Ch 6 – Population Ecology

Special Topics

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Population CharacteristicsCharacteristic Why it matters ExampleSize Helps us understand how healthy the

population isCA condor population reached a critical low of 22 triggering the captive breeding program

Density Helps us understand how the population works together, how to protect them and how to manage resources and protections

Population densities can help us manage fish populations by setting limits in certain areas or designated MPAs

Distribution Helps us understand how the population works together, how to protect them and how to manage resources and protections

Clumped is the most common because resources are often clumped.

Sex ratio Varies by specie, but large imbalances can be concerning

China male : female ratio. Male preference has led to a sex imbalance in China which is resulting is social consequences

Age Structure Helps us understand how fast a population will grow. Lots of young usually indicates growth and lots of old indicates shrinking

The Amur leopard population currently has less than 20 adults and only 5-6 cubs indicating a serious decline

Biotic Potential• Factors that encourage a population to

increase under ideal conditions, potentially leading to exponential growth– Abiotic Contributing Factors:

• Favorable light

• Favorable Temperatures

• Favorable chemical environment - nutrients

– Biotic Contributing Factors:• High reproductive rate

• Generalized niche

• Ability to migrate or disperse

• Adequate defense mechanisms

• Ability to cope with adverse conditions

• Results in a J curve• Cannot be sustained over

a long period of time because resources are limited

Environmental Resistance• All the factors that act to limit the

growth of a population– Abiotic Contributing Factors:

• Unfavorable light• Unfavorable Temperatures• Unfavorable chemical environment - nutrients

– Biotic Contributing Factors:• Low reproductive rate• Specialized niche• Inability to migrate or disperse• Inadequate defense mechanisms• Inability to cope with adverse conditions

• Results in an S curve once carrying capacity is reached

• Populations that grow too fast may experience an overshoot and die-off

Metapopulations• When isolated populations have some level of interaction

– Occasional immigrants from larger nearby populations can add to the size of a small population and introduce new genetic diversity

– The number of species that exist as metapopulations is growing because human activities have fragmented habitats, dividing single large populations into several smaller populations.

– Identifying and managing metapopulations is thus an increasingly important part of protecting biodiversity.

Isle Royale Case Study• http://

www.wbir.com/video/2751732909001/1/The-plight-of-the-wolves-of-Isle-Royale

• Top down population control – when predators keep a population from growing as large as it could

• Bottom-up population control – when food availability keeps a population from growing as large as it could

http://www.isleroyalewolf.org/

Occupying the same niche• Partial niche overlap

– both compete in the overlapping parts of the niche.

– If the overlap is minimal, both species can coexist by specializing.

– Called resource partitioning.

• Full niche overlap– both compete directly for the same

resources– One specie will be more suited and out-

compete the other specie– Called the Competitive Exclusion Principle

http://zoology.muohio.edu/oris/cunn06/cs6_04.htm, http://www.biologycorner.com/APbiology/ecology/ch47_communities.doc

Resource Partitioning Examples

Species Interactions• The tickbird is eating

the ticks off the zebra. This partnership feeds the bird and keeps the zebra from having ticks sucking on it.

• What type of relationship is this?

Mutualism

Species Interactions• The seal has hunted and

captured the penguin for dinner

• What type of relationship is this?

Predation

Species Interactions• The anemone fish lives among

the forest of tentacles of an anemone and is protected from potential predators not immune to the sting of the anemone. The fish increases the water flow and provides more food for the anemome.

• What type of relationship is this?Mutualism

Species Interactions

• Commensalism

• Barnacles live on Grey Whales without harming the whale. Barnacles benefit because they feed on the water as the whale swims.

http://www.learner.org/jnorth/tm/gwhale/Hitchhikers.html

Species Interactions• The deer tick feeds off

of the blood of mammals and often transmits diseases such as lyme disease.

• What type of relationship is this?

Parasitism

Keystone Species• Sea Otters• http://

www.youtube.com/watch?v=0UryWICizN4

• Predator-mediated competition

• Elephants• http://ca.pbslearningmedia.org/r

esource/5071aea2-7262-4af2-894e-9d3af57d34f5/5071aea2-7262-4af2-894e-9d3af57d34f5/

• Ecosystem engineers

Succession• Succession is a series of changes that

occur as an ecosystem develops– Initial species are called pioneer

species – they set the stage for the appearance of other species eventually resulting in a climax community.

• Primary– succession that occurs on newly formed

soil– ex.: volcanic flows, glacier movement, etc

• Secondary– Succession that occurs post an ecological

disruption– Ex: post mining, post fire, post flood

Ecological Succession

http://bcs.whfreeman.com/thelifewire/content/chp55/55020.html

Human Impacts on populations1. Fragmentation and degrading habitat2. Simplifying natural ecosystems (monocultures)3. Interfering with primary productivity, thus altering food

webs4. Strengthening some populations of pest species and

disease-causing bacteria by overuse of pesticides5. Elimination of some predators6. Introduction of non-native species7. Over-harvesting of renewable resources8. Interfering with nutrient cycles9. Over dependency on non-renewable resources

Population Equations• Pop Change = (births + immigration) - (deaths + emigration)

• The growth rate is the rate at which a population is growing.• Growth Rate (%) = Birth Rate - Death Rate

10

– Birth rate = # of live births per 1000• Ex: if 50 babies are born per 1000 people, then the birth rate is 50.

– Death rate = # of deaths per 1000• Ex: if 25 people die per 1000, so the death rate is 25.

• Current Population size = Pop0 + (b + i) - (d + e)

• Zero Population Growth : (b + i) = (d + e)

• Nt = Noert (requires calculator so won’t be on AP EXAM!)

• Doubling Time = 70/Growth Rate (%)(no calculator needed)

Exponential growth is not realistic due to limited resources - Carrying capacity – the maximum number of individuals an ecosystem can support over a given period of time due to environmental resistance - Overshoots - usually occur due to a time lag – it takes time for the birth rate to fall and the death rate to increase

Reproductive Strategies• Goal of every species is to produce as many offspring as possible• Each individual has a limited amount of energy to put towards

life and reproduction• This leads to a trade-off of long life or high reproductive rate• Natural Selection has lead to two strategies for species: r -

strategists and K - strategists

r-strategists K-strategists• Focus on reproduction• Insects, bacteria, mice, rabbits• Have lots of offspring, but most will not survive to

adulthood• Short period of time between birth and

reproduction

• Focus on a long life• Elephants, humans, redwoods• Have few offspring and take care of them for a long

time• Long period of time between birth and

reproduction

R strategists• Many small offspring• Little or no parental care and

protection of offspring• Early reproductive age• Most offspring die before

reaching reproductive age• Small adults• Adapted to unstable climate

and environmental conditions

• High population growth rate• Population size fluctuates

wildly above and below carrying capacity (boom and bust)

• Generalist niche• Low ability to compete• Early successional species

K-strategist• Fewer, larger offspring• High parental care and protection of offspring• Later reproductive age• Most offspring survive to reproductive age• Larger adults• Adapted to stable climate and environmental conditions• Lower population growth rate• Population size fairly stable and usually close to carrying

capacity• Specialized niche• High ability to compete• Late successional species

Survivorship Curves• Late Loss: K-strategists - few young - care for young until

reproductive age - lowjuvenile mortality• Constant Loss: intermediate reproductive strategies with

constant mortality (birds)• Early Loss: r-strategists - many offspring - high infant mortality -

high survivorship once a certain size/age