Think / Pair / Share What factors affect the human population of Brampton/Caledon? Are these the same factors that affect other cities?

Population Dynamics

Population a group of organisms of the same species living in a particular area Population Density the number of organisms living in a given unit of space, such as a square metre (m2) D= N/S D= Population density N= Number of organisms S= Unit of space

Factors Affecting Population Size There are four main factors that affect population size in an area: BIRTHS (Natality = Birth Rate) - number of new individuals being added to a population by births 2. DEATHS (Mortality = Death Rate) - number of individuals dying from all causes 3. Immigration – number entering an area (Moving into) 4. Emigration – number leaving an area (Moving out)

Types of Populations Open populations Closed populations All 4 factors (birth, death, immigration and emigration) are acting on the population most natural ecosystems Closed populations Not affected by migration; only affected by birth and death rates Some islands, laboratory, and zoos

Growth Rate of a Population Tells how much population size changes in one year Expressed as a percentage Growth Rate = (births-deaths) + (immigration – emigration) x 100% initial population size = ______ %

Some fun facts Field mice have litters with 6 or more pups They can reproduce every 6 weeks They reach sexual maturity at an age of 6 weeks In 6 months, a population of 20 could reach 5120

Exponential Growth Without limits population growth of a species will accelerate!

Limiting Factors All population growth is limited! It can not grow forever! Limiting factor: a factor that stops the growth of a population in an ecosystem Light Temperature Food Predators diseases Examples of limiting factors: Availability of water & food would affect how many, if any, organisms can live in an area Predators to an area would affect the number of organisms (prey) living in the area Temperature of the area affects which animals live there (ex., polar bears will not be in a desert) Common limiting factors: amount of sunlight, climate, temperature, water, nutrients/food, fire, soil, chemistry, space, other organisms

Abiotic Biotic Adequate food supply Suitable habitat POPULATION SIZE GROWTH FACTORS Favorable light Favorable temperature Favorable chemical environment Abiotic Biotic Adequate food supply Suitable habitat Ability to compete for resources Ability to defend against predators Ability to resist diseases & parasites Decrease factors Too much or too little light Temperature too high or too low Unfavorable chemical environment Inadequate food supply Unsuitable or destroyed habitat Too many competitors Insufficient ability to hide from or Defend against predators Inability to resist diseases and parasites

Limiting Factors DENSITY DEPENDENT: factors that are based on population size (e.g. disease, predators, food, etc.) DENSITY INDEPENDENT: factors that are NOT based on the populations size (e.g. temperature, weather, volcano, earthquake, ozone holes, etc.)

Limited Growth Growth is slowed by limiting factors. Growth levels off when factors are in balance.

Carrying Capacity Carrying capacity is the largest number of individuals that an ecosystem can support when a population is maintained at its carrying capacity, the size of the population is at an equilibrium Births + Immigration = Deaths + Emigration If a population is NOT maintained at its carrying capacity, the population will eventually crash

Limited Growth Carrying Capacity.

Population Crashes

Something to Consider… Today: 7.1 Billion People 2040: 12 Billion People

UN 2010 predictions

Credits Mrs K Casha