Ecosystems and Biogeography

Chapter 19

Read these notes and Chapter 19 in your text.  Your text goes into more detail on some topics than necessary – use these notes as a guide.  For instance, I am not emphasizing all the details of “Terrestrial succession” through to the Focus Study on the Great Lakes, 4CE, pp.632-633, 3CE pp. 614-617.  This is interesting stuff, but more detail than you are required to know.

There is an introductory video here:


“Out of the stump of David’s family will grow a shoot — yes, a new Branch bearing fruit from the old root.

And the Spirit of the LORD will rest on him – the Spirit of wisdom and understanding,

the Spirit of counsel and might, the Spirit of knowledge and the fear of the LORD.

He will delight in obeying the LORD.

He will never judge by appearance, false evidence, or hearsay.

He will defend the poor and the exploited.

He will rule against the wicked and destroy them with the breath of his mouth.

He will be clothed with fairness and truth.

In that day the wolf and the lamb will live together; the leopard and the goat will be at peace.

Calves and yearlings will be safe among lions, and a little child will lead them all.

The cattle will graze among bears.  Cubs and calves will lie down together.

And lions will eat grass as the livestock do.  Babies will crawl safely among poisonous snakes.

Yes, a little child will put its hand in a nest of deadly snakes and pull it out unharmed.

Nothing will hurt or destroy in all my holy mountain.

And as the waters fill the sea, so the earth will be filled with people who know the LORD.”

Isaiah 11:1-9 (NLT)

Solar energy, climate, and soils make life on earth possible.  However the forms that life takes – both animals and plants – vary from place to place.  Some places have little vegetation.  Others have vast amounts of vegetation. Some locations have few species of animal life.  Others have thousands of species.  In this chapter we begin to investigate the spatial distribution of life forms.  This called biogeography:  the geography — spatial distribution — of biological elements.

In 4CE, notice the report on changing species distribution due to climate change.

I. Biogeography and Ecology

  1. Biogeography
  • Biogeography is defined as the study of the origin, distribution, adaptation and association of plants and animals within a spatial context. 

In other words, biogeography looks at how various species are distributed differently in different parts of the world, and seeks to understand why, by looking at various factors, including climate, soils, and geology.

Biogeography focuses on the biosphere, the thin layer of the earth/atmosphere that can support life (the biosphere, the zone within the earth-atmosphere system where life exists, extends from the bottom of the ocean floor to about 8 km into the atmosphere).  Biogeography emphasizes the spatial distribution of ecological relationships.  Biogeography studies the spatial patterns created by plants/animals at the present moment, how these have changed in the past, and how they might emerge in the future.

2. Ecology
  • Ecology is the study of the relationships between organisms and their environment and among the various organisms in the biosphere

Ecology studies the organism/environment relationships in a more general manner than biogeography, often without in-depth concern about their spatial location.  Ecology emphasizes biological relationships.  Ecology is about the inter-relationships.  Biogeography specifically emphasizes the spatial location of those biological relationships.

19 buffalo waterton

This bison’s habitat is the short grass prairie. It’s niche is a herbivore (eating grass) and as a food source for wolves, coyotes (and, back in the day), aboriginal peoples. (Waterton Lakes National Park, AB)

undamental concepts to both biogeography and ecology are the terms:

  • habitat – this refers to the environment where an organism is found (i.e. its geographic address),
  • niche – its function in the environment (i.e. its job)

Thus, a student’s habitat could be considered the college; their niche would be to study and learn.

Or, in the real world, a lion’s habitat might be the African savanna; his niche would be as predator who keeps zebra herds healthy by preying on the weak and sick.

Or, a swallow’s habitat might be your backyard; her niche would be to eat mosquitoes in the summertime (and make your life much more bearable).

II. Ecosystems

The biosphere can be subdivided into distinct ecosystems.

Ecosystem was a term was first coined by Sir Arthur Tansley in 1935 to refer to distinct vegetation units – such as salt marshes, alpine tundra, ponds, etc. – with associated animal populations and habitat conditions of soil, topography, microclimate.  The same type of ecosystem (a pond, a slat marsh) can be found in many parts of the world with similar conditions

Ecosystems are self-sustaining ecological units consisting of both living organisms and their biotic (living) and abiotic (non-living) environment in which energy in the form of inorganic materials is constantly being exchanged between living organisms and their environment.  Ecosystems, then, include the vegetation and fauna (biotic) and soil and local atmosphere (abiotic).

