The Convention on Biological Diversity (CBD) defi nes an “ecosystem” as a “dynamic complex of plant, animal and micro-organism communities and their non-living environment interacting as a functional unit” (see also Tansley, 1935; Christopherson, 1996). The basic idea is that living (and dead?) organisms are permanently involved in the exchange of energy, material and information with their environment. Ecosystem function is governed by organisms acting at various stages within the system. Primary producers (green, photosynthetically active plants and bacteria) form the base of the system. They have the unique ability to fi x and conserve the energy of extraterrestrial radiation and produce digestible carbohydrates, lipids and proteins. They are hierarchically followed by herbivorous/phytophagous organisms feeding on them. The fi rst order consumers are the prey for second order consumers (carnivores) which hunt and feed on herbivores. There may be further levels and steps in carnivorous consumers depending on the ecosystems selected. Finally, decomposers (destruents and reducers) are mineralizing dead organic material, thus playing their role in organic material recycling – a prerequisite for plant growth. There is a broad spectrum of ecosystems including terrestrial and aquatic ones. Deep see, coral reefs, sea shores, ponds, rivers and creeks are aquatic ecosystems as are tundra, taiga, deserts, or grass lands on the terrestrial side. But also anthropogenically infl uenced systems may be called ecosystems like urban areas, gardens or waste land. Ecosystems can be threatened by various stressors. The toxicity of introduced elements (toxic gases, heavy metals, pesticides) or the aggressiveness of newly introduced or invasive species (global warming, economic globalization) are only a few examples of gradually unbalancing existing ecosystems.

V konvenciji o biološki raznolikosti (CBD) je ekosistem opredeljen kot dinamičen kompleks združb rastlin, živali in mikroorganizmov ter njihovega neživega okolja, ki skupaj delujejo kot funkcionalna enota (glej tudi Tansley, 1935; Christopherson, 1996). Osnovna ideja je, da so živi (in odmrli?) organizmi stalno vključeni v izmenjavo energije, snovi in informacij s svojim okoljem. Delovanje ekosistema poganjajo organizmi s svojim delovanjem na različnih stopnjah sistema. Primarni producenti (zelene, fotosintetsko aktivne rastline in bakterije) so baza ekosistema, ker lahko sprejmejo in zadržijo energijo zunajzemeljskega sevanja in proizvedejo razgradljive ogljikove hidrate, maščobe in beljakovine. Naslednjo stopnjo predstavljajo rastlinojedi organizmi. To so potrošniki prvega reda in predstavljajo plen za potrošnike drugega reda (mesojedci), ki rastlinojedce lovijo in se z njimi hranijo. V izbranem ekosistemu je lahko več zaporednih stopenj mesojedih potrošnikov. Končno pa razkrojevalci razgradijo mrtev organski material in igrajo ključno vlogo v recikliranju snovi, potrebnih za rast rastlin. Obstaja mnogo ekosistemov, vključno s kopenskimi in vodnimi: globoko morje, koralni grebeni, obale, ribniki, reke in potoki so primeri vodnih ekosistemov, tako kot so tundra, tajga, puščava in travišča primeri kopenskih. Med ekosisteme lahko prištevamo tudi antropogene, kot so urbane površine, vrtovi, odlagališča odpadkov. Na ekosisteme lahko vplivajo različni stresni dejavniki (strupeni plini, težke kovine, pesticidi) ali agresivnost novih oz. invazivnih vrst (globalno segrevanje, ekonomska globalizacija).