The Environment

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Ecology

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Scientific study of the relation between organisms and their environment

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Environmental factor

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Any factor, abiotic or biotic, that influences living organisms is called environmental factor (or ecological factor or ecofactor)

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Pedology

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The study of soil

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Composition of soil

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Mineral particles, organic matter, air and water

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Mineral particles of soil

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Sand (0.05-2.0 mm)

Silt (0.002 - 0.05 mm)

Clay (<0.002 mm)

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Soil texture

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Relative proportions of sand, silt and clay

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Organic matter of soil

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Living biomass, detritus and humus

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Humus

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An amorphous and a colloidal mixture of complex organic substances

Made up of humic and non-humic substances

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Non-humic substances

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Include carbohydrates, proteins, lignins, lipids, organic acids etc.

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Humic substantces

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Stable end products derived from the decomposition of plant and animal residues

80-90% of the soils organic matter

Primarily composed of carbon, oxygen, hydrogen, nitrogen and sulfur

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Three fractions of humic substances

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Fulvic acid, humic acid and humin

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Humins

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Not soluble in water at any pH

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Humic acids

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Insoluble in water under acidic conditions but are soluble in water under alkaline conditions

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Fulvic acids

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Mixture of weak aliphatic and aromatic organic acids which are soluble in water at all pH

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Soil air

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The mixture of gases that are present in soil pores that are not filled with water

Effects many processes eg nitrification and denitrification

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Soil water

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Water content in the soil depends on soil type

Water holding capacity of soil is described in terms of field capacity

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Water capacity of soil

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The drier the soil becomes the more tightly the remaining water is retained and the more difficult it is for the plant roots to extract it

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Lapse rate

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Decrease of temperature with altitude in the troposphere by an average of about 6.5 C/km

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Stratosphere

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Goes up to 50 km

Ozone layer is present at the height of 15 to 30 km

Troposphere and stratosphere are known as the lower atmosphere

Top of the stratosphere is called the stratopause

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Permanent wilting percentage

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The amount of water soil contains at which plants wilt beyond recovery

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Water available for the uptake of plants

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The amount of water held by the soil between field capacity and the permanent wilting point is the plant available water

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Hygroscopic water

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Water present as a thin film around soil particles and remains firmly attached is called the hygroscopic water

It is not not utilized by plants hence itnis unavailable to plants

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Capillary water

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Water present in thin and narrow capillaries firmed by soil particles and widely utilized by plants

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Chresard

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Water available in soil which can be utilised by plants

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Gravitational water

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Water percolates deep into the soil due to the gravitational force of the Earth that constitutes groundwater

Not available to plants

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Troposphere

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More than 80% of the Earth’s atmosphere and virtually all of the water vapour, clouds and precipitation occur in the troposphere

From 8 to 18 km depending on latitude or season

At poles - upto about 8km and equator to 18 km

Top of the troposphere is called the tropopause

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Atmosphere

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Gaseous mass or envelope surrounding a celestial body especially the one surrounding Earth and is retained in the celestial bodies gravitational field

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Troposphere

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More than 80% of the Earth’s atmosphere and virtually all of the water vapour, clouds and precipitation occur in the troposphere

From 8 to 18 km depending on latitude or season

At poles - upto about 8km and equator to 18 km

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Mesosphere

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This layer starts from about 50 km above the Earth’s surface and goes upto 85 km

Boundary between the mesosphere and the thermosphere is called mesopause

As we move up the mesosphere the temperature gets colder

Top of the mesosphere is the coldest part of the Earth’s atmosphere (the temperature is around -90C)

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Thermosphere

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Extends from about 85 km to about 600 km in the atmosphere

Temperature rises continually and goes beyond 1000 C

There is a relatively dense band of charged particles called ionosphere

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Exosphere

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Outermost layer of the Earth

Top of the atmosphere is upto 10000 km

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Light

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Electromagnetic radiation and represents a part of the electromagnetic spectrum (~400-700)

Visible light is also called photosyntheticallt active radiation (PAR)

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Ultraviolet Radiation

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Electromagnetic radiation with wavelength from 100 nm to 400 nm

Three major ranges in UV radiation are UV-C (100-280), UV-B (280-320) and UB-A (320-400)

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Light radiation on Earth

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Amount and duration of solar radiation intercepted at any point on the Earths surface caries with latitude

Except equator daylight hours are longest in summer and shortest in winter

At higher altitudes radiation hits the earths surface at smaller angles, spreading sunlight over a larger area

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Effect of light on plants

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The quality (wavelength), quantity (intensity) and the duration (photoperiod) of light influence photosynthesis and many growths and development features of plants

In plants photosynthesis occurs in the blue and red light

Plants in general can be divided into two groups : shade-tolerant species and shade-intolerant species

