FLIGHT ADOPTATIONS
Flight -Main mode of locomotion used by most of the world's bird species.
Birds use flight
to obtain prey on the wing,
for foraging,
to commute to feeding grounds and
to migrate between the seasons.
Also used by some species to display during the breeding season and
to reach safe isolated places for nesting.
The most obvious adaptation for flight is the wing.
Forelimbs modified into the wings.
Attached high up on the thorax.
Equipped with special flight muscles and have been developed as instruments of propulsion through air.
The elongated flight- feathers of wings are called the remiges ;help in flight and also provide wing shape.
The expanded membranous part or vane of each remex forms a flexible and continuous surface for striking the air in flight.
The flight- feathers of a wing form a broad surface for supporting the bird in air.
The particular shape of the wing, with a thick strong leading edge, convex upper surface and concave lower surface, causes reduction in air pressure above and increase below, with minimum turbulence behind.
This helps in driving the bird forwards and upwards during flight.
Down feathers are soft and meant for insulation.
Tail feathers are called rectrices which stretch sideways so that tail can be used like a rudder for turning and balancing.
WEIGHT REDUCING ADAPTATIONS
Thin hollow bones
Extensive bone fusion especially in the pelvic and pectoral regions
Fusion of bones makes the skeleton light as well as strong.
Coracoid, furcula, and scapula form a sturdy tripod -supports the wings and broad surfaces for the attachment of large flight muscles.
The fusion of caudal bones into single pygostyle supports the tail feathers.
Most of the skull bones are firmly fused together.
The rigidity of the dorsal part of vertebral column due to fusion of vertebrae, provides a firm fuAdditional bony structures are fused into the pelvic girdle providing support to legs and rigidity.
Ribs are mostly fused with the vertebrae, pectoral girdle and sternum.
lcrum for the action of wings.
Except in flightless birds, the sternum bears a large keel for anchoring of flight muscles.
Bones in the forelimbs are highly modified for flight.
Some bones fused or reduced.
Fused clavicles form an elastic furcula that stores energy as it flexes during wing beats.
Extremely light feathers
Provide lightweight wing, tail and body contouring.
Elimination of teeth and jaws
Lack teeth or even a true jaw, instead having evolved a keratin beak - lightweight.
Elimination of tail vertebrae and some digits
To make it more efficient for flying
Elimination of most skin glands
A system of branching air sacs
They act as balloons providing lightness to the body and reduce the specific gravity of the body as they contain warm air
They act as accessory respiratory organs. They act as reservoir of air which is forced into lungs for ventilation during each expiration. Thus fresh air is available to lungs during inspiration as well as expiration.
Oviparous external egg reproduction
The expanded end of the oviduct receives the "naked" eggs.
Fertilization takes place in the upper oviduct before albumin and shell are added.
Special glands add albumin (white) to the egg as it passes down the oviduct.
Farther down, the shell membrane, shell, and pigments are secreted.
Eggs are laid outside the body- Less weight.
The atrophy of gonads between breeding season
Reproductive organs are small for the greater part of the year -decrease the birds’ weight for flight.
Only during mating season do reproductive organs (Ovaries and testes) reach functional size.
Only one ovary and oviduct
In most females, the left ovary and oviduct develop and the right ovary and oviduct degenerate or is greatly reduced -decrease the weight of body.
Female liver is displaced to the right to compensate for weight difference
Small testes
Males have small testes until the approach of the breeding season, when they may enlarge by 300 times.
Males of most species lack a penis; mating involves bringing cloacal surfaces in contact.
Rapid and efficient digestion minimizes weight of digesting food
The digestive system is extremely efficient in absorbing energy from small amounts of food at a rapid rate.
Because birds lack teeth they possess a gizzard.
Composed of four muscular bands that act to rotate and crush food by shifting the food from one area to the next within the gizzard.
Depending on the species, the gizzard may contain small pieces of grit or stone/pebbles that the bird Many birds possess a muscular pouch along the oesophagus called a crop.
The crop functions to both soften food and regulate its flow through the system by storing it temporarily.
The crop of pigeons, doves and some parrots, also produces a lipid / protein-rich "milk."
has swallowed to aid in the grinding process.
