Community Dynamics

The Ever Changing Pattern of Living Organisms

Community dynamics describes the changes in the collection of living organisms in any given locality.  Even when a community appears stable as a grassland, forest, coral reef, or lake, it is in fact constantly changing in species composition, numbers, age structure, and other characteristics.  Individual plants and animals are constantly dying and being replaced, varying weather conditions favor the well-being of some species and diminish others. 

Humans will most likely never understand completely what is occurring in any community, especially now that we know that there are millions, perhaps billions of microorganisms in every community that are not even named or described yet. The relationships between and among this multitude of organisms, large and small, is little understood and almost unimaginable in its complexity.

Community dynamics is the most vital of all the ecosystem processes, as without plants to transform solar energy into useable energy – life – neither the water or mineral cycle, nor energy flow can function effectively.  Because of this fact it is important for us to maintain healthy biological communities no matter where they are.  We still have much to learn about the dynamics of organisms, but there are some general principles that can be learned and used for this purpose.  They are based on the research of many ecologists and the four key insights.

There Are No Hardy Species

Hardy is a relative term, all organisms are adapted to specific environments where they establish and flourish.  When they are removed or try to establish in an environment that does not suit their parameters, they either do not establish or remain weak and fragile or perish.  For instance, a Sequoyah would have great difficulty becoming established in the Sonoran Desert.

As organisms arrive and set up in a community, it alters the microenvironment nearby, for instance by providing shade and holding a dew a little longer, making it easier for the organism to survive and flourish.  It may also be more inviting for insects or other small organisms which in turn further alter the microenvironment.  It may be that the changes over time make this microenvironment less conducive for the survival of the original organism, but allows another organism to establish itself.  With each subtle or dramatic change brought about in the microenvironment, other plants, insects, birds, and other animals find either a worsening or improving place for their growth.  The community changes constantly, even if humans don’t notice them that often.

Nonnative Species Have Their Place

As with all of nature, biological communities develop as wholes over time as species join, interact, change, and depart them.  Yet, we all know cases of communities being destroyed by the introduction of a new species – rabbits in Australia, goats and cats on various islands, zebra mussels in the Great Lakes.  Species with no defenses against the new species quickly die off and other species, dependent on the first, soon follow.

But not all introductions have been calamitous, the European honey bee into the Americas, corn and potatoes from Central and South America into the rest of the world, coffee from Ethiopia around the world.  There are many examples and it is also clear that animals, insects, and plants have been traveling the world for millennia. Once any species becomes established in a community, it becomes part of that community and changes occur both to the community and to the species.

The importance of this idea is that many in the US are obsessed with “nonnative” species and are doing doing all they can to destroy them all at every turn. It appears to be a functionary term as who decides at what date a species is native or nonnative?  The elk and humans are classified as native, having arrived in North America at roughly the same time, yet the horse which developed in North America, moved to Asia and Europe to be returned by the Spanish is nonnative.

And as with any illegal immigrant that arrives, these species fill a vacuum nature or mismanagement provides in a given community just as easily as legal immigrants.  Snakeweed, mesquite, cedar, rodents and grasshoppers (all legal species) fill the vacuum in the same manner as knapweeds, leafy spurge, or fireants (illegals).  Billions of dollars have been expended to annihilate each of these “noxious” weeds or animals, yet they are just as prevalent today, if not more so, than ever. Laws abound across the US about killing various plants, insects, and animals as nonnative species, even if those species fit into a local community, providing forage, ground cover, nutrient cycling, or prey for native predators.  Since the mass spraying of herbicides has done nothing but make matters worse in many cases, perhaps it is time that we begin managing for the whole community instead of focusing on one or two newly established members.  In many cases these “invaders” are filling the vacuum created by monoculture plantings.

Collaboration Is More Apparent Than Competition

The collaboration, or symbiosis, of and between species, is much more prevalent than most people have been led to believe.  Symbiosis, that is mutually beneficial relationships that occur among species in a community, are much more important and easily found than the competition so often cited by those who exaggerate Darwin’s theories.  Studies on island communities show that species evolve to avoid competition with others within the same niche. One only has to think about the cattle egrets following cattle and eating the biting flies to see symbiosis in practice.  There are many more examples, endophytes that help fescue, etc.

A great deal of the competition seen in natural settings, invasive plants crowding out local beneficial plants, for instance, are typically the result of human mismanagement or natural calamity – fire, storms, etc. – that either produces bare soil or diminishes the microclimate favored by the preferred plants.  That allows plants that are favored by the current microclimate to establish and flourish.  If your paradigm is competition, you tend to view everything as competition, if it is functioning wholes, collaboration, and synergy you are more apt to see those.

