Ecology is the branch of biology which deals with the study of distribution, structure and interaction of organisms with their environment. The term ‘ecology’ was coined by Reiter. Ecology is derived from two Greek words ‘olikos’ meaning house and ‘logos meaning study. According to warming ‘ecology is the study of organisms in relation to their environment’.
According to odum ‘ecology is the study of organisms I relation to their environment’.
Different levels of organization in ecology are:
Cells- tissues- organs – organ systems - organism - population – community - ecosystem - biosphere.
Population: it sis a group of similar individuals belonging to the same species found in an area.
Ecosystem: it is the structural and functional unit of nature. The interaction between the biotic and abiotic components is called an “ecosystem”.
Community: A community is an assemblage of all the populations belonging to different species occurring in an area.
Warming classified plant communities on the basis of water relations into three categories:
Hydrophytes, Mesophytes and Xerophytes
Hydrophytes: The plants which grow in water or very wet places are called hydrophytes. They may be further classified into
1. Free floating (Pistia)
2. Rooted hydrophytes with floating leaves (Nelumbo)
3. Submerged suspended (Hydrilla)
4. submerged rooted (Vallisnaria)
5. Amphibious plants (Sagittaria)
Hydrophytes show certain morphological and anatomical adaptations to survive in water. Generally the hydrophytes have poorly developed roots, slender stems, dissected or floating leaves and some of them show hererophylly. Internally the hydrophytes lack cuticle and stomata, the mechanical tissues like collenchyma and sclerenchyma are less developed, poorly developed vascular tissues and aerenchyma is well developed.
Xerophytes: the plants which grow in habitats where water supply is deficient or soil is physiologically dry are called “Xerophytes”. They are classified into:
1. Ephemerals (Tribulus)
2. Succulents (Opuntia)
3. Non-succulents (Calotropis)
Xerophytes also show certain morphological and anatomical adaptations to over come water deficit. Generally they have well developed root system, short and stunted stems and reduced leaves (spines or scales). Internally they possess thick cuticle, multilayered epidermis, waxy coating on the epidermis, hypo stomatal condition, and we developed mechanical tissues and vascular tissues.