Ecosystems are well-defined units of distinct functional relationships.  Within an ecosystem, the plant and animal life is relatively consistent, but different from surrounding areas.  This is in direct response to local climate, soil, and geologic conditions.

Ecosystems are one unit within a hierarchy of organization extending from:

  1. the planet – the entire Earth and atmosphere
  2. the biosphere – that portion of the Earth/atmosphere where organisms can live
  3. the ecosystem – a distinct, self-sustaining homogeneous unit within the biosphere (e.g. aspen parkland-woodland)
  4. the community – a specific example of an ecosystem (e.g. the forest near a university, grassland near a college)
  5. the population – one species within that community (e.g. the rabbits in the grassland/forest)
  6. the individual – one individual of a species (e.g. Billy, that one white rabbit that lives under the 561st tree, in the forest)

Thus ecosystems are part of a continuum of scale in organization on the earth.

Within an ecosystem are biotic (living) components

  • primary producers (plants)
  • consumers (animals)
  • decomposers and detritus feeders (worms, bacteria, fungi)

And abiotic (non-living) components:

  • solar energy
  • nutrients including gases, water, and minerals, released through various cycles (discussed below)
  • heat energy

The primary energy source that powers all ecological processes is solar energy.  One of the primary ways this occurs is through the process of photosynthesis.  Plants (in terrestrial ecosystems) and algae (in aquatic ecosystems) use the sun’s energy directly to produce their own food using carbon dioxide as their sole source of carbon.  These organisms are called autotrophs (self-feeders) or producers, by changing solar energy into chemical energy through photosynthesis.  These producers are then available as food for other organisms.

A by-product of this process is oxygen gas.  The oxygen gas in the earth’s atmosphere (which we breathe) is all the byproduct of photosynthetic activity by plants and algae.  In plants, leaves are “solar-powered chemical factories.”  Carbon dioxide, light, and oxygen enter and exit a leaf through small pores, stomata, which are most numerous on the underside of the leaf.

Within a leaf are also chloroplasts, containing a green, light sensitive pigment, chlorophyll (which is why leaves are green).  When light stimulates the molecules of this pigment, a photochemical (light-driven) reaction occurs:

CO2 (carbon dioxide) + H2O (water) + Light (solar energy) → C6H12O6 (carbohydrate, glucose) + O2 (oxygen)

This reaction, then, removes carbon dioxide from the atmosphere (which is why areas like the Amazon rain forest are important to maintain, to limit global warming), requires water (why you have to water your plants), and requires light (why plants compete for sunlight, and your houseplant needs to be by a window).  Photosynthesis also produces the “food” necessary for other organisms (carbohydrates), and the gas necessary for other organisms to breathe (oxygen).

Ecosystems can be compared on the basis their net primary productivity (the amount of new organic matter they produce each year).  Woodlands, which once covered most of the earth but now (because of agriculture) only cover about 25%, are the most productive land ecosystems in the world.  Most productive of all are tropical rain forests, producing an average 22 kilograms per square metre per year.  That’s a lot of “stuff”!

See Figure 19.4 “Net primary productivity” and Table 19.1, “Net Primary Productivity …” 4CE, p.609-610 and 3CE p. 595.  The most important column is the “Mean” – the annual average net primary productivity for a given area. 

 Your text gives this in an awkward unit – grams/square metre/year.  This tells you how many grams of organic matter would be produced on a square meter of land in a year!  This is hard to imagine! 

I find it easier to imagine things in terms of kilograms/square metre/year.  To do this, simply move the decimal place two places to the left.  Thus saying tropical rain forests produce 22 kg/m2/year is the same as saying they produce 22000 g/m2/year!  However you talk about it, that’s a lot of stuff!

10 Singapore

Tropical rainforests (like these in Singapore, at the Equator) are way more productive than forests in our area because of the moderate climate and lots of moisture.

Net primary productivity is directly linked to both sunlight and precipitation.  Regions with high solar energy and high precipitation (ITCZ), are most productive.  Regions with high solar radiation but low precipitation (subtropical high/desert areas) have much lower productivity.  And regions with lower insolation, but reasonable precipitation (like coastal regions of Canada) have lower productivity.  Areas like the Arctic, with low insolation and low precipitation, are least productive.

In our region:

  •  our forests (boreal forests), produce about 0.8 kg/m2/year  (just less than 1 kg per square metre).
  •  our natural woodland-shrubland regions, produce about 1-1.2 kg/m2/year.
  •  our cultivated farmland produces about 0.65 kg/m2/year.

