In the earlier Chapters we saw how vegetation, through the process of photosynthesis, absorbs energy from the sun and then make it available to plants and animals ensuring their existence. Just the right amount of biomass is produced at each trophic level to uphold a dynamic balance of organisms.
We also saw how the circulation of elements in the ecosystem continuously ensures growth to avoid stagnation. The continual growth and decay are kept in balance by nature. The trees in a forest will e.g. forever grow and yet the total biomass of the forest stays constant. In this chapter we will focus on control mechanisms (checks and balances) in ecological systems that ensure that balance or equilibrium is maintained. Ecosystems must for example have just the right amount of non-living (abiotic) elements like sunlight and water, as well as the correct balance of species variety (biotic communities) to stay in equilibrium. Too many or too few of a particular species can cause a population to crash. Individual population crashes can in turn be devastating for ecosystems as a whole.
Figure 6.1: Decreasing energy available to the next trophic level
As the natural world functions as an interconnected system, everything is connected to its surroundings. Nothing exists or functions on its own. As soon as anything is separated from other elements, it is unable to continue to function. Therefore, any influence on one element is bound to have a ripple effect throughout the system on all other elements that are directly or indirectly attached to it. If soil is e.g. damaged or removed from an area, the biological life will decline up to the top Trophic level.
Figure 6.2: Once the ‘tipping point’ has been exceeded, it is impossible to regain balance
Ecosystems however have the ability to adapt to such change and thereby they resist collapse. We compared it in chapter 3 (Figure 3.3) to a “Tumbling Tower” game where each player in the circle gets a chance to remove a single block from the stack of blocks. At some stage the once stable tower will give in and topple over. Nature has an inherit stability that protects itself against interference from outside. This is called the resilience of an ecosystem. But once this resilience is challenged too far, it will collapse and will not be able to re-establish itself again. Imagine sitting on a chair and rock backwards. As long as you keep your weight in the centre you stay balanced and remain upright. But if you exceed the pivotal point, you will lose your balance and fall backwards. This is called the “tipping point”.
For ecosystems to remain sustainable it is important to stay in balance for as soon as the balancing point is exceeded the whole system may collapse. When adding sewerage to a body of water the inherent cleaning mechanism of a water body and its biota (living bodies) will absorb the foreign substances. There is however a tilting point when stress gets too much and the fish, insect and plant life in the water body will no longer be able to survive. Also, as soon as the minimum number of cheetahs in an area is reached, the species will become extinct due to the degenerative effect of inbreeding. The list of species in danger of extinction today is extensive. Due to the ripple effect, for every one species that is lost, many others depending on it will also become vulnerable. For example the seeds of the ‘Dodo tree’ (Calvaria major) must pass through the abrasive gut of a large animal in order to germinate. As the last remaining seeds (Figure 6.3) are only found on the island of Mauritius and the only local animal able to swallow the seed was the now extinct Dodo bird, this tree will also disappear.
Figure 6.3: An example of the seed of the ‘Dodo Tree” that could only germinate once it passed through the gut of the huge Dodo birds now extinct
How then do ecosystems remain in a state of equilibrium?
How then do ecosystems remain in a state of equilibrium?
As we have seen in the previous chapter, each ecosystem has a functional food web that starts with producers (autotrophs). These are organisms that produce their own food like plants and phytoplankton (T1). Primary consumers or herbivores (T2) consume vegetation (T1). These animals, like antelope and rabbits are far fewer in number than the vegetation in the area. Let us now have a closer look at nature’s ‘balancing act’.
In a simple ecosystem such as a desert dune, there are relatively few organisms and thus also fewer links in the food chain. If a single link is removed, the system could stop functioning altogether. The analogy of removing the wheel from a bicycle has been shown in Chapter 1. The bigger the biodiversity of any ecosystem, the better chance all the components have to survive challenges and remain in a balanced state as there is a complex food web with many links that can act as alternative food sources for species. If all the springboks are removed from an ecosystem, there will still be many other herbivores like rhinos and rabbits to keep the system going.
Figure 6.4: Trophic level changes due to environmental stress factors
This balance is however a dynamic balance. Suppose we have a Savanna ecosystem with perfect balance between all trophic levels. It is in a so-called climax state. See Fig. 6.4. Should the vegetation at T1become depleted as a result of a drought, or due to the increase in numbers of a rabbit population that exceeds the carrying capacity of the veldt, their food will become insufficient, and most of the rabbits will soon die.
