1. Interactions in Populations
Chapter 14

2. Habitat and Niche Habitat Niche
All the biotic and abiotic factors in an area where an organism lives
Niche
All the physical, chemical, and biological factors needed to survive
Habitat is where an organism lives
Niche is how an organism survives
A niche includes food, abiotic conditions, and behavior (reproduction activities)

3. Habitat and Niche Competitive Exclusion Principle
Two species competing for the same resources
One will be better suited than the other
One species will be pushed into another niche
The reason you have this is because of the fact eventually there will be a winner and a loser
One species will somehow have an ever so slight advantage over the other species and will either go extinct or evolve.
This is also known as Gause’s law.

4. Habitat and Niche Secondary Outcomes of Competitive Exclusion
Niche Partitioning
Dividing the niche so two species can share
Evolutionary Response
Divergent evolution could take place to allow two species to survive

5. Habitat and Niche Ecological Equivalants
Similar species with similar niches in different geographical regions
Sign of convergent evolution
Emerald Tree Boa – South America
Convergent evolution – similar species must adapt to environments in different areas – kit fox and red fox
Green Tree Python - Australia

6. Community Interactions
Competition – when organisms try to use the same ecological resources
Resources – any necessity of life
Interspecific Competition
Intraspecific Competition
Direct competition will often result in a winner and a loser – eventually
Resources – water, nutrients, light, food, space
Interspecific – two different species compete for a resource - space
Intraspcific – members of the same species compete for a resource – water, birds with mates

7. Community Interactions
Predation – one organism captures and feeds on another
Predator
Prey

8. Community Interactions
Symbiosis – any relationship where two species live closely together
There are different types of symbiosis
mutualism
commensualism
parasitism
Symbiotic relationships are essential to any ecosystem

9. Community Interactions
Mutualism – both species benefit
Flowers and bees
Clownfish and anemones
Tangs and cleaner shrimp

10. Community Interactions
Commensalism – one species benefits the other is unharmed
Sharks and ramoras
Barnacles and whales

11. Community Interactions
Parasitism – one species benefits and the other is harmed
One organism lives in or on another organism harming it along the way
Tapeworms, fleas, ticks, lice

12. Population Density and Distribution
Characteristics of Populations
Geographic distribution – the area inhabited by a population
Population density – the number of individuals per unit area
Population – a group of individuals of the same species living in the same area
Four main characteristics of a Population – geographic distribution, population density, growth rate, and a population’s age.
Geographic distribution can range from a few centimeters to millions of square kilometers.

13. Population Density and Distribution
Population Dispersion
The amount populations are spread out in relation to one another
Clumped
Uniform
Random
Clumped – live close together in groups-facilitates mating, gains protection, access to food resources
Uniform – territoriality and intraspecies competition leads to this; specific distances from one another
Random – Random distribution around an area

14. Population Density and Distribution
Survivorship Curves
Number of individuals surviving over time
Type I
Type II
Type III

15. Population Density and Distribution
Type I
Common among large mammals
Low infant mortality
Generally long life

16. Population Density and Distribution
Type II
Birds, small mammals, some reptiles
Constant threat of death

17. Population Density and Distribution
Type III
Invertebrates, fish, amphibians, plants
High infant mortality rate

18. Population Growth Patterns
Population Growth – birth rate, death rate, or migration
Immigration – the movement into an area
Emigration - the movement out of a area
Populations may stay at or near the same amount for some time or they may fluctuate greatly over many years.
There are three factors that can affect the population size:
1. Births
2. Deaths
3. Movement into or out of the population.
Basically, a population varies based upon the number of individuals added or removed from the population.

19. Population Growth Patterns
Exponential Growth – individuals reproduce at a constant rate
Under ideal conditions, a population will grow exponentially.
Suppose a bacteria has a doubling time of 20 minutes – 1 will be come 2 in 20 min. etc.
In one hour there will be 64 bacteria, in one day there will be 4.7 x 1021 bacteria present
This is how you get infections that can be extremely serious.
If this were graphed out (number vs. time), the graph would look like a J
Due to the constant reproduction of individuals, the growth initially is very slow but eventually it will grow infinitely.

21. Population Growth Patterns
Logistic Growth – populations growth slows or stops following a period of exponential growth
Carrying capacity – the largest number of individuals that the environment can support
Population Crash
Exponential growth would result in the bacteria discussed covering the earth – obviously this hasn’t happened.
After a period of exponential growth, the population growth will start to slow due to resources not being as abundant.
This leads to an S-shaped curve which signifies logistic growth – exponential growth followed by logistic growth.
This is not to say there are not fluctuations in the population – the losses and additions just tend to average out.
There will be a point at which the number of individuals within an ecosystem is at a max – carrying capacity.
Population crash – a dramatic decline in the population due to a sudden drop in carrying capacity – could be due to a sudden drop in food amounts

22. Population Growth Patterns
Limiting Factors – something that causes population growth to decrease
Limiting factors can be food, pressure from predators, availability of shelters.
These particular factors can affect the long term survival of a species.

23. Population Growth Patterns
Patterns of Population Growth
Demography – the scientific study of human populations
Scientists have figured out that the population will not grow forever, but what will limit the growth or keep it in check?
There are certain criteria that that scientists look at to determine the growth – birth rates, death rates, age of the population

24. Population Growth Patterns
Demographic Transition – a dramatic change in the birth and death rates
U.S., Europe, and Japan
China and India
Because of advances in medicine and health, birth rates are starting to far outweigh the death rates – this leads to rapid increases in populations.
Eventually, as societies modernize, increase their education levels, and raise the standard of living then they have less children – this causes the birth rate to fall until it meets the death rate – this is when the demographic transition is complete.

25. Population Growth Patterns
Age Structure
What does it mean if there are lots of older people?
What does it mean if there are lots of younger people?
Age structure diagram
The graph in the middle suggests that a slow steady growth will occur
The graph on the left suggests that the population may double in the futures

26. Population Growth Patterns
Future Population Growth
Is the human population increasing?
Will the human population continue to increase forever?
What factors will cause the human population to slow?
The population is currently growing and may be over 9 billion by 2050

27. Population Growth Patterns
Density-dependent factors – limiting factor that depends on population size
This may include competition, predation, parasitism, and disease
These factors only come into play when the population reaches a certain size.

28. Population Growth Patterns
Density-independent factors – factors that affect all populations regardless of size
Weather
Natural disaster
Seasons
Human activities
Human interactions such as hunting, damming rivers and streams, or cutting down forests.

29. Ecological Succession
Often times when we view an ecosystem we look at it has always been the way it appears
However, every ecosystem is always changing – in response to human intervention, and natural occurences.
Not every thing dies at the same time or at the same rate.
This is what we call ecological succession - a series of predictable changes in the physical environment

30. Ecological Succession
Primary Succession – new species grow where no soil exists
This is the type of succession that occurred after Mt. St. Helens – the land was covered with volcanic ash and lava, there was no dirt.
The first species to populate an area under primary succession is called the pioneer species. Often these are lichens – organisms made from fungus and algae that are closely related to bacteria and can perform photosynthesis.
As these grow they will break up rock and create soil.

31. Ecological Succession
Secondary Succession – a disturbance changes the existing community without removing the soil
Land cleared by plowing for farming and then left abandoned
Also occurs when wildfires burn down forrests
Some seeds have even evolved to the point that they will not sprout unless exposed to fire