Population Growth What is Population Growth An increase

Population Growth • What is Population Growth? – An increase in the size of a population over time • Some things exhibit Linear Growth – As time goes by, growth occurs at a steady rate – when graphed, it is a straight line

How do Populations Grow? • Populations show a J-shaped curve • Initial increases are slow, but as the population gets larger, it grows faster – Why? There are more organisms available to reproduce • This pattern is called Exponential Growth

Can it go on Forever? • Eventually, population growth will be affected by limiting factors – Such as: availability of food and space • The number of organisms an environment can support is called the Carrying Capacity • In time, the population growth will level off making an s-shaped logistical growth curve

Environmental Limitations • Two main types of Limitation Factors – Density-Dependent – Density-Independent • Density-Dependent Factors have an increased effect as population increases (more organisms, more risk) – – Disease Competition Parasites Predation

Environmental Limitations • Density-Independent Factors affect all populations regardless of their density (more organisms, same risk) – Temperature – Storms – Natural Disasters • (floods, hurricanes, etc) – Drought – Habitat Destruction – Pollution • Most are abiotic factors

Energy Flows through an Ecosystem in a Complex Network of Feeding relationships called a FOOD WEB. http: //www. brainpop. com/science/ecologyandbehavior/foodchains/

Food Web

Food Chain Food chain: one series of trophic levels

Obtaining Energy • Autotrophs - use the continuous supply of energy from the sun • Heterotrophs – must consume their energy, relying on the flow of energy from one population to another – – Herbivores Carnivores Omnivores Detritivore (AKA decomposers)

Herbivores • Eat plants (autotrophs)

Carnivores • Eat other heterotrophs – Predators – kill their own food – Scavengers – eat animals that are already dead

Omnivores • Eat both autotrophs and heterotrophs (plants and animals)

Detritivore • AKA decomposers – decompose organic matter and return nutrients to soil, water, and air – Ex. fungus, bacteria

Energy Pyramid • The energy pyramid is made of several trophic levels • A Trophic Level (or feeding level) is a group of organisms whose feeding source is the same number of steps from the Sun. – Primary Producers (Autotrophs) are the First Trophic Level. – Primary Consumers (Herbivores) are the Second Trophic Level. – Secondary and Tertiary Consumers (Carnivores and Omnivores) are the Third and Fourth Trophic Levels. – Most Animals feed at more than one Trophic Level.

Trophic Levels • Energy is Lost or Used as it Flows through the Trophic Levels of an Ecosystem. • Producers (Plants) absorb Energy from the Sun, but only about ½ of the Energy capture from the Sun becomes part of the Plants Body. The other ½ is used for Living and Growing or Lost as HEAT. • At each Trophic Level, the Energy stored in an organism is about 1/10 that of the Level Below it. (10%).

Trophic Levels • Because Energy diminishes at each successive Trophic Level, Few Ecosystems can contain more than 4 or 5 Trophic Levels. • Organisms at Higher Trophic Levels, Large Carnivores, tend to be Fewer in number than those at Lower Trophic Levels, Producers.

Number and Biomass Pyramids • The number of organisms at each trophic levels decreases as you step up the pyramid. • Biomass (living organic matter) is reduced at each trophic level as well

Bioaccumulation/Biomagnificatio n • Energy is not the only thing that is passed along through the food web. • If contaminants are introduced at any level, those organisms that consume the contaminated food, will absorb the contaminants as well. • Because the amount of energy required gets higher at each level, those organisms have to consume more and thus can accumulate higher levels of the contaminants in their bodies – bioaccumulation. • Example – A pesticide that you put of your yard is consumed by the grasshoppers that live there. The partridge eats 10 grasshoppers. The hawk eats 3 partridges. – If the grasshopper consumed 1 mg of the pesticide, the partridge ingested 10 mg, and the hawk consumed 30 mg.