POWER INCREASING ADAPTATIONS
Heat conserving plumage
The light feathers hold a considerable blanket of enveloping air around the body and add much to its buoyancy.
The non-conducting covering of feathers insulates the body perfectly.
Prevents loss of heat. Enables the bird to endure intense cold at high altitudes and also to maintain a constant body temperature
Zoology in the Classroom - is a blog for teachers and students of zoology. I have been teaching as Zoology teacher for the last 30 years. I post the notes or handouts that I supply to my students in my classroom. Hope this will benefit Zoology fraternity
Wednesday, March 16, 2016
Tuesday, March 8, 2016
ENVIRONMENTAL STUDIES NOTES
1. Define Ecosystem? Explain the Structure and function of an ecosystem.
The term Ecology was coined by Earnst Haeckel in 1869. It is derived from the Greek words Oikos- home + logos- study. So ecology deals with the study of organisms in their natural home interacting with their surroundings. The surroundings or environment consists of other living organisms (biotic) and physical (abiotic) components. Modern ecologists believe that an adequate definition of ecology must
specify some unit of study and one such basic unit described by Tansley (1935) was ecosystem. An ecosystem is a group of biotic communities of species interacting with one another and with their non-living environment exchanging energy and matter. Now ecology is often defined as the study of ecosystems..
STRUCTURAL FEATURES
Composition and organization of biological communities and abiotic components constitute the structure of an ecosystem.
I. Biotic Structure
The plants, animals and microorganisms present in an ecosystem form the biotic component. These organisms have different nutritional be- haviour and status in the ecosystems and are accordingly known as Producers or Consumers, based on how do they get their food.
(a) Producers: They are mainly the green plants, which can synthesize their food themselves by making use of carbondioxide present in the air and water in the presence of sunlight by involving chlorophyll, the green pigment present in the leaves, through the process of photosynthesis. They are also known as photo autotrophs (auto=self; troph=food, photo=light). There are some microorganisms also which can produce organic matter to some extent through oxidation of certain chemicals in the
absence of sunlight. They are known as chemosynthetic organisms or chemo-autotrophs. For instance in the ocean depths, where there is no sunlight, chemoautotrophic sulphur bacteria make use of the heat generated by the decay of radioactive elements present in the earth.s core and released in ocean.s depths. They use this heat to convert dissolved hydrogen sulphide (H2S) and carbon dioxide (CO2) into organic compounds.
(b) Consumers: All organisms which get their organic food by feeding upon other organisms are called consumers, which are of the
following types:
(i) Herbivores (plant eaters): They feed directly on producers and hence also known as primary consumers. e.g. rabbit, insect, man.
(ii) Carnivores (meat eaters): They feed on other consumers. If they feed on herbivores they are called secondary consumers (e.g. frog) and if they feed on other carnivores (snake, big fish etc.) they are known as tertiary carnivores/consumers.
(iii) Omnivores: They feed on both plants and animals. e.g. humans, rat, fox, many birds.
(iv) Detritivores (Detritus feeders or Saprotrophs): They feed on the parts of dead organisms, wastes of living organisms, their castoffs and partially decomposed matter e.g. beetles, termites, ants, crabs, earthworms etc.
(c) Decomposers: They derive their nutrition by breaking down the complex organic molecules to simpler organic compounds and ultimately into inorganic nutrients. Various bacteria and fungi are decomposers.
In all the ecosystems, this biotic structure prevails. However, in some, it is the primary producers which predominate (e.g. in forests, agroecosystems) while in others the decomposers predominate (e.g. deep ocean).
II. Abiotic Structure
The physical and chemical components of an ecosystem constitute its abiotic structure. It includes climatic factors, edaphic (soil) factors, geographical factors, energy, nutrients and toxic substances. (a) Physical factors: The sunlight and shade, intensity of solar flux,
duration of sun hours, average temperature, maximum-minimum temperature, annual rainfall, wind, latitude and altitude, soil type, water availability, water currents etc. are some of the important physical features which have a strong influence on the ecosystem. We can clearly see the striking differences in solar flux, temperature and precipitation (rainfall, snow etc.) pattern in a desert ecosystem, in a tropical rainforest and in tundra ecosystem.
