Ecology : It is also known as environmental biology. In ecology we study plants and animals in relation to their environment. Plant ecology is concerned with the study of plants in relation to their environments.
Different scientists have defined ecology as follows—
Concept of Ecology Given By
Heackel (1869)—Ecology is the science of treating reciprocal relations of organisms and the external world.
Odum (1963)—Ecology is the study of structure and function of nature.
Misra (1967)—Ecology is the study of interactions of form, function and factors.
Pianka (1973)—Ecology is the study of relations between organisms and biological and physical factors affecting them or affected by them.
Fitzpatrick (1974)—Ecology is the study of interrelationships between individual organisms, and between organisms and their environment.
Environment
Environment is studied under two categories viz. biotic environment which consists of non-living things affecting the life of plants and animals, and abiotic environment which include physical agents such as light, temperature pressure, soil, etc., and chemical agents such as water, gases, phosporus, minerals etc.
Both biotic and abiotic environments influence the animals and plants.
Ecological Spectrum
Plants and animals with respect to environment is studied under four headings namely—
1. Populations, 2. Communities, 3. The Ecosystems and 4. Biosphere.
1. Populations : A large group of plants and animals of one species in a particular area is called populations.
2. Community : This is also called Biocoenoses. A community includes all the populations of different species in a given area.
3. Ecosystem : The ecosystem involves inputs of energy and matter between living and non-living entities. In a ecosystem the organisms interact with one another and with the environment.
4. Biosphere : This is also called ecosphere. The regions of earth where the ecosystems operate, form the biosphere. Biosphere includes the atmosphere, lithosphere and hydrosphere. Biosphere is divided into three divisions; namely—
(a) Land bicycle (b) Limnotec or fresh water and (c) Marine or sea bicycle.
Branches of Ecology
1. Autecology : This branch is concerned with the study of individual species and organisms in relation to their environment.
2. Synecology (or community ecology) : This deals with the study of communities in relation to their environments. It is also called community ecology.
3. Population ecology : It is the study of groups of organisms of the same species in relation to their environment.
4. Human ecology : It is the study of human relations to his environment.
Ecosystem
An ecosystem can be considered as the functional unit of the biosphere. It deals with the living and non-living environment in a given area where there is physiological interrelationship.
Ecosystems are of three types—
I. Natural Ecosystems
II. Artificial Ecosystems
III. Microecosystems.
I. Natural Ecosystems : This includes aquatic and fresh water systems. In aquatic waters sea water, rocky shore, and coral reefs are included. It also take care of terrestrial or land inhabitants.
II. Aritificial Ecosystems : These are man managed ecosystems. It includes of cropland, garden and aquariums.
III. Microecosystems : This is the artificial ecosystem which is created in the laboratory by men. It considers micro-organisms.
The Food Chain
Food chain is defined as flow of food energy through a chain of organisms. Food chains are of several types; namely—
1. Prey-Predator Food chain : This is also called grazing food chain. It starts with producers and the grazing animals feed on the producers. Example are—
(a) Marshcommunity chain : Sun energy—green plants—butterfly—dragon fly —frog—snake—hawk.
(b) Forest community chain : Sun energy—green plants—ungulates—tigers.
(c) Grassland ecosystem chain : Sun energy—grasses—grasshopper—frog—snake—hawk.
(d) Pond Ecosystem chain : Sun energy—algae—aquatic insects—small fishes —large fishes.
(e) Marine ecosystem chain : Sun energy—marine algae—small fishes—large fishes—sharks.
II. Detritus Food Chain : This is also called saprophytic food chain. In this chain micro-organisms decompose organic matter into detritus. Certain animals feed on these detritus. Such a food chain is called detritus food chain. e.g. Sun energy ® mangrove ® mangrove leaves ® detritus ® crabs and shrimps ® small fishes ® large fishes.
III. Parasitic Food Chain : In this food chain parasites live on or inside the body of the host. Parasite gets nutrition from the host and host gets harmed. e.g. Sun energy—green plants—sheep—liverfluke.
Food Web : Each food chain is interconnected by different components. Interconnected food chains are called food webs.
