CHAPTERS 4: POPULATION BIOLOGY

BELLRINGER How many time would you have to fold a piece of paper to reach: How many time would you have to fold a piece of paper to reach: The sun? The sun? The edge of the known universe? The edge of the known universe?

POPULATION DYNAMICS Population: Same species, same place, same time Population: Same species, same place, same time Must interbreed. Must interbreed. If conditions were ideal, and there was nothing holding numbers down, populations could grow at astounding rates. If conditions were ideal, and there was nothing holding numbers down, populations could grow at astounding rates.

EXAMPLE OF EXPONENTIAL GROWTH: FOLDING A PIECE OF PAPER A piece of paper is roughly.1mm thick A piece of paper is roughly.1mm thick After 1 fold, N (t) =(0.1mm)(2)^1=0.2mm After 1 fold, N (t) =(0.1mm)(2)^1=0.2mm After 20 folds, N (t) =(0.1mm)(2)^20=1.04km After 20 folds, N (t) =(0.1mm)(2)^20=1.04km After 50 folds, N (t) =(0.1mm)(2)^50=1.12x10^8km (this is almost the distance to the sun) After 50 folds, N (t) =(0.1mm)(2)^50=1.12x10^8km (this is almost the distance to the sun) After 100 folds, N (t) =(0.1mm)(2)^100=1.3x10^24 km (About the radius of the universe) After 100 folds, N (t) =(0.1mm)(2)^100=1.3x10^24 km (About the radius of the universe) After 103 folds, N (t) =(0.1mm)(2)^103=1.0x10^30 km(Would be longer than the universe) After 103 folds, N (t) =(0.1mm)(2)^103=1.0x10^30 km(Would be longer than the universe)

BACTERIA ON A COUNTERTOP Assuming that you use a cleaner that kills all but 1 bacteria, how many will there be in 24 hours later? Assuming that you use a cleaner that kills all but 1 bacteria, how many will there be in 24 hours later? 5* * ,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000, ,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000

GRAPH OF EXPONENTIAL GROWTH “J-SHAPED CURVE” Growth increases with time Growth increases with time

DOES THIS ACTUALLY OCCUR IN NATURE? It would if conditions were ideal. It would if conditions were ideal. They are not. They are not. Limiting factors Limiting factors Anything that limits the number of organisms in an environment Anything that limits the number of organisms in an environment

CARRYING CAPACITY The number of organisms of a species that an area can support indefinitely. The number of organisms of a species that an area can support indefinitely. S-shaped curve S-shaped curve

WHEN A POPULATION OVERSHOOTS CARRYING CAPACITY Ecosystem cannot support this many, so deaths begin to outnumber births. Ecosystem cannot support this many, so deaths begin to outnumber births. This drives the population under the carrying capacity This drives the population under the carrying capacity Once the population goes underneath the carrying capacity, the population is able to grow again, and will once again overshoot. Once the population goes underneath the carrying capacity, the population is able to grow again, and will once again overshoot. And so on… And so on…

MORE REALISTIC POPULATION GROWTH CURVE

LIFE-HISTORY PATTERNS Small organisms typically have rapid population growth Small organisms typically have rapid population growth i.e. Bacteria, mosquitoes, etc. i.e. Bacteria, mosquitoes, etc. Quick reproduction times and short lives Quick reproduction times and short lives Larger organisms have slow population growth. Larger organisms have slow population growth. i.e. Elephants, whales, humans, etc. i.e. Elephants, whales, humans, etc. Develop slowly and reproduce later in life Develop slowly and reproduce later in life

POPULATION DISTRIBUTION PATTERNS 3 main types 3 main types 1.Random 2.Uniform 3.Clumped

RANDOM DISTRIBUTION Organisms are equally likely to be found anywhere within the area Organisms are equally likely to be found anywhere within the area

UNIFORM DISTRIBUTION Roughly equal space between individuals in a population Roughly equal space between individuals in a population

CLUMPED DISTRIBUTION Organisms are more likely to be found in some areas than others. Organisms are more likely to be found in some areas than others.

FACTORS AFFECTING POPULATION GROWTH Density-Dependent Density-Dependent Depends on density Depends on density Density-Independent Density-Independent Does not depend on density Does not depend on density

DENSITY-DEPENDENT FACTORS Factors that have increasing effects as the population size increases in a given area Factors that have increasing effects as the population size increases in a given area Disease Disease Competition Competition Predation Predation Parasites Parasites Food Food Etc. Etc.

DENSITY-INDEPENDENT FACTORS Affect populations regardless of their size Affect populations regardless of their size Most are abiotic Most are abiotic Temperature Temperature Storms Storms Floods Floods Drought Drought

INTERACTIONS LIMIT POPULATION SIZE Predation Predation Competition Competition Crowding and stress Crowding and stress

PREDATION When numbers of prey are up, the number of predators increases When numbers of prey are up, the number of predators increases With more predators, the numbers of prey are rapidly decreased. With more predators, the numbers of prey are rapidly decreased. This makes it so there is less food, so the numbers of predators that can be supported decreases. This makes it so there is less food, so the numbers of predators that can be supported decreases. This allows prey numbers to increase because they are not being eaten as rapidly This allows prey numbers to increase because they are not being eaten as rapidly This allows the ecosystem to support more predators This allows the ecosystem to support more predators And so on, and so on… And so on, and so on… This is density-dependent (depends on numbers of prey and predators in an area) This is density-dependent (depends on numbers of prey and predators in an area)

PREDATORS NEED PREY

COMPETITION WITHIN A POPULATION There is a limited supply of resources in an area. There is a limited supply of resources in an area. When the population increases, the resources become depleted faster. When the population increases, the resources become depleted faster. This is a density-dependent factor. This is a density-dependent factor.

CROWDING AND STRESS When too many organisms are in an area, resources and space are limited. When too many organisms are in an area, resources and space are limited. This puts stress on the populations. This puts stress on the populations. Can cause aggression, decreases in parental care, decreased fertility, and decreased resistance to disease Can cause aggression, decreases in parental care, decreased fertility, and decreased resistance to disease Density-dependent Density-dependent

HUMAN POPULATION Demography-the study of human population size, density and distribution, movement, and birth rate vs. death rate. Demography-the study of human population size, density and distribution, movement, and birth rate vs. death rate. We have found ways around many density-dependent factors We have found ways around many density-dependent factors Not all Not all Little control of density-independent factors Little control of density-independent factors

CALCULATING POPULATION GROWTH Population Growth Rate (PGR)=(Births + immigration) – (Deaths + emigration) Population Growth Rate (PGR)=(Births + immigration) – (Deaths + emigration) Because immigration and emigration is hard to track (people going back and forth often) we usually ignore these numbers and simplify it it: Because immigration and emigration is hard to track (people going back and forth often) we usually ignore these numbers and simplify it it: PGR=Births – deaths PGR=Births – deaths If births=deaths, there is no growth If births=deaths, there is no growth If births > deaths, the population increases If births > deaths, the population increases If births < deaths, the population decreases If births < deaths, the population decreases

AGE STRUCTURE Proportions of the population that are at different age ranges Proportions of the population that are at different age ranges