(b) Chemical factors: Availability of major essential nutrients like carbon, nitrogen, phosphorus, potassium, hydrogen, oxygen and sulphur, level of toxic substances, salts causing salinity and various organic substances present in the soil or water largely influence the functioning of the ecosystem. All the biotic components of an ecosystem are influenced by the abiotic components and vice versa, and they are linked together through energy flow and matter cycling as shown diagrammatically in Fig. 3.1.
The term Ecology was coined by Earnst Haeckel in 1869. It is derived from the Greek words Oikos- home + logos- study. So ecology deals with the study of organisms in their natural home interacting with their surroundings. The surroundings or environment consists of other living organisms (biotic) and physical (abiotic) components. Modern ecologists believe that an adequate definition of ecology must
specify some unit of study and one such basic unit described by Tansley (1935) was ecosystem. An ecosystem is a group of biotic communities of species interacting with one another and with their non-living environment exchanging energy and matter. Now ecology is often defined as the study of ecosystems..
STRUCTURAL FEATURES
Composition and organization of biological communities and abiotic components constitute the structure of an ecosystem.
I. Biotic Structure
The plants, animals and microorganisms present in an ecosystem form the biotic component. These organisms have different nutritional be- haviour and status in the ecosystems and are accordingly known as Producers or Consumers, based on how do they get their food.
(a) Producers: They are mainly the green plants, which can synthesize their food themselves by making use of carbondioxide present in the air and water in the presence of sunlight by involving chlorophyll, the green pigment present in the leaves, through the process of photosynthesis. They are also known as photo autotrophs (auto=self; troph=food, photo=light). There are some microorganisms also which can produce organic matter to some extent through oxidation of certain chemicals in the
absence of sunlight. They are known as chemosynthetic organisms or chemo-autotrophs. For instance in the ocean depths, where there is no sunlight, chemoautotrophic sulphur bacteria make use of the heat generated by the decay of radioactive elements present in the earth.s core and released in ocean.s depths. They use this heat to convert dissolved hydrogen sulphide (H2S) and carbon dioxide (CO2) into organic compounds.
(b) Consumers: All organisms which get their organic food by feeding upon other organisms are called consumers, which are of the
following types:
(i) Herbivores (plant eaters): They feed directly on producers and hence also known as primary consumers. e.g. rabbit, insect, man.
(ii) Carnivores (meat eaters): They feed on other consumers. If they feed on herbivores they are called secondary consumers (e.g. frog) and if they feed on other carnivores (snake, big fish etc.) they are known as tertiary carnivores/consumers.
(iii) Omnivores: They feed on both plants and animals. e.g. humans, rat, fox, many birds.
(iv) Detritivores (Detritus feeders or Saprotrophs): They feed on the parts of dead organisms, wastes of living organisms, their castoffs and partially decomposed matter e.g. beetles, termites, ants, crabs, earthworms etc.
(c) Decomposers: They derive their nutrition by breaking down the complex organic molecules to simpler organic compounds and ultimately into inorganic nutrients. Various bacteria and fungi are decomposers.
In all the ecosystems, this biotic structure prevails. However, in some, it is the primary producers which predominate (e.g. in forests, agroecosystems) while in others the decomposers predominate (e.g. deep ocean).
II. Abiotic Structure
The physical and chemical components of an ecosystem constitute its abiotic structure. It includes climatic factors, edaphic (soil) factors, geographical factors, energy, nutrients and toxic substances. (a) Physical factors: The sunlight and shade, intensity of solar flux,
duration of sun hours, average temperature, maximum-minimum temperature, annual rainfall, wind, latitude and altitude, soil type, water availability, water currents etc. are some of the important physical features which have a strong influence on the ecosystem. We can clearly see the striking differences in solar flux, temperature and precipitation (rainfall, snow etc.) pattern in a desert ecosystem, in a tropical rainforest and in tundra ecosystem.
(b) Chemical factors: Availability of major essential nutrients like carbon, nitrogen, phosphorus, potassium, hydrogen, oxygen and sulphur, level of toxic substances, salts causing salinity and various organic substances present in the soil or water largely influence the functioning of the ecosystem. All the biotic components of an ecosystem are influenced by the abiotic components and vice versa, and they are linked together through energy flow and matter cycling as shown diagrammatically in Fig. 3.1.
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