Unit 19 Human Influences on the Ecosystem Section 19.1 How Populations Grow Section 19.2 Human Populations Section 19.3 Resources and Growth Section Types of Pollution Section : Conservation

What is a Population? Group from one species spread over it geographic range (all habitat areas) at a specific time Density  the number of individuals in the population 3 Ways population spread: 1)Random No real pattern Spiders/Flowers 2)Uniform Even across habitat Pine trees/ fish 3)Clumped (Aggregated) Random but in groups Elephants/fungi

Population Growth Factors Growth Rate is effected by several factors: 1)Age Structure  number of males/females and their ages 2)Birthrate  number of babies born a year 3)Death rate  number of deaths a year 4)Immigration  members entering the range 5)Emigration  members leaving the area Growth Rate= (BR-DR)+(IM-EM)

Phases of Sigmoid Growth Most populations obey the a sigmoid growth curve: 1) Lag phase 2) Exponential phase 3) Stationary phase 4) Death phase J-shaped Growth 1) Lag phase  growth in population is slow due to low starting numbers birthrate slow but increasing 2) Exponential phase  as population increases, rapid doubling cause quick growth birthrate higher than deathrate Why is growth so quick? No limiting factors; lots of space, food, water, etc… to support new organisms J-shape growth

Phases of Sigmoid Growth Exponential phase cannot continue forever S-shaped Growth 3) Stationary phase  as resources become limited birthrate and deathrate are almost equal growth slows down Growth hits the maximum possible population size (carrying capacity) 4) Death phase  population is higher than carrying capacity deathrate is higher than birthrate negative growth S-shape growth

 Carrying capacity Limits to Growth The number of organisms of one species that an environment can support indefinitely (for all time at those conditions) is its carrying capacity When a population overshoots the carrying capacity, then limiting factors cause the Death Phase to lower the population till it can grow again

Reproduction Patterns life-history pattern Are all species effected by carrying capacity? No. Depends on their life-history plan if they ever reach carrying capacity Rapid life-history organisms: - have a small body size, grow rapidly, reproduce early, and have a short life span - Rarely hit carrying capacity Slow life-history organisms: -reproduce and grow slowly, have a long life span -they maintain population sizes at or near carrying capacity 1 Day 150 years

Limits to Growth Limiting Factor  any factor that limits a populations size Food, predators, space, water, etc.. 2 Types: Density-Dependent Increase/decrease with population’s size Density-Independent Size of population has no affect

Density-Dependent Limiting Factors 1)Competition More members the more food/water that is required Kills off weaker members 2)Predation Prey and Predator numbers are effected by each other 3)Overcrowding Stress of crowds weakens immune systems and increases fighting 4)Parasitism and Disease Overcrowding spreads disease faster

Density-Independent Limiting Factors 1)Weather Patterns Ruin food supply Run out of fresh water Limit time to hunt/reproduce 2)Natural Disasters Massive lowering of population numbers Change the ecosystem Remove important food supply

Human Population Growth Human’s used to have a very high birthrate but also a very high death rate Today the birthrate is 4.3 births/sec but the death rate is much lower (1.7 deaths/ sec) Human global population is predicted to double every 46 years! What factors lowered our death rate? More food through better agriculture Less death due to medicine Less childbirth death Longer lifespan due to health Doubling time is getting shorter  J-growth

Demographic Transition Demography  study of human populations Periods of Growth: 1)High birth and death rates in unstable environments - No control of environmental factors 2)Lowering of death rates as environment becomes more stable - Gain control of environmental factors 3)Birthrates fall to meet death rates as resources become limited 4)Birthrate almost equal to deathrate - Only in developed countries African Countries China and India USA, Europe, Canada Japan and Russia  Negative growth!!

Age Structure’s Effects on Growth Populations with high numbers teens and young adults will lead to fast massive growth Large number in the older generation will have slower growth Most stable growth is having near even numbers in all age groups India China USA/Europe