This will send a ripple effect throughout the ecosystem. Secondary consumers (T3) like foxes that live on the rabbits as part of their diet will also diminish, and so will the tertiary consumers (T4) like lions or eagles that feed on the foxes. As soon as the pressure from T4 (top carnivores), T3 (carnivores) and T2 (herbivores) diminishes due to less numbers, the vegetation at level T1 will recover and T2 can start to increase again. So also T3, and T4 until the original balance is restored. Should a drought or another environmental crisis such as a fire consume parts of the ecosystem, the process will repeat itself. There are thus dynamic pulsating processes that keep al the trophic levels in dynamic balance
These patterns for populations of organisms apply to all ecosystems. There should normally be large numbers of producers and smaller numbers of tertiary consumers. Too many or too few at any level of the food chain can have catastrophic effects. Exotic species tend to take over natural ecosystems because they do not have indigenous “enemies” or animals that feed on them. Too much invasion of exotic species into an ecosystem may thus disrupt the balance in the system.
Therefore, to ensure the continuation of an ecosystem all organisms must be functionally integrated. One way to ensure survival of organisms per species is for individuals to produce an offspring of at least more than two. But if this rate of population increase continues without any natural checks and balances, individuals would be multiplying at the expense of the rest of the ecosystem. To prevent species numbers to ‘get out of hand’ as it were, there should be a return to a state of equilibrium, also known as homeostasis. To make such conditions possible, certain control mechanisms operate as a result of ecosystem feedback.
Figure 6.5: Un-checked population growth (positive feedback) can be catastrophic to ecosystems
Positive (unrestrained one-directional) feedback will encourage behaviour to continue indefinitely. For example, a population explosion in a community could be characterized by run-away births for some time as long as enough food is available. This could also happen when food is artificially provided to a herd of elephants. Soon as the elephant numbers increase, the vegetation in the community will experience stress due to trampling. Under natural conditions the process of Negative feedback will inhibit this population growth and the system will return to a balanced condition as it always penalizes an increasing effect. As a result, there will be a reduction in numbers through famine for example, to bring the number of individuals back to a stable state of equilibrium.
To make such conditions possible, certain control mechanisms operate as a result of ecosystem feedback. Positive (unrestrained one-directional) feedback will encourage behaviour to continue indefinitely. For example, a population explosion in a community (e.g. rabbits) could be characterized by run-away births for some time as long as enough food is available. This could also happen when food is artificially provided to a herd of elephants. Soon the vegetation in the community will experience stress. Under natural conditions the process of Negative feedback will inhibit this growth course and the system will return to a balanced condition as it always penalizes an increasing (positive growth) effect. As a result, there will be a reduction in numbers through famine for example, to bring the number of individuals back to a stable state of equilibrium.
Homeostasis is thus a self-regulating process by which ecosystems tend to maintain stability while adjusting to conditions that are optimal for long-term survival. If homeostasis is successful, life continues; if unsuccessful, death ensues. The concept of ‘dynamic equilibrium’ is often used to describe the continuous change that occurs within certain boundaries. In this way stability is attained and relatively uniform conditions prevail
Figure 6.6: Once environmental impacts like deforestation of indigenous tropical forests or draining of marsh land, exceed the threshold of an ecosystem the regenerative capacity to recover could be lost forever.
If we thus remove the natural animals to introduce domesticated cattle, we must also ensure that there is a balance between number of cattle and available fodder. Thus, vegetation plays the most important role in determining the carrying capacity of a piece of land. Carrying capacity is a measure of the biotic components the environment is able to accommodate without degradation. As long as the animal community produces offspring just enough to survive in the ever-circulating plant community (through seed dispersal, germination and growth), numbers of animals will thrive and compete healthily with other species in the community.
As limiting factors develop within a community or population, such as a lack of food or shelter in the case of animals, and in the case of plants, space and sunlight, competition amongst and between species for the same resources will ensue.
Figure 6.7: Competition between individuals of the same species is greater than competition between species from different populations.
This may lead to aggressive interaction (see Fig.6.7). If one species prevails over the other species, it usually means that it is better adapted to the particular habitat than the other.
But there may also be ‘peaceful’ cooperation between species. We refer to such arrangements as symbiosis. Parasitism is a form of biological control where the parasite get nourishment from the host but do not kill it, otherwise it will lose its source of nutrients.
Figure 6.8: Ox-pecker birds pick at parasites on the mammal’s body keeping the animal’s parasite load under control, whilst the birds get an easy meal.
Herbivory is where an herbivore gains energy and nutrients whilst plants are consumed. Predation is where the “bread of the one, is the death of the other” – where animals eat each other.
Competition between individuals of the same species in a community is often greater than competition between individuals from species from different populations as they compete for identical resources. For example when some game are browsers and other game are grazers, they do not compete with each other. White rhino and Black rhino can live side-by-side in the same ecosystem without competing as White rhino eats grass and Black rhino feeds on leaves. Zebras that feed on rough grass do not compete with Springbuck that eat softer species of grass. We thus conclude that interspecies competition is less than intra-specie competition.
Let us now consider the impact that land-use has on the environment.
