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Ecology and ecosystems
Ecology and ecosystems

Basic knowledge in natural sciences like physics, biology, chemistry and ecology is necessary to understand what happens to Earth, the planet on which we all live.

  1. Ecology is the study of environmental systems and how they intra- and interact.
    This includes the abiotic (non-living) environment; the litosphere, the hydrosphere (water), the atmosphere (air), the cryosphere (the frozen areas) and the biosphere (the living).

    Photo: Å. Bjørke. Cape Town.
    An ecosystem:
    • Litosphere: the ground; earth, rocks, dust, gravel.
    • Hydrosphere: the river. (any body of water)
    • Atmosphere: the air.
    • Biosphere: the vegetation and animals

  1. In principle we start out with a big piece of rock and dust. The crust of our planet is termed The Litosphere.
    To the litosphere we add water: The hydrosphere.
    On top of this we add air - The atmosphere. The atmosphere has several layers, but in this connection the emphasis will be on the two major layers; the lower layer where most living organisms are able to breathe, and the upper layer, where the air is too thin for normal organisms to survive.
    Close to the litosphere is The troposphere - about 10 km up in the air is The stratosphere.

    With energy from the sun, the system is ready for the next step:
    The biosphere.
    The biosphere includes all living organisms: plants, animals, bacteria, fungi.

    The ecosphere is the area where we can find ecosystems, or it can refer to a planetary ecosystem consisting of the influence of the solar system, the geosphere (the planet), the atmosphere, the hydrosphere and the biosphere.
    Recipe for an Ecosphere (NASA)

    In order for complex ecosystems to thrive, it is necessary to have a fairly stable temperature.
    When day and night temperatures vary by more than 30 centigrades, more complex living organisms have to struggle to maintain homeostasis.

    Most organisms - plants and animals - have periodic life cycle events. These life cycles are influenced by seasonal and interannual variations in climate, and of course by long term climatic changes. A separate field of ecological study called phenology focuses on such life cycles. Several phenological studies indicate impacts of climate change.

    Greenhouse gases in the atmosphere prevent drastic temperature falls at nighttime or in dark periods by slowing down the outward going energy that is leaving the planet in the form of infrared light.
    On our planet such gases comprise roughly 1% of the atmosphere, water vapour included.
    In other words, we do not need very much greenhouse gas to obtain the desired effect.

    With a fairly stable average global temperature of around 14 centigrades, rather than 30 centigrades colder,
    as it would have been without greenhouse gases, the basis for higher forms of life is present.
    Without greenhouse gases, freshwater would freeze every night.
    Frozen water, The cryosphere, is difficult to access for living organisms.

    In other words; the biosphere will not thrive if the hydrosphere is only available in the form of a cryosphere. On the other hand, mountain glaciers provide important freshwater storages, feeding meltwater into rivers during the warm seasons. Without mountain glaciers, several rivers would dry up during summer seasons, in other words periodically removing the hydrosphere from the ecosystem.

    A "correct" chemical composition of gases in the atmosphere is thus crucial for the development of higher forms of life.

    The biosphere is divided in producers or plants, consumers or animals and parasites at various levels and decomposers: worms, bacteria and fungi.

    Photo: P. Prokosch. Waterbuck (1st consumer), Masai Mara
  1. Ecosystems
    According to the Millennium Ecosystem Assessment, an "ecosystem is a dynamic complex of plant, animal, and microorganism communities and the nonliving environment interacting as a functional unit".

    Ecosystems are composed of a part of the litosphere, water, air, living organisms.
    These components interact with each other and with their environment within the ecosystem.
    In this interaction, energy is exchanged and cycles of elements emerge.
    In a sustainable ecosystem everything moves in cycles.
    Nothing can accumulate at points within the system for longer periods.
    There is no waste or garbage.

