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How Does Life Work?

Symbiosis and Interliving

Lives live with, on and within each other

Introduction to Symbiosis
Interliving—System-Wide Symbiosis
Five Enormous Interlivings




Symbiosis is a Basic Organizing Pattern of Life

clownfish in host anemone
cleaner shrimp on coral reef

yucca moth placing pollen
on yucca stigma

an ant protector about to receive its reward from an acacia nectary


The most inventive and novel of all schemes in nature, and perhaps the most significant in determining the great landmark events in evolution, is symbiosis, which is simply cooperative behavior carried to its extreme. But something vaguely like symbiosis, less committed and more ephemeral, a sort of wish to join up, pervades the Biosphere.

—Lewis Thomas, in The Fragile Species

Introduction to Symbiosis

To understand any organisms, you study how they interact with other life forms in their ecological communities, for all lives on Earth are communal and depend on each other. This means that all organisms in natural communities relate, interact, and communicate. These interdependencies are what ecology is all about. There is no way to resign from these interdependencies. Humans have decided that we are above Nature and have ignored our interdependence. We take, but do not give back; we expect free lunch, but there is none, and never was. This one-sided taking without giving back is at the root of the ecological crisis/collapse taking place worldwide.

Until recently, mutually helpful symbiosis, which simply means 'living together', was regarded by many scientists as an exception to the rule of
etition. Cooperation was regarded as a curiosity, not to be taken seriously.

In the past fifty or so years, the role of symbiosis has been shown to be central to the evolution of all animals and plants, including our own. Symbiosis is extremely common and complex, and takes many forms. Virtually all macro-organisms live in association with gut microbes that not only help digest food by providing enzymes, but in many cases also provide vitamins and amino acids which may not occur in the organism's diet. This greatly improves survival and reproductive fitness.

The word "Symbiosis" means, at root, living together. The word has come to mean different things to different scientists. For some symbiosis refers to all long-term intimate relationships in which differing organisms live on or inside each other. This may include parasitism, where one partner benefits as the other is harmed. For other scientists, symbiosis refers to long-term intimate relationships where no harm takes place--the focus being on cooperation. When both partners benefit, it's called Mutualism. When one partner benefits and the other is not harmed, it's called Commensalism.

For present purposes, in Morning Earth Symbiosis pages, we will use the word Symbiosis to include all non-harmful intimate relationships, including behavioral symbioses that are seasonal and cyclical, such as plants offering fruit to birds at migration time, when the seeds in the fruit will be most widely dispersed as they pass through the birds. We will also include behavioral symbiosis that is the result of choice rather than necessity, such as mixed bird flock foraging, or mutual hunting by two species, such as grouper fish and giant moray eels.

Obligate Symbiosis & Symbiosis by Choice,
aka Facultative Symbiosis

Some organisms cannot survive without their symbionts. They are obliged to live in symbiosis. This is called obligate symbiosis. Examples include hot vent tube worms with bacteria, bee with flower pollination, grazers with rumen protozoans and rumen protozoans with endosymbiont bacteria.

Other organisms can live outside of symbiosis, although they may not thrive. This is called facultative or optional symbiosis. Many behavioral symbioses seem to be chosen. Examples include cooperative hunting of groupers with moray eels, oxpecker birds with grazing mammals, and mixed- species flocks of foraging songbirds.

Interliving—System-Wide Symbiosis

Symbiosis is traditionally seen as a narrow relationship between individual organisms; this is a small-scale concept. However, there are enormous large-scale symbioses that permeate the entire biosphere and affect all life.

Gas Exchange: Plants exhale oxygen and animals exhale carbon dioxide. We have all co-evolved to live off the other’s waste products.

Gut Symbiotes: No animals can fully utilize their food without the help of microbial partners in their guts. The symbiotes are bacteria, archaea and protozoans.

Mycorrhiza: Virtually all plants earthwide thrive only in partnership with fungi, in an association called mycorrhiza (fungus-root)

Nitrogen-Fixing: plant life earthwide depends on nitrogen-fixing microbes

 For such biosphere-wide symbioses we will use the word “Interliving.”

As we begin to understand natural communities and the many ways all the members connect and depend on each other, we begin to also grasp that the separations we make between life’s kingdoms—plant, animal, fungi, bacteria, archaea--while clearly useful-- may have also blinded science to the discovery that life on Earth has evolved to be symbiotic consortiums, or associations. As each organism leafed out on the tree of life, microbial life co-evolved in partnership right along with them, typically inside. The very cells inside the bodies of plants and animals and protists originated as associations of different kinds of bacteria.

In the past 50 years, microbiologists and geneticists, using new tools, have demonstrated that we life forms all live in close association with other, genetically unrelated life forms. We are all combined beings. A kind of obligatory cooperation permeates the entire biosphere.

One implication is that the balance of competition and cooperation in ecosystems must be re-weighted in our daily thinking.

Interliving includes the widest possible spectrum of relationships among living organisms that are beneficial to the Biosphere. Cooperation for mutual benefit is at the very root of how the Biosphere evolves and functions.

Five Interlivings at Biosphere Scale
Look through these clarifying lenses to see the
Why & How

click to enlarge

Gas Exchange
Photosynthetic life creates oxygen; animal life creates carbon dioxide. We breathe each others' by-products.
Some soil bacteria (land), some cyanobacteria (oceans and land), cryptobiotic crusts (deserts) and some lichens have the ability to "fix" or pull nitrogen from the atmosphere and preserve it in chemical forms that can be used by organisms. Without nitrogen, no life.
In all terrestrial biomes, and some in freshwater, fungi partner with plant roots. These "fungus roots" vastly increase the plant's ability to absorb nutrients. The plant supplies its partner with carbon compounds. 95% of plants thrive through mycorrhizal interliving. Mycorrhizal plants are better able to tolerate environmental stresses than are plants without mycorrhiza.
Animal Gut Bacteria
The vertebrate digestive system depends on bacteria. Most arthropod and worm digestive systems do as well. Some bacteria digest cellulose; some synthesize amino acids; some synthesize vitamins; some synthesize enzymes. In humans, bacteria supply vitamin K. Over 500 kinds of bacteria are found in the human gut. Animals don't receive sufficient nourishment without their intestinal fauna. Lab-raised "germ-free" rodents are unhealthy and do not thrive. Developing immune systems require the presence of gut bacteria.
The eucayote (nucleated) cell structure that led to multicellular plants and animals originated through a series of symbioses in which some bacteria invaded a host and learned to live peaceably inside the host for mutual benefit. Each of the billions of cells inside your body originated in Interliving.

"Life did not take over the globe by combat, but by networking."

--Lynn Margulis

Cooperation among living organisms is at least as prevalent as competition. Mutual cooperation between life-forms and within natural communities is one of the driving forces of evolution.

Biologist Lynn Margulis, famous for her work on serial endosymbiosis and Gaia theory, demonstrates that symbiosis is a major driving force behind evolution. Darwin's idea of evolution driven by competition, she says, is overemphasized, and argues that evolution is strongly based on co-operation, interaction, and mutual dependence among organisms.

Look through these clarifying lenses to see the
& How of Interlivings.

For Cleaning
For Protection & Shelter

Ants:Monarchs of Symbiosis

Giraffes and Acacias: one case focus
For Reproduction
Wheels Within Wheels
To Pioneer & Fix Nitrogen


Explore Symbiosis




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