Our region isn’t nearly as productive as the rain forest!  This is a function of our insolation, climate, etc.  If we were warmer, nice and wet, and had lots of sun all year long (like at the Equator) we would be more productive, too.  Most of Canada has a growing season of only 6-8 months.

(Note, that the most productive ecosystems of all are actually in the oceans – algal beds and reefs [warm, shallow, mineral rich waters around tropical coral islands] – 25 kg/m2/year of “stuff” – that’s a lot of algae and other aquatic gunk!).

  1. Inputs and Outputs to Ecosystems

Ecosystems do not exist in isolation; there are many inputs and outputs from the system.  Energy and matter flows in and out of the ecosystem.

In general, the energy inputs to the system equal the outputs so the system is stable, in a state of steady-state equilibrium.  Usually, ecosystems do not change significantly over time.

However, if the inputs and outputs are not balanced, the system is in a state of change.

  1. Inputs to the ecosystem

1. Solar energy is the main input that drives the ecosystem.  Without solar energy, life would be impossible!  People cannot alter the amount of solar energy an ecosystem receives.  However we can alter the effectiveness of the solar energy in reaching specific parts of an ecosystem.  For instance, by cutting down large trees we can increase the amount of solar energy that reaches plants on the ground.  This will change the ecosystem.

2. Water, from all sources (atmosphere, soil, water bodies, ground water, irrigation).  Without water, living organisms cannot survive.

People can alter ecosystems by increasing the amount of water in a region through irrigation.  Or people can decrease water in ecosystems by consuming groundwater faster than it can be restored.  Human effects on the water coming into a region will change the ecosystem (For example, in natural desert areas, if humans irrigate, much vegetation – and new wildlife – can flourish in previously sparse locations.  Or, by overuse of groundwater, humans can cause vegetation to be reduced, also reducing the ability of the ecosystem to support wildlife).

People can also pollute groundwater, causing organisms (both plants and animals) to die.  E coli, implicated in the deaths of at least 7 people in Walkerton, ON (2000) was a virus introduced into groundwater, likely by intensive livestock farming.

3. Living organisms (biota), such as animals and plants, may migrate or seed themselves in an ecosystem.  Or they may be artificially introduced by people – through importing animals (horses, cows, cats, dogs) or planting non-native plants (canola, daffodils, etc.).  Artificially introducing organisms will change the ecosystem (For example, in my region, natural short grassland species have been removed by people, who introduced other species [canola, wheat, corn – and irrigation water], dramatically changing the ecosystem, including the wildlife).

4. Nutrients, specific minerals needed by organisms, can come naturally from gasses, dust, feces from animals, and weathering of rocks.  They may also be introduced by humans through the use of fertilizers.  Artificially introducing nutrients will change the ecosystem.

  1. Outputs from the ecosystem

Outputs from an ecosystem often take a similar form to the inputs.  As long as the outputs are similar in number and type to the inputs, the ecosystem will remain much the same.  However if an output is significantly different from an input – either greater or less – then the ecosystem will change in response.

  1. Longwave radiation is exported as heat energy.  Human beings have little direct effect on the amount of longwave radiation emitted from an ecosystem

2. Water is lost through processes including evapotranspiration, runoff, and groundwater flow.

Humans can increase the amount of water lost in an ecosystem by:

  • increasing the amount of plants (thus increasing evapotranspiration), for instance by introducing crops into a desert environment
  • increasing the amount of runoff (by paving land, compacting soil, etc.)
  • increasing groundwater flow (introducing sewer and drain systems).

Humans can decrease water loss in an ecosystem by:

  • removing plants (thus reducing evapotranspiration) by harvesting or clear-cutting.  Pooling and flooding may occur where previously water was utilized by plants.
  • decreasing the amount of runoff by building dams, ponds, etc.
  • decreasing groundwater flow by compacting soil or blocking natural springs.

3. Biota, plants and animals can move out of an ecosystem.

Animals can migrate out of an ecosystem.  This may be encouraged by human activity that makes an ecosystem less attractive.  For instance, clearing a forest to build a subdivision, encourages animals – from bears to birds – to vacate.

Plants can seed themselves outside of an ecosystem.  They can also be removed form an ecosystem by human activity.  When human harvest trees, for lumber, pulp, or firewood, they are removing plants from an ecosystem.  Or, when people harvest grains for food, we are removing plants from an ecosystem.

