Post on 17-Jan-2016
Biotic and Abiotic Population Influences within Ecosystems• Limiting factors• Tolerance• Biotic & Abiotic population
influences• Symbiosis• Predator-Prey relationships• Population equation• Exponential growth
Limiting Factor• Abiotic factors determine where a species can
live (temperature, precipitation, etc.)• Biotic factors determine the species’ success
(number of predators, available food, etc.)• A limiting factor is any factor that places an
upper limit on the size of a population.
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 because they would overheat)
• Factors that limit one population in a community may also have an indirect effect on another population.
• Example: lack of water limits the growth of flowers
less flowers = less food for caterpillars less caterpillars
less caterpillars = less food for frogs less frogs
less frogs less snakes
less snakes less owls
Tolerance• The ability of an
organism to withstand a range of biotic and abiotic factors.
• Different species have different ranges of tolerance.
Tolerance
• Optimal Zone = best conditions for the organism to survive
• The further you go from the optimum zone, the lower your population
• The range of tolerance are the conditions that the organism can continue to exist in.
• Outside the range of tolerance, the organism will not survive.
Abiotic Impacts on the Biomes of the World
Carrying capacity - number of organisms of one species that an environment can support indefinitely (forever).
Biotic Influences
Do all organisms get along with each other?
• How organisms live together in an ecosystem is called symbiosis.
• There are 3 types of symbiosis:1. Mutualism2. Parasitism3. Commensalism
Mutualism• Both species benefit from the relationship.• E.g. Clown fish and sea anemones. Clown fish
are protected from predators by the stinging tentacles of the sea anemones and in return, the anemone receives protection from animals that would prey upon it.
Parasitism• One species benefits at the expense of another species.• Parasites usually don’t kill their host (the animal they live
on). Why would they kill the thing that is providing them food and a home?
• Example – ticks on a dog– A tick is a parasite that feeds off the nutrients in the
dog’s blood. The dog doesn’t get the nutrients so it is harmed.
Commensalism• Occurs when one species benefits from a
partnership (gets food, protection, etc.) without benefiting or harming the other.
• E.g. Tigers and golden jackals. These jackals will attach themselves to a particular tiger, trailing it at a safe distance in order to feed on the big cat's kills.
Symbiosis: Mutualism, Commensalism, and Parasitism
Predator – Prey Relationship• Predator – a type of consumer that will seek
out and eat other organisms.• Prey – the animal that the predator eats.• Examples – cat & mouse; lion & antelope
Predator – Prey!!
Predator – Prey Relationship• In many cases they act to regulate each other. • E.g. If there are more predators, the population
of prey will decrease. If prey numbers decrease, there is less food for the predators so their population decreases.
Predator = Lynx, Prey = Hare
Predator = WolfPrey = Moose
Population Factors
• How a populations change (increase or decrease)
• Natality (Births)• Mortality (Deaths)• Immigration (Animals coming in)• Emigration (Animals leaving)
Population Factors
The Population equation
New Population =
Old Population + Natality + Immigration – Mortality – Emigration
Exponential Growth• Rapid, uncharacteristic growth which only occurs
under certain circumstances for a short period of time
• Can be seen when an organism enters a new habitat that has a lot of resources or when predators are removed
• E.g. In South Africa, elephants became protected after many years of hunting for their tusks. This graph shows the result of the hunting ban instituted in 1960.