The specific venture that the land or habitat is intended to be used for, will determine the resulting impact on the landscape or ecosystem. If a game farm has tourism as its main aim, it will require the maximum number of animals and therefore require addition of water and forage to increase the carrying capacity. But if the purpose is trophy hunting, it may require the weaker animals to be eliminated to optimize the reproduction of better wildlife stock. A meat producing farmer will have yet a different approach to veldt management and carrying capacity by building and managing feedlots, far removed from the natural ecosystem. Modern factory farming is an extreme example where chickens, pigs, and other animals are kept in small confinements – so small that they cannot even turn around–and fed hormones in order to gain weight as fast as possible.
Humans have thus introduced artificial control mechanisms to maintain ecosystems and to increase the carrying capacity of land.
In doing so humankind has overcome to a large extent the relationship with and dependency on nature’s inherent feedback systems. We have installed an artificial balance in environmental systems that has to be kept in place with additional energy and matter input above that which is provided by natural processes. Because of the various artificial control mechanisms that we have put in place, we have created an unsustainable positive feedback scenario.
Figure 6.9: If left un-checked the volumes of waste generated in highly populated areas will clog up natural systems.
Civilizations can in this way flourish in locations where numbers far surpass the land’s natural ability to provide. With the help of dams and irrigated fertilizer-enriched farmlands, huge cities can support their ever-increasing populations. The more people there are in a city, the more extra water and produce is needed. The more water and food that are provided, the more people can move to the city: a never-ending spiral process. This positive feedback system needs to be artificially manipulated by human technology to provide above that what nature provides. As a result, nature suffers as dams inhibit the flow of rivers and the intermittent flow of the rivers impact on their associated ecosystems. Accelerated food production by increasing fertilizers and pesticides is harming the long-term natural productiveness of soils and this too can become a positive feedback system diminishing soil fertility overtime.
Figure 6.10: Growth of water hyacinths in a dam due to Eutrophication because of excessive nutrients.
With limited resources, humankind must recognize that development potential is not infinite, hence the cliché: “we live in a spaceship economy”. We have only “so much” resources, and nothing more.
In our endeavours to supply enough food for a growing human population, more and more extensive areas are being earmarked for agriculture. Unsustainable methods of industrial farming, like conventional ploughing of the land causes huge-scale erosion. Furthermore this is also disrupting the organic compound composition in the soil.
The extensive use of pesticides and genetically engineered crops are compromising insect numbers and associated ecosystems.
It is important to develop agricultural methods that restore the soil component. For example regenerative agriculture aims to return what it takes out of nature back to nature. Organic matter must be replenished after the crops have been taken off the field. Cattle manure for example must replace organic matter taken off through grazing. Soil must be carefully managed by not disrupting the organic component within the soil by means of ploughing. Limiting fertilizers and insecticides and by practicing rotational grazing, and by enhancing the biodiversity of crops, and animals in our agricultural practices, one could imitate nature’s directives.
Because we are forever trying to circumvent and modify the checks and balances of nature to enhance living conditions for the present, we are in effect causing long term poverty to millions more. The natural ecosystems as we know it will soon no longer be able to support our ever-growing need for more energy, food, and material ‘stuff’. If we are not able to reduce our impacts on the environment and its resources in favour of a sustainable approach to life, the current increasing development trend of ‘more for all’ will be replaced by a downward spiral, where progress will come to a standstill because of ecosystem bankruptcy.
We as humans have failed to notice the impact our actions have on our life-supporting ecosystem services. In whichever way we would like to look at it, the feedback systems of nature ultimately apply to us as humans as well. In the mid-14th century, the Black Plague struck Europe and of the 100 million people then on earth, it is estimated that 70 million died. Today we can see the effects of EBOLA, AIDS and COVID on population numbers. Droughts during the early 60’s have created extensive starvation in Ethiopia and surrounding states. Currently there are unprecedented high temperatures worldwide associated with excessive wildfires causing destruction.
Figure 6.11: Do we as the human race have the socio-economic will and discipline to adopt a way of life that is in harmony with our natural resource base?
Rivers previously perennial, are drying up such as the once mighty Euphrates in the Middle East and the Colorado river in the USA. These and similar examples could well be regarded as “normal” ecological processes whereby nature tries to keep human behaviour in check with nature’s supply of resources. This is due to our inability to adapt to nature’s laws.
Almost 50 years ago, and in line with the more recent theory of Ecological Intelligence,
scientist James Lovelock introduced the so-called Gaia hypothesis – arguing that the Earth is a self-regulating super-organism. He predicted already in 1965 that, if we do not restrain our pressure on natural systems, the main problem of the world in 2000 would not be socio-political but its environmental condition. Although initially ridiculed by many scientists as “new age nonsense”, today the theory forms the basis of almost all climate science.
To conclude this chapter: Today we do have the scientific knowledge to establish a sustainable future. The final question remains: do we as the human race have the socio-economic will and discipline to adopt a way of life that is in harmony with our natural resource base? Time will soon tell.