Primary abiotic factors and adaptations of organisms

Primary abiotic factors are temperature, light and humidity. Adding the termination of "Phil" (Gr. I like) indicates that the species has adapted to high doses of factor.

Vital activity of organisms essentially depends on the environmental temperature. Organisms living in stationary conditions of low temperatures are called cryophiles. Organisms living in stationary conditions of high temperatures are called thermophiles.

How can organisms regulate body temperature? So, first of all, many organisms do not. The body temperature of these organisms, called poikilotherms, varies directly with environmental temperatures. Of the organisms that regulate body temperature, most use external sources of energy and combination of anatomy and behaviour. Animals that rely mainly on external sources of energy for regulating body temperature are called ectotherms.

Organisms that rely heavily on internally derived metabolic heat energy are called endotherms. Among endotherms, birds and mammals use metabolic energy to heat most of their bodies. Other endothermic animals, including certain fish and insects, use metabolic energy to selectively heat critical organs. Endotherms that use metabolic energy to maintain a relatively constant body temperature are called homeotherms. The only homeothermic organisms are birds and mammals.

Light is the main source of energy for many ecosystems and a driving factor in fundamental ecological processes like photosynthesis and evapotranspiration. So, understanding and quantifying light effectively reaching Earth and living organisms can be of primary importance.

Plants may be classified ecologically according to their light requirements:

1) Sun-loving plants or heliophytes are adapted to a habitat with a very intensive insolation, because of the construction of its own structure and maintenance (metabolism).

2) Shade-loving or sciophytes are plants of the low layer of shady woods, caves and deep-water plants; they badly sustain the strong light of direct sun rays. Adaptation includes thinner leaves with a relatively higher chlorophyll content per unit leaf volume; lens-shaped epidermal cells that focus incoming light into and within the mesophyll;

3) Shade-tolerant plants can tolerate more or less shadowing, and grow well even in the light; they are capable of adapting to the influence of changing light conditions.

For animals the sunlight is not the necessary factor as for green plants as all heterotrophs finally exist at the expense of the energy saved by plants. There are different kinds of them: light-loving (photophilous) and shade-loving (photophobic); euryphotic adapted to a wide range of light exposure, and stenophotic adapted to limited light exposure conditions. Light for animals is the necessary condition for vision, visual orientation in space.

Freshwater is a vital resource for all living organisms. Most organisms have a water content of 50-90% and there is a critical threshold that they must maintain in order to survive and reproduce. Regardless of the environment, water availability is a driving force that shapes both aquatic and terrestrial species assemblages.

According to adaptation of land plants to short-term fluctuations of conditions of water supply and evaporation there are poikilohydric and homohydric plants.

Poikilohydric plants have not constant water ratio in tissues and it depends on degree of humidifying of environment. They cannot regulate transpiration, and easily and quickly lose and absorb water using moisture of dew, fogs, short rains; in dry condition they are in anabiosis.

Homohydric plants are capable to maintain relative constancy of tissues watering, among them is the majority of the higher land plants.

Hydatophytes are aquatic plants, completely or mostly submerged in water. Some hydatophytes are not attached to the ground by their roots (duckweed and Canadian pondweed), and others (the waterlily) are attached. Hydatophytes are classified according to their course of development. True hydatophytes are plants submerged in water, and their growth and development occur only in water (some species of Ceratophyllaceae). Submerged aerohydatophytes are plants totally submerged in water; their growth occurs in water, but the pollination of their flowers takes place above water (spiral wild celery). Floating aerohydatophytes are plants a part of whose leaves and stems is immersed in water and the other part of which floats. The pollination of their flowers occurs above water. Many hydatophytes turn into peat. Their stomata are reduced and there is no cuticle.

A plant that grows wholly or partly submerged in water. Because they have less need to conserve water, hydrophytes often have a reduced cuticle and fewer stomata than other plants. Floating leaves have stomata only on their upper surfaces, and underwater leaves generally have no stomata at all. Because water is readily available, hydrophytes also have a reduced root system and less vascular tissue than other plants (which also makes plant parts less dense and helps them float). Hydrophytes tend to have less supportive tissue as well, since they are buoyed by water.

A Hygrophyte is a plant living above ground that is adapted to the conditions of abundant moisture pads of surrounding air. These plants inhabit mainly wet and dark forests and islands darkened swamp and very humid and floody meadows. Within the group of all types of terrestrial plants, they are at least resistant to drought. According to the environmental attributes are a group of plants between categories hydrophytes (aquatic plants) and mesophytes (plants in moderate environmental conditions).

Mesophytes are adapted to short and not so strong drought. These are the plants growing at average humidifying, moderately warm mode and with good supply of mineral food. These are evergreen trees of the upper layers of rainforests, deciduous trees of savannas, tree species of damp evergreen subtropical woods, deciduous hardwoods of moderate belt, underbrush bushes, grassy plants of nemorose wideherbs, plants of flooded and not too dry meadows, deserted ephemers and ephemeroids, many weed plants and the majority of cultivated plants.

A xerophyte is a plant that has adapted to survive in an environment with little liquid water, such as a desert or an ICE - or snow-covered region in the Alps or the Arctic. The morphology and physiology of xerophytes are variously adapted to conserve water, and commonly also to store large quantities of water during dry periods.

Xerophytes are divided into two main types: succulents and sclerophytes.

Succulent plants store water in their stems or leaves. They include the Cactaceae family which has round stems and can store a lot of water. The leaves are often vestigial, as in the case of cacti, wherein the leaves are reduced to spines, or they do not have leaves at all.

Sclerophytes are plants, on the contrary, dry by sight, often with the narrow and small leaves sometimes curtailed into a tubule. Leaves can be also parted, covered by hairs or wax bloom. Sucking force of roots to several tens of atmospheres allows to extract successfully water from soil.

Answer these questions:

1. How many types of environmental factors are there? Name it.

2. Why is an organic horizon generally absent from desert soils?

3. Give examples of aquatic habitat inhabitants

4. Give examples of terrestrial inhabitants

5. Give examples of soil inhabitants

6. Name the limiting factors of aquatic habitat.