The climatic regions of the Earth gave origin to a large variety of natural environments. Each habitat is formed by a community of animals and plants, called ecosystem, that, in order to survive, must adapt to the surrounding environment exploiting its resources as best they can. 550 million years ago plants began to grow on the Earth, creating the first environment that was suited for animal life; initially mosses and ferns were dominant, then conifers developed, and then flowering plants. At the same time, also herbivorous animals evolved and the foundations for the complex ecosystems of today were laid.
An ecosystem is a complex system composed of organisms living in a given habitat. Plants and animals are the biotic components of the ecosystem, while the subsoil, water, air, light, temperature, the climate, rains are part of the abiotic components. In an ecosystem, the biotic components that inhabit it and the abiotic ones establish a set of relationships with each other that characterise the ecosystem itself and bring it to a temporarily “balanced” state.
According to their task within an ecosystem, the biotic components (living organisms) can be divided into:
- producers (plants, algae and some bacteria): these are “autotrophic” organisms that produce by themselves the organic matter they need to live and grow, using such simple inorganic molecules as water, carbon dioxide (CO2) and nitrates;
- consumers are defined as “hetero-trophic” organisms, since they cannot produce their own nourishment, but feed on producers (for instance, the herbivore consumers, such as cows and sheep, that eat grass) or on other consumers (carnivore consumers, such as lions or man);
- decomposers are fungi and bacteria that feed themselves by decomposing the tissues of dead organisms.
Each ecosystem contains a given amount of organic matter that includes all its vegetal and animal organisms: the weight of such matter is called biomass and is calculated dry and per surface unit occupied by the ecosystem.
The relations between the different components of an ecosystem are so close that, if one of them is damaged, the whole ecosystem is affected. The main relations are those established between energy flows and nutrient flows. The ecosystem is an open system as far as energy is concerned, that is energy continuously gets in and out of the system. The energy enters mainly from the sun, goes through and biotic community and its food chain, and goes out as heat, organic matter and resulting organisms.
The trophic chain
There are two types of food chains: the pasture chain and the waste chain. The first part of green plants passes through the pasturing herbivores, then moves to the first-level carnivores that fed on herbivores, then to second-level carnivores that feed on other carnivores. The second part of the dead organic matter passes through the micro-organisms, from these they move to the animals that feed on waste, then finally to their predators, that is, carnivore animals. Food chains are tightly interconnected, this is why we speak of a trophic (or food) network.
Differently from energy that gets in and out of the ecosystem according to a linear process, the matter follows a circular route, passing from the abiotic section to living organisms, and then comes back to the abiotic section. These routes are defined as biogeochemical cycles. Carbon, hydrogen, nitrogen, phosphorous, and calcium are necessary to living organisms in large quantities and therefore they are defined as macronutrients. Other elements like iron, magnesium, manganese and zinc, etc. are necessary in lower quantities and for this reason they are defined as micronutrients.
The primary productivity of an ecosystem is defined as the speed at which the solar energy is turned into an organic substance by chlorophyll in the photosynthesis. It is defined as follows: gross primary productivity (GPP), the total photosynthesis speed (therefore also called total photosynthesis); net primary productivity (NPP), the speed at which the organic matter produced is stored, net of that used by the plant to live (therefore also called apparent photosynthesis);
- net productivity of the community (NPC), it is the speed at which the organic matter not used by herbivore and carnivore animals is stored…
Changes in the food chain
Technological innovations applied to agriculture in the fight against crop-damaging parasites led to the use of large quantities of pesticides for long periods of time. These substances are toxic and their accumulation varied the balance of the biosphere, as they have harmful effects on organisms, man included. DDT is a substance that, when introduced into the environment, provoked damages to the ecosystem, creating a phenomenon of pesticide pollution at world level.
Researches that studied the quantity of DDT that is present in the environment, confirmed its presence in fish all around the world, in Eskimo populations, animals that live in polar regions and mother’s milk.
