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Population Biology. Populations Population: a group of organisms of the same species that live within a given area Key characteristics: –Growth Rate –Population.

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Presentation on theme: "Population Biology. Populations Population: a group of organisms of the same species that live within a given area Key characteristics: –Growth Rate –Population."— Presentation transcript:

1 Population Biology

2 Populations Population: a group of organisms of the same species that live within a given area Key characteristics: –Growth Rate –Population density –Dispersal Patterns –Life-History Patterns Ostriches are nomadic, wandering in small groups. Aspen trees are quick to pioneer areas that have been disturbed by fire.

3 Populations Populationslarge and smallare DYNAMIC –Meaning, they change over time Humans face the same problems as large and small populations in nature


5 Population Growth Exponential Growth J-Curve –Unchecked growth due to unlimited resources –As a population gets larger it grows faster –Birth Rate is greater than Death Rate


7 Population Growth Logistic Growth S-Curve –Carrying Capacity Number of organisms the environment can support –Carrying capacity limited by resources –Birth Rate is equal to Death Rate at carrying capacity


9 Self Check Which of the following would you expect to observe after a population exceeds its carrying capacity? D. population growth rate is unaffected by limiting factors C. deaths exceed births B. births exceed deaths A. population increases exponentially Characteristics of Population Growth Exponential growth J curve S curve Population Time Carrying capacity The answer is C.

10 Population Size Perils of Small Populations –low genetic diversity –subject to inbreeding –less likely to adapt to environmental changes Problems being a Large population –Increase food shortages & diseases –Decrease in space, clean water –Live at carrying capacity so can experience huge crash

11 Factors That Influence Population Size Population growth rate is determined by: Natality or Birth rateNatality or Birth rate Death rateDeath rate It is also influenced by the number of individuals that enter and leave a population. Immigration – move into populationImmigration – move into population Emigration – move out of populationEmigration – move out of population

12 Limits on Population Growth Limiting Factors- any factor that causes a population to decrease Density Dependent Limiting Factors –Depends on the size of the population Ex. Food, Water, Shelter, Disease, Competition Density Independent Limiting Factors –Can affect populations regardless of their density Ex. Weather, Climate –Floods, Drought, Tornadoes, Fire, Volcanoes Water and shelter are critical limiting factors in the desert. Fire is an example of a Density independent Limiting factor.

13 Limiting Factors Density-dependent factors –Disease –Competition –Predators –Parasites –Food Density-independent factors –Volcanoes –Temperature –Storms –Floods –Drought –Habitat disruption

14 Other population factors Predation Competition

15 Predator & Prey Predator: Organism that eats all or part of another organism Prey: an organism that gets eaten by another organism

16 Competition: two or more organisms using the same resources Between different species and the same species

17 Population Density Population density is total population size per unit of area. Population densities depend on: –Interactions within the environment –Quality of habitat –Density dependent factors –Density independent factors –Birth rate and death rate

18 Dispersal Patterns Within Populations Three common patterns of distribution are:

19 Dispersal Patterns Random Clumped Uniform

20 When Studying Populations… The best way to determine population size is to collect an absolute number. –Count up all the individuals in the population. More frequently used is population density. –The number of individuals per unit area. –Can be measured using a variety of sampling techniques.

21 Random Sampling random sampleA method of selecting a sample from a statistical population in such a way that every possible sample that could be selected has a predetermined probability of being selected (random sample). BEST FOR: Stationary Populations –Ex. Plants Even Dispersal Patterns

22 Mark and Recapture A method of sampling an animal population where animals are caught alive and tagged, and then returned (unharmed) to their habitat over time animals from the pop are trapped and those with marks/tags are counted mathematical formula estimates the pop size

23 Patterns in Populations Reproductive pattern = life-history pattern Variety of patterns, but TWO extremes

24 Patterns Rapid life-history patterns –Changing or unpredictable environment –Small –Mature rapidly –Reproduce early –Short life span

25 Patterns Slow life-history pattern –Large species –Stable environments –Reproduce slowly –Matures slowly –Long life span –Stay at or near carrying capacity

26 Reproductive Strategies Rapid (maximum growth rate, below carrying capacity) –Early reproduction –Short life span –High mortality rate –Little or no parental care –Large investment in producing large numbers of offspring –Below carrying capacity –Examples: Bony fish Grasshoppers Slow (maximizes population size near carrying capacity) –Late reproduction –Long life span –Low mortality rate –Extensive parental care –Greater investment in maintenance and survival of adults –At or near carrying capacity –Examples: Sharks Elephants

27 Survivorship in Populations

28 Survivorship Curves Patterns of Mortality –Populations show three patterns of mortality or survivorship curves : Type I (low mortality until late in life) Type II (constant mortality throughout life) Type III (high mortality early in life followed by low mortality for the remaining life span)

29 Survivorship in Populations

30 Rapid Life History Pattern Type III Survivorship Type III Species: –have high reproductive rates –tend to occur in unpredictable environments –Ex. Fish, Plants

31 Slow Life History Pattern Type I Survivorship Type I Species: –occur near carrying capacity –experience effects of population density –have low reproductive rates, high parental care –Ex. Humans, Elephants

32 Human Populations Age Structures and Human Growth

33 Age Structure –A populations age structure indicates the percentage of individuals at each age. –The right side shows females; the left, males –The x-axis is number is populations size Usually in millions –The y-axis is age ranges usually 0-4, 5-9, , etc…

34 Population Age Structure Differences in environmental conditions and past history may cause populations to differ in their age distributions. The future growth of a population depends on its current age distribution.




38 Yall me

39 History of Human Population Growth The Development of Agriculture –About 10,000 to 12,000 years ago, the development of agriculture increased the growth rate of the human population.

40 What happened in the 1600s? The Population Explosion –Around 1650, improvements in hygiene, diet, and economic conditions further accelerated population growth. –After World War II, the human population grew at the fastest rate in history, largely because of better sanitation and medical care in poorer countries.

41 Advances in Human Technology = Growth


43 Human population growth rate has been growing more than exponentially. Limited resources eventually will cause human population growth to slow, but global human carrying capacity is not known. Human Population Growth

44 1. What is the difference between linear growth and exponential growth as plotted on a graph?

45 2. Why dont populations of organisms grow indefinitely? 3.What is the relation ship of births to deaths in a population before the population reaches the environments carrying capacity? 4.What happens when the population exceeds the carrying capacity? 5. What are some limiting factors that can curb population growth?

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