Populations IB Topic 5.3. Populations How do populations grow and maintain themselves? Recap: A...
-
Upload
clyde-griffin -
Category
Documents
-
view
213 -
download
0
Transcript of Populations IB Topic 5.3. Populations How do populations grow and maintain themselves? Recap: A...
Populations
IB Topic 5.3
Populations
How do populations grow and maintain themselves?
Recap:A population is a group of individuals of the same
species that have the potential to breed with each other
Some populations are stable, some have rapid growth, some crashPopulations can vary greatlyWhy? What factors in an ecosystem control population
size?
Population growth
Think of the situation where a small number of young rabbits enter a large, well stocked meadowWhat would happen to the population size? What would eventually happen to the amount of
available resources? How might population growth be affected?
Population growth curve
If we were to graph this situation (# of individuals vs. time), the shape of the graph would be sigmoidal (S-shaped curve)
Figure 5.6 in your book
Lag phase
Stages of population growth
1. Lag phase Little or no growthPeriod of adaptability
2. Exponential growth or log phase Number of individuals
increases at a faster and faster rate
Lag phase
Stages of population growth
3. Transitional phase or linear growth Growth rates slows
down considerably Population is still
increasing
4. Plateau phaseNumber of individuals
has stabilizedNo more growth
Causes for exponential growth
Plentiful resources Food, space, light
Little or no competition from other inhabitants
Favorable abiotic factors Temperature, dissolved oxygen
Little or no predation or disease
Causes for the transitional phase
Increasing competitionPredators, attracted by a growing food
supply, start to move into the areaLimited space leads to opportunities for
disease to spread
Causes for the plateau phase
Less spaceLimited food supply
Results in less offspring
Predators and disease In this phase, the number of births = the
number of deaths No growth
Exponential growth cannot be maintained
Populations cannot continue to grow and grow forever
As a population increases, it begins to experience environmental resistance Space and resources are reducedCompetition increases
There comes a time in growth when its numbers stabilize
Carrying Capacity
The maximum number of individuals that a particular habitat can support is called the carrying capacity Represented by the letter K
If numbers start to increase above K, shortage of resources reduces the numbers of offspring producedPopulation regulates itself at the carrying capacityPopulations tend to be naturally self-regulating
Population Fluctuation
Most populations do not show significant fluctuations, but show varying degrees with time
Why?
4 main factors that affect population size
The birth rate (natality) variesThe death rate (mortality) variesMobile members move away (emigration)New members move in (immigration)
Which two factors cause population growth?Which two factors cause population decline?
Limiting factors can affect population size
Limiting factors define the carrying capacity of a habitat
Examples: Availability of resources (water, sunlight,
shelter, space, oxygen)Build up of waste (excrement or excess carbon
dioxide)PredationDisease
Two categories of limiting factors
Density-dependent limiting factorsRelated to population size
Competition for resourcesPredationDisease
Density-independent limiting factorsUnrelated to population sizeDrought, intense cold
What’s our carrying capacity?
Many biologists, environmental groups, economists, and governments wonder what is the carrying capacity of Earth for human population
We are in exponential growth phaseWill climate change, competition, and
disease lead to a transitional phase or plateau phase?
In conclusion
The size of a population depends on births, deaths, immigration, & emigration
Populations tend to follow sigmoidal-shaped growthLag phaseExponential phaseTransitional or log phasePlateau phase
The carrying capacity (K) is the max number of individuals that the region can support
Exit Slip
You need a sheet of notebook paperProper headingTitle: Populations Exit Slip
Exit Slip
1. Draw and label a population growth curve (also be sure to label the axis).
2. Suggest what factors might lead to an increase in a population of songbirds.
3. Suggest what factors might eventually limit the growth of that population.