Ecology – Part 3 – General Biology Carrying Capacity Population Growth Human Population Biodiversity

What is a population? Groups of individuals that belong to the same species and live in the same area.

Exponential Growth Populations grow if the birthrate is greater than the deathrate. Under ideal conditions with unlimited resources, a population will grow exponentially. This is called exponential growth.

Exponential Growth This is represented by a J-shaped curve.

Exponential Growth Curve Population Growth of Houseflies 1 million 500, One year Population size

Carrying Capacity: the largest # of individuals that a given environment can support indefinitely.

Exponential growth does not occur in natural populations for long. Eventually resources (food and space) become less available and growth slows down. This is called logistic growth.

The J-shaped curve levels off as the population reaches carrying capacity (K). This is represented by an S- shaped curve.

In an undisturbed environment (no human intervention), populations will fluctuate around carrying capacity (equilibrium).

Carrying Capacity vs. Exponential Growth J-shaped curveS-shaped curve

Carrying Capacity The maximum number of organisms of a particular type that can be supported in an area…

Carrying Capacity This graph shows an S- curve As the population size approaches the carrying capacity (dashed-line), the growth slows down (note the blue arrows) Time Population

Figure Population cycles in the snowshoe hare and lynx

What limits population growth and maintains balance (equilibrium) in an ecosystem? Density-dependent and density- independent limiting factors

Limiting Factors Limit the organisms that can live in an area: can be biotic can be abiotic

What are some factors that would keep the population at a steady level? Competition - organisms struggling for limited resources

Competition 1. Competition: when the demand for resources such as food, water, space, and other essentials exceeds the supply. Some organisms avoid competition by migrating seasonally to areas where climate is better and more food is available

Predator-prey relationships: controls numbers of predators and prey

Figure 41.9 Bulk-feeding: a python

Parasitism and Disease: crowding leads to an increase in parasitism and resistance to disease.

Other limiting factors: 1. Unusual weather: such as extreme hot or cold temperatures 2. Natural disasters: such as hurricanes, tornados, floods, or droughts. 3. Human activity: such as damming a river or clear-cutting a forest.

PBL Task #3 List some ways that the climate would have to change in order for your organism to display a J-shaped growth curve. Do they at least represent an S-shaped growth curve right now? Please explain why or why not. Explain how the biodiversity of your organism’s environment has changed in the last years. Look at the slides about Human Population and do the Age Structure Activity with your group members. Everyone must have their OWN graph!

Human Population Demography – the study of human population size –Census –Birth rate (live births/1000 people) –Death rate (deaths/1000 people)

Human Population

Human Population (con’t)

Age Structure Graph – number of people at each different age - see p.103 in textbook

Age Distribution Graphs Activity You will get this from your teacher.

Really cool Population Website!!

Population Biology

Biodiversity A wide range of different species of organisms living in an ecosystem More biodiversity = More stability in the ecosystem –Biodiversity – forest –No biodiversity – corn field Biodiversity allows ecosystems to better survive a catastrophic environmental event Loss of Biodiversity can lead to: –Extinction, endangered species, & threatened species

Figure Which forest is more diverse?

Biodiversity Smart Board See p.8, 9

Biodiversity – True or False?

Answers –9. true –10. false –11. false –12. true –13. false –14. true –15. true

Complete the Age Distribution Graphs Activity At some point you need to answer any questions from the back of the paper and turn yours in! Then begin ppt #4