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Section #1: How Populations Change in Size

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Presentation on theme: "Section #1: How Populations Change in Size"— Presentation transcript:

1 Section #1: How Populations Change in Size

2 Population: all the members of a species living in the same place at the same time a reproductive group – breed with each other also deals with the number of individuals

3 Population described in terms of: size – how many
density – the # of per unit area or volume dispersion – arrangement of individuals within a given space

4 How Does a Population Grow?
growth rate = births – deaths growth rate = change in the size of a population over a given period of time can be positive, negative or zero

5 How Fast Can a Population Grow?
Biotic Potential – the fastest rate at which a population can grow Reproductive Potential – the maximum # of offspring that each member of a population can produce

6 Reproductive Potential
increases when individuals: produce more offspring at a time reproduce more often reproduce earlier in life (generation time – the time it takes to reach sexual maturity)

7 Exponential Growth a large # of individuals is added to the population in each succeeding time period population has plenty of food, space, no competition, little disease


9 What Limits Growth? natural conditions that are neither ideal or constant lack of resources environmental change disease

10 Carrying Capacity the maximum population that the ecosystem can support indefinitely capacity can change over time populations may increase beyond this #, but cannot stay


12 Carrying Capacity Example
Australia originally did not have rabbits until they were introduced in 1859 no competition, no predators, & plenty of food led to rapid growth population eventually crashed because of disease & starvation

13 Resource Limits plant growth is limited by water supplies, sunlight, & mineral nutrients a species reaches its carrying capacity when it consumes a particular natural resource at the same rate at which the ecosystem produces the resource

14 Competition members of the same population compete for the same resources as the carrying capacity nears can also compete for social dominance, territory, mates, etc.

15 Density Dependent or Independent
cause of death is density dependent when populations are crowded (limited resources, predation, disease) ex. = disease carrying beetle can spread quickly through dense pine forests


17 Density Dependent or Independent
cause of death is density independent when a certain # of individuals die regardless of density ex. = severs weather, flooding, storms, etc. that affect all populations in that area equally


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