Ecological pyramids

 Ecological pyramids :  An important feature of energy flow is that most of the energy going from one trophic level to the next, in a food chain and food we, dissipated into the environment as a result of the second law of thermodynamics. Ecological pyramids oft tern graphically represent the relative energy values of each trophic  level. There are three  main types pyramids – a pyramid of numbers, a pyramid of biomass and pyramid of energy.

 Ecosystem productivity:  The gross primary productivity (GPP) of an ecosytem is the rate at which energy is captured during photosynthesis in a given period of time. In  addition, a plant respires to provide energy for its won use; this acts as a drain on photosynthesis. Energy in plant tissues after celluar respiration has occurred is net primary productivity (NPP). Both GPP and NPP are expressed as energy per unit area per unit time. Humans consume (32%) far more of earth’s resources than any other of  animal species. If we want our planet to operate sustainable, we must share terrestrial photosynthetic product with other organisms.

   In environments that show variations in salinity, temperature and other environmental conditions, food webs tend to have short chains. In stable environments, such as parts of the deep ocean, food chains are longer. In additon to energy inputs, primary productivity and  ecosystem structure require a cycling of nutrients. Water and minerals move slowly through the physical environment, rapidly  through organisms, and back to the environment in biogechemical cycles. Water moves through a hydrological cycle.  In land ecosystems, plants stabilize soil and minim nutrient loss during  cycle as runoff. In atmospheric cycles, a nutrient prevails mainly in gaseous form (such as carbon  in carbon dioxide). In the carbon cycle , carbon dioxide is the main gas in the atmosphere. The ocean is carbon’s main reservoir. Burning of fossil fuels, logging and conversion of natural ecosystems for farming disrupt the global carbon budget and may be responsible  for global warming.

     Nitrogen is a limiting factor in the total net productivity of ecosystem on land. Gaseous nitrogen is abundant in the atmosphere.  Nitrogen- fixing bacteria covert N₂to ammonia and nitrates,  which producers take up. Mycorrhizae and root nodules, two symbiotic interactions, enhance the nitrogen uptake. Sedimentary cycles interact with the hydrological cycle to me mineral nutrients to and from ecosystems.

   Certain human activities are depleting minerals from ecosystems, as when weathered soil of tropical forests is cleared for agriculture.

   Some  human activities are accelerating the process of eutrophication. They are adding nutrients such as nitrates an phosphates to aquatic ecosystems. This promotes growth of destructive algal blooms. The excessive growth of plants leads to the  depletion of oxygen in the water, which threatens fishes and other animal populations.