    An ecosystem may contain one or more habitats, with varying amounts of water, shade, minerals, wind, salt, light, temperature and other species. A habitat is an area inhabited by a particular species of animal or plant. Some plants and animals are very specialised, and must have certain conditions in the ecosystem fulfilled to be able to survive in their habitat. The more specialised the animal or plant is, the more sensitive or vulnerable it is to change in e.g. climate, increased acidity, pollution, lack of certain minerals or lack of certain other species of plants and animals with which it interacts.
    Opportunistic or invasive species may enter the habitat and may decimate or exterminate the specialised species.
    Every habitat has distinct life forms living in it. The habitats may in turn form complex communities of interdependent organisms. Such a complex community of plants and animals in a region is called a biome. "Biomes" and "ecosystems" are often used as synonyms.

    The more diverse species in the ecosystem, the more resilient the system is against disasters or changes. Homogeneous ecosystems or monocultures are more vulnerable. Whenever a species in an ecosystem is removed, be it plant, animal, fungus or micro-organism, the ecosystem is depleted and loses resilience.

    Photo: Å. Bjørke: Leopard (second consumer). Masai Mara
  1. Energy flow and pollution

    The basic structure of interaction in biological communities is the "trophic pyramid", which describes the way food energy is passed from one trophic level to another along a food chain. See Trophic pyramid (Encyclopedia Britannica)

    Energy flows from:
    • producers - the plants (or autotrophs) - to the heterotrophs:
    • 1st consumers - plant-eaters to
    • 2nd and 3rd etc consumers - the meat-eaters and parasites- to
    • Decomposers: worms, snails, bacteria, fungi




    When certain chemicals enters the food chains, they may accumulate in the fatty tissues or bones and increase in amount for every step in the food chain. Persistent Organic Pollutants (POPs) are regarded as particularly dangerous accumulating chemicals.



    Photo: Å. Bjørke: Coral reef. A complex ecosystem. Cape Town aquarium
  1. Ecosystems can be disrupted
    Eosystems may change suddenly or over time. If the change happens over a long period of time, most species can adapt to the new conditions.

    Ecosystems may be disrupted through natural causes, such as a natural change in climate, or natural disasters like earthquakes, volcanic eruptions and tsunamies. Human activities may also disrupt ecosystems, locally as well as globally. Human activities may enhance existing natural processes or cycles, such as the greenhouse effect, or create completely new conditions, such as depleting the ozone layer with ozone depleting chemicals, or add POPs to the energy flow in the food chains.

    Pollution through high concentrations of waste and secreta may affect water bodies and cause eutrophication.

    Ecosystem services
    Ecosystem services are the benefits people obtain from ecosystems. These include provisioning services such as food, water, timber, and fiber; regulating services that affect climate, floods, disease, wastes, and water quality; cultural services that provide recreational, aesthetic, and spiritual benefits; and supporting services such as soil formation, photosynthesis, and nutrient cycling (Millennium Ecosystem Assessment - Synthesis).

    More comprehensive information


    Unfortunately human activities have already depleted several ecosystems and drastically changed others. The planet "Earth" as we knew it fifty years ago no longer exists. We have changed the chemistry of the atmosphere irreversibly. We have made the oceans much more acidic. We have exterminated thousands of species and depleted fish stocks, brought several species of birds and animals to the verge of extinction and cut down more than half of the rain forests of the world. We have accumulated enormous amounts of more or less toxic garbage, and added persistent, accumulating and very poisonous chemicals to all food-chains. We have already changed the climate, bringing more droughts, floods and violent storms than we have been used to. We have severely depleted vital freshwater resources by pumping up fossil water from deep underground acquifers. Many lakes and rivers are polluted and suffer from eutrophication. Huge areas of land suffer from soil depletion and have become deserts.

    The human ecological footprint has increased drastically the last thirty years, and we keep building up an ecological debt that will be increasingly difficult to handle.
    Unless we manage to change our way of life in a more sustainable direction, this negative trend will accellerate.

    Photo: Jens Timenes. Water hyacinth - eutrophication, Sri Lanka
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