Chapter 24 Section 2

Competition I. Animals compete for food and space. ◦ Competition occurs when 2 or more organisms seek the same resource at the same time ◦ Ex. Gila woodpecker lives in Arizona and Mexico. They live in holes in saguaro cactus.

Competition I. Competition limits population size If nesting spaces are limited some woodpeckers won’t be able to raise their young II. If food becomes scare some woodpeckers might not survive to reproduce

Competition I. Limits on population growth are food, living space, or other resources II. The most intense competition comes from individuals of the same species They need the same type of food They need the same type of shelter III. Competition also occurs among different species

Population Size I. Ecologists often need to measure the size of a population. Counts of the population can indicate if a population is healthy and growing or in danger of disappearing.

Population Size I. Ways to measure population size 1.Trap-mark-release a)Trap the animals without injuring them b)Mark the animal and release c)Later another sample of animals is captured d)Some of the animals will have marks and others will not e)By comparing the marked animals to the unmarked ecologists can estimate the population size

Population Size I. To measure rabbits in a large population Ecologists use sample counts 1.Determine the area of the population (Ex. 100 acres) 2.Count the number of rabbits in 1 acre 3.Multiple it by 100 to estimate the population size

Population Size I. Limiting Factors: Anything that restricts the number of individuals in a population. Can be living and non-living features Can affect more than one population

Population Size Example: Lack of rain limits plant growth in a meadow Fewer plants = fewer seeds For seed eating mice this causes less food availability Fewer mice means less prey for hawks and owls

Population Size I. Carrying Capacity Largest number of individuals of one species that an ecosystem can support When the population begins to exceed the carrying capacity some individuals will NOT have enough resources With a lack of resources animals die or move out of the population

Population Size What would happen if there were no limiting factors that restricted the growth of a population? ◦ The highest rate of reproduction under ideal conditions is a population’s biotic potential ◦ The larger the number of offspring produced by parent organisms = a higher biotic potential of the species

Population Size Biotic Potential Example ◦ Compare an avocado tree to a tangerine tree ◦ Each avocado = 1 large seed ◦ Each tangerine fruit = a dozen seeds or more ◦ Because the tangerine produces more seeds per fruit it has a higher biotic potential than the avocado tree

Changes in Populations Birthrate and Death rate influence the size of a population – also affects the rate of growth A population gets larger when the # of individuals born is greater than the # that die.

Changes in Populations How does a population get smaller then? ◦ There are more deaths than births Ex: In Central Park one year 900 squirrels were born and 800 died ◦ This shows the population increasing by 100 If the next year 400 squirrels were born and 500 die then the population is decreasing by 100 squirrels

Changes in Population The same is true for human populations Look at Table 1 on page 692 What is happening in Zimbabwe? What is happening in Germany?

Moving Around Animals moving from place to place can affect population size Why would animals move from place to place? ◦ Food ◦ Mates ◦ Space ◦ Natural disaster or human causes

Moving Around Birds move during annual migrations ◦ Orioles live in eastern North America during the summer and migrate to Central America for the winter ◦ Move due to temperature and food resources

Moving Around Plants and Microscopic organisms move too ◦ Wind ◦ Water ◦ Being carried by animals Seeds and spores are carried by the wind Spine-covered seeds cling to the fur of animals and clothing on humans Others are carried by water currents

Exponential Growth What happens when a species moves somewhere with a lot of available food, living space, and other resources? ◦ The population grows quickly What type of growth do we call this? ◦ Exponential Growth

Exponential Growth Exponential growth means that the larger the population is the faster it grows What happens when it reaches its carrying capacity? ◦ The population can’t support any more animals ◦ The better adapted survive and reproduce ◦ Some move to different area

Exponential Growth Do you think that the Earth has a carrying capacity? ◦ Yes ◦ By the year 2050 our population could be over 9 billion ◦ As our population grows we are forced to live closer together ◦ Diseases spread faster ◦ ◦