Natural and artificial ecosystems

Author: Mária Höhn

Plant communities, animal populations which depend on plants and decomposers together with the environmental factors build up the ecosystems.

Therefore, ecosystems have both biotic (living organisms) and abiotic (environmental factors) components, between which nutrients and energy flow in space and time. Ecosystems are the basic functional units of the biosphere. Each living organism on Earth belongs to an ecosystem and within an ecosystem to a trophic level, in which they play a specific functional role.

Ecosystems are not higher organization levels of the living world; instead, they represent models of the ecological systems, e.g. of the interaction between different populations or organizational levels and the environment (Figure 1.)

Figure 1. The structure of ecosystems.

8. 1. Ecosystem characteristics

- All ecosystems on Earth are open systems because they exchange energy and matter with the surrounding environment. Most ecosystems use solar radiation as energy source and inorganic components of the environment such as CO₂, NH₄⁺, NO₃^-, PO ₄^3- as a source of nutrients. Only a few cave ecosystems and deep water marine ecosystems use chemical- or geothermal energy instead of solar energy.

- Ecosystems possess self-regulation ability, meaning that their functioning is maintained by different control mechanisms of which the most important is the negative feed-back. Negative feed-back ensures that all ecosystem parameters are maintained within optimum intervals.

- Ecosystems may differ in composition, population structure and environmental characteristics, but the basic functioning rules are always the same.

- The ecosystem’s functional and structural components are in dynamic equilibrium with the environment.

8. 2. Ecosystem functioning

- Different functional levels of an ecosystem are linked together by the nutrient cycle. Therefore these levels can be considered trophic levels. One of the main indicators of ecosystem functioning are the biogeochemical cycles, which refer to the circulation of nutrients and of water along characteristic pathways within ecosystems. For example, we can speak of C, N, O, and H₂O cycles. Mineral cycles are different in that the chemical elements are excluded at least one time from the nutrient pathway by being deposited in (geological) sediments (e.g., P, S, Mg, and Ca). These elements are reactivated from sediments from time to time.

The nitrogen cycle, one of the most important biochemical cycles of the ecosystems is shown in Figure. 2

Figure 2.: The nitrogen cycle (according to Mátyás Cs.)

The ecological functioning of an ecosystem would not be possible without the primary producers that are able to produce organic material from inorganic substances by autotrophic metabolism. They form the base of the food chain. Most of the primary producers produce organic substances utilizing solar energy, through the process of photosynthesis. The rate at which the solar energy is used can be expressed in units of energy, units of dry organic matter, or the quantity of carbon included in the organic matter.

The primary organic matter produced (as either live or dead tissues and organic particles) „flows” towards the next trophic level, the consumers, wich possess heterotrophic metabolism. All heterotrophic levels transfer rapidly the organic matter by consumption or predation. The rate of organic matter production by consumers is called secondary production. Depending on the type of food which they consume there are primary (herbivores), secondary and high-level consumers (carnivores). Unconsumed plants and animal remains are broken down by the decomposers/detritivores (fungi, bacteria and many kinds of microorganisms). The result of decomposers’ activity can be mineralization i.e., a total decomposition of the organic matter into inorganic substances that are either reincluded in the trophic pathway by plants or are temporarily deposited in the soil.

The flow of organic matter through the trophic pathway is always accompanied by loss of material (e.g., through conversion to heat via respiration, undigested rests of food, emigration of living organisms from the systems, etc).

- In every ecosystem the energy flow is unidirectional. Starting from the solar radiation fixed by autotrophic organisms or any other source of energy that enters the ecosystem, the energy follows the general laws of thermodynamics: it never disappears only it gets transformed, and the energy flow is accompanied by significant loss. Producers, consumers and decomposers generate large quantities of heat during respiration, which is released from the system.

The pathway of nutrient cycle and energy flow that links different trophic levels within ecosystems is called food chain. The functional groups of organisms can participate in many types of food chains, which may be ecosystem- specific. In natural ecosystems, the food chains are short and consist of only 4-6 levels; more than that seems not to be profitable because of the rate of matter and energy loss.

A food chain is unbranched because there are simple feeding relationships between populations, and all populations have a determined position along the chain. In a food web there are multiple links between different species, and the functional groups can be linked through many trophic interactions (Figure 3).

Figure 3: Types of food chain and food webs

The main parameters that describe ecosystem functioning and efficiency are:

- Biomass production

Primary production of autotrophic organisms (production of organic matter through the process of photosynthesis) is the most important parameter that influences ecosystem functioning. All other ecosystem components depend on the primary production. A large quantity of matter and energy from the primary production is lost by passing from one level of the food chain to another. Consumers get not more than 10% of the energy produced in the primary production; secondary consumers get around 1%, while tertiary consumers less than 1%.