Ecosystems are everywhere: a wood, a lake, a river, a lawn, a beach, the sea, even the green areas of our towns. Briefly, every centimetre of our planet is or belongs to an ecosystem. Ecosystems can markedly vary in size. The temperate forest that covers most of North America, Europe and Northern Asia, and the cavity filled with water and life of a beech from the same forest are both considered as ecosystems (in this case, a “micro-ecosystem”). The Earth itself may be regarded as one big ecosystem.
Ecosystems on Earth
According to the type of vegetation that mainly characterizes them, ecosystems can be recognized and divided into: deserts; savannahs; steppe; temperate forest; tropical forest; boreal forest (taiga); tundra; mediterranean scrub.
Water ecosystems can instead be divided into: freshwater ecosystems (lakes and ponds, rivers and torrents, marshes and swamps) and marine ecosystems (reef; oceans, continental plateaus, nutrient upstream-flowing areas, estuaries).
The ecological succession
The history of an ecosystem from birth to maturity is called ecological succession. The ecological succession is essentially an uninterrupted sequence of changes in the biotic and abiotic components of an area, which leads to a stable ecosystem (the one that is defined as the "climax"), in which components are balanced, i.e. no one prevails over the others, making then disappear. The sequence of communities that replace each other with time within the ecosystem is called "sere" and the different transition stages are called “seral stages”.
An artificial ecosystem
A typical example of an artificial ecosystem is a farmland or agro-ecosystem. This is a natural system altered by man through farming. It differs from a natural ecosystem for four reasons: it is simpler, because the farmer gives priority to one type of plant only, fighting against all those animal and vegetal species that might damage it; the energy is supplied by man, through machinery, fertilisers, plant chemicals, selected seeds, farming practices…
Terrestrial and water ecosystems are complex and perfectly organised natural “factories” that produce all that is required for life on Earth and to cover man’s basic requirements: food, fibres, water. Some of these functions of the ecosystems are essential to man, such as air and water depuration, climate control, the nutrient cycle, soil fertility. In addition, some ecosystems (beaches, woods, lakes, high mountains, secluded valleys) are our ideal places for recreation, tourism and meditation, so we can say that the ecosystems have permitted our society and economy to develop. 50% of the world’s population are still engaged in farming, forestry and fishing. This proportion becomes 70% if we take the sub-Sahara, Asian and Pacific countries alone. 25% of the world’s countries have economies that still depend, almost entirely, on the sectors above. Farming alone produces 1.3 trillion dollars of food and fibres a year.
Man and the ecosystem
The human processes of farming, industrial production and consumption (or use) of commodities are carried out by similar rules as those of the matter and energy flows of the natural ecosystems. Also in the production and consumption of commodities, matter and energy are derived from nature, pass through the productive processes and get to the consumption stage. Waste and scrap are generated and disposed of in the environment during the production and consumption of commodities.
Ecosystems and Sustainability
In 1987 the World Commission on Environment and Development (WCED) issued its first report, the Brundtland Report (from the name of the Norwegian Prime Minister Gro Harlem Brundtland who at the time was President of the Commission). In 1992 was called the World Conference on Environment and the Earth Summit in Rio de Janeiro; on both occasions, the principle of “sustainable development” was officialised on a global scale. Sustainable development aims not to compromise the possibility of future generations of complying with their own development and counting on the same amount of resources we currently enjoy.
The carrying capacity of an ecosystem
The carrying capacity of an ecosystem is its natural capacity of producing regular resources for the species living in it without posing risks for their survival. Every year thousands of species become extinct, ranging from microorganisms to large mammals. The estimated average extinction rate has become from 1000 to 10,000 more rapid over the last 60 million years. Hence, there is reason to believe that another mass extinction could take place, the first ever caused by mankind rather than as a result of a natural process. 9 species out of 10 are endangered especially by the decay and destruction of their habitat.
Ecosystems at risk: why?
Man has always thought he would be able to alter the environment in which he lives to fulfil his own needs. Often though, he has not considered the consequences of this behaviour, and actually man has acted to obtain a certain effect, achieving instead the absolute opposite. A typical example may be the destruction of very productive ecosystems, such as estuaries and swamps, for the sake of reclaiming farmlands that are assumed to be “more” productive. But the special function of estuaries and swamps was not taken into consideration.
