Ch 6Principles of Ecology — Class 12 Botany, concept-first.

Before turning to formal definitions, the chapter frames ecology as the branch of biology concerned with how organisms relate to the environment they live in.

The word ecology comes from the Greek oikos (house or dwelling place) and logos (study) — literally the 'study of the household' an organism lives in; the term was originally coined as oekologie.

Different pioneers defined ecology in slightly different words, but each definition captures the same central idea — organisms and their surroundings cannot be studied in isolation from each other.

As organisms interact with their surroundings, they naturally fall into a nested series of organisational levels called the ecological hierarchy (or levels of ecological organisation).

Ecology is broadly divided into two branches based on how many species are being studied at once. Autecology, also called species ecology, is the ecology of a single, individual species — how that one…

Habitat and niche are two of the most commonly confused terms in ecology, but they describe genuinely different things.

Ecological equivalents are species that are taxonomically unrelated — sometimes from entirely different families, genera, or even continents — but that occupy very similar niches in similar habitats f…

Every organism exists inside a surrounding environment made up of physical, chemical and biological components.

Climatic factors are the class of abiotic factors that arise from the atmosphere and weather, and they are among the most powerful natural controls on plant life anywhere on Earth.

Light is essential for the core physiological processes of a plant — photosynthesis, transpiration, seed germination and flowering all depend on it.

Temperature governs almost every metabolic reaction a plant carries out, and every physiological process has an optimum temperature at which it runs fastest.

Water is arguably the single most important climatic factor, since life itself is believed to have originated in water, and water still covers more than 70% of the Earth's surface today.

Wind — air in motion — is a vital ecological factor in its own right, and its composition mirrors that of the atmosphere as a whole: roughly 78% nitrogen, 21% oxygen, 0.03% carbon dioxide, and 0.93% a…

Fire is an exothermic factor produced by the chemical process of combustion, releasing both heat and light; most fires are man-made, though some arise naturally from friction between tree surfaces.

Edaphic factors are the abiotic factors tied specifically to soil — its physical and chemical composition in a given area — and the dedicated study of soil is called pedology.

Topographic factors describe the surface relief of the land — its topography — and they influence vegetation both directly and indirectly.

Latitude is the angular distance from the equator, ranging from 0° at the equator to 90° at the poles, while altitude is simply how high a location sits above sea level.

The direction (aspect) a mountain slope faces has a real ecological effect, because the north-facing and south-facing sides of the very same hill can receive markedly different amounts of humidity, ra…

The steepness of a mountain or hill slope decides what happens to rainfall once it lands: on steep terrain, rain tends to run off quickly rather than soak in, so the ground loses water fast and the re…

Biotic factors are the interactions among living organisms — plants with plants, and animals with plants — and they can cause substantial, sometimes decisive, effects on vegetation, whether directly (…

In a positive interaction, at least one of the two participating species benefits and neither is harmed.

In a negative interaction, one of the participating species benefits while the other is harmed (or, in one special case, both are harmed).

Beyond the simple beneficial/harmful interactions, species that stay associated with one another over long stretches of evolutionary time can develop much more elaborate strategies.

Ecological adaptations are the structural, anatomical and physiological changes a plant undergoes so that it can survive and function successfully in a particular kind of habitat.