8. Ecosystem Ecology

• • ECOSYSTEM
  • biological community together with the abiotic environment where it is situated
  • Consists of several components that interact with each other and carry out specific functions
• • Arthur G. Tansley
  • Father of british ecology
  • in 1935, first proposed the concept of an ecosystem whereby the climate, soils, plants and animals functioned as part of a system, each with a functional relationship with the other (Sheail, 2005).
• • Eugene P. Odum
  • in 1964, established the systems approach in the study of ecology. 
  • He “represented ecosystems as flows of energy starting from photosynthesis
• • An ecosystem has both biotic and abiotic components as follows (Odum, 197]):

  1. Autotrophs 
  2. Heterotrophs
  3. Inorganic nutrients
  4. Air, water, soil,and climatic factors
• 1. Autotrophs 
  2. that produce energy for the ecosystem.
• 1. Heterotrophs
  2. that eat other organisms to obtain energy;this includes animals,detritivores and decomposers (bacteria, fungi)
• 1. Inorganic nutrients
  2. N, P, K+, Ca++, Mg++, Fe+++, Zn++, etc.
• 1. Air, water, soil,and climatic factors, like
  2. humidity, light intensity etc.
• 1. Autotrophs 
  2. rooted or floating plants growing in shallow water

  Phytoplankton, minute floating algae, bacteria, protozoa
• primary consumers (herbivores) that feed on plants/phytoplankton

  1. zooplankton
  2. benthos (benthic organisms)
• 1. secondary consumers (carnivores)

  • such as predaceous insects and fish capable of moving about at will in the water 
• 1. detritivores

  • feed on the “rain” of organic particles from the autotrophic layers above
  • detritivores in a pond, like worms, also serve as food for carnivores
  • land examples: earthworm, flies, and vultures
• 1. ecomposers

  • heterotrophic bacteria, protozoa, fungi especially abundant at the mud-water interface of the pond
• • The abiotic factors with which the pond organisms interact or are affected by are 
  • water and its temperature, 
  • sunlight, 
  • air, and 
  • the substratum, especially the nutrients present.
• • TWO FUNCTIONS OF ECOSYSTEMS
  • flow of energy
  • cycling of nutrients
• • Decomposers 
  • occur at each trophic level to break down complex compounds into minerals that can be absorbed by plants, in the process of nutrient cycling.
• • Energy
  • flow through the ecosystem and not recycled because as it is passed along the food chain, some energy is released as heat to the environment
• • Second Law of Thermodynamics 
  • which states that energy being utilized is always degraded from higher quality to lower quality. 
• • ToF: High quality energy can be used to do work (True) 
• ToF:

  • Low quality energy (e.g , heat from our bodies) cannot be used to do work.  (True)
• TOF:

  • Some energy is always wasted because our body and other machines are not 100% efficient (True)
• Law of Entropy, which states that all things (a car, house, the human body) on earth tend to go into disorder.
• •  Living organism
  • need energy and all energy from the earth comes from the sun. 
• • Plants 
  • make use of the sun's energy to make food during photosynthesis.
• • Gross primary productivity 
  • refers to the rate of production of organic material or biomass (gm/m2/wk.or.kg./ha./yr.)by all autotrophs in the ecosystem.
• • Biomass
  • the amount of mass of organic material in the bodies of organisms in an ecosystem.
• • Net primary productivity (GPP-R=NPP) 
  • Gross primary productivity minus the organic material used by plants for their own needs, such as respiration to make ATP.
  • significant because it represents the energy budget that is available to the heterotrophs in the community. 
• • Secondary productivity
  • Production of biomass or organic material by heterotrophs (animals, fungi, bacteria, protists) (Molles, 2013).
• • The productivity of the forest biomes decreases from the equator towards the poles
  • Highest productivity
  • Tropical rainforest
  • Lowest productivity
  • Tundra 
• • Aside from temperature and precipitation, the lack of nutrients in the soil is also a factor which limit productivity.
• • Some recent researches suggest that the average annual NPP of an ecosystem reaches a peak of 10-40 producer species. 
• • In the seas,

  the main factor limiting productivity is lack of nutrients, namely, nitrogen and phosphorus.
• • Aside from nutrients, light also influences aquatic productivity. 
• ToF: the open ocean has a low productivity per unit area but the huge volume of oceans results in a large contribution to the earth's productivity. (True)
• In the tropics, vertical mixing does not occur because there is a permanent thermocline with warm water staying on the surface and cold, nutrient-rich water remaining in the bottom
• Primary productivity can be affected by consumers, known as top-down control.
• • In top-down processes, 
  • ecosystem function is regulated by trophic interactions, particularly from the highest trophic level. 
• • If top-down processes dominate an ecosystem, 
  • the effects of increase in the population of the top predators cascade down the food web through the herbivores and producers (Molles, 2013).
• • Grazing increases the growth rate of many grass species, a response to grazing called compensatory growth, due to reduced self-shading and improved water balance due to reduced leaf area (Molles, 2010).
• • Top-down regulation 
  • predominate in ecosystems with few trophic levels and low species richness. 
  • These ecosystems have only one or a few species of dominant herbivores, but these species have a strong impact on producer populations