Populations

Rates That Affect Population Size

• Natality- the birth rate; the number of births over time

• Mortality- the death rate; the number of deaths over time

Rates That Affect Population Size

• Immigration- the rate of individuals entering the population from a different population; the number of individuals entering over time

• Emigration- the rate of individuals leaving a populations to go to a different population; the number of individuals leaving a population

Population Growth

• Two Types of Growth:– Exponential– Logistic

Exponential Growth

• Occurs when the individuals in a population reproduce at a constant rate

• Under ideal conditions with unlimited resources, a population will grow exponentially

Exponential Growth

J-Curve

Logistic Growth

• Occurs when a population's growth slows or stops following a period of exponential growth

Logistic Growth

S-Curve

• Carrying Capacity- the maximum population size that environment can sustain.– Usually determined by a limiting factor

• As resources become less available the growth of a population slows or stops.

• New or early populations show exponential growth

• Old, stable populations show no growth, but stay near the carrying capacity of the environment

• What happens if a population exceeds its carrying capacity?

• If a population exceeds the carrying capacity of its environment, the carrying capacity decreases

Human Population

• Is the human population growing exponentially or logistically?

Niches and Communities

• Niche - range of physical and biological conditions in which a species lives and the way the species obtains what it needs to survive and reproduce.

• Different Factors:– Tolerance – ability to survive and reproduce under

a range on environmental circumstances.

Tolerance Graph

Niche cont.

• Resources – food, water, nutrients, etc• Physical – abiotic factors• Biological – biotic factors• Competition – exactly what you would think• Competitive Exclusion Principle – no two

species can occupy exactly the same niche in exactly the same habitat at exactly the same time.

Predator-Prey Relationships

• Predation – interaction in which one animal (predator) eats another animal (prey)– Predators affect the size of prey populations

within a community and determine the places where the prey can live.

• Herbivory – Same concept at predation just with plants

Predator-Prey Graph

Symbioses

• Two creatures living in harmony and helping each other survive.

• Mutualism – both benefit (Clown fish – Anemone)

• Parasitism – one organisms lives inside or on another organisms and harms it (Tapeworms)

• Commensalism – one organism benefits and the other is neither harmed nor helped. (Barnacles and Whales)