How Populations Grow Ms. Simons 2015

3 important characteristics of a population Its geographic distribution Its density Its growth rate

Geographic distribution Is the area inhabited by a population. This can vary in size A few cm for bacteria living on a rotting apple Millions of kilometers for a population of whales.

Population Density The number of individuals per unit area. http://2fm9xz2drvqemrbu.zippykid.netdna-cdn.com/wp-content/uploads/2012/10/population-density.jpg

3 factors that affect population size # births # deaths # of migrations (entering or leaving) A population will increase or decrease in size depending on how many individuals are added or removed from it.

Population Growth Birth rate > death rate = Growth Birth rate < death rate = Pop shrinks Birth rate = death rate = Pop stays the same

Immigration- the movement of individuals into an area. Emigration- the movement of individuals out of a population.

Exponential Growth Occurs when the individuals in a pop reproduce at a constant rate. At 1st the growth is slow Over time the growth increases at a faster rate. Under ideal conditions with unlimited resources, a pop will grow exponentially.

Rabbit population after 10 years shows exponential growth

Looking back Look at your graph from the deer population activity. At which point did the deer, lion, and resource populations grow exponentially?

Logistic Growth (S shaped curve) Occurs when a pop’s growth slows (or stops growing exponentially) -As resources become less available, the growth of population slows or stops.

Looking back Look at your graph from the deer population activity. At which point did the deer, lion, and resource populations show logistic growth?

Carrying Capacity This is the largest # of individuals an environment can support. This is where the growth levels off When the carrying capacity is reached the growth rate is zero.

Looking back Look at your graph from the deer population activity. At which point did the deer, lion, and resource populations reach carrying capacity?

Biotic Factors Biotic factors are the biological influences on organisms within an ecosystem. These are living influences, such as prey, predators, producers, and other cohabitating organisms.

Density-dependent factors Factors that influence the growth rate of a population Density of the population matters Usually biotic factors Examples: predation, disease, food availability, migration, & parasitism The density dependent factors are factors whose effects on the size or growth of the population vary with the population density. There are many types of density dependent limiting factors such as; availability of food, predation, disease, and migration. However the main factor is the availability of food. For example when the food supply of jack rabbits get depleted, they start to die or migrate to another places causing the foxes or the secondary consumers to have a shortage of food; also causing them to die or migrate. 

Abiotic Factors Abiotic factors are physical nonliving factors that shape an ecosystem. Ex. Climate (temperature, precipitation), sunlight, wind, limiting nutrients, etc.

Density-independent factors Any factor limiting the size of a population whose effect is not dependent on the number of individuals in the population Usually abiotic factors Examples: natural disasters, climate, precipitation

A Habitat A habitat is the area where an organism lives. A habitat includes both the biotic, and abiotic factors. Together biotic and abiotic factors determine the survival of both an organism and the productivity of the organism’s ecosystem.

Community Interactions Competition Predation Symbiosis Mutualism Commensalism Parasitism

Competition Competition occurs when two organism (of the same or diff species) attempt to use a resource in the same space at the same time. A resource is any life necessity. (food, water, light, shelter, etc.)

Competitive Expulsion Principle (CEP) CEP states that no 2 species can occupy the same niche in the same habitat at the same time.

Predation Predation is when one organism captures and feeds on another organism. The organism that does the killing is called the predator. The organism that gets killed is called the prey.

Symbiosis Symbiosis is any relationship in which 2 species live closely together. There are 3 main types of symbiosis. Mutualism- both species benefit from the relationship. Commensalism- One organism is helped by the relationship, the other, is neither helped nor harmed.

3. Parasitism- One organism lives on or inside another organism, and harms it. The parasite receives all or part of its nutrition from the host organism. The host is weakened, but not usually killed. Ex. tapeworm