1. Population

2. Members of the same species living in a specific geographic area. Species – A group of similar organisms that can breed and produce fertile offspring Factors that effect population size: Availability of Food Weather conditions Space Breeding Patterns

3. Population When studying a population boundaries are set to limit or make a study easier Population Density – The number of individuals of a particular species per unit area or volume Can be expressed as a formula: –Individuals / Unit Area –1000 Trees / 50 km² = 20 Trees/km² 20 Trees per km²

4. Limits to Growth “Factors” Exponential Growth – Population multiplies by a constant factor at constant time intervals A populations ability to grow depends partly on the rate at which an organism can reproduce. Reproduction – the formation of new individuals. –Bacteria reproduce very fast –Rabbits fast –Panda – S L O W – one reason they are critically endangered – fewer than 1000 in the wild

5. Exponential Growth Exponential growth is usually represented by a J – shaped curve

6. Limiting Factors A condition that can restrict a population growth Space –“Normal” cells stop dividing when they run out of room to grow Cancer cells do not; they loose this restriction and continue to grow beyond available space. Lung Cancer Cells

7. Limiting Factors Food Disease Carrying Capacity – The number of organisms in a population that the environment can maintain or “carry” with no net increase or decrease. As you near the Carrying Capacity death rate may increase or birth rate may decrease or BOTH –Continues till about equal

8. Carrying Capacity It is usually represented by an S – shaped curve.

9. Factors Affecting Population Growth Density – Dependent Factors – A factor that limits a population more as population density increases. Availability of food Disease that spreads easier among organisms in a dense population; than one that is less dense.

10. Factors Affecting Population Growth Density – Independent Factors – Factors that limit populations but are unrelated to population density. Extreme Weather: Hurricanes, blizzards, droughts These conditions have the same effect on population regardless of its size Fires, floods, habitat changes like deforestation

11. Factors Affecting Population Growth Growth Cycles “boom-and-bust” Growth Cycles A rapid increase in population for a period of time; followed by a rapid decrease in number –An uncontrolled growth cause a hormonal secretion making animals sterile (rodent) A limit to food

12. Human Population: Birth Rate vs. Death Rate History As with all other species, the human population growth depends on birth and death rates. –Birth rates go up and death rates go down population goes up

13. Human Population: Immigration & Emigration Immigration – individuals move into an area from elsewhere Increase the population Emigration - individuals move out of the population Decrease a population

14. Human Population 10,000 years ago farming replaced hunting and gathering –Provided a consistent food supply –More food = increase population Death rates over the last few centuries have decreased.

15. Predicting Population Growth Age Structure – the proportion of people in different age groups In the U.S. age groups are balanced Some nations (Sweden) have a declining growth rate –Low birth rates and a top heavy age structure Sweden’s Growth Rates Blue – Certified Birth Rates Red – Certified Birth Rates

16. Age Population Pyramids

17. Predicting Population Growth Species interact in Biological Communities  Populations do not live in isolation; they interact with other populations  They do not live in isolation  In some cases they compete for resources such as food, water, or shelter.

18. Competition Community – all inhabitants living in a particular area. From the organisms in the soil all the way up the food chain Interspecific Competition – competition between species This competition within a single species limits the growth of the population This happens when two or more species rely on the same limited resource

19. Disturbances and Communities Communities change continuously –Natural disturbances: Fires Volcanic Eruption Floods Storms Droughts –Changes not always negative –Some plants require extremely hot temperatures (in a forest fire) to sprout Destroy Organisms Change resources such as shelter and water

20. Disturbances and Communities Man made disturbances:

21. Disturbances and Communities Positive “man made” natural disturbances:

22. Human Activities / Species Diversity Humans have the greatest impact on communities world wide Land Clearing Areas cut down for lumber, planting crops, building (homes)