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EcologyThe driving force for

natural selection


General Ecological Components

Ecology – study of the interaction among organisms and between organisms and their environment

Population – all the individuals of a species in a given area Niche – an organisms “occupation” how it gets its resources for survivalHabitat – the “workplace” environment where an organism finds its resources


Types of Niches

Producer- energy from sunPhotosynthetic organisms: plants, algae, cyanobacteriaCapture sun’s radiant energy


Types of Niches

Consumers- energy from other organismsHeterotrophic organisms: animals, fungi, bacteriaMost diverse group- mostly insects


Types of Niches

Decomposers/Recyclers- energy from deathHeterotrophic organisms: fungi, animals, bacteriaFungi and bacteria only organisms to decompose woodMycorrhizal fungi help most plants recycle phosphorus


Only 2% of Solar Radiation captured by plants

meter2

SUN1,700,000kcal/m2/yr

Lost Energy1,680,000kcal/m2/yr

Captured Energy20,800 kcal/m2/yr


Each consumer level gets 10% of Energy

63% producers

24% recyclers

11% herbivores

<15% consumers

1.2% 2nd carnivores

0.1% 1st carnivores


13.1 Population Structure

Population dispersion – how a population is distributed in space.

Clumped – high densities in resource-rich areas, low densities elsewhereUniform – spacing between individuals tends to be equalRandom – no compelling feature pushing individuals together or apart

Figure 13.2


13.1 A Growing Human Population -Population Growth: An Overview

Archaeologists have been able to estimate the size of human population to about 10,000 years ago

Human population is an example of exponential growthExponential growth is in proportion to population sizeAs population grows, growth also increases

Figure 13.3

1999: 6 billion

2007: 6.6 billion

1970: 4 billion

1930: 2 billion

1800: 1 billion

Dawn of Christianity: 250 million

Egyptian empire: 100 millionAgricultural era: 5 million

Year

Hum

an p

op

ula

tio

ns (

bil

lions)


13.1 A Growing Human Population - A Closer Look: Population Growth

Historically, human population growth rate has been lowGrowth rate was ~0.1% per year 2000 years agoBy 1750 growth rate was ~2% per yearCurrently growth rate is ~1.2% per yearCurrent population of earth 6.6 billion, at 1.2% growth rate this means population increases by 77 million people/year


13.1 A Closer Look: Population Growth

Consider growth rate as time it takes a population to double

Figure 13.4bGrowth rate (% increase per year)

(b)139

70

4735

28Tim

e u

nti

l p

op

ula

tio

nd

oub

les (

ye

ars

)


13.2 Limits to Population Growth

Studies of non-humans species show that no population can grow to unlimited numbers

Elk in Yellowstone Park in 1970s had high mortality after large population degraded environmentNorway lemmings population grows so large that resources become scarce and population undertakes mass migration


13.2 Limits to Population Growth - Carrying Capacity and Logistic Growth

Populations have the potential to grow exponentially, but they are limited by environmental resources – food, water, shelter, and space.Carrying capacity – the maximum number of individuals that can be supported indefinitely in a given environment

Figure 13.6

NoGrowth

Carrying capacity

Time

Po

pu

lati

on

siz

e


13.2 Limits to Population Growth - Carrying Capacity and Logistic Growth

Limits on population growth:Density-dependent factors – factors that increase with population size

Limited food supply, increased risk of disease, increase in waste levels Can cause decrease in birth rates, increase in death rates, or both

Density-independent factors – not influenced by population numbers

Droughts, temperature extremes, natural disasters


13.2 Limits to Population Growth - Earth’s Carrying Capacity for Humans

There is uncertainty about future human population growth rates

Human population growth rates at highest in 1960s, ~2%Growth rates now about 1.2%Unclear what future trends are, UN has released 3 projections

Figure 13.8

Year

Medium growth rate

High growth rate

Low growth rate

Hu

ma

n p

op

ula

tio

n (

bil

lio

ns)



Signs that the Earth is Not Near Carrying Capacity

One reason for declining growth rates is choiceEarth’s resources can be measured by net primary productivity – the total amount of plant growthEstimates of net primary productivity indicate that a human population of 20 billion could be supported

This assumes that all plant growth fed humans and nothing else



Signs that the Population is Nearing Carrying CapacityPopulations require more than simply food, thus NPP estimates might be too high.

Difficult to estimate population impact on water supplies. Humans need certain amount of water, but also produce waste.Many essential supplies are non-renewable resources.Material consumption is affected by lifestyle and affluence.

USA accounts for ~5% of world’s population but consumes 24% of resources.


13.3 The Future of the Human Population - A Possible Population Crash?

The cycle of growth beyond carrying capacity leads to population crashes and, sometimes, rebounds.

Figure 13.11

Boom-and-bust cycle may persist… …or population may stabilize at carrying capacity.

Boom

Crash

Carryingcapacity

Time Time

Po

pu

lati

on

siz

e


13.3 The Future of the Human Population - A Possible Population Crash?

Avoiding ExtinctionFor humans, other factors also affect population growth rate, including income and social policies can have large impacts on human population growth.The question of how many people the earth can support is not just one of science, but of values and ethics.


Symbiotic RelationshipsRole in community development

Symbiosis= Two or more species living together1. Parasitism= one species using another solely

for its own advantage. Often pathogenic but rarely virulent. The parasite weakens the host.

