1. Ch 6 – Population Ecology
Special Topics
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2. Population Characteristics
Why it matters
Example
Size
Helps us understand how healthy the population is
CA 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
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

3. 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

4. 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

5. 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.

6. Isle Royale Case Study
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

7. 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

8. Resource Partitioning Examples

9. Mutualism 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

10. Species Interactions Predation
The seal has hunted and captured the penguin for dinner
What type of relationship is this?
Predation

11. Species Interactions Mutualism
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

12. Species Interactions
Barnacles live on Grey Whales without harming the whale. Barnacles benefit because they feed on the water as the whale swims.
Commensalism

13. Species Interactions Parasitism
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

14. Keystone Species Sea Otters Elephants
Predator-mediated competition
Elephants
Ecosystem engineers

15. 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

16. Ecological Succession

18. Human Impacts on populations
Fragmentation and degrading habitat
Simplifying natural ecosystems (monocultures)
Interfering with primary productivity, thus altering food webs
Strengthening some populations of pest species and disease-causing bacteria by overuse of pesticides
Elimination of some predators
Introduction of non-native species
Over-harvesting of renewable resources
Interfering with nutrient cycles
Over dependency on non-renewable resources

19. 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)

20. 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

21. 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

22. 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

23. 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

24. 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