Balance change and consequences
When ecosystems are exploited, their balance is modified. As a consequence, health and productive capacity are compromised. Each human intervention on the environment management should therefore be studied according to the consequences that it might have for the ecosystem well being and its productivity. Such a perspective requires the whole of the ecosystem to be considered. At this respect it is necessary to know the ecosystem in a detailed way and assess its productive capacity and the consequences that the human intervention might have.
A typical example of artificial ecosystem is a cultivated field or agro-ecosystem. This is a natural system altered by men through agricultural activity. It’s different from a natural ecosystem for four main characteristics:
simplification: a farmer favours a plant species removing all other animal or plant species which could damage it;
the energy intake employed by men in the form of machinery, fertilizers, pesticides, selected seeds, processings;
the biomass (harvest) which is removed when ripe. This makes the ecosystem an open system, which means it depends from external processes to reintroduce fertilizing substances suitable to nourish a new growth and development process of organic material (plants). A natural ecosystem, instead, self-fertilizes as the biomass remains in its original setting;
the introduction of pollutant substances which, in the case of intensive agriculture, are chemical fertilizers, antiparasitics and other chemical non-biodegradable substances which accumulate in the ecosystem or which seep in the subsoil, in some cases getting to the point of seriously polluting groundwaters, seas and rivers.
A home is also a small artifical ecosystem. Objects, food, solar energy, water, etc. are introduced inside houses from outdoor and solid and liquid waste generated by human activities is removed outdoor. The city functions in the same way. A city, in fact, depends from external areas for water and food supplies as well as building materials and other resources necessary for its development and waste generated in a city is unloaded outside the urban area (in landfills and incinerators), which means everything which doesn’t contribute to the survival of the urban ecosystem is deposited in these areas.
Land to feed us
Cultivating land and feeding on its products has always been an activity men carry out keeping into consideration climatic and environmental conditions typical of every territory. Men have slowly overcome limits set by the environment thanks to progress and modern technologies and have thus been enhancing environmental stress. Men have therefore modified landscapes to increase productivity transforming land into cultivated fields, reclaiming wetlands, terracing slopes, and converting forests into pastures.
Agriculture and climate change
Earth’s climate is changing and there is scientific evidence about this. The average temperature of the planet has been rising by 0,8 °C in the past century (in Europe it has been rising by 1 °C). It’s been time since some gases have been identified as causes for global warming and the so-called "greenhouse effect", especially carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), naturally occurring in the atmosphere, but produced in high concentrations by human activity, as the use of fossil fuels for transportation and industrial activities, land-use change and deforestation.
Cultivating according to new climates
If we want agriculture to keep being a productive sector it’s necessary to implement solutions adapting old agricultural systems to the new climatic conditions. The goal is reducing the vulnerability of cultivations and increasing the resilience of rural areas from both an environmental and economical point of view, which means enhancing the capacity of agricultural activities of regaining productivity after catastrophic events, as droughts, hurricanes and floods.
The gap between water supplies and water demand is increasing in many areas of the world: in those areas where water scarcity is already occurring, increasing drought will be the major constraint to agricultural growth and development. Climate changes will cause, above all, a decrease in annual water availability in many areas of the world. In Europe, especially in southern and central European areas, water availability will decrease more and more due to the constant decline of summer rainfall and high-water demand for cultivations.
Biologists have tried several times to calculate the number of living organisms, with results that are sometimes conflicting. They range from an estimate of 10 million to 100 million. Moreover, the number of species (between 100 million and two billion) that have succeeded one another since life appeared on Earth is even more uncertain. However, it is possible to calculate more precisely how many species are known to science so far: a total of 1,700,000. The most numerous living beings in the biologists' 'catalogue' are animals (1,400,000 species), more than half of which are insects (800,000), while the rest are mammals (4,200 species), birds (8,700 species), reptiles (6,300 species), amphibians (3,000 species) and fish (23,000 species).