The biomass of an ecosystem refers to the total quantity of biologically produced organic matter built up by the living organisms in their body. The biological material produced in the primary production is called phytomass. The quantity of biomass / phytomass can be calculated on individual, population, biocenosis or on biome level.

Other parameters that describe ecosystem characteristics:

- net ecosystem production is the difference between the gross primary production and total system respiration,

- the respiratory coefficient is the proportion of eliminated CO₂ and incorporated O₂

- the quantity and deposition rate of the detritus (waste products, and other organic debris)

- species composition and diversity of functional groups.

A significant change in any of the parameters mentioned above can indicate disequilibrium and even ecosystem decline.

The natural ecosystems of the Earth evolved more than 3 billion years ago and they have functioned unimpeded for a long time. Their species composition and trophic structure might have changed over time but their functioning principles remained the same.

However, during the last 5000 years the Earth’ traditional ecosystems suffered dramatic changes as a result of increasing human activity. Humans discontinued their links to the natural ecosystems and have fundamentally modified them from outside. In our so-called anthropogenic age, natural ecosystems are disappearing and are being replaced by artificial and ruin ecosystems. There is a difference between the latter two: artificial ecosystems are affected by human activity but are able to maintain their equilibrium, whereas ruin ecosystems need substantial human intervention for functioning. Agricultural ecosystems such as arable fields, fallow farmlands and parks around settlements are ruin ecosystems. See Table 1 for examples.

The proportion of artificial ecosystems on Earth increased enormously during the last centuries. More than 50% of the terrestrial ecosystems are already disturbed with some signs of a strong human impact. 85% of the territory of Hungary is dominated by artificial ecosystems.

Although more than half of the human population lives in urban ecosystems, these occupy not more than 7% of the whole surface of the Globe.

The remainder natural ecosystems are not untouched either, because the negative impacts of the human activity (e.g., increased CO₂ concentration in the atmosphere, greenhouse effect, acid rains, thinning of the ozone belt) impact them from a distance.

 Table 1: The main features of natural and anthropogenic ecosystems (Vida 2004)

8.3. Ecosystem services, ecosystem degradation and ecological footprint

The most important prerequisite of human life is to maintain the normal functioning of ecosystems and to use the benefits of ecosystem production. Ecosystem services can support human needs only by a normal functioning and under an equilibrated usage of these services. Excessive use and overexploitation by humans will result in ecosystem decline.

Recently a new indicator value has been introduced to measure and quantify the use of ecosystem services by humans: this is the ecological footprint.

The calculated value of the ecological footprint of a human on Earth in 2007 was around 2.3 ha, but only a maximum of 1.9 ha is available to all inhabitants of the Earth. This means that ecosystems are plundered by humans because the use of benefits happens at a more accelerated pace than the ecosystem renewal capacity. The rational use of ecosystem services is of a major interest to all of us, as even the modern technology will not be able to compensate the growing deficit.

Although we have recognized the consequences of the depletion of our limited resources, less has been done to handle this significant threat.

The negative impact of the irrational use of ecosystem goods and services resulted in degradation of ecosystems.

Major consequences of the human impact:

- degradation of many natural habitats;

- fragmentation of natural habitats;

- Species extinctions;

-Overharvest of some species, advantaging some species by preferential breeding and cultivation while suppressing others; breaking the natural equilibrium of species; spread of weeds;

- Allochtonous species introduced to new habitats became weeds, many of them invasive.

- Distribution of foreign pests and pathogens. E.g. phylloxera, introduced from America and the downy mildew destroyed thousands hectares of vineyards in Europe.

- Drought, desertification because of irrational use of water resources on mainland;

- Water and soil pollution;

Not surprisingly, ecologists are today speaking about an ecological crisis. This means vanishing natural resources, growing waste and garbage in ecosystems, degradation of the natural environment and of the living environment.

It is imperative to change our attitude towards the natural ecosystems and our way of thinking in order to maintain the sustainability of our ecosystems. It is for the best interest of all people on Earth.

References

- Cain, M., Bowman, V.D., Hacker, S.D. 2011. Ecology. (2nd ed). Sinauer Associates Inc.

- Mátyás Cs. 1997: Erdészeti Ökológia. Mezőgazda kiadó, Budapest.

- Pásztor E., Oborny B. (szerk.) 2007: Ökológia. Nemzeti Tankönyvkiadó, Budapest.

- Simon T. (szerk.) (2001): Növényföldrajz, Társulástan és Ökológia. Tankönyvkiadó, Budapest.

- Turcsányi G. (szerk.) 1998: Mezőgazdasági növénytan. Mezőgazdasági Szaktudás Kiadó, Budapest. 2. kiadás

- Vida G. 2004: Helyünk a bioszférában. Neumann Kht., Budapest