# Population Growth Sharks Fish Clarifying Objective 2.1.4 Explain how ecosystems can be relatively stable over hundreds or thousands of years, even though.

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Population Growth Sharks Fish Clarifying Objective 2.1.4 Explain how ecosystems can be relatively stable over hundreds or thousands of years, even though populations may fluctuate due to availability of food and shelter, as well as the number of predators, or disease.

A population includes any species living in a particular area. Most organisms live in social groups because doing so provides several advantages: increased protection from predators, increased chances for mating, and effective hunting techniques. Populations

Population growth refers to an increase in the size of a population over time Population Growth = Birth Rate - Mortality Rate An increase in birth rate or a decrease in mortality rate will cause an increase in population growth

Population growth can also be affected by immigration, individuals moving in, or emigration, individuals moving out.

Graphs are used to analyze population growth X axis - Years Y axis Number of Grocery Stores Number of grocery stores in Randolph County

Linear Growth is when the numbers increase steadily by the same amount (2, 4, 6…) X axis - Years Y axis Number of Grocery Stores Number of grocery stores in Randolph County

Exponential Growth is when the numbers increase by a larger amount each time (2, 4, 16, 256…) X axis - Years Y axis Number of Grocery Stores Number of Grocery Stores in Wake County

Populations tend to increase exponentially in that as they grow larger they begin increasing faster Slow Increase Rapid Increase

The J – Curve Shows Exponential Population Growth

All ecosystems have a limited amount of resources or factors to support populations All organisms need water, food, space for habitats, and sanitary conditions.

As populations increase, there is more competition for the same resources Populations begin to die out due to disease, starvation, or thirst

Therefore, any ecosystem can only support a certain amount of individuals Carrying Capacity refers to the maximum number of individuals an ecosystem can support

If a population goes above the carrying capacity, it cannot be sustained and eventually the population will crash.

If the population size, after a population crash, goes below a critical number, it will not be able to revive its population and is classified as endangered.

Most natural populations fluctuate around the carrying capacity

The S – Curve shows logistic growth where a population begins to stabilize as it reaches its carrying capacity The carrying capacity is determined by limiting factors such as amount of available resources or ability to fight off diseases

Limiting factors that restrain population growth and do not depend upon the initial size of the population are called Density-Independent Factors FloodsFiresEarthquakes Cold Spells Hot Spells Drought

Limiting factors that restrain population growth and do depend upon the initial size of a population are called Density-Dependent Factors Food Shortages Water Shortages Diseases Habitat Space

Competition between species that compete for the same resources can also affect population growth Gray Seal Sabel Island Lance Fish Harbor Seal

One population will usually out compete the other causing a decline in the other population Harbor Seal in Grey Seal in mixed Months

Predator – Prey Relationships also affect Population Growth Increase in predators cause a decrease in prey As prey decreases, the predator decreases As predators decrease, prey increases As prey increases, predator increases

There is always a delayed relationship in growth and decline between the two populations

Predation not only removes the very old, the very young, and the weaker members from a population, it also helps regulate the prey population.

If the predators do not keep the prey population in balance, the carrying capacity is exceeded and the prey may starve due to overgrazing.

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