Limits on Population

1. Limits on Population can the world be taken over by one organism?

2. Consider this… Mouse litters are 6+ It takes a mouse 6 weeks to reach sexual maturity Mice can reproduce every 6 weeks So… why hasn't the world been covered in mice? Limits on all populations!

3. Each Population is LIMITED • Because there are a limited number of resources available in an ecosystem, not every organism born survives • These factors are known as LIMITING FACTORS (because they limit populations) • Organisms basically need 3 things to survive: • Food • Water • Shelter

4. Biotic Potential maximum number of offspring a species could produce with unlimited resources Controlled by 4 factors Birth potential Capacity for survival Procreation Length of reproductive life

5. Factors That Determine Biotic Potential Birth Potential • maximum number of offspring per birth • e.g. whooping crane females lay 2 eggs per year and only 1 chick survives Capacity for Survival • number of offspring that reach reproductive age • e.g. female sea turtle lays many eggs, but only a few offspring even reach the sea, and few still reach sexual maturity

6. Factors That Determine Biotic Potential Procreation • The number of times that a species reproduces each year • e.g. elk mate only once per year (during the fall) while farm animals will breed more than once a year Length of Reproductive Life • The age of sexual maturity and the number of years the individual can reproduce • e.g. African elephants reach sexual maturity at about 15 years of age, but may reproduce until they are 90

7. Limiting Factors An environmental factor that prevents an increase in the number of organisms in a population or prevents them from moving into new habitats

8. Example: Fern • Ideally, ferns should produce 50,000 spores per year • Abiotic Factor • Drier weather reduces population • Biotic Factor • Grazing animals reduces population

9. Carrying Capacity • maximum number of individuals of a species that can be supported indefinitely by an ecosystem • i.e. the “room” available in the ecosystem • determined by the availability of resources (food, shelter, water) • communities tend toward stability • achieved when an ecosystem is in equilibrium (i.e. balance)

10. Carrying Capacity THEREFORE, IF THE CARRYING CAPACITY IS REACHED, THERE CAN BE A MASSIVE POPULATION CRASH! • Population can exceed carrying capacity for a short time • If more organisms come in, there is more competition for space and resources • All available food eaten • As resources disappear, organisms die off because they can’t get resources needed • Lack of food leads to illness • Easier prey • Population decreases again to or below carrying capacity

11. Density Density refers to the number of organisms in a certain space

12. Low Density BIG SPACE SMALL SPACE Small space with a few organisms • Big space to spread out

13. High Density BGI SPACE SMALL SPACE Crowded • Crowded

14. Limits of Tolerance • Living organisms need certain level of nutrients and conditions to survive • Law of Minimum: • nutrient in LEAST supply limits growth • Law of Tolerance: • organism can survive within a certain range of an abiotic factor (above and below this limit… the organism cannot)

15. Law of Tolerance • population of fish likely increases as water temperature is close to optimum • no fish survive when it’s too hot or too cold

16. Density Independent Factors Affect members of population regardless of population density… kill organisms randomly, regardless of how many are around e.g. fires, floods, tornados, pesticides, temperature, lack of rain, habitat destruction

17. Density Dependent Factors Affect population because of a large population density e.g. food supply, water quality, mates, sunlight, territory, increase predators and disease (easier to catch a disease in a crowded place) Lower food supply means energy lost to competition

18. Definitions • Limiting Factors • Birth Potential • Capacity for Survival • Procreation • Reproductive Life • Carrying Capacity • Density • Law of Minimum • Law of Tolerance • Density Dependent Factors • Density Independent Factors

19. Homework • Suppose that there is a forested park in which squirrels are reproducing very quickly because there is so much food available. In this situation, the population will grow until it reaches the carrying capacity. What will define the carrying capacity of the squirrel population? • Identify the following limiting factors as either abiotic or biotic • Wind blows the seeds of a dandelion into a pond. The seeds fail to grow. • A population of grasshoppers eats all the available food and their numbers drop dramatically. • A bacterium causes a deadly disease in a herd of reindeer and some of them die. • Plants growing beneath the trees in a forest are unable to get enough sunlight. • Cockroaches are insects that reproduce very rapidly. Suggest reasons why the world is not covered in cockroaches. • Limiting factors normally control a population from expanding past its carrying capacity in a specific area. Most of the limiting factors that would normally control the human population have been removed through various technologies. How does this affect your quality of life? How might it affect your children’s or grandchildren’s lives?