Resources contributing to competition among organisms, Biology tutorial


Inadequate supply of at least one resource (like food, water, and territory) utilized by both is needed. Competition both within and between species is the significant topic in ecology, particularly community ecology. Competition is one of numerous interacting biotic and abiotic factors which affect community structure. Competition among members of same species is called as intraspecific competition, whereas competition between individuals of different species is called as interspecific competition. Competition is not always simple, and can take place in both direct and indirect fashion

Territory (animal):

In ethology the term territory refers to any sociographical area that the animal of specific species consistently defends against conspecifics (and, occasionally, animals of other species). Animals which defend territories in this way are referred to as territorial.

i) Classic territories:

Territorial animals defend areas which have a nest, den or mating site and adequate food resources for themselves and their young. Several territorial mammals use scent-marking to signal boundaries of the territories; marks may be deposited by urination, by defecation, or by rubbing parts of bodies which bear specialized scent glands against substrate. For instance, dogs and other canids scent-mark by urination and defecation, whereas cats scent-mark by rubbing their faces and flanks against objects, and by notoriously persistently smelly spraying of urine by tomcats.

ii) Spraying:

Spraying (also called as territorial marking) is behavior utilized by animals to recognize their territory. Most commonly, this is scent marking, achieved by depositing strong-smelling chemicals like urine at important locations within territory. Frequently scent has carrier proteins, like major urinary proteins, to stabilize odors and keep them for longer. Not only marking communicates to others of same species, but it is also noted by prey species and avoided. For instance felids like leopards and jaguars spot by rubbing themselves against vegetation.

iii) Defense:

Territories may be held by individual, a mated pair, or a group. Territoriality is not fixed property of the species: for instance, robins defend territories as pairs during breeding season and as individuals during winter, while some nectarivores defend territories merely during mornings (when plants are richest in nectar).

Territoriality is only illustrated by minority of species. More commonly, individual or group of animals will have area that it usually uses but doesn't essentially defend; this is called its home range. Home ranges of different groups frequently overlap, and in overlap areas groups will tend to avoid each other rather than seeking to expel each other.

Several birds, mainly seabirds, although they nest in dense communities, are none the less territorial in that they defend their nesting site to inside distance that they can reach while brooding. This is essential to prevent attacks on their own chicks or nesting material from neighbors. Commonly resulting superimposition of short-range repulsion on long range attraction characteristically leads to well-known roughly hexagonal spacing of nests. Interestingly, one gets the similar hexagonal spacing resulting from territorial behavior of gardening limpets like species of Scutellastra.


Sunlight, in broad sense, is total frequency spectrum of electromagnetic radiation given off by Sun. On Earth, sunlight is filtered through Earth's atmosphere, and solar radiation is obvious as daylight when Sun is above horizon. When direct solar radiation is not blocked by clouds, it is experienced as sunshine, combination of bright light and radiant heat. When it is blocked by clouds or reflects off of other objects, it is experienced as diffused light.

i) Calculation:

To calculate amount of sunlight reaching ground, both elliptical orbit of Earth and attenuation by Earth's atmosphere has to be taken in account. Extraterrestrial solar illuminance (Eext), corrected for elliptical orbit by using day number of year (dn), is given by

Eext=Esc.(1+0.033412.cos(2 Π(dn-3/365)))

where dn=1 on January 1; dn=2 on January 2; dn=32 on February 1, etc.

In this formula dn-3 is used, as in modern times Earth's perihelion, closest approach to Sun and thus the maximum Eext takes place around January 3 each year. Value of .033412 is determined knowing that ratio between perihelion (0.98328989 AU) squared and aphelion (1.01671033 AU) squared must be about 0.935338. Solar illuminance constant (Esc), is equal to 128×103 lx. Direct normal illuminance (Edn), corrected for the attenuating effects of the atmosphere is given by:

Edn= Ext e-cm

Where c is atmospheric extinction coefficient and m is relative optical airmass.

ii) Solar constant:

Solar constant, the measure of flux density, is amount of incoming solar electromagnetic radiation per unit area which would be incident on plane perpendicular to rays, at distance of one astronomical unit (AU) (about mean distance from Sun to Earth). "Solar constant" comprises all kinds of solar radiation, not just visible light. It's average value is about 1.366 kW/m² but this does differ slightly with solar activity.

iii) Total Solar Irradiance (TSI) (upon Earth) and Spectral Solar Irradiance (SSI) (upon Earth)

Total Solar Irradiance on Earth (TSI) was earlier estimated by satellite to be approximately 1.366 kilowatts per square meter (kW/m²), but most lately NASA cites TSI as "1361 W/m2 as compared to ~1366 W/m2 from earlier observations.

iv) Composition:

