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• A group of members of the same species that live in the same area.
• The size of any population is constantly changing.
• WHY?Limiting factors - an environmental factor that
prevents an increase in the number of organisms in a population or prevents them from moving into new habitats
Limiting Factors that affect populations in ecosystems:
2 types:1) Abiotic
- a) resources available- b) climate- c) natural and human disturbances
2) Biotic - a) competition among organisms- b) predation- c) cooperation and symbiosis- d) presence of disease
ABIOTIC:WHAT IS A RESOURCE?
Anything needed by an organism for life
Examples:
_____________________________Nutrients, water, sunlight/energy, space
ABIOTIC:What are examples
of climate?• temperature, humidity, atmospheric pressure, wind, rainfall
These in turn can cause/contribute to some natural disturbances like:
storms, droughts, fires
ABIOTIC:What are examples of human
disturbances?
• logging• development and construction
BIOTIC:What is competition?
• interaction between 2 or more organisms competing for the same resource in a given habitat
• Can occur between members of same species- Example: male mountain goats compete to determine who will mate and produce offspring
• Members of different species may compete for the same resources- Example: raccoons and ravens might both try and feed on eggs from the same nest of a common bird
BIOTIC:Competition
• For similar species to live together in the same area, they must have slightly different niches.
WHAT CAN ORGANISMS COMPETE FOR?
- All the abiotic factors!
- Mates!
COMPETITION
FOOD
Organisms in an ecosystem have to compete with each other for available resources.
When one tugs at a single thing in nature, he finds it attached to the rest of the world.
~John Muir, naturalist, Sierra Club founder
• Have you ever wondered why we don’t see millions of mice running around when we look out the window if they reproduce so quickly?
• The environment can only support a maximum number of individuals because of limited resources
Characteristics of a Population:• As a population grows, each individual gets a
smaller share of the resources in the area.• If resources are scarce, some organisms will
starve and populations will decrease.• The organisms become stressed. Some die,
others aren’t able to reproduce.• This may lead to fewer births and more
deaths. Eventually, the number of births = number of deaths
• The population is in EQUILIBRIUM
REMEMBER: EVERYTHING IS CONNECTED !
•A decrease in the prey population means some predators will starve.•Fewer predators mean prey population will increase.
•Increase in prey means more food for predators.•Predator population will increase until there is not enough food . . . and the cycle repeats itself.•Rabbit/Wolf simulation: http://www.shodor.org/interactivate/activities/RabbitsAndWolves/