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Understanding Populations

Understanding Populations. How Populations Change in Size. What is a Population?. Population is all the members of a species living in the same place at the same time. i.e. school of fish, palm trees on the same island

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Understanding Populations

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  1. Understanding Populations How Populations Change in Size

  2. What is a Population? • Population is all the members of a species living in the same place at the same time. • i.e. school of fish, palm trees on the same island • Population also refers to the size of the species that make up the population.

  3. Properties of Populations • Populations can be described in terms of size, density, or dispersion. • Density is the number of individuals per unit area • Dispersion is the relative distribution or arrangement of its individuals within a given amount of space. • Can be even, clumped, or random

  4. How Does a Population Grow? • A population gains individuals with each new offspring or birth and loses them with each death. • Growth rate is the change in the size of a population over a given period of time Growth Rate = births – deaths • The growth rate can be positive, negative, or zero.

  5. How Fast Can a Population Grow? • A species biotic potential is the fastest rate at which its populations can grow. • Reproductive potential is the maximum number of offspring that each member of the population can produce. • i.e. it can take elephants hundreds of years to produce a million descendents where as it only takes bacteria a few days or weeks.

  6. How Fast Can a Population Grow? • Reproductive potential increases when individuals produce more offspring at a time, reproduce more often, and reproduce earlier in life. • Reproducing earlier in life has the greatest effect on reproductive potential. • Reproducing early shortens the generation time, or the average time it takes a member of the population to reach the age when it reproduces.

  7. How Fast Can a Population Grow? • Populations can also undergo exponential growth. • They grow faster and faster. • A larger number of individuals is added to the population in each succeeding time period. • Exponential growth only occur in when populations have plenty of food and space, and no competition or predators.

  8. What Limits Population Growth? • Population growth never stays consistent. • Several events such as the reduction of resources, increase in deaths, and/or decrease in births can change a populations growth drastically. • Every ecosystem has a carrying capacity. • The maximum population that an ecosystem can support indefinitely.

  9. What Limits Population Growth? • Carrying capacity is the largest population that an environment can support at any given time. • A population may increase beyond this number but it cannot stay at this increased size. • Because ecosystems change, carrying capacity is difficult to predict or calculate exactly. However, it may be estimated by looking at average population sizes or by observing a population crash after a certain size has been exceeded.

  10. Carrying Capacity

  11. What Limits Population Growth? • A species reaches its carrying capacity when it consumes a particular natural resource at the same time it is produced. • Limiting resource • As the population approaches its carrying capacity members of the population start competing for resources.

  12. Two Types of Population Regulation • Populations are regulated through death • Two types of cause of death in a population • Density dependent • Density independent • Cause of death is density dependent deaths occur more quickly in a crowded population i.e. limited resources, predation, and disease. • Cause of death is density independent a certain proportion of a population may die regardless of the population density. • i.e. severe weather and natural disasters.

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