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Interdependence of Living Things

Interactions of organisms with the environment that are vital to survival.

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Interdependence - Advanced

What does it mean to be interdependent?

Do species live alone, or do many live in communities with other organisms? All species rely on other species in some way for their survival. They may rely on other species for food, shelter or to help them reproduce. Here the bee is helping the flower spread its pollen. Species are not independent, they are interdependent.

Interdependence of Living Things

Biological interactions are the interactions between different organisms in an environment. In the natural world, no organism is cut off from its surroundings. Organisms are a part of their environment which is rich in living and non-living elements that interact with each other in some way. The interactions of an organism with its environment are vital to its survival, and the functioning of the ecosystem as a whole.

These relationships can be categorized into many different classes. The interactions between two species do not necessarily need to be through direct contact. Due to the connected nature of ecosystems, species may affect each other through such relationships involving shared resources or common enemies.

The term symbiosis comes from a Greek word that means “living together.” Symbiosis can be used to describe various types of close relationships between organisms of different species, such as mutualism and commensalism, which are relationships in which neither organism is harmed. Sometimes the term symbiosis is used only for cases where both organisms benefit, sometimes it is used more generally to describe all kinds of close relationships, even when one organism is killed by another, as shown in Figure below. Symbiosis can also be used to describe relationships where one organism lives on or in another, called parasitism, or when one organism kills and eats another organism, called predation. These relationships will be further described in Ecology - Advanced.

There are many different types of symbiotic interactions between organisms. Clockwise from top left: Escherichia coli bacteria live inside your intestines in a mutualistic relationship: the bacteria produce Vitamin K for you, and they get their food from what you eat. Clownfish that live among the tentacles of sea anemones protect the anemone from anemone-eating fish, and in turn the stinging tentacles of the anemone protect the clownfish from its predators (a special mucus on the clownfish protects it from the stinging tentacles). Similar to the E. coli, this bee has a mutualistic relationship with the flower, the bee feeds from the flower, and the flower gets pollinated by the bee. Lions are predators that feed on other organisms such as this Cape buffalo.

A flock of starlings looks out, before searching for parasites on a red deer stag.

Competition is as an interaction between organisms or species, for the same resources such as water, food, or hunting grounds in an environment, shown in Figure below. Eventually, the species that is less able to compete for resources will either adapt or die out. According to evolutionary theory, competition for resources plays an important role in natural selection.

Competition between organisms and species. These male deer are competing for females during rutting (mating) season. Trees in this Bangladesh forest are in competition for light.

Animals that eat decomposing organic material also have an important interaction with the environment. They help to decompose dead matter and assist with the recycling of nutrients. By burying and eating dung, dung beetles, such as the one shown in Figure below, improve nutrient cycling and soil structure. They make the dead organic matter available to bacteria that break it down even further.

Dung beetles have important interactions with the environment, through which many other organisms benefit.

Organisms are not independent, they are interdependent. They cannot live alone; they need other organisms to survive. The same is true for species. All species need other species to survive.

Levels of Organization

In studying how organisms interact with each other, biologists often find it helpful to classify the organisms and interactions into levels of organization. Similar to the way an organism itself has different levels of organization, the ways in which organisms interact with their environment and each other can also be divided into levels of organization. For example:

The biosphere includes all living things within all of their environments. It includes every place that life occurs, from the upper reaches of the atmosphere to the top few meters of soil, to the bottoms of the oceans. An ecosystem is made up of the relationships among smaller groups of organisms with each other, and with their environment. Scientists often speak of the interrelatedness of living things, because, according to evolutionary theory, organisms adapt to their environment, and they must also adapt to other organisms in that environment.

A community is made up of the relationships between groups of different species. For example, the desert communities consist of rabbits, coyotes, snakes, birds, mice and such plants as sahuaro cactus, ocotillo, and creosote bush. Community structure can be disturbed by such dynamics as fire, human activity, and over-population.

A population is a group of individuals of a single species that mate and interact with one another in a limited geographic area. For example, a field of flowers which is separated from another field by a hill or other area where none of these flowers occur.

