● Temperature is the most `color{violet}("ecologically relevant environmental factor")`.

● The `color{violet}("average temperature")` on land varies seasonally, decreases progressively from the `color{violet}("equator towards the poles")` and `color{violet}("from plains to the mountain tops")`.

● It ranges from subzero levels in `color{violet}("polar areas")` and high altitudes to `> 50^0C` in `color{violet}("tropical deserts")` in summer.

● There are, however, unique habitats such as `color{violet}("thermal springs")` and `color{violet}("deep-sea hydrothermal vents")` where `color{violet}("average temperatures exceed")` `100^0 C`.

● It is general knowledge that mango trees do not and cannot `color{violet}("grow in temperate")` countries like Canada and Germany, `color{violet}("snow leopards")` are not found in Kerala forests and `color{violet}("tuna fish")` are rarely caught beyond `color{violet}("tropical latitudes in the ocean.")`



● The `color{violet}("significance of temperature")` to `color{violet}("living organisms")` can be readily appreciated when it is realised that it affects the `color{violet}("kinetics of enzymes")` and through it the `color{violet}("basal metabolism")`, activity and other `color{violet}("physiological functions")` of the `color{violet}("organism.")`

● A few organisms can `color{violet}("tolerate and thrive")` in a wide range of temperatures (they are called `color{violet}("eurythermal")`), but, a vast majority of them are restricted to a narrow range of temperatures (such organisms are called `color{violet}("stenothermal")` ).

● The levels of `color{violet}("thermal tolerance")` of different species determine to a large extent their `color{violet}("geographical distribution")`.

● In `color{violet}("recent years")`, there has been a growing concern about the gradually `color{violet}("increasing average global temperatures")`.

● If this trend continues, the `color{violet}("distributional range")` of some species would be `color{violet}("greatly affected.")`

● Next to `color{violet}("temperature, water")` is the most important factor influencing the `color{violet}("life of organisms")`.

● In fact, `color{violet}("life on earth")` originated in water and is `color{violet}("unsustainable without water.")`

● Its `color{violet}("availability")` is so `color{violet}("limited in deserts")` that only special adaptations make it `color{violet}("possible to live there.")`

● The productivity and distribution of plants is also `color{violet}("heavily dependent on water.")`

● Even the `color{violet}("organisms living in oceans, lakes")` and `color{violet}("rivers")` should face `color{violet}("many water-related problems")`.

● For `color{violet}("aquatic organisms")` the quality (`color{violet}("chemical composition, pH")`) of water becomes important.

● The salt concentration (measured as salinity in parts per thousand), is less than `color{violet}("5 percent")` in inland waters, `color{violet}("30-35 percent")` the sea and > 100 percent in some `color{violet}("hypersaline lagoons")`.

● Some organisms are `color{violet}("tolerant")` of a wide range of `color{violet}("salinities (euryhaline)")` but others are restricted to a narrow range `color{violet}("(stenohaline).")`

● Many `color{violet}("freshwater animals")` cannot live for long in `color{violet}("sea water")` and vice versa because of the `color{violet}("osmotic problems")`, they would face.

● Since plants produce food through `color{violet}("photosynthesis")`, a process which is only possible when `color{violet}("sunlight")` is available as a `color{violet}("source of energy")`, we can quickly understand the importance of `color{violet}("light for living organisms, particularly autotrophs.")`

● Many species of `color{violet}("small plants (herbs and shrubs)")` growing in forests are adapted to `color{violet}("photosynthesise optimally")` under very `color{violet}("low light conditions")` because they are constantly `color{violet}("overshadowed")` by `color{violet}("tall, canopied trees.")`

● Many plants are also dependent on `color{violet}("sunlight")` to meet their `color{violet}("photoperiodic")` requirement for flowering.

● For many animals too, light is important in that they use the `color{violet}("diurnal")` and `color{violet}("seasonal variations")` in light
intensity and duration `color{violet}("(photoperiod)")` as cues for timing their `color{violet}("foraging, reproductive")` and `color{violet}("migratory activities.")`

● The availability of `color{violet}("light on land")` is closely linked with that of temperature since the `color{violet}("sun")` is the source for
both.

● But, deep (> 500m) in the oceans, the environment is perpetually `color{violet}("dark")` and its `color{violet}("inhabitants")` are not aware of the existence of a celestial source of energy called `color{violet}("Sun")`.

● The `color{violet}("spectral quality")` of `color{violet}("solar radiation")` is also important for life.

● The `color{violet}("UV component")` of the `color{violet}("spectrum")` is `color{violet}("harmful to many organisms")` while not all the colour components of the `color{violet}("visible spectrum")` are available for `color{violet}("marine plants living")` at different depths of the `color{violet}("ocean.")`

● The nature and properties of `color{violet}("soil")` in different places vary; it is dependent on the `color{violet}("climate, the weathering process")`, whether `color{violet}("soil is transported")` or `color{violet}("sedimentary")` and how soil development occurred.

● Various `color{violet}("characteristics of the soil")` such as `color{violet}("soil composition, grain size")` and aggregation determine the `color{violet}("percolation")` and `color{violet}("water holding capacity")` of the `color{violet}("soils.")`

● These characteristics along with `color{violet}("parameters")` such as `color{violet}("pH, mineral composition")` and `color{violet}("topography")` determine to a large extent the vegetation in any area.

● This is in `color{violet}("turn dictates")` the type of `color{violet}("animals")` that can be supported.

● Similarly, in the `color{violet}("aquatic environment, the sediment-characteristics")` often determine the type of `color{violet}("benthic animals")` that can thrive there.