1. Growth Limitations Human Population
POPULATIONS
Growth
Limitations
Human Population

2. Stable Populations
Stable ecosystems are established by keystone species.
Keystone species are the population of organisms that keep the ecosystem in balance; without this population the ecosystem would disappear.
Sea otters are a keystone species in the kelp forest aquatic ecosystem.
Sea otters eat sea urchins; sea urchins eat kelp. If the sea urchins grew too large numbers then they would completely destroy the kelp forest which is home to hundreds of other animals. If the sea otter disappears then the kelp forest will be destroyed.

3. Characteristics of all Populations
Geographic distribution- Where?
Density- How many per unit of area?
Growth Rate- How fast do they reproduce and grow?
Population Age Structure- How old are the individuals in the population?

4. Density (Population Spacing)
Dispersal patterns within a population
Provides insight into the environmental associations & social interactions of individuals in population
clumped
Within a population’s geographic range, local densities may vary substantially. Variations in local density are among the most important characteristics that a population ecologist might study, since they provide insight into the environmental associations and social interactions of individuals in the population. Environmental differences—even at a local level—contribute to variation in population density; some habitat patches are simply more suitable for a species than are others. Social interactions between members of the population, which may maintain patterns of spacing between individuals, can also contribute to variation in population density.
random
uniform

5. Population Growth Factors that affect size: Number of births
Number of deaths
Number of individuals that enter or leave the population (immigration, emigration)

6. How fast can a population grow?
Populations usually stay about the same size from year to year because various factors kill many individuals before they can reproduce.
Predation
Disease
Natural disasters
Competition

7. Exponential Growth Population grows fast
When graphed it forms a J-shaped curve
Occurs in nature under conditions where plenty of food, water and space are available and there is minimal competition and predation

8. Logistic Growth
Population growth slows or stops after exponential growth
Population growth slows when it reaches carrying capacity
Carrying capacity (K) is determined by limited resources
500
400
300
200
100 20 10 30 50 40 60
Time (days)
Number of cladocerans
(per 200 ml)

9. Resources have limits
Resource limits: A species reaches its carrying capacity when it consumes a resource at the same rate that the resource is produced. This resource is then called the limiting factor for the species.

10. Limiting Factors
DENSITY DEPENDENT: death occurs more quickly in crowded populations rather than in a sparse population. Limited resources, predation, and disease often result in higher death rates in a high density population
DENSITY INDEPENDENT: a certain proportion of a population dies regardless of the density. This affects all members of a population in a uniform way. Severe weather and natural disasters are often density independent causes of death

11. Methods for measuring population size
Random Sampling- rather than count all individuals in an area a grip can be used to identify the number per unit of area and then multiplied to the complete area
Capture and Release-each captured organism is tagged and released. Then a recapture is done and the population size can be estimated by comparing the number captured that are tagged vs not tagged.

12. The Human Population
The human population grew more in 20th century than ever before (Exponential growth) Why? Increased food production Improved hygiene with industrial and scientific revolutions Can it continue?

13. Human Population Growth
Significant advances
in medicine through
science and technology
Industrial Revolution

14. Demography 2 Categories:
Developed Countries: have higher average incomes, slower population growth, and diverse industrial economics
Developing Countries: lower average incomes, simple and agricultural based economics, and rapid population growth.

15. Distribution of population growth
uneven distribution of population:
90% of births are in developing countries 11 10
high fertility
uneven distribution of resources:
wealthiest 20% consumes ~90% of resources increasing gap between rich & poor 9 8
medium fertility 7
low fertility 6
World total
World population in billions 5 4
Developing countries 3 2 1
Developed countries
1900
1950
2000
2050
Time

16. Age structure Diagram Relative number of individuals of each age
What do these data imply about population growth in these countries?

17. Women and Fertility What leads to decreases in birth rates?
Increased education
Economic independence for women
Large families are valuable in communities in which children work or take care of older family members
Movement of people seeing children as a financial burden rather than an asset
Fertility rate
Developed countries: 1.6 children/woman;
Developing countries: 3.1 children/woman