The maximum rate at which a population could increase is called the biotic potential.
Different populations have different biotic potentials.
The age at which reproduction begins, the life span during which the organisms are capable of reproducing, the number of reproductive periods in the lifetime, and the number of offspring the organisms is capable of reproducing are all factors.
Regardless of whether a population has a large or small biotic potential, certain characteristics about growth are common to all organisms.
The simplest model for population growth is one with growth that is uncontrollable.
There is no competition in this population.
It is in an environment with unlimited resources and has no immigration or emigration.
This is a characteristic of a population that has recently been introduced into an area.
The human population has been in the growth phase for over 300 years.
The density of individuals can exceed the system's resources.
There is a limit to the number of people that can live in one place.
The carrying capacity is the limit.
Each environment has its own carrying capacity around which the population size changes.
As the environmental conditions change, the carrying capacity changes as well.
A fire may have destroyed several acres of forest habitat.
Population growth can be limited by limiting factors.
Density- dependent and density-independent factors are divided into two categories.
Density- dependent factors increase as the population density increases.
Competition for food, waste, and disease are included.
Density-independent factors are not related to population density.
There are earthquakes, storms, and naturally occurring fires and floods.
Some species reproduce quickly when the environment is not crowded and resources are plentiful.
They are called r-strategists.
The K-strategists live in a dense population near a fierce competition.
r-strategists are organisms that have a big bang pattern of reproduction.
In an unusual wet year, it suddenly sends up a large flowering stalk, produces seeds, and then dies.
When the environment is changing and the population is decreasing, the plant has evolved a strategy to increase probability of success through sheer numbers.
In a stable environment where competition for resources is intense and adults are more likely to survive to breed again, repeat reproducers are favored.
A few large offspring may have a better chance of survival.
The loggerhead sea turtle lays about 300 eggs per year and may lay eggs for 30 or more years.
The Hudson Bay Company kept records of the pelts sold by trappers from 1850-1930, which is an excellent study in population growth.
The hare and the lynx are feeding on the grass.
The cycles in the lynx population are caused by fluctuations in the hare population.
The hare population experiences rapid growth and crashes.
The hare population cycles are probably due to a limited food supply for the hare due to a combination of overcrowding and overgrazing.
Populations interact with the environment and each other in communities.
They are characterized by their density and diversity.
There are two components to species diversity.
There is a number of different species in the community.
The different species have relative abundance.
Diverse communities are more productive because they are more stable.
They are better able to recover from environmental stresses such as a drought or an incursion by an Invasive species.
There are five different categories of interactions within a community.
In terms of species composition and species diversity, the structure of a community is measured.
The competitive exclusion principle was developed by the Russian scientist G. F. Gause.
He worked with two very similar species.
Each population grew quickly and leveled off at the carrying capacity when he cultured them separately.
The other species was driven to extinction by P. aurelia when he put the two cultures together.
Two species cannot coexist in a community if they use the same resources, according to his principle.
If two species are in the same niche and compete for resources, there will be two related outcomes.
Natural selection will allow one of the species to exploit different resources.
Resource partitioning is what it is.
There is a possibility of what happened on the Galapagos Islands.
Natural selection resulted in different beak sizes for finches and they were able to avoid competition by eating different kinds of seeds.
Character displacement is a divergence in body structure.
Predation can refer to an animal eating another animal or to an animal eating plants.
Plants and animals have evolved defenses for protection.
Animals have evolved defenses such as hiding, fleeing or defending themselves.
These can be very expensive in terms of energy.
Animals have evolved passive defenses that make it difficult to spot their prey.
Distribution and abundance of populations are affected by interactions among populations.
Aposematic coloration is the bright red or orange color of poisonous animals as a warning to avoid them.
One harmless animal mimics the color of a poisonous animal.
One example is the viceroy butterfly, which is harmless but looks very similar to the monarch butterfly, which stores poisons in its body from the milkweed plant.
In M U llerian mimicry, two or more poisonous species resemble each other and gain an advantage from their combined numbers.
A predator learns to avoid any prey with that appearance.
An interaction in which an organisms eats part or parts of a plant or alga is known as herbivory.
Invertebrates eat vegetation.
In the oceans, there are animals like snails and sea urchins.
Adapted to the right plant body or flower, such as specialized teeth or a modified digestive system, herbivores are similar to predators.
Plants have evolved to fight off attacks from animals.
The relationship between two or more species is called symbiotic.
These relationships can be positive or negative.
Both organisms benefit from the relationship.
The human intestine is home to the bacteria that produce vitamins.
Mycorrhizae is an example of mutualism, it is a relationship between roots and fungi that enhances the absorption of vitamins and minerals.
There is a symbiotic relationship between two organisms where one benefits and the other is unaware of the other.
Barnacles attach themselves to the underside of a whale to gain access to a variety of food sources as the whale swims into different areas.
The whale is not aware of the barnacles.
The parasites benefit from the host being harmed in a symbiotic relationship.
A tapeworm is an example of a parasites.
Organisms can have positive effects on the survival and reproduction of other species without living in direct and intimate contact with them.
A good example of facilitation is the black rush Juncus gerardi, which makes the soil more hospitable for other species in New England salt marshes.
It helps keep salt out of the soil by shading it.
For the next 25 years, Earth will be bombarded with enough sunlight to meet the needs of the human population.
Most solar radiation is absorbed by the atmosphere.
Less than 1% of green plants are actually converted to chemical bond energy.
The basis for almost all of Earth's food chains is that energy.
Ecologists talk about energy flow on Earth in terms of gross primary productivity and net primary productivity.
The amount of light energy that is converted to chemical energy is called gross primary productivity.
Net primary productivity is equal to the GPP minus the energy used by producers for their own cellular respiration.
The total or global NPP of Earth is affected by the different ecosystems in their NPP.
Tropical rainforests are among the most productive and contribute a large portion of Earth's net primary production.
Coral reefs occupy a tiny part of the planet and have a very high NPP, but they don't contribute much to the global NPP.
The open oceans are not the same as coral reefs.
It is very low per unit area.
Because they occupy three-fourths of the globe, their contribution to the global NPP is higher than any other.