Ecology 1 Flashcards
types of ecosystems
it is convenient
to divide it into two basic categories, namely the
terrestrial and the aquatic. Forest, grassland and desert
are some examples of terrestrial ecosystems; pond, lake,
wetland, river and estuary are some examples of aquatic
ecosystems. Crop fields and an aquarium may also be
considered as man-made ecosystems.
what is an ecosystem ?
Interaction of biotic and abiotic components result in a physical
structure that is characteristic for each type of ecosystem.
2 parameters to define an ecosystem
Identification and enumeration of plant and animal species of an ecosystem gives its species composition.
Vertical distribution of different species occupying different levels is called stratification.
For example, trees occupy top
vertical strata or layer of a forest, shrubs the second and herbs and grasses occupy the bottom layers.
4 components of ecosystem
The components of the ecosystem are seen to function as a unit when
you consider the following aspects:
(i) Productivity;
(ii) Decomposition;
(iii) Energy flow; and
(iv) Nutrient cycling
explain ecosystem with the help of a pond
(i) A pond is a shallow water body in which all the above mentioned four basic components of an ecosystem are well exhibited.
(ii) The abiotic component is the water with all the dissolved inorganic and organic substances and the rich soil deposit at the bottom of the pond. The solar input, the cycle of temperature, day-length and other climatic
conditions regulate the rate of function of the entire pond.
(iii) The autotrophic components include the phytoplankton, some algae and the floating, submerged and marginal plants found at the edges. The consumers are represented by the zooplankton, the free swimming and bottom dwelling forms. The decomposers are the fungi, bacteria and flagellates especially abundant in the bottom of the pond.
(iv) This system performs all the functions of any ecosystem and of the biosphere as a whole, i.e., conversion of inorganic into organic material with the help of the radiant energy of the
sun by the autotrophs; consumption of the autotrophs by heterotrophs; decomposition and mineralisation of the dead matter to release them back for reuse by the autotrophs, these event are repeated over and over again.
(v) There is unidirectional movement of energy towards the higher trophic levels and its dissipation and loss as heat to the environment.
what is primary production and productivity
Primary production is defined as the amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis. It is expressed in terms of weight (gm–2) or
energy (kcal m–2).
The rate of biomass production is called productivity.
It is expressed in terms of gm–2
yr–1 or (kcal m–2) yr–1 to compare the productivity of different ecosystems.
GPP and NPP
Gross primary
productivity of an ecosystem is the rate of production of organic matter during photosynthesis.
A considerable amount of GPP is utilised by plants in respiration.
Gross primary productivity minus respiration losses (R), is the net primary productivity (NPP).
GPP – R = NPP
Net primary productivity is the available biomass for the consumption
to heterotrophs (herbiviores and decomposers).
secondary productivity
Secondary productivity
is defined as the rate of formation of new organic matter by
consumers.
what does primary productivity depend upon
Primary productivity depends on the plant species inhabiting a
particular area. It also depends on a variety of environmental factors,
availability of nutrients and photosynthetic capacity of plants.
NPP of world and form land and sea
The annual net primary
productivity of the whole biosphere is approximately 170 billion tons
(dry weight) of organic matter. Of this, despite occupying about 70 per
cent of the surface, the productivity of the oceans are only 55 billion tons.
Rest of course, is on land.
types of food pyramids
a) pyramids of number
b) pyramids of biomass
c) pyramids of energy
a) For grassland ecosystem, the pyramid is upright.
b) For grassland ecosystem, the pyramid is upright. For acquatic ecosystem, the pyramid is inverted.
c)in both ecosystem, the pyramid is upright.
things to keep in mind
- Any calculations of energy content, biomass or numbers, has to include all organisms at that trophic level. No generalisations we make will be true if we take only a few individuals at any trophic level into account.
-Also a given organism may occupy more than one trophic level
simultaneously. One must remember that the trophic level represents afunctional level, not a
species as such. A given species may occupy more than one trophic level in the same ecosystem at the same time; for example, a sparrow is a primary consumer when it eats seeds, fruits, peas, and a secondary consumer when it eats insects and worms.
describe pyramids of biomass and number
- In most ecosystems, all the pyramids, of number, of energy and biomass are upright, i.e., producers are more in number and biomass than the herbivores, and herbivores are more in number and biomass than the carnivores.
- Also energy at a lower trophic level is always more than at a higher level. There are exceptions to this generalisation: If you were to count the number of insects feeding on a big tree what kind of pyramid would you get? Now add an estimate of the number of small birds depending on the insects, as also the number of larger birds eating the smaller.
The pyramid of biomass in sea is generally inverted because the
biomass of fishes far exceeds that of phytoplankton.
pyramid of energy
Pyramid of energy is always upright, can never be inverted, because when energy flows from a particular trophic level to the next trophic level, some energy is always lost as heat at each step. Each bar in the energy pyramid indicates the amount of energy present at each trophic level in a given time or annually per unit area.
drawbacks of pyramids
However, there are certain limitations of ecological pyramids such as it does not take into account the same species belonging to two or more trophic levels.
It assumes a simple food chain, something that almost
never exists in nature; it does not accommodate a food web.
Moreover, saprophytes are not given any place in ecological pyramids even though
they play a vital role in the ecosystem.