4. Nutrients can be removed from ecosystems by a variety of processes including erosion, leaching and – volatilisation (the direct absorption of nutrients into the atmosphere).

Human activity may encourage these processes to happen more rapidly.  For instance, clear-cutting a forest removes the natural protection for the soil provided by trees.  During heavy rainfalls, the soil is easily eroded.

Human activity may also decrease the loss of nutrients.  Replacing evergreen trees with deciduous trees or grasses, for instance, decreases leaching.

Note, however, that whether human activity increases or decreases the amount of these outputs that are lost, the fact that human activity changes anything, will result in a changed ecosystem.

For example, replacing an evergreen forest with grassland will reduce leaching (nutrient loss), but will also create a whole new ecosystem.  The animals and other plant life that existed in the forest will have to relocate.  New species will find their habitat in the new ecosystem.

III. Cycling processes in ecosystems

Energy and matter are cycled through ecosystems, a process called biogeochemical cycling (See the section entitled, “Elemental Cycles,” 4CE, p. 610 (3CE p. 597)).

Biogeochemical cycling refers to the fact that chemicals move through biological organisms (plants and animals) as well as through abiotic components of ecosystems (soil, air, water).

The nutrients required by plants flow through ecosystems in complex series of interactions among the main ecosystem components: soil, plants and animals.

Nutrients, the chemicals involved in the process, are defined as elements or compounds which are required by plants to grow.

There are eighteen essential nutrients, which are normally divided into two groups – macro- and micro-nutrients.

Macro-nutrients are those elements or compounds required in large quantities by plants (the ones you need to know are highlighted):

  1. carbon (C),
  2. oxygen (O),
  3. nitrogen (N),
  4. calcium (Ca),
  5. potassium (K),
  6. phosphorus (P),
  7. sulphur (S)
  8. magnesium (Mg)

Micro-nutrients are those elements and compounds used in much smaller proportions (but still essential), including manganese, iron, silica, sodium and chlorine, and trace elements including boron, copper, zinc and molybdenum (you do not need to know these for an exam!)

A.  Nutrient Cycles
  1. Oxygen (O) and Carbon (C) Cycles

See Figure 19.5, 4CE p. 611. 

Oxygen and carbon are intimately linked through the process of photosynthesisplants absorb carbon dioxide (utilizing the carbon component) and release the oxygen into the atmosphere.  Animals use this oxygen for respiration.  Animals in return, release carbon dioxide back into the atmosphere.  A symbiotic relationship exists between plants and animals:  plants “use” carbon dioxide and release free oxygen; animals “use” oxygen and release carbon dioxide.

Plants and animals (including humans) need each other.

Oxygen – that is available to us – is largely stored in the atmosphere.  There is oxygen  within the earths crust, in various minerals like silicates (for instance quartz) and carbonates (like limestone), but it is not available to us.

All life forms on earth are “carbon-based” (Star Trek fans know this! – yes, it’s true!).  “Organic chemistry” – the branch of chemistry concerned with living organisms demonstrates that all life forms on earth (including human beings) have carbon as an essential component.  Life (on earth) – plant or animal – does not exist without carbon.

Thus, when organic material is burned – grasslands, forests, or fossil fuels such as coal, gasoline, natural gas, or other hydrocarbons – carbon (CO2) is released into the atmosphere. The removal of those photosynthetic organisms (especially trees), also removes organisms which removes CO2 from the atmosphere.

This is why the loss of forests – particularly those with high productivity (like the rainforests) – is a big deal.  The vegetation helps reduce the amount of carbon dioxide in the atmosphere, thus helping mitigate global warming.  The less dense vegetation, the less atmospheric carbon dioxide removed.  Burning vegetation – such as wood – and fossil fuels (oil, coal, etc) – also releases more and more carbon into the atmosphere.  Thus clearing and burning forests is particularly nasty – more and more carbon is released through the clearing/burning process, and less and less is removed from the atmosphere as there is less and less vegetation to utilize it.

  1. The Nitrogen (N) cycle

Figure 19.6, 4CE p. 612

As we noted early in the course, the majority of the air we breathe – 78% – is actually nitrogen (N).

Nitrogen is also critically important in the makeup of organic molecules, especially proteins.  Therefore is is an important and often the most limiting nutrient for plant growth.  A good supply of nitrogen stimulates root growth and development, uptake of other nutrients, and foliage growth (if you want a really green lawn, you want nitrogen).  For nitrogen to be available for plants, soil micro-organisms and bacteria are very important

Most nitrogen is derived from atmospheric sources.  It is “fixed” or stored by soil micro-organisms and bacteria, although minor amount comes through precipitation or lightening.  Plants can then access nitrogen through their roots, absorbing it from the soil.