Spectrum of the Sun's solar radiation is close to that of black body with the temperature of approx 5,800 K. Sun emits EM radiation across most of the electromagnetic spectrum. Though Sun produces Gamma rays consequently of Nuclear fusion process, these super high energy photons are converted to lower energy photons prior to they reach Sun's surface and are emitted out in space, so Sun does not give off any gamma rays to speak of. Sun does, though, emit X-rays, visible light, ultraviolet, infrared, and even Radio waves. When ultraviolet radiation isn't absorbed by atmosphere or other protective coating, it can cause damage to skin called as sunburn or trigger adaptive change in human skin pigmentation. Spectrum of electromagnetic radiation striking Earth's atmosphere spans range of 100 nm to approx 1 mm. This can be divided in 5 regions in increasing order of wavelengths:

a) Ultraviolet C or (UVC) range that spans range of 100 to 280 nm. Term ultraviolet refers to fact that radiation is at higher frequency than violet light.

b) Ultraviolet B or (UVB) range spans 280 to 315 nm. It is also really absorbed by atmosphere, and along with UVC is responsible for photochemical reaction leading to production of ozone layer.

c) Infrared range which spans 700 nm to 106 nm (1 mm). It is liable for significant part of electromagnetic radiation which reaches Earth. It is also divided in 3 kinds on the basis of wavelength:

i) Infrared-A: 700 nm to 1,400 nm

ii) Infrared-B: 1,400 nm to 3,000 nm

iii) Infrared-C: 3,000 nm to 1 mm.

v) Surface illumination:

Spectrum of surface illumination depends on solar elevation because of atmospheric effects, with blue spectral component from atmospheric scatter dominating during twilight before and after sunrise and sunset, respectively, and red dominating during sunrise and sunset. These effects are evident in natural light photography where principal source of illumination is sunlight as mediated by atmosphere.

vi) Climate effects:

On Earth, solar radiation is apparent as daylight when sun is above horizon. This is during daytime, and also in summer near poles at night, but not at all in winter near the poles. When direct radiation is not blocked by clouds, it is experienced as sunshine, combining perception of bright white light and warming. Warming on body, the ground and other objects depends on absorption (electromagnetic radiation) of electromagnetic radiation in form of heat. Amount of radiation intercepted by planetary body varies inversely with square of distance between star and planet.


Water in 3 states: liquid, solid (ice), and (invisible) water vapor in air. Clouds are accumulations of water droplets, condensed from vapor-saturated air. Water is chemical substance with chemical formula H2O. Its molecule has one oxygen and two hydrogen atoms connected by covalent bonds. Water is liquid at ambient conditions, but it frequently co-exists on Earth with solid state, ice, and gaseous state (water vapor or steam). Water also exists in liquid crystal state near hydrophilic surfaces. Water covers 70.9% of Earth's surface, and is very important for all known forms of life. Clean drinking water is necessary to humans and other life forms. Access to safe drinking water has enhanced steadily and considerably over last decades in almost every part of world.

i) Chemical and physical properties:

Major chemical and physical properties of water are:

- Water is liquid at standard temperature and pressure. It is tasteless and odorless. Intrinsic color of water and ice is very slight blue hue, though both appear colorless in small quantities. Water vapor is really invisible as gas.

- Water is transparent in visible electromagnetic spectrum. Therefore aquatic plants can live in water as sunlight can reach them. Ultra-violet and infrared light is strongly absorbed.

- Water is good solvent and is frequently referred to as universal solvent. Substances which dissolve in water, like, salts, acids, sugars, alkalis, and some gases - particularly oxygen, carbon dioxide (carbonation) are called as hydrophilic (water-loving) substances, whereas those that don't mix well with water (like, fats and oils), are called as hydrophobic (water-fearing) substances.

- Water has second highest molar specific heat capacity of any known substance, after ammonia, and a high heat of vaporization (40.65 kJ·mol-1), both of which are result of extensive hydrogen bonding between molecules. These two unusual properties permit water to moderate Earth's climate by buffering large fluctuations in temperature.

ii) Distribution in nature:

In the universe:

Much of the universe's water is produced as the byproduct of star formation. When stars are born, their birth is accompanied by the strong outward wind of gas and dust. When this outflow of material finally impacts surrounding gas, shock waves which are created compress and heat gas. Water observed is rapidly produced in warm dense gas. Water has been detected in interstellar clouds inside galaxy, Milky Way.

Water vapor is present in:

- Atmosphere of Mercury: 3.4%, and large amounts of water in Mercury's exosphere

- Atmosphere of Venus: 0.002%

- Earth's atmosphere: ~0.40% over full atmosphere, usually 1-4% at surface

- Atmosphere of Mars: 0.03%

- Atmosphere of Jupiter: 0.0004%

- Atmosphere of Saturn - in ices only

Water and habitable zone:

Existence of liquid water and to lesser extent its gaseous and solid forms, on Earth are very important to existence of life on Earth. Earth is located in habitable zone of solar system; if it were somewhat closer to or farther from Sun (approx 5%, or approx 8 million kilometers), conditions that permit three forms to be present at the same time would be far less likely to exist.

Surface temperature of Earth has been comparatively constant through geologic time in spite of changeable levels of incoming solar radiation (insolation), indicating that dynamic process governs Earth's temperature using combination of greenhouse gases and surface or atmospheric albedo. This proposal is called as Gaia hypothesis.

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