How Ecological Interdependence Affects You
or Why We Can’t Stop Holding Hands with all our Biota Neighbors
Copyright 2002-2012 David Dilworth
- Sea Otters and Kelp (c) Copyright 2008 David Dilworth
Here are some principles and examples of how very different species need each other to stay alive.
Species Interdependence
The life of every animal and plant depends upon other biota.1
When one species is removed for human use, other biota, not directly touched and perhaps even unnoticed by humans, can suffer because they depend on that species. Even worse, such damage can cause a second species’ irreversible decline into extinction.
Ecological Interdependence
When an ecosystem service (e.g. soil retaining ground moisture) is lost or weakened it can harm many species.
Sea Otters, Kelp and Sea Urchins
Lets take a look at a simple system involving Sea Otters, Kelp and Sea Urchins. They all depend upon each other. Kelp is eaten by Sea urchins, sea otters eat sea urchins, and sea otters get predator protection from kelp.
Kelp Loss
If we let industry harvest too much kelp, Sea Otters leave or decline in population because they have nowhere to sleep and hide from predators such as sharks and Orcas. They must move to find other protected foraging areas. When Sea Otters leave or decline sea urchins thrive and eat too much kelp and the remaining kelp forest dies.
In 2012 the number of Sea Otter deaths due to sharks skyrocketed to 30 percent from just a few percent. About a decade earlier the state of California allowed huge increase in Kelp harvesting in the heart of the Sea Otter range. Coincidence? No, this was completely predicted by us (at HOPE) and others at the time of the Kelp Forest destruction application.
Sea Urchin Loss
If we let industry harvest too many sea urchins, Sea Otters have to find other food and may leave. When Sea Otters leave or decline sea urchins can rebound and destroy a kelp forest preventing sea otters’ return.
Sea Otter Loss
If we let sea otters decline sea urchins thrive and can destroy a kelp forest. The California kelp forest was decimated by sea urchins after Southern Sea Otters were hunted to near extinction by 1900.
Monterey Pine Forest Ecosystem Interdependence
For another example, lets look at how woodpeckers, Monterey pine trees bark beetles and pine pitch canker interact.
Animals, Pines and Insects
Bark beetles carry the dreaded Pine Pitch Canker. Woodpeckers eat insects which damage trees, including Bark beetles. Woodpeckers depend on dead standing trees for homes mainly because dead trees have softer wood. Woodpeckers can carve a nest cavity much easier in soft, dead wood than in hard live wood.
This means that to minimize Pine Pitch Canker we must not disturb Woodpeckers or their homes – dead standing Monterey pine trees. When all dead standing trees are cut down, woodpeckers leave. When woodpeckers leave, bark beetles abound and kill many trees and spread the Pine Pitch Canker which kills many more trees.
We All Depend On Soils
“We must stop treating soils like dirt.” — David Brower
Humans cannot dine on rocks or dirt, but plants must. Since essentially everything we eat is either a plant, or an animal which ate plants, and that plants depend upon soils it is vital to our survival that we protect soils so they are no lesser in quality and quantity than when we were born.
Lichens
Lichens create the original soils from which plants can grasp nutrients. It is reasonable to say that all terrestrial life owes its existence to
lichens.
Trees
Trees, flowers and plants depend on Soil for food (nutrients).
Trees also depend on mycorrhize fungus to help their roots absorb water.
Fruiting Trees depend on Bees for pollination.
Flowers
Forest flowers and plants depend on trees for shade and wind protection as well as soils for nutrients.
Bees
Bees depend on flowering plants and trees for food.
Humans depend upon Bees for not only honey but, for fruit from trees they pollinate.
Insects
Birds eat insects. Widespread eradication of insects would harm bird populations as well.
Fish
Fish, such as Steelhead trout (Anadramous Salmon) depend on trees to shade and cool their streams so they do not die of overheating.
Freshwater fish, including steelhead, depend on insects for food.
Fungi and MicroOrganisms
Decomposers depend on dead trees for food. When a Park is “cleaned up” by removing its dead trees, decomposers decline.
Redwoods and other giant trees depend on a tiny Mycorrhize fungi which greatly help the trees absorb water and nutrients from the soil. Pesticides can kill the fungi and thus indirectly kill a forest.
Web Elasticity Can Snap
All interdependent biosystems have some resilience or elasticity that allows each species to expand and shrink by small amounts without irreversibly destroying the system. However when humans take biota from the system, that elasticity is often stretched beyond its limit just like a rubber band pulled too tight or a balloon blown up too much.
How Close are We to Ecological Irreversibility?
A big problem is how we have only the faintest hint of an idea how close the limit of extraction is for any species in an ecosystem web. The only way humans have ever found out how close we are is when we have extracted too much – and we can’t get them back. But of course by then, it is too late.
A less recognized problem is how the risk of irresponsibility is much greater when we remove amounts of two or more interdependent species, rather than just one. Thresholds of reversibility get even closer, extracting smaller amounts of biota can cause species extinction locally (called extirpation), such as when we remove multiple interdependent species as sea otters and sea urchins, or Monterey pines and woodpeckers.
When a key species is killed off it can start an ecological chain reaction that devastates an entire ecosystem – that can harm or extinguish what you can eat.
Notes:
1: While humans need hundreds of other large species to survive – from plants and animals for food to stomach microbes for digestive health, the only known species dependent upon humans are small to tiny and few would ever argue for their protection: the Smallpox virus (which made it easy to eradicate), Gonorrhea, Syphilis and Head Lice.