1. 5 POPULATIONS

2. 5.1 HOW POPULATIONS GROW

3. Describing Populations
-researchers study populations' geographic range, density, and distribution, growth rate, and age structure.
-involve dramatic changes in the size of a population.

4. - area inhabited by a population is called its geographic range
-a populations range can vary enormously in size, depending on the species
-a hydrillas natural range is Korea, while humans have carried it through every continent

5. Growth rate
-A population’s growth rate determines whether the size of the population increases, decreases, or stays the same.
-Hydrilla populations in their native habitats have a growth rate of around zero
-Cod populations decrease with size

6. Age Structure
- age structure is the number of males and females of each age structure.
-most plants and animals cannot reproduce until they reach a certain age
-among animals, only females can produce offspring.

7. Population Growth
-A population will increase or decrease in size depending on how many individuals are added to it or are removed from it.
- Factors that can affect population size are birthrate, death rate, and the rate at which individuals enter or leave the population

8. Birthrate and Death Rate
-Populations grow if more individuals are born than die in any period of time
- A population can grow when its birthrate is higher than death rate
- If the death rate is greater than the birth rate the population is likely to shrink

9. Immigration and Emigration
-immigration is when a population moves into its range from elsewhere
-emigration is when a population may decrease in size when individuals move out
- young animals approaching maturity may emigrate from their native areas

10. Exponential Growth -the larger a population gets, the faster it grows
-under ideal conditions with unlimited resources, a population will grow exponentially

11. Organisms that reproduce rapidly
- If you the size of a population over time you get a J-shaped curve
- It rises slowly at first then faster and faster
- If nothing interferes, the populations becomes larger at a faster rate

12. Organisms that reproduce slowly
- Many organisms grow faster than bacteria
- Newborn elephants take 10 years to mature
- If exponential growth continues, the results would be impossible

13. Organisms in new environment
- Sometimes when an organism is moved to another environment, a population grows exponentially
- Gypsy moths were accidentally released from a laboratory in Boston
- They devoured the leaves of many acres

14. -bacteria, elephants, hydrilla, and moths don’t cover the earth
Logistic Growth
-natural populations don’t grow exponentially for long
-bacteria, elephants, hydrilla, and moths don’t cover the earth

15. Phases of Growth
-after a short time, the population begins to grow exponentially
-in real world populations exponential growth does not continue for long’
- at some point the population growth drops to zero

16. The logistic growth curve
-occurs when a populations growth slows and then stops following a period of exponential growth
- population growth may slow for several seasons
- growth may also slow as death rate increases

17. Carrying Capacity
-maximum number of individuals of a particular species that a particular environment can support
- when immigration equals emigration, population growth stops
- on a graph, the point at which the horizontal line intersects the y-axis represents the carrying capacity

18. 5.2 Limits to Growth

19. -factor that controls the growth of a population
Limiting Factors
-factor that controls the growth of a population
-limiting factors determine the carrying capacity of an environment for a species

20. Density-Dependent Limiting Factors
- Operate strongly when population density reaches a certain level
Factors include, competition, predation, herbivory, parasitism, disease, and stress

21. - Competition of animals for food, water, and space
- Competition is a density-dependent limiting factor
- May occur among members of different species who want the same overlapping resources

22. Predation and Herbivory
- Populations of predators and prey may cycle up and down over time
- From a plants perspective, herbivores are predators
- Human activity limits population

23. Parasitism and disease
-parasites feed at the expense of their host
- the denser the host population, the most parasites
- parasitism and disease are density-dependent effects

24. Stress from Overcrowding
Some species fight amongst themselves if overcrowded
- The fighting may weaken the body’s ability to fight disease do to stress’
- This can lower birthrates and raise the death rate

25. Density-Independent Limiting Factors
-affects all populations in similar ways, regardless of size and density
- Examples are unusual weather such as hurricanes, drought, or floods

26. True density independence?
- Effects can vary with population density
- Human activities can place ecological stress in ways that can hamper it
- It is hard to say that a limiting factor acts only in a density –independent way

27. Controlling Introduced Species
Limiting factors keep the hydrilla population under control
- Pests or diseases weaken these populations
- This results in runaway population growth

28. 5.3 Human Population Growth

29. Historical overview
-the rate of population increase has changed dramatically over time
- predators and disease were once common and life-threatening

30. Exponential Human Population Growth
- As civilizations advances, life became easier, and human pops. Began to grow
- Several factors including nutrition and sanitation, reduced deathrates
- Lower death rates and higher birthrates, led to exponential growth

31. The Prediction of Malthus
-Suggested that only famine and disease can limit population growth
- He thought human populations were regulated by competition
- His work was important to Charles Darwin

32. World population growth slows
- Exp. Growth continued until the second half of the twentieth century
- It reached a peak and then began to drop
- It now takes longer for the global population to grow by 1 billion than it did 20 years ago

33. Patterns of Human Population Growth
- Demography: study of human populations
- The age structure of a population helps predict why some countries have higher birth rate than others

34. The demographic transition
- A dramatic change from high birth and death rates to low for both
- Divided into 3 stages
- US, Japan, and Europe have completed the transition

35. Age structure and Population growth
-used to understand the population growth in different countries
- In the US, there are almost an equal number of people in each age group
- The age structure shows a steady growth

36. Future Population Growth
- Demographers use age structures and the effect of diseases to predict the worlds populations
- It is suggested that by 2050, the population will reach 9 billion
- Global human populations will grow more slowly over than next 50 years than in the last 50