1. Populations
Wednesday, August 24th, 2016

2. Populations
= Individuals of a species that live in the same place at the same time
Are dynamic – constantly changing
Evolution occurs at this level

3. Population Dynamics
Population dynamics refers to changes in a population over time
Population dynamics includes four variables:
Age Distribution
Size
Density
Dispersion

4. 1. Age structure
The age structure of a population is usually shown graphically
The population is usually divided up into prereproductives, reproductives and postreproductives
The age structure of a population dictates whether is will grow, shrink, or stay the same size

5. Age structure diagrams
Pyramid
= + growth
Vertical edges = growth
Inverted Pyramid
= - growth

6. 2. Population growth Exponential Logistic
Populations show two types of growth
Exponential
Logistic

7. Exponential growth J-shaped curve
As early as Darwin, scientists have realized that populations have the ability to grow exponentially
All populations have this ability, although not all populations realized this type of growth
J-shaped curve

8. The graph at right shows what exponential growth looks like
Exponential growth is growth that is independent of population density

9. Doubling time/ Rule of 70 Doubling time is the amount of
time that is takes for a population
to double in size when growing
exponentially
It is calculated as
Doubling Time = 70 / percent increase
Ex. A rabbit population has an r value of 1.5, so the percent increase = 150%
D.T. = 70/150 = .46, or 5.5 months

10. Do all species enjoy exponential growth?
NO!
The exponential growth of most populations ends at some point
Two general outcomes can be observed….

11. 1. Populations increase so rapidly that they over shoot the pop size that the environment can support, and the pop size crashes
ex. reindeer

12. 2. Populations increase to some level, and then maintain that stable level
ex. sheep

13. What limits population growth?
Density-independent factors:
affect populations randomly (without respect to density)
ex. Hurricanes, tornadoes, fire, drought, floods
poor regulators of populations
Density-dependent factors:
affect populations when densities are high
ex. Disease, competition, predation, parasitism
good regulators of populations

14. Population Regulation/Logistic Growth
Most populations grow exponentially until the effect of density- dependent factors increases and limits population growth
S-shaped growth curve (logistic growth)

15. 1. The population experiences exponential growth.
2. Population size (and density) increases, the growth rate decreases.
3. The population approaches the carrying capacity, K, the number of individuals that the environment can support

16. 3. Population Density
Population density (or ecological population density) is the amount of individuals in a population per unit habitat area
Some species exist in high densities ex. mice
Some species exist in low densities ex. Mountain lions
Density depends upon
social/population structure
mating relationships
time of year

17. 4. Population Dispersion
Population dispersion is the spatial pattern of distribution
There are three main classifications
clumped: individuals are lumped into groups
ex. Flocking birds or herbivore herds
due to resources that are clumped or social interactions
most common

18. Uniform: Individuals are regularly spaced in the environment
ex. Creosote bush
due to antagonism between individuals, or do to regular spacing of resources
rare because resources are rarely evenly spaced
Random: Individuals are randomly dispersed in the environment
ex. Dandelions
due to random distribution of resources in the environment, and neither positive nor negative interaction between individuals
rare because these conditions are rarely met

19. Species Distribution Related to THREE things:
Fundamental Niche (abiotic conditions that it can tolerate)
Ability to disperse to a new area
Interactions with other species (symbiosis)

20. Interactions Among Organisms
Symbiosis
An intimate relationship between members of 2 or more species
Participants may be benefited, harmed or unaffected by the relationship
Results of co-evolution
Types: Competition, Predation, Mutualism, Commensalism

21. Competition
Interaction among organisms that vie for the same resource in an ecosystem
Intraspecific
Competition between individuals in a population
Interspecific
Competition between individuals in 2 different species

22. Limiting Resources
Any environmental resource that, because it is scarce or at unfavorable levels, restricts the ecological niche of an organism

23. Predation
Predation- the use of one species as a resource by another species.
True predators: the consumption of one species by another
Prey is killed by predator
Herbivores
Parasitism: relationship in which one species is benefited and the other is harmed
Parasites rarely kill their hosts

24. Mutualism A relationship in which both organisms benefit
Example: Honey guide birds alert and direct badgers to bee hives. The badgers then expose the hives and feed on the honey first. Next the honey birds eat. Both species benefit.
Example: Oxpeckers feed on the ticks found on a rhinocerous. The oxpeckers get a meal and the rhinocerous is helped by the removal of ticks.

25. Commensalism
A relationship in which one organism benefits and the other is not harmed nor helped.
Example: Barnacles attach to whales. Barnacles get a free ride, but it doesn’t affect the whales.
Example: A sparrow will build its nest under the next of the osprey. The smaller bird gets protection. The osprey is neither helped nor harmed.

26. Interactions between species and their effects
Type of Interaction
Species 1
Species 2
Competition -
Predation +
Mutualism
Commensalism