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]):
Autotrophs
Heterotrophs
Inorganic nutrients
Air, water, soil,and climatic factors
Autotrophs
that produce energy for the ecosystem.
Heterotrophs
that eat other organisms to obtain energy;this includes animals,detritivores and decomposers (bacteria, fungi)
Inorganic nutrients
N, P, K+, Ca++, Mg++, Fe+++, Zn++, etc.
Air, water, soil,and climatic factors, like
humidity, light intensity etc.
Autotrophs
rooted or floating plants growing in shallow water
primary consumers (herbivores) that feed on plants/phytoplankton
zooplankton
benthos (benthic organisms)
secondary consumers (carnivores)
such as predaceous insects and fish capable of moving about at will in the water
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
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