Ecological Pyramids
Ecological Pyramids : The relationship between different trophic levels can be expressed by diagrams or pyramids called ecological pyramids.
Pyramid of Numbers : Here the number of individual organisms at each trophic level is taken into account for the construction of pyramid.
Pyramid of Biomass : Here the quantitative relationship of the standing crop at each trophic level is taken into account.
Pyramid of Energy : Here the energy accumulation pattern or amount of energy which passes through each trophic level in a given period of time, is taken into account.
Energy Flow : The energy flows from organism to organism in an ecosystem by feeding process. The energy transformation that occurs within the ecosystem is known as flow of energy. The flow of energy is always unidirectional and non-cyclic.
Aquatic Ecosystems : Ecosystems operating in aquatic habitats are called aquatic ecosystems. They may be fresh water or saline water (marine) ecosystems.
Terrestrial Ecosystems : Ecosystems operating on land are called terrestrial ecosystems. The major terrestrial ecosystems of the world are desert, grassland, forest and man engineered.
Biogeochemical Cycles
The cyclic pathways through which chemical elements travel from the environment into the organisms and from the organisms into the environment regularly and continuously, are called biogeochemical cycles. Both macronutrients and the micronutrients circulate between the environments and the organisms. These are divided into two types :
1. Sedimentary types : In it the reservoir pool is in deep sediments.
2. Gaseous type : In it the air is the reservoir pool.
Following are the cycles :
(a) Sulphur Cycle : The cycle of sulphur between organisms and the aquatic environment is an example of ‘sedimentary type’.
(b) Carbon Cycle : Carbon cycle is a gaseous type cycle. Carbon cycle is an example of ‘perfect cycle’. In this the same carbon is used repeatedly.
(c) Nitrogen cycle : This is also a ‘gaseous type’ cycle. Nitrogen cycle is an example of relatively ‘less perfect cycle’ due to the possible loss of some nitrogen in the form of nitrates, from lands, fresh waters and shallow seas, to the deep ocean sediments.
(d) Phosphorus cycle : It is a sedimentary type of biogeochemical cycle. It is an example of imperfect cycle, since a good amount of phosphorus is lost into deeper sediments of the sea.
Thus, the study of biogeochemical cycles tells that the atoms of vital elements are used again and again by organisms.
Plant Succession
The same area becomes colonised by different groups of commu-nities—a process known as plant succession.
A group of different kinds of plants and animals, etc., living in a common climate, is called biome.
The basic structural and functional units of nature are ecosystems.
Energy is the driving force of the ecosystem.
The flow of energy is always from the producers to the consumers and unidirectional.
The biotic components of an ecosystem are linked as food chains.
Plant Communities Hydrophytes
Hydrophytes are those plants which grow in water or in extreme wet soil, where water is available to plants in abundance.
Mesophytes
These are land plants which grow in moist habitats and need well aerated soils.
Roots are well developed.
Stems are aerial, erect, solid, and branched.
Leaves are large, broad, thin, green and porous.
Cuticle in all aerial parts is thin and moderately developed.
Epidermis has thick cell walls.
Stomata are present.
Mechanical and vascular tissues are well developed.
Xerophytes
Plants, which grow in dry areas are called xerophytes.
Drought escaping plants or ephemerals : These are short lived.
Drought enduring plants : e.g. Perennial grasses.
Drought avoiding plants or succulents : Stem succulents : Opuntia, Euphorbia tirucalli, E. antiquorum and many cacti.
Leaf succulents A: Agave, Aloe, Bryophyllum, etc.
Root succulents : Asparagus, Cieba parviflora, etc.
True xerophytes : e.g. Casuarina, Zizyphus, Nerium, Calotropis, etc.
Morphological adaptations : Root system of these plants is very well developed.
The stems are reduced in size and show slow growth.
In extreme xerophytes like Cacti, the leaves are reduced to scales or spines.
Anatomical Adaptations
Stems : Cuticle is thick. They have a few stomata and are sunken.
Hypodermic is several layered.
Sclerenchymatous. Mechanical and vascular tissues are well developed.
Leaves : The epidermal cells of the leaf serve as water storage organs.
They have well developed. mechanical and vascular tissues.
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