC 5 Million0001 AD 250 Million1650 AD 500 Million1831 AD 00 1 B illion


ApproximateWorld PopulationYear


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Today we add anotherbillion persons to our population

every twelve to fifteen years

8000 BC 5 Million0001 AD 250 Million1650 AD 500 Million1831 AD 00 1 B illion


ApproximateWorld PopulationYear


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While nature h ad all of h uman h istory until 1830to adjust to the impact of our first billion,

today we are making the same demands(and more, because we are industrialized)

every twelve to fifteen years


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2013 7 B illion20 28 8 B illion2053 9 B illion

U.N. medium assumptions projectthe following for the decades ahead

What about the future?

CarryingCapacityandHumanPopulationGrowth

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