The study of the interactions of organisms with each other is called E cology.
Here are some words for the topic.
A population is a group of people who live in the same area and have the ability to interbreed.
The organisms living in one area make up a community.
All the organisms in a given area, as well as the abiotic factors with which they interact, are included in an ecosystems.
Abiotic factors include temperature, water, sunlight, wind, rocks, and soil.
The global environment is referred to as the biosphere.
You should know the properties of populations.
N is the total number of individuals in a population.
The number of individuals per unit area is called density.
It is difficult to count the number of organisms in an area.
Imagine trying to count the ants in a small area.
Scientists use sampling techniques to estimate the number of organisms.
Mark and recapture is a sampling technique used to estimate the size of a population.
The organisms are captured, tagged, and then released.
50 zebra mussels are captured, marked, and released.
A week later, 100 zebra mussels are captured and 10 are found to have markings.
The total population would be 500 zebra mussels.
The pattern of spacing of individuals within an area is called dispersion.
clumped is the most common pattern of dispersion.
There is safety in numbers when fish travel this way.
The populations are spread in a pattern.
Certain plants may have toxins that keep other plants away.
Random spacing happens in the absence of special attractions.
There are trees in a forest.
The size and composition of a population can be shown by survivorship or mortality curves.
There are three types of curves.
There are organisms with low death rates in young and middle age and high mortality in old age.
The high survival rates of the young can be attributed to a lot of parenting.
This is a characteristic of humans.
The type 2 curves describe a species with a constant death rate.
The hydra, reptiles, and rodents are described.
The type 3 curves show a high death rate among the young but then show that death rates decline for those few individuals that have survived a certain age.
This is a characteristic of fish and invertebrates that release thousands of eggs, have no parenting, and have external fertilization.
Both biotic and abiotic factors affect the stability of populations.
The age structure of populations is important.
The age structure diagram shows the relative numbers of people.
The pyramidal shape is characteristic of developing nations with half the population under the age of 20.
The population in 20 years will be enormous even after taking into account disease, famine, natural disasters, and emigration.
The United States has a stable population and no population growth, and the birth rates and death rates are about the same in each age group.
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.
All living systems rely on free energy.
The food chain is where food is moved from one level to another.
Most of the energy stored in trophic levels is converted to organic matter at the next trophic level.
The food chain can support only 10 kJ of tertiary consumers if you start with 10,000 kJ of plant matter.
Food chains are short because of the loss of energy from one level to the next.
They don't have more than four or five levels.
Long food chains are less stable than short ones.
Local extinction of top predator is caused by population fluctuations at lower levels.
A good model to demonstrate the interaction of organisms in the food chain is the food pyramid.
Food chains are interwoven with other food chains into a food web.
An animal can occupy different levels in a food chain.
Humans can be primary consumers when eating vegetables, but tertiary consumers when eating a steak.
There are two components to species diversity, the variety of kinds of organisms that make up a community.
There is a number of different species in the community.
The proportion of different species within a community is called relative abundance.
Communities that have a lot of diversity are better able to fight off invaders.
They are able to recover from environmental stresses.
One unfortunate example of the importance of diversity in a community is here.
Communities are made up of populations of organisms.
The Cavendish is the only banana variety cultivated in the world.
The Cavendish is being attacked by a fungus.
It has destroyed crops in Taiwan, Indonesia, and Malaysia and threatens plantations in South and Central America.
The lack of diversity in banana culture has left the banana vulnerable to disease and may leave us with no bananas to eat.
In a community, the species that are most abundant are the ones that have the highest amount of biomass.
They control the distribution of other species.
There are sugar maples in North American forests.
They affect the abiotic factors, such as shade and soil nutrients, which in turn provide special habitats for many other species.
There are not many keystone species in the community.
They control other species in the community.
There are sea otter in the North Pacific.
They are high in the food chain and feed on sea urchins.
There aren't many sea otter and there aren't many sea urchins and kelp forests.
In contrast, where orcas feed on sea otter, sea urchins and kelp are rare.
There are two models for the structure of a community.
Influence from lower to higher trophic levels is the focus of the bottom-up model.
Increasing the availability of minerals in the environment will increase the amount of wood produced by the producers, and will increase the amount of wood used by the trophic level.
The effect will not extend down to the bottom levels if you add or remove predators.
The top-down model was developed in 1963.
An increase in the mass of producers can be achieved by removing the top carnivores from a community.
The model is called the trophic cascade.
An excellent example is what happened in the park.
The wolves were reintroduced in the park in the 1990s after public sentiment shifted.
When there were no wolves, the aspen tree population in the park decreased from 6 to 1%.
The density of the aspen trees increased when wolves were reintroduced into the park.
It is thought that the pressure on the elk population was caused by the wolf population.