To increase agricultural yields, many companies add nitrogen to the soil in the form of synthetic, inorganic fertilizers.   Yes, this does increase crop production.  However, it also often ends up leaching or being washed into aquatic ecosystems in streams, lakes, and oceans, which can led to excessive plant, algae, and phytoplankton growth, choking streams and lakes, and changing ecosystem dynamics.  Your text notes that “dead zones” in river and ocean systems can result from this kind of pollution – too much of one “good” nutrient that can dramatically alter ecosystem (please read “Dead Zones” (4CE p. 613) and “Geosystems in Action 19:  Coastal Dead Zones” (4CE pp.614-615).

  1. The Phosphorous (P) Cycle

Phosphorus occurs as a negatively charged particle, or anion (e.g. PO3 and PO4).  It is normally released into the environment through rock weathering.  Phosphorus is returned to the soil through organic matter decomposing or in animal wastes.  It also is found in large quantities in animal bones.  The fertilizer, “bone meal,” is essentially phosphorus.  It promotes vigorous root growth.

  1. Potassium (K) cycle

Potassium occurs as a positively charged particle or cation (K+).  The slow weathering of minerals within clays generates 90% of all potassium released into the environment.  Potassium is particularly important for healthy vegetables and tubers, buds and flowers, and to promote drought tolerance in plants.

B. Limiting Factors and the Law of the Minimum

The term limiting factor refers to the one nutrient or other condition that limits plant growth.  Usually one particular requirement will determine how much – or how little – growth will occur.

For instance, in a field with good soil, good climate, and good amounts of nitrogen and phosphorus, if there is very little potassium, then plants will not grow in a healthy way.  Potassium is the limiting factor. 

Or, in a field with plenty of nutrients and good soil, a lack of moisture (water) may be a limiting factor, reducing plant productivity.

This principle implies that, in order to encourage a species to develop, you must identify the specific limiting factor.  Thus, if a lack of potassium is the problem, adding more water, sunlight, lime, etc. will all be futile!  Correct analysis of the limiting factor is critical!

19 law of miminum

Law of the Minimum Footnote 1

This is also known as the law of the minimum.  One factor will be “minimum” (potassium? water?  copper?), limiting plant growth.  In order to improve productivity, one has to discover what the limiting factor is, and address it.  However, solving the problem of the first limiting factor will result in the next lowest factor becoming limiting.  Productivity may increase somewhat, but another limiting factor may become influential.  Further analysis is necessary to address this issue!  (For those of you who have heard of “Natural Church Development” … Christian Schwarz borrowed this concept and applied it to healthy (or not-so-healthy) church life)

Because nitrogen, phosphorus and potassium are often limiting factors, these are the most commonly provided in commercial fertilizers.  If you notice, most commercial fertilizers have three numbers:  for example 10-20-10.  these refer to the proportion of these three critical nutrients.

The numbers are always listed in order:  N – P – K .

 The numbers refer to percentage in the mix, by weight.  So, a fertilizer 10-20-10 has

  • 10%, by weight, nitrogen
  • 20%, by weight, phosphorus
  • 10%, by weight, potassium

Know this!  It will show up in an exam somehow!   You may even be able to apply this information to help your garden to grow better some day!  As a result of this course you will be an awesome gardener!  (Note to the wise — learn from my mistakes — before you do add fertilizer to your lawn or garden it is helpful to get your soil tested so you know what you are starting with — remember the “law of the minimum”?  Simply adding a typical N-P-K fertilizer to green up you lawn may not work if another nutrient is low and is the limiting factor!)

C.  Food Webs (or Food Chains)

Part of the biogeochemical cycling process is the fact that nutrients cycle through different organisms in the ecosystem.  This is referred to as the food web (or food chain).

Organisms have specific roles \ levels \ positions of importance within a community:  these are niches.

Organisms also tend to occupy specific sites or locations or habitats in the ecosystem as well.