2. Commensalism= two species interacting in which one species benefits without harm to the other.

3. Mutualism= two species interacting in which both benefit to enhance survival.



Parasitism= one species using another solely for its own advantage. Example Malaria caused by a protozoan that livesin the blood.



Commensalism= two species interacting in which one species benefits without harm to the other.

Example The mosquito vector

transmitting the malaria parasite


Symbiotic RelationshipsRole in community developmentMutualism= two species interacting

in which both benefit to enhance survival.

Examples Mycorrhizae= fungi infecting plant roots to trade P for plant & C for fungus

Lichens= fungi and algae acting as a single organism


14.1 The Sixth Extinction - The Causes of Extinction

The most severe threats to species loss come from four general categories:

Loss or degradation of habitatIntroduction of non-native speciesOverexploitationPollution


14.1 The Sixth Extinction - Habitat Destruction

As human population increases, pressure on natural areas increases

Species area curve – the number of species that a natural area of a given size can supportHabitat destruction not limited to rainforests; freshwater lakes and streams, grasslands, and temperate forests are also threatenedIf worldwide habitat destruction continues at present rate, as many as 25% of world’s species could become extinct


14.1 The Sixth Extinction - Habitat Fragmentation

Usually human activity results in habitat fragmentation –large natural areas subdivided into smaller areas

Large predators are threatened because they require large home ranges

Figure 14.5b


14.1 The Sixth Extinction - Introduced Species

Introduced species –non-native species introduced to a new area either purposely or accidentally by human activity

Often destructive because they have not evolved with local speciesBrown tree snake, introduced to Guam, caused many local bird species to go extinctDomestic cats in Wisconsin kill 39 million birds/year

Figure 14.5c


14.1 The Sixth Extinction - Overexploitation

When human use of a natural resource exceeds its reproductive rate, overexploitation occurs.

Can occur if species is highly prized by humans, which can spur illegal hunting.Can also occur if species competes with humans (i.e., wolves and ranchers)


14.1 The Sixth Extinction - Pollution

The release of poisons, toxins, excess nutrients, and other waste products –pollution – is another threat to biodiversity.

Excess fertilizer runoff leads to eutrophication of waterwaysEutrophication is the excess growth of bacteria that depletes oxygen from the waterCarbon dioxide is another atmospheric pollutant, associated with climate change


14.2 The Consequences of Extinction - Loss of Resources

Loss of species can lead to economic impacts for humans

Some biological resources harvested directly include wood (lumber and fuel), shellfish (protein), and algae (gelatin)Wild species provide biological chemicals (medicines)Wild species have alleles that are not present in domestic species, which can increase vigor of domesticated speciesWild species can contribute other means of combating pests (biological control)

Figure 14.11


14.2 The Consequences of Extinction -Keystone Species: How Wolves Feed Beavers

Keystone species are key figures in determining the food web of an ecosystem

Wolves were eradicated from Yellowstone Park in 1920sWith wolves gone, biologists noted declines in aspen, cottonwood, and willow treesTrees declined due to predation by elk Trees are crucial for beavers, songbirds, and fishWith reintroduction of wolves, trees and other species rebounded


14.2 The Consequences of Extinction -Disrupted Energy and Chemical Flows

Energy flow - only a small portion ( ~10%) of the energy in one level of a trophic pyramid can be converted to biomass at the next levelDiversity also affects energy flow, such as in more diverse grasslands, more biomass is produced

Figure 14.8

About 10% of energy takenin by deer is available tomountain lion.

About 10% of energytaken in by grass isavailable to deer.

Biomass in grass population

Biomassin mountain lions

Biomassin deer

population


14.2 The Consequences of Extinction -Disrupted Energy and Chemical Flows

The soil community has an important role in nutrient cycling

Introduction of non-native earthworms in NE U.S. had dramatic impact on forest plantsNon-native worms changed the soil community

Figure 14.19


14.3 Saving Species - Protecting Habitat

Less than 2% of the earth’s surface contain up to 50% of the earth’s mammal, bird, reptile, and plant species. These areas are biodiversity hotspots.

Figure 14.21

Brazil’sCerrado

Brazil’sAtlanticCoast

TropicalAndes

Cape FloristicProvince

W. AfricanForests

MediterraneanBasin

Caucasus

SouthwestAustralia

New Zealand

Philippines

India-Burma

South CentralChina

NewCaledonia

Polynesia/Micronesia

SucculentKaroo

WesternGhats andSri Lanka

Wallacea

Madagascar

Tanzaniaand

KenyaSundaland

CaliforniaFloristicProvince

Mesoamerica

Diversity hot spots

CentralChile

Choco/Darien

WesternEcuador


Caribbean


MediterraneanBasin

Tanzaniaand

Kenya



14.3 Saving Species - Protecting Habitat

Decreasing the Rate of Habitat DestructionConverting wild areas to agricultural production is a major cause of habitat destruction.

Altering our consumption patterns can help decrease habitat destruction.Eating low on the food chain (less meat and dairy) makes a difference.Increased financial aid to developing countries can also help.So can slowing human population growth rate.

Ecology - hirrel.com · ... study of the interaction among organisms and between organisms and ... Consumers- energy from other organisms ... Keystone species are key figures in

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