Populations

1. Populations Chapter 8

2. Population • Definition: All the members of the same species living in the same place at the same time. • Can be described in three ways: • Size • Density • Dispersion

3. POPULATION DENSITY: • Quantity of organisms per unit of area. • Such as the population density in rural areas is less than the population in city areas. • Armada, MI vs. New York, NY

4. Population Dispersion • The relative dispersion or arrangement of individuals. • Can be described as Clumped, Even (uniform) or Random

5. What kinds of animals would use each? • Uniform (even) distribution: • Territorial animals, like lions or penguins. • Animals that require a lot of space for hunting, or in competition for resources, like plants.

6. Clumped Distribution • Most common type of distribution. • Usually occurs with species who are using a limited resource or serve as prey. Herding animals. Schooling of fish.

7. Random distribution: • unpredictable spacing, is the least common form of distribution. • occurs where the position of each individual is independent of the other individuals: they neither attract nor repel one another. Random distribution is rare in nature as biotic factors, such as the interactions with neighboring individuals, and abiotic factors, such as climate or soil conditions, generally cause organisms to be either clustered or spread apart. • Random distribution usually occurs in habitats where environmental conditions and resources are consistent. • Dandelion seed dispersion

8. How does a population grow? • Growth = births – deaths • When births are greater than deaths, the population grows and when deaths exceed births, the population shrinks. • Other factors that affect growth rate: • Age of first reproduction (greatest affect on reproductive potential) • Number of births per individual (sea turtle example) • Reproductive potential (max # that can be born dependent upon number of individuals per birth and spacing between births)

9. Growth Patterns: • Exponential: resources are unlimited. • Logistic: limiting factors, population levels off at the carrying capacity (K). J-curve S-curve

10. Carrying Capacity

11. Competition: • Members of a species compete with each other for mates, food, and homes. This is one of the selective pressures that drives natural selection.

12. Two types of population regulation: • Density dependent: deaths occur more quickly in a crowded environment. • If a resource is limited, some individuals will die because they don’t compete as well as others. • When a disease enters a population it travels through the population quicker the denser the population • Density independent: regardless of the number of individuals, deaths occur at the same rate. • Severe weather and natural disasters are examples.

13. How do scientists measure the size of a wild population • Mark and recapture • Scientists take a sampling of a wild population, mark them, release and then recapture. Using the following formula they can estimate with reasonable accuracy the number of organisms in an area.

14. How do the numbers work? • Large capture, large recapture (with small amount marked)would be a large population…why? Because few recaptures in a large sample means the population must be big overall. • Therefore, small capture, small recapture with many marked would be a small overall population. • Sample size is extremely important! And you must recapture at least one marked individual! = 2 million = 1,333

15. How species interact with each other Lesson 8.2

16. Niche • The unique role an organism plays in it’s environment. • Physical home, the biotic and abiotic factors needed to keep it alive. • Different that habitat, because that only accounts for it’s location. • A lions niche is different in nature than it is in a zoo. In nature it has many social interactions with other organism whereas in a zoo it has way fewer. • May still be fed upon by mosquitos, but will not have opportunity to fight with Hyenas or eat a zebra.

17. Ways to interact with other organisms:

18. Competition: • Individuals attempting to use the same limited resource. • Both species generally lose a portion of their niche. • Fundamental vs. Realized niche • Fundamental all the biotic and abiotic components desired. No limiting resources. • Realized niche is a portion of the fundamental niche consisting of what is actually available to an organism.

19. Realized niche Fundamental niche

20. When two species directly or indirectly compete: • Competitive exclusion principle

21. Predation: • When one organism feeds on another organism • Populations tend to increase and decrease in distinct patterns:

22. Symbiosis • A situation where two (or more) organisms live in close relationship with one another.

23. Parasitism • Different than predation because the parasite may not necessarily kill its host.

24. Mutialism • When two species depend on each other and they both benefit from their relationship.

25. commensalism • One benefits while the other is neither helped nor harmed Cattle egrets eat insects flushed out of the grass by grazing buffalo. It is not clear if the buffalo benefits at all.