Organisms in food chains are either

  • Autotrophs, who produce their own food through photosynthesis (primarily plants, but also some bacteria and micro-organisms).  These are also called producers.
  • OR heterotrophs, who rely on other living organisms to provide their energy (generally animals).  These include:
    • Herbivoreswho eat plants (examples of herbivores would be deer, moose, rabbits, chickens, etc.).  These are primary consumers – they eat the producers.
    • Carnivores: who eat other animals (examples of carnivores would be lions, wolves, eagles, etc.).  They may eat herbivores; [secondary consumers] or other carnivores [tertiary consumers])
    • Omnivores: who eat plants and animals – they eat it all (examples of omnivores would be bears … and people).  These may be, at any given time, be either primary, secondary, or tertiary consumers, depending on what they are eating.

There are huge amounts of producers, and fewer and fewer numbers of organisms the higher you go up the “pyramid.”  This is typical in most ecosystems:  there are huge numbers of producers (plants), a fair number of primary consumers (herbivores), less secondary consumers (carnivores who prey on herbivores), and very few tertiary consumers (carnivores who prey on other carnivores).  Figure 19.10 (“Energy pyramids and biomass pyramids” 4CE p. 619) illustrates this.

For example, in Waterton National Park, in the southern Rocky Mountains:

  • There are huge amounts of individual grass plants, shrubs, and trees (producers).
  • There are a fair number of elk, deer, and rabbits (primary consumers).
  • There are fewer foxes and coyotes, who will hunt the smaller primary consumers, like rabbits (foxes and coyotes are secondary consumers).
  • While grizzly bears are omnivores, they will feed on both primary and secondary level consumers. But there are very few grizzly bears (tertiary consumers) in the park.

You can also look at it this way:

  • One blade of grass (producer) needs a tiny piece of ground in which to grow (a few millimeters).
  • One rabbit (primary consumer) needs a larger piece of ground to grow all the grass it needs to eat (many square metres).
  • One fox (secondary consumer) needs a larger piece of ground, still, to support all the rabbits it needs to eat (a few square kilometres).
  • One grizzly bear (tertiary consumer) needs a huge piece of ground to support all the food it needs to eat (dozens of square kilometers).

Thus the “higher” you go in the food web, the fewer organisms there will be.  And the higher you go in the food web, the more territory an organism needs to survive.

Because tertiary consumers eat secondary consumers who eat primary consumers who eat producers, toxic chemicals – pollutants – tend to get concentrated in the upper levels of the food web.

This has been particularly studied in hawks and other birds of prey (at the top of the food chain).  Levels of toxins in their systems can be incredibly high.

Have a look at (and read the descriptions in the text associated with)

  • Figure 19.7 “Energy, nutrient, and food pathways” (4CE p. 616)
  • Figure 19.8 “A simplified Antarctic Ocean food web” (4CE p. 617)
  • Figure 19.9 “Temperate forest food web” (4CE p. 618). 

In the real world, the flows of energy, nutrients, and food – these interconnected webs – get VERY complicated very quickly.

IV.  Ecological Stability and Succession

A.  Ecological stability

When inputs and outputs into an ecosystem are equal, the ecosystem is “stable” – it stays the same over time.  Many mature, well-established ecosystems are stable.  There is little change over time.  The ecosystems in most national parks, for instance, protected from most major human interference, are fairly stable.

A critical component of ecosystem stability is biodiversity.  In an ecosystem with:

  • a diverse number of species (lots of different kinds of plants and animals),
  • and diversity within each species (lots of individuals of each species, with lots of genetic variation),

the ecosystem is relatively stable.  It has high biodoversity.

An ecosystem with high biodiversity can survive short-term challenges without major problems.  For instance a severe storm or a dry summer may result in the deaths of some individuals of each species, but overall the ecosystem comes through unchanged,

Or, for instance, in an ecosystem with much biodiversity, if a disease that effects one tree species enters the ecosystem, there are other species that will take the place of the dying trees.  The ecosystem will survive. However in an ecosystem with little biodiversity, that one tree species may be the only tree species.  If it were to die, there would be no trees, and the ecosystem may collapse.

  • Ecosystems with high biodiversity are relatively resilient, able to survive environmental challenges quite well.
  • Ecosystems with low biodiversity are not very resilient, and are not able to survive environmental challenges quite well.

In an ecosystem with little biodiversity:

  • only a very few number of species (few different kinds of plants and animals)
  • little diversity within each species (few individuals of each species, with little genetic variation),

the ecosystem is relatively unstable.

In this circumstance, a catastrophic event like a storm or drought could decimate the entire ecosystem very easily.  The one tree species, if it contracted a disease, could be completely wiped out, resulting in no trees at all.