Plants use photoreceptors such as phytochrome or cryptochrome to sense photoperiod which they take as signals for many growth and developmental processes

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Factors that influence temperature

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Latitude, altitude, topography, vegetation and others

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Worlds vegetation on the basis of temperature

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Megatherms, mesotherms, microtherms and hekistotherms

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Megatherms

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Where high temperatures prevail throughout the year and dominant vegetation is tropical rainforests

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Mesotherms

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With high temperature alternating with low temperature and dominant vegetation is tropical deciduous forests

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Microtherms

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Where low temperatures prevail and vegetation is of mixed coniferous forest type

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Hekistotherms

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With very low temperature and alpine vegetation being dominant

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Factors that influence temperature

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Latitude, altitude, topography, vegetation and others

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Acclimation

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When an organism is subjected to changed condition in laboratory

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Xerophytes

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The plants which grow in dry or xeric conditions - plants of dry habitat

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Xerophytic habitat can be of different types

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Physical dryness - in these habitats, soil has very little water due to inability of soil to hold water or low rainfall

Physical dryness - in such habitat, water is sufficiently present but plants are unable to absorb it eg. salty soil, acidic soil

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Xeromorphic plants

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Surface area reduction, sunken stomata and hairs, waxy leaf surface, opening of stomata at night, CAM photosynthesis succulence ( storage of water), extensive root system and other

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Three categories of xerophytes

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Ephemerals, succulents and non-succulent plants

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Ephemerals

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Also termed drought escapers (drought evaders)

Complete their life cycle in a very short period before the approach of actual dry conditions (eg. Argemone mexicana)

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Succulents

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Drought enduring eg. Opuntia, Aloe

Xerophytes that store water in their roots or stem or leaves for the dry period

CAM photosynthesis, reduction in the number of stomata, waxy and hairy, or spiny outer surface

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Non - Succulent

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Drought resistant such as Calotropis procera, Casuarina equisetifolia

Are trie xerophytes

They face both external and internal dryness

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Homeostasis

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Property of a living organism to regulate its internal environment to maintain a stable, constant condition under varying external environment

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Two geoups of homeostasis

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Homeothermic animals

Poikilothermic animals

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Worlds vegetation on the basis of temperature

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Megatherms, mesotherms, microtherms and hekistotherms

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Homeothermic

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Animals like birds and mammals are able to maintain their body temperature at a constant level irrespective of the environmental temperature

Maintaining homeothermy consumes about 90% of the energy intake of the animal

They have high metabolic rates and low thermic conductance

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Poikilotherms

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Animals like reptiles, fishes and amphibians are not able to maintain their body temperature at a constant level

Liw metabolic rates and high thermal conductance

Environmental conditions control their rate of metabolism

Poikilotherms have a upper and lower limit they can tolerate

The range of body temperature at which poikilotherms carry out their daily activities is the operative temperature range

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Hibernation

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To escape the long, cold winters, many terrestrial poikilotherms go into a long, seasonal torpor

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Torpor

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A state of decreased physiological activity in an animal

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Endo, ecto vs. homeo, poikilo

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Ectotherm and endotherm emphasise the mechanisms that determine body temperature

The other two terms homeotherm and poikilotherm represent the nature of body temperature

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Bergmann’s Rule

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Individuals of species in cooler climates tend to be larger than those in warmer climates

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Allen’s Rule

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States that endothermic animals from colder climates tend to have shorter extremities or appendages (eg. ears and tails) than closely related species from warmer climates

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Hesse’s Rule (heart weight rule)

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Which states that species inhabiting colder climates have a larger heart in relation to body weight than closely related species inhabiting warmer climates

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Megatherms

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Where high temperatures prevail throughout the year and dominant vegetation is tropical rainforests

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Mesotherms

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With high temperature alternating with low temperature and dominant vegetation is tropical deciduous forests

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Microtherms

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Where low temperatures prevail and vegetation is of mixed coniferous forest type

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Hekistotherms

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With very low temperature and alpine vegetation being dominant

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Precipitation

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Any product of the condensation of atmospheric water vapour that falls under gravity

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Causes of precipitation

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It is associated with areas of rising air and low pressure

In regions of high pressure air is descending the atmosphere is stable the skies are usually clear and the precipitation is rare

Precipitation is highest in the region of the equator, declining as one moves north and south

Two troughs occur in the mid-latitudes interrupting the general patterns of decline in precipitation from the equator towards the poles

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Adaptations

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Involves acquisition of genetic traits that enable an organism to survive, grow, and reproduce under the prevailing environmental conditions

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Acclimatisation

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Involves physiological, anatomical or morphological adjustments within a single organism that improves performance or survival in response to environmental change within the organisms lifetime