1. How Populations Grow Chapter 5 Section 1

2. Let’s Review! WWWWhat is a population? A group of similar organisms that can breed and produce fertile offspring Species or not a species?

3. Characteristics of Populations  Populations often change due to a variety of influential factors  There are three important characteristics of a population. 1. Geographic distribution – the range of area inhabited by a population

4. Characteristics of Populations 2. Population density – the number of individuals per unit area

5. Population Density  Can vary tremendously depending on the species and its ecosystem  A fewsaguro cactus  A few saguro cactus  A field of sunflowers  A flock of birds  Turtles grouped to sun

6. Population Density  What are some benefits of living close together or in a clumped population? 1. Help finding food 2. Protection from predators or wind 3. Easier to find species

7. PopulationDensity  What are some drawbacks (negatives) of living in a clumped population? 1. Crowded living areas 2. Battles over food/shelter 3. Easier for disease to spread

8. Characteristics of Populations 3. Growth rate- the amount by which a population’s size changes in a given time

9. Population Growth  Three factors affect population size 1. Number of births 2. Number of deaths 3. Number of individuals that enter or leave

10. Population Growth  Migration- periodic movements of populations away from and back to their place of origin (not what we are talking about here) (not what we are talking about here)  Irregular movements of some individuals out of an area, into a new area, with no return - affects population size  Immigration – movement of individuals into an area  Population increases in size  Emigration – movement of individuals out of an area  Population decreases in size

11. Population Growth  Why would an animal immigrate to or emigrate from a population? Competitive pressures on some individuals Competitive pressures on some individuals To find food, better living condition, or a mate To find food, better living condition, or a mate

12. Exponential Growth  If a population has plenty of food and space and is protected from predators and disease, what will happen to the size of the population? It will increase! It will increase!

13. Exponential Growth  Example: Bacteria  reproduce in ~20 minutes by splitting in half 1 bacteria after 20 min = 2 bacteria 1 bacteria after 20 min = 2 bacteria 2 bacteria after 40 min = 4 bacteria 2 bacteria after 40 min = 4 bacteria 4 bacteria after 60 min = 8 bacteria 4 bacteria after 60 min = 8 bacteria In 180 min (3 hours) = 512 bacteria In 180 min (3 hours) = 512 bacteria In one day = 4,720,000,000,000,000,000,000 bacteria In one day = 4,720,000,000,000,000,000,000 bacteria

15. Exponential Growth  Exponential growth occurs when the individuals in a population reproduce at a constant rate Creates a “J” shaped curve Creates a “J” shaped curve Under ideal conditions with unlimited resources and no predation, a population will grow exponentially Under ideal conditions with unlimited resources and no predation, a population will grow exponentially This is what a graph of bacterial growth would look like if the growth went unchecked

16. Logistic Growth  Do bacteria cover the planet?  Exponential growth does not continue in populations very long.  As resources become less available, the growth of a population slows or stops  What might cause population growth to stop or slow down? Predators, less food, less space, less resources, loss of habitat, disease, etc. Predators, less food, less space, less resources, loss of habitat, disease, etc.

17. Logistic Growth  Logistic growth occurs when a population’s growth slows or stops following a period of exponential growth Creates an “S” shaped curve Creates an “S” shaped curve  Population growth may slow or stop for a number of reasons: Birthrate ↓ death rate ↑ immigration ↓ emigration ↑ Birthrate ↓ death rate ↑ immigration ↓ emigration ↑  At some point, the growth of a population will level off

18. Logistic Growth Time (hours) Number

19. Logistic Growth  Occurs after a period of exponential growth  When a population reaches carrying capacity

20. Logistic Growth  Carrying capacity – the largest number of individuals an environment can support Most plant and animal populations follow this type of growth Most plant and animal populations follow this type of growth Time (hours) Number of Yeast Cells Carrying capacity

21. Comparing Exponential and Logistic Growth

22. Limits to Growth LLLLimiting Factor: any factor that causes population growth to stop LLLLimits the size of a population AAAAlmost anything can be a limiting factor… EEEExamples: competing for sunlight, space, water, food, etc. PPPPredation, parasitism, disease, natural disasters, etc.

23. AAAAs a population increases, so does competition NNNNot all individuals will get what they need to survive and will die TTTThe number of births decreases and the number of deaths increases The population gets smaller

24.  Plant roots compete for space, nutrients, and water with the roots of other plants  Taller plants block out sun for shorter plants

25. Limiting Factors of Growth  Limiting Factor-a factor that causes population growth to decrease. Two types: Two types: 1. Density Dependent Factors 1. Density Dependent Factors 2. Density Independent Factors 2. Density Independent Factors

26. Density-Dependent Factors  Density-dependent limiting factor- a limiting factor that depends on population size.  Density-dependent factors become limiting only when the population density--the number of organisms per unit area-- reaches a certain level. Density-dependent factors include: Density-dependent factors include: 1. competition1. competition 2. predation2. predation 3. parasitism and disease3. parasitism and disease

30. Competition  When two organisms compete over the same limited resource

31. Predation  When one organism captures and feeds on another organism

32. Parasitism and Disease  When a parasite or disease needs close contact to be spread from organism to organism

33. Density-Independent Factors  Density-independent limiting factors- affect all populations in similar ways, regardless of the population size. Density independent factors include: Density independent factors include: Unusual weatherUnusual weather Natural disastersNatural disasters Seasonal cyclesSeasonal cycles Certain Human ActivitiesCertain Human Activities

37. Density-Independent Factors  A limiting factor that affects a population in similar ways regardless of the population’s size  Examples: Weather (Seasonal Cycles) Weather (Seasonal Cycles) Human Activities Human Activities Natural Disasters Natural Disasters

38. Weather (Seasonal Cycles)  Extreme Cold or Heat  Winter Frost  Heavy Rainfall

39. Human Activities  Deforestation  Hunting  Buildings and Roads

40. Natural Disasters  Hurricanes, Tornados, Flooding  Earthquakes, Mudslides, Forest Fires