Ecosystems with low biodiversity are very fragile and not very resilient.  They can be easily damaged or destroyed.  Note that this includes most human-modified agricultural areas.  Human activity tends to eliminate the wide variety of naturally occurring plants and animals, replacing them with a single crop (or a very limited number of crops).  This makes these areas very susceptible to drought, or other natural challenges.

High biodiversity is good!  It represents a resilient ecosystem.  Low biodiversity is not good – it represents an ecosystem easily damaged or destroyed.

An excellent site to explore principles of biodiversity is the Center for Biodiversity and Conservation of American Museum of Natural History.  Among the very practical information on this site are topics such as

  • Biodiversity and your food
  • biodiversity and your water supply
  • biodiversity and your energy use
  • biodiversity and what you buy

Some practical ideas (from Center for Biodiversity and Conservation at AMNH) (to understand WHY check out their website):

  • use tap water, not bottled water
  • choose locally grown food
  • use plain rather than antibacterial soaps
  • plant native plants
  • use water wisely and sparingly
  • choose organic food
  • keep pets indoors
  • plastic or paper bags? — neither!
  • compost
  • reduce use of herbicides and pesticides
  • use the “carbon footprint calculator” to determine your carbon footprint
  • use mini-fluorescents (and recycle them appropriately)
  • choose green energy
  • adjust your thermostat down 2 degrees
  • look for energy star appliances
  • wash and dry efficiently
  • unplug charger when not in use
  • go vegetarian at least once a week
  • don’t use bug zappers
  • choose shade-grown coffee
B. Ecological Instability

Instability can result when inputs and outputs are not equal.  In these circumstances, ecosystems change. The changes may be naturally or human induced.

Natural events that can change the input-output balance, and thus the ecosystem, include:

  • volcanic eruptions
  • forest fires (often sparked by lightning)
  • mass movement (landslides, avalanches)
  • flooding
  • iolent weather (hurricanes, tornadoes)
  • natural climatic changes (El Nino, La Nina, ice ages)

For instance, in Yellowstone National Park, huge forest fires (mostly sparked by lightning) removed most of the trees, shrubs, and grasses in huge areas of the park.  Animal species either died or left the devastated area.  The established ecosystem was gone.  But a new ecosystem quickly developed, with new plant species.  And new animal species.  The new ecosystem was different than the previous ecosystem.  But it was a viable ecosystem.

Human induced changes to the input-output balance, and thus the ecosystem, include:

  • clearing forest (either to use the wood products or to provide agricultural land)
  • building dams, roads, railways, town, cities
  • changing natural drainage patterns
  • water, soil, and air pollution
  • human-induced climatic changes

Human activities are the primary cause of ongoing extinctions. Biologists foresee an extinction of between 5%-50% of the number of plant and animal species on the Earth within the next 30 years!

Like all other organisms, humans modify their environment in the course of their lives. Because of the size of the human population and the rate of resource consumption, however, the environmental impacts of humans are significantly different from those of all other species.  Human activities cause species loss from habitat degradation and destruction, the introduction of non-native species into natural habitats, and the over-exploitation of wild plant and animal species. Additionally, various actions at both individual and societal levels degrade habitats via pollution which contributes to significant physical and biotic changes at all levels, from local populations to ecosystems to the global climate.

Biodiversity, mentioned above, is a critical component in the stability-instability of an ecosystem.  In ecosystems with few species and little genetic variation within species, the potential for instability is very high.  A slight change – in weather, disease, nutrients – can have a devastating impact on the whole ecosystem.

Biodiversity is very good!  This is one concern with most modern agricultural practices – a farmer may plant his entire land with one or two crops.  What if it is a dry year, and the crops he planted all require much moisture?  His year is a total loss!  With diversity – planting many crops – the farmer may lose some productivity during a dry year, but will not suffer a total loss.

How will biodiversity loss (ecological instability) affect humans?  Check out the resources from the Center for Biodiversity and Conservation.

C. Ecological Succession

Over time, ecosystems sometimes pass through natural stages.

Ecological succession is the observed process of change in the species structure of an ecological community over time. The time scale can be decades (for example, after a wildfire), or even millions of years after a mass extinction.

The community begins with relatively few pioneering plants and animals and develops through increasing complexity until it becomes stable or self-perpetuating as a climax community.

For instance, after a forest fire, the first ecosystem to be established usually includes a few grasses, flowers (fireweed), and small insects, rodents, and birds.  Over time, that ecosystem naturally makes way for a more complex ecosystem with grasses, shrubs, young trees, and more wildlife.  After decades, a very different ecosystem will have developed with large trees, shrubs, and even more wildlife.

