PYRAMID MODELS AND INTERACTIONS

IN ECOSYSTEMS

Pyramid Models Used to show amount of matter and

energy in an ecosystem

Shows the general flow of energy from producers to consumers and the amount of organisms at each trophic level

Each level of a food chain contains less energy than the one below it.

Transfer of Energy

Only 10% of available energy is transferred from one trophic level to the next

90% of energy is lost as heat

Energy pyramid: Shows how available energy is distributed

among trophic levels in an ecosystemUnit of measurement is kcal (kilocalories)

Energy Pyramid

Biomass Pyramids Shows the total

amount of living tissue within a given trophic level (biomass)Represents the amount

of potential food available for each trophic level

Pyramid of Numbers Shows the number of

individual organisms at each trophic level in an ecosystem

Can be used to show the vast number of producers and consumers needed to support an ecosystem

Habitat and Niche Habitat: all the biotic and abiotic

factors in the area where an organism livesExample: A lions habitat might include

shade trees, tall grasses and watering holes

Niche: the way an organism interacts with its environment; composed of all the physical, chemical and biological factors a species needs to survive, stay healthy and reproduce

Habitat and Niche Think of a habitat as where as a

species lives and a niche as how it lives within the habitat.

A niche includes:Food: the type it eats, how it competes

with others, where it fits in the food webAbiotic Conditions: range of conditions

such as temperature and amount of water available

Behavior: time of day the species is active and where and when it reproduces

Community Interactions

1. Competition: when organisms attempt to use the same ecological resource at the same time

2. Predation: one organism captures and feeds on the other

3. Symbiosis: any relationship in which organisms live closely together

Community Interactions: Types of Symbiosis1. Mutualism: both species benefit from

the relationship- Ex. flowers and many insects: flowers

provide food, insects help flowers reproduce

2. Commensalism: one organism benefits and the other is neither helped or hurt- Ex. barnacles on whales

3. Parasitism: one organism lives on or in another and harms it- Ex. tick on a dog

Population Density and Distribution

Population Density: a measurement of the number of individuals living in a defined spaceExample: rural area vs. city

Population Dispersion: the way individuals in a population are spread in an area Clumped dispersion: live close togetherUniform dispersion: live at specific

distances from each otherRandom dispersion: individuals spread

randomly

Population Growth

Affected by:Number of births (increase)Number of deaths (decrease)Number of individuals that enter or

leave a population○ Immigration: movement of individuals

into an area○ Emigration: movement of individuals out

of an area

Exponential Growth Occurs when the

individuals in a population reproduce at a constant rateOccurs under ideal

conditions with unlimited resources

Logistic Growth Occurs when a

population’s growth slows or stops following a period of exponential growthMost common type of

growthAs resources become less

available, the growth of a population will slow or stop

Reaches carrying capacity: largest number of individuals that a given environment can support

Limits to Growth Limiting factors: factors that cause

a populations growth to decreaseCompetitionPredationParasitism and diseaseDrought and other climate extremesHuman disturbances

Density-Dependent Factors

Limiting factors that depends on population size

○ Affect mostly large populations○ Do not really affect small,

scattered populations○ Include: competition, predation,

parasitism and disease

Density-Independent Factors

Limiting factors that affect all populations in similar ways, regardless of population sizeUnusual weather, natural disasters,

seasonal cycles, human activities

Ecological Succession

Ecosystems are constantly changingNatural and human disturbancesOlder inhabitants die out, new

organisms move in Ecological Succession: phases of

growth from barren rock to a climax forest.

Primary Succession

Succession that occurs where no soil existEx. After volcanic eruption, retreating glacier

Pioneer species: first to appear in area (usually lichens)Mosses GrassesShrubs and trees

Primary Succession

Secondary Succession Disturbance of some kind changes

an existing community without moving the soilEx. Abandoned farmland, after wildfires