Understanding Population Growth and Regulation

1. Objectives • Describethe three main properties of a population. • Describeexponential population growth. • Describehow the reproductive behavior of individuals can affect the growth rate of their population. • Explainhow population sizes in nature are regulated.

2. What Is a Population? • a group of same species organisms that live in a specific area and interbreed • population came mean • the group • the size [of the population] • number of individuals

3. Properties • Density: number of individuals of a species in a given area. • Dispersion: pattern of distribution of organisms • even, clumped, or random.

4. How Does a Population Grow? • Growth rate represented by the equation: • Computed for a specific period of time • Changes because birth & death rates increase/ decrease. • Can be positive, negative, or zero

5. Zero: average births = average deaths • each pair of adults have two offspring who survived to reproduce • Negative: adults not replaced by new births, population shrinks

6. How Fast Can a Population Grow? • In most cases barely change year to year • Factors controlling growth • Biotic potential: fastest rate of population growth • Reproductive potential: maximum number of offspring organism can produce

7. Reproductive Potential • increases • produce more offspring at a time • reproduce more often • reproduce earlier in life • has the greatest effect on reproductive potential • Small organisms-high potentials • Large organisms-low potentials

8. Exponential Growth • logarithmic growth • populations must have plenty of food & space, no competition or predators • Ex: bacteria or molds grow on a new source of food • large number s added each succeeding time period

9. What Limits Population Growth? • Natural conditions limit growth • resources used up • environment changes • deaths increase or births decrease • Natural selection only allows some members to survive and reproduce • properties of a population can change over time

10. Carrying Capacity • largest population an environment can support at any given time. • may increase beyond this number, can’t stay there • estimated by: • looking at average population sizes • observing a population crash after a certain size has been exceeded

12. Resource Limits • Population at carrying capacity when a particular natural resource consumed at rate produced • Resource is limiting • supply of the most severely limited resources determines the carrying capacity

13. Competition Within a Population • Members use the same resources in the same ways, so they will eventually compete as population approaches its carrying capacity • may compete for social dominance or for a territory • Indirect resource competition: space , shelter, food, or breeding sites

14. Two Types of Population Regulation • Density dependent • deaths occur more quickly in a crowded population than in a sparse population • limited resources, predation and disease result in higher rates of death in dense populations

15. Density independent • a certain proportion of population dies regardless of the population’s density • affects all populations same way • typical causes: severe weather, natural disasters