Stability Tends to Increase with Increasing Complexity

The early stages of development or the loss of biodiversity in biological communities display major fluctuations in species composition and numbers. Disease outbreaks, insects, weeds, rodent, and bird infestations are more likely as well.  The instability correlates with weather patterns. High rainfall years brings masses of annual plants, while in low rainfall years few if any plants may germinate.  Depending on amount and timing of precipitation, one plant or another may dominate. Insect or small animal infestations may be absent for years then one year there is a plethora of them. Above-average rainfall years can bring destructive floods while below average years bring drought. Humans tend to blame the weather instead of the mismanagement that has led to the loss of biodiversity and bare ground.

As communities become more complex and diverse, fluctuations in numbers within species decreases and community-wide stability increases. The web of interdependence increases as well as the number of species increases. Weather related pest outbreaks decrease and the amount of community biomass fluctuates less. An exception is in true deserts where communities maybe simple, but the constant dryness keeps them stable.  Still, after a rain, flowering annuals are common or a plague of locusts may develop.  When grasslands in more brittle environments begin to decrease and die out, usually from over rest, many claim that the increasing complexity does not lead to stability, but they are ignoring the loss of grazing animals and their predators, and their associated species.

While scientists have long believed that complex biological communities have greater stability it was not until 1996, when researchers in the American Midwest provided definitive evidence through a field experiment involving 147 grassland plots.

Most of Nature’s Wholes Function at the Community Level

Nature consists of and functions as wholes within wholes.  Each individual plant or animal consists of billions of cells, each a whole within itself. The individual plant or animal does not belong to a whole population but to a community consisting of many species.  This distinction is important because a population of any one species does not make a community, even if we attempt to manage some populations as if they were.  Members of any one species cannot exist without relationships with millions of other organisms of other species.  When we concentrate on rare, endangered, or preferred species, we lose the fundamental importance of the whole community and the 4 ecosystem processes within and surrounding it. While many rangelands are classified as being in good condition, it is usually because preferred species are present.  But the community may be stunted and bare ground abounds.  The perennial grasses may only be able to reproduce asexually, i.e. clones of the mother plant.

In many ways we can hardly be blamed, given the teaching we have received.  Communities and their importance are ignored in favor of specialized disciplines: zoology, botany, etc.  By concentrating on communities within those disciplines, we ignored the interdependence and interaction of them with the soil and humans as well. Communities include all of these, plus organisms below ground and in the atmosphere.  Some even suggest that the whole planet is a living organism that adjusts the atmosphere through the activity of living organisms.  This helps explain the transition of the original atmosphere to the one that exists today that nurtures the lifeforms now found.

The use of fire, the destruction of many species of all sizes and locations over the last 50,000 years has changed the atmosphere and the environment in may ways. Since it took millions of years to reach the stage was before the widespread use of human induced fire, we can not expect it to adjust to the increased presence of carbon dioxide and other greenhouse gases in as short period as 50 thousand years.

Most Biological Activity Occurs Underground

While we concentrate on the surface of the ground, any changes brought about above ground by our management, or lack thereof, are multiplied exponentially below ground.  The reason?  On average, the upper soil layers contain 7.75 tons of microorganisms per acre.  This total includes bacteria, fungi, earthworms, mites, nematodes, protozoa, and many others.  The richest soils can contain up to 15 tons of microorganisms per acre.  European pastures in excellent shape carrying large numbers of cattle are calculated to contain earthworm populations, alone, double the weight of the cattle.  If one adds the plant roots into the equation, the tonnage of living organisms underground is astonishing. Scientists estimate that between 75 and 85 percent of an American prairie’s biomass is underground.  Knowing this, it becomes apparent the importance of avoiding excessive soil compaction, soil exposure and capping, inadequate drainage, fertilization, pesticide poisoning, or any other action that will affect the organisms beneath the soil surface will directly and negatively affect the soil surface and the organisms above ground.

Change Generally Occurs in Successional Stages

The process of change of biological communities from bare rock to mature grasslands, forests, lake, etc. is called succession.  There is a gradual, often uneven, increase in species diversity and biomass, together with changes in the microenvironment, which stimulates further diversification.   Mr. Savory compares this movement from simplicity to complexity as “…a coiled spring, , which, whenever pressed down by human intervention or natural catastrophe, will, by its nature, rebound as soon as the pressure is taken away.” (Savory, 139)

This can be seen after a wildfire has raced through the prairie, burning the grass, forbs, brush, and trees, leaving the soil bare and black.  As time goes by, given moisture, species begin to return, or new species arrive. Over time, more and more species come back, plants, insects, animals return as the previous species change the microenvironment to one that better suits them, which may cause the previous species to decline.  Eventually, the grasslands, brush, and trees return, though possibly with a number of different species than before.

It should be noted that some species attempt to block succession after a certain point that favors them, such as plants that have a bitter taste or produce chemicals that retard the growth of other plants.  The algal and lichen crust communities in several western US national parks are protected, even though they are not early successional, but evidence of a deteriorated community.  The crust prevents grasses and other plants from establishing.