It is thus possible to study biology at many levels, from collections of organisms or communities, to the inner workings of a cell (organelle). More about the interactions of organisms will be discussed in Ecology - Advanced.

This picture shows the levels of organization in nature, from the individual organism to the biosphere.

The Diversity of Life

Evolutionary theory and the cell theory give us the basis for how and why organisms relate to each other. The diversity of life found on Earth today is the result of 4 billion years of evolution. Some of this diversity is shown in Figure below. The origin of life is not completely understood by science, though limited evidence suggests that life may already have been well-established a few 100 million years after Earth formed. Until approximately 600 million years ago, all life was made up of single-celled organisms.

The level of biodiversity found in the fossil record suggests that the last few million years include the period of greatest biodiversity in the Earth's history. However, not all scientists support this view, since there is a lot of uncertainty as to how strongly the fossil record is biased by the greater availability and preservation of more recent fossil-containing rock layers. Some researchers argue that modern biodiversity is not much different from biodiversity 300 million years ago. Estimates of the present global species diversity vary from 5 million to 30 million species, with a best estimate of somewhere near 10 million species. All living organisms are classified into one of the six kingdoms: Archaebacteria (Archaea), Eubacteria (Bacteria), Protista (Protists), Fungi, Plantae (Plants), and Animalia (Animals).

New species are regularly discovered and many, though already discovered, are not yet classified. One estimate states that about 40 percent of freshwater fish from South America are noa few of the many members of the animal kingdom are shown in Figure below. The animal kingdom is just a tiny portion ot yet classified. Every year, scientists discover the existence of many hundreds more archaea and bacteria than were previously known. Just f the total diversity of life. More about the diversity of living creatures will be discussed throughout numerous concepts.

Animal diversity. This figure shows just a fraction of the diversity of life. The diversity of organisms found in the five kingdoms of life, dwarf the number of organisms found in the animal kingdom. The other kingdoms of life are Eubacteria, Archaebacteria, Protista, Fungi, and Plantae.


  • biodiversity: The variety of life and its processes; including the variety of living organisms, the genetic differences among them, and the communities and ecosystems in which they occur.
  • biological interactions: The interactions between different organisms in an environment.
  • biosphere: The areas of Earth where all organisms live; extends from about 11,000 meters below sea level to 15,000 meters above sea level.
  • commensalism: A symbiotic relationship in which one species benefits while the other species is not affected.
  • community: The populations of different species that live in the same habitat and interact with one another; the biotic component of an ecosystem.
  • competition: The relationship between organisms that strive for the same limited resources.
  • ecosystem: A natural unit consisting of a community (the biotic factors) functioning together with all the nonliving (abiotic) physical factors of the environment.
  • interdependent: The notion that organisms (species) cannot live alone; they need other organisms (species) to survive.
  • mutualism: A type of symbiotic relationship in which both species benefit.
  • parasitism: A symbiotic relationship in which one species (the parasite) benefits while the other species (the host) is harmed.
  • population: A group of individuals of a single species that mate and interact with one another in a limited geographic area.
  • predation: A relationship in which members of one species (the predator) consume members of other species (the prey).
  • symbiosis: A close relationship/association between organisms of different species in which at least one of the organisms benefits from the relationship.


  • The interactions of an organism with its environment are vital to its survival, and the functioning of the ecosystem as a whole.
  • An ecosystem consists of the relationships among smaller groups of organisms with each other, and with their environment.
  • Symbiosis can be used to describe various types of close relationships between organisms of different species.
  • Competition is as an interaction between organisms or species for the same resources in an environment.


Use this resource to answer the questions that follow.

  • http://www.hippocampus.org/Biology \begin{align*}\rightarrow\end{align*} Non-Majors Biology \begin{align*}\rightarrow\end{align*} Search: Interactions Within Communities
  1. How do organisms within a community interact with each other?
  2. Describe and give examples of the two types of competition.
  3. How may predation benefit the prey population?
  4. Describe the various types of symbiotic relationships. Provide examples of each.


  1. What is biological interactions?
  2. What is the difference between mutualism and commensalism?
  3. What is predation?
  4. What are the levels of organization that organisms interact with their environment and explain them.
  5. Give an example of how you are interdependent from another organism.

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