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Population Biology Population Biology Questions • What is a population? • Describe how populations grow. • What is the difference between an S shaped curve and a J shaped curve? • What is a life history pattern? • Describe the two types of life history patterns. • What is the difference between densitydependent and density-independent limiting factors? Principles of Population Growth • What is a population? – A group of organisms that are of the same species and live in the same area • How do populations grow? How Do Populations Grow? • Population growth is not linear: In linear growth, the population grows by adding a fixed amount each time period Ex: Every minute, 5 individuals are added to the population How Do Populations Grow? • Population growth is not linear. • Population growth can be exponential. -Exponential growth indicates that as a population gets bigger, it also grows at a faster rate How Do Populations Grow? • Population growth is not linear. • Population growth can be exponential. – Exponential growth can be J shaped or S shaped -J shaped curves have no upper limit so they continue to grow forever. S Shaped curves have an upper limit so they stop growing and level off at some fixed point What limits growth on an S shaped population curve? • Carrying capacity: the number of organisms of one species that an environment can support Where are birth rates higher than death rates? Where are birth rates and death rates the same? Where are death rates higher than birth rates? Principles of Population Growth • What is a population? – A group of organisms that are of the same species and live in the same area • How do populations grow? – Not linear – Exponential • J shaped • S shaped – Carrying capacity Graph this. Population SizeTime (millions) (seconds) 2 10 6 20 8 30 15 40 33 50 59 60 Reproductive Patterns • Why don’t populations reach carrying capacity and remain stable? – To answer this question we have to study lifehistory patterns – Life-history pattern: an organism’s reproductive pattern Life History Patterns • Rapid life history pattern: population increases rapidly, then declines when there are sudden environmental changes • Organisms with rapid life-history patterns are usually small and have a short life span Life History Patterns Slow life-history pattern: individuals reproduce and mature slowly and have a long life span – Population sizes are maintained at or near carrying capacity Density factors and population growth • There are three patterns of population dispersal: Density factors and population growth • There are three patterns of population dispersal: clumped, spaced, and random • There are two kinds of limiting factors that affect population dispersal: – Density independent factors: limiting factors that affect population size regardless of their density • temperature, storms, floods, habitat disruption – Density dependent factors: • disease, parasites, or food availability Reproductive Patterns • Why don’t populations reach carrying capacity and remain stable? – It depends on whether they have a rapid or slow life history pattern, and it depends on the combination of density dependent and independent factors that are around Organism Interactions that Limit Population Size • Predation • Competition • Density – Effects of crowding and stress Principles of Population Growth • What is a population? – A group of organisms that are of the same species and live in the same area • How do populations grow? – Linear vs exponential (J vs S shaped) • Reproduction Patterns – Life history patterns (rapid vs slow) – Density dependent vs Density independent limiting factors • How do organisms affect population size? – Predation, competition Population Biology Questions • What is a population? • Describe how populations grow. • What is the difference between an S shaped curve and a J shaped curve? • What is a life history pattern? • Describe the two types of life history patterns. • What is the difference between densitydependent and density-independent limiting factors?