The successional process on bare soils in very brittle environments with their daily and seasonal extremes is a very slow one indeed.  And they emphasize the necessity of a holistic approach.  Plants have great difficulty establishing due to the temperature, moisture, and the physical actions from precipitation, freeze-thaw cycles, wind, and animal life, especially on smooth, steep or vertical slopes.  The process can be accelerated to some degree by old material covering an/or the mechanical opening of animal hooves or machinery.  In such environments the presence of large grazing animals is the only cost-effective way to break up the soil and provide sites that seeds can germinate and grow.

In nonbrittle environments, succession is almost impossible to stop.  Even after fires, destructive weather events, or human activity, species rush headlong to fill in the bare soil, often within days or weeks at most plants begin colonizing bare soil or any surface. Picture the plant covered ruins in nonbrittle areas of the world compared to the bare ruins in arid regions; i.e. Cambodia vs. Egypt.

Community Dynamics and Management

Understanding community dynamics presents numerous avenues for improvement in management of land, water, and all life.  Realizing that the ecosystem process Community Dynamics and the tool Living Organisms are describing the same thing from different perspectives allows the manager to optimize his/her actions for greater production in any situation.  Since all life is successional and dynamic, the future resource base is based on community dynamics.  We can no longer afford to manage living organisms in isolation as we have for millennia, but must recognize that only by managing for the community do we have the opportunity to create a sustainable system.

Seeking a profit from livestock or game, a productive grassland will be part of one’s future resource base.  In one case that means inducing succession from desert shrubs and bare soil to perennial grasslands, in another if means preventing the succession from grasslands to forests.  In any case, certain plants, insects, predators, and other life forms can be either foes or friends, depending on the understanding their place in succession.

In order to favor a species, whether animal, plant, insect, or bird, the successional movement of the community must be directed toward the optimum environment for that species to thrive by using whatever tools produce that environment over time, not by intervening through using some technological tool.  Protecting that one species will not save it, though that may be a short-term step.  It must be seen as part of the community and the environment in which it thrives has to be created for its survival.

If the landscape contains too many of an undesirable species, the future landscape in one’s holisticgoal will describe a community that is less than ideal for that species and more for species that are desirable.  That means that the basic biology of those species must be understood: What life stage is it most vulnerable, what conditions are required to survive that stage?  Providing the appropriate conditions at that point will greatly influence whether either species will increase or decrease in numbers.

Grasshoppers need bare, dry, warm soil to lay their eggs and survive.  Therefore a damaged water cycle creates those conditions, but few if any entomologists consider that fact when thinking about reducing hopper numbers.  The incredible amount of pesticides used since the end of World War II in the US has actually doubled the amount of damage from insects due to simplifying the community, i.e., reduced predation by other species and pesticide-resistance allows the grasshoppers to more frequently reach dangerous numbers.  By improving the water cycle, that is reducing bare soil and runoff, grasshoppers will find fewer breeding areas and thus lower numbers.

By nature, succession moves upward.  Any successful approach to management will keep this, and the image of the coiled spring, in mind.  The intentional or accidental application of one or more of the Tools of Holistic Management by humans has resulted in downward shifts, or compressing the spring.  Once the pressure is reduced or ceases, the upward momentum returns and communities become more diversified.  Since we seem to steadily increase the downward pressure by using pesticides, traps, or guns of all types, we miss the opportunity to allow successional changes to make the difference we want.

In any community, fluctuations of species is natural, especially among short-lived organisms with high reproductive rates. A prolonged downward movement to lower successional communities is entirely unnatural, and in most case betrays human intervention, with occasional natural disasters a distant second.

The current monoculture agriculture, hyped as more efficient and economical, trades the farmer’s labor and time for increased use of fossil fuels for not only fuel, but all types of pesticides and fertilizer.  The increased difficulties in managing these monocultures have led to the reduction of the farmer’s labor and his ability to retain ownership of his property.  The survival of humans may hinge on the development of an agriculture that mimics nature through the use of perennial, deep-rooted crops and more complex, not simpler, communities.  And in the more brittle environments, the use of grazing animals as part of that complexity.

Leaving It to Nature

Many people believe that the management of living organisms should be left to nature, assuming that nature knows best.  It is likely that given enough time, most communities would regenerate, in less brittle environments this would occur fairly rapidly.  In more brittle environments, it is more likely that the time would be in geologic, not human, terms.  As we look at the land surrounding abandoned cities in brittle environments throughout the world, it is still deteriorating in most cases.  The chance that they will recover on a human time line is negligible unless herding animals are used to reproduce the effects of the ancient herds and associated predators.  Otherwise it could take millions of years for new species to develop, which is not practical or desirable.  Humans must take up this responsibility seriously.

Conclusion

Having an idea of how biological communities function allows one to better write a holisticgoal that adequately describes the future resource base required, that is one rich in biodiversity.  While the description for only one’s surrounding community does not need to be too detailed, one describing the future resource base of land actually managed must be more so, especially if one is attempting to maintain a particular species or landscape.