This natural process of ecosystems “taking over from” or succeeding one another over time is called ecological succession.

For example on bare land (after a fire, clearing, etc.) a typical sequence of communities appears to develop in each particular environmental region:

  • pioneer stage is dominated by widely, quickly dispersing plants that are tolerant of the environmental conditions prevalent on newly available sites (lots of sun, wind, etc.).
  • soil fertility rises, microclimate conditions improve and more plants can occupy the site.  This is referred to as secondary succession
  • eventually the system that becomes established is self perpetuating, efficient, productive and stable – for any region it is assumed that a climax stage will be achieved where these conditions are met.

The classic studies of succession consider the development of vegetation on abandoned farmland in the U.S. mid-west.  Typically grasses grow first.  Gradually shrubs take over, choking out many of the grasses.  A pine forest often succeeds the shrubs, followed by a taller mixed hardwood forest that shades out most of the earlier plant life.  This process can take 100 years +.

Take a look at the examples in your text:

  • Figure 19.19, “The pace of change in the region of Mount St. Helens” (4CE p. 626)
  • Figure 19.20, “Idealized lake-bog-meadow succession” (4CE p. 627).
Worth reflecting on …

Reflecting on human interactions with the environment, Calvin De Witt, former professor at Calvin College and the University of Michigan, Director of Au Sable Institute of Environmental Studies, describes the Seven Degradations of Creation:

“We live at an unusual time in Earth’s  history: we have just discovered that we possess enough power to degrade and destroy land, creatures, water, and air not only in our neighborhoods, but around the globe.

“The once puzzling passage, “the time has come… for destroying those who destroy the Earth” (Rev 11:18) is clear now: we are capable of such destruction, and note with alarm our participation and complicity in its execution, placing Earth in crisis.

“What is this crisis?


(1) alteration of Earth’s energy exchange with the sun that results in global warming and destruction of the Earth’s protective ozone shield;

(2) land degradation that reduces available land for creatures and crops by “adding house to house and field to field” and destroys land by erosion, salinization and desertification;

(3) deforestation and habitat destruction that each year removes primary forest the size of Indiana and degrades an equal amount by over-use;

(4) species extinction that finds more than 3 species of plants and animals eliminated from Earth each day;

(5) water degradation that defiles groundwater, lakes, rivers and oceans;

(6) global toxification that results in DDT in Antarctic penguins and pesticides in a remote lake on Isle Royale in Lake Superior; and

(7) human and cultural degradation that threatens and eliminates long-standing knowledge of native and some Christian communities on living sustainably and cooperatively with Creation, together with the loss of long-standing garden varieties of food plants.

We know from the scriptures that it is neither the will of the Creator, neither should it be for us as God’s people, that human beings so behave that Earth and its creatures are degraded and destroyed.

While expected to enjoy the Creation and its fruitfulness, people are not granted license to destroy Earth or its fruitfulness. While human beings are expected to be fruitful, so is the rest of Creation: “Let the water teem with living creatures, and let birds fly above the earth and across the expanse of the sky… Be fruitful and increase in number and fill the water in the seas, and let the birds increase on the earth” God commands (Gen. 1:20-21).

As we study the Bible, pray and worship in the context of the degradations so evident around us, may we ever grow in our stewardship, giving good reason for the Creation’s expectation of the coming children of God.

For the Creation waits with eager longing
for the children of God to be revealed . . . .
Romans 8:19


Feel free to discuss this quote on the course discussion site …

  1. An academic career can go in unexpected directions. But for Professor Ian Hutchinson, his faith certainly was a strong factor in his motivation to work in a field where the outcomes might benefit the rest of humankind.  Hutchinson is professor of nuclear physics at MIT.

To review …

Check out the resources at Welcome to mygeoscience place.

This page is the intellectual property of the author, Bruce Martin, and is copyrighted © 2018 by Bruce Martin.  This page may be copied or printed only for educational purposes by students registered in courses taught by Dr. Bruce Martin.  Any other use constitutes a criminal offence.

Scripture quotations marked (NLT) are taken from the Holy Bible, New Living Translation, copyright © 1996. Used by permission of Tyndale House Publishers, Inc., Wheaton, Illinois 60189. All rights reserved

  1. Graphic from By DooFi (Own work) [Public domain], via Wikimedia Commons