UNIT 1: LESSON 3 AND 4

Lesson 3: Population dynamicsLesson 4: Interactions in Communities

MOVIN’ OUTBy Immigration and Emigration• Populations can grow bigger

or get smaller.• Immigration – when

individuals join a population.– Into a new population.– Population gets larger.

• Emigration – when individuals leave a population.– Exiting a population.– Population gets smaller.

By Birth and Death• Birth = increase in population.• Death = decrease in population.• The number of births compared to the

number of deaths tells if a population is increasing or decreasing.

MOVIN’ OUT

Population

Births

MOVIN’ OUT

Immigration Emigration

Deaths

KNOW YOUR LIMITSResource Availability• Each environment has different

amounts of resources that living things need, such as food, water and space.

• Resources influence population size.

• If resources decrease then population size will decrease.

• If resources increase then population size will increase.

Resource Availability• Carrying Capacity – the maximum number

of individuals of one species that the environment can support.

• Carrying capacity changes when the environment changes.

• Population crash = carrying capacity drops– Examples include: natural disasters like forest

fires, harsh weather, drought, etc.• Population growth = favorable

environmental conditions.– New food growth, great weather, etc.

KNOW YOUR LIMITS

Limiting Population Size• Limiting Factor – a part of the environment

that keeps a population’s size at a level below its full potential.

• They can be living or nonliving things.• Abiotic Factor – nonliving parts that are

needed for survival.– Water, nutrients, soil, sunlight, temperature,

living space.• Biotic Factor – living organisms

interacting.

MAXIMUM CAPACITY

ORGANISM INTERACTIONS

• Sometimes interactions can help one individual, harm another or help both.

• Competition – when 2 or more individuals or populations try to use the same limited resources such as food, water, shelter, space, sunlight, etc.

• Cooperation – occurs when individuals work together.

• It helps individuals get resources, which can make populations grow.

• Example: hunting in groups, stay close together for warmth, structured social order in bees and ants.

ORGANISM INTERACTIONS

PREDATOR vs PREYFeeding Relationships• Predator – eats another animal.• Prey – an animal that is eaten.• An animal can be both predator and

prey!

Feeding Relationships• Animals have adaptations that help aid

in survival.• Examples include: talons, claws, sharp

teeth, webs, camouflage, defense chemicals.

PREDATOR vs PREY

Camouflage

• If a prey population grows or shrinks, the number of predators the community can support changes as well.

PREDATOR vs PREY

SYMBIOTIC REALTIONSHIPS

Living Together• Symbiosis – a close long-term relationship

between different species in a community.• They might benefit, be harmed or remain

unaffected.3 types• 1. Mutualism – Both organisms benefit.

Living Together• 2. Commensalism – one benefits and the

other is unaffected.

• 3. Parasitism – One benefits and the other is harmed.– Parasite = benefits Host = one harmed

SYMBIOTIC REALTIONSHIPS