chapter 13 ecology:organism and population. 2014 by mohanbio
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organism and population.TRANSCRIPT
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Watch video
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• Ecology: Ecology is the branch of science that studies the relationship between organisms and their physical & biological environment.
• Level of Organization in ecology:1. Organisms: living organism of environment at individual level.2. Species: Group of individuals which resembles each other and
interbreed among themselves.3. Population: Sum total of all individuals of a species in a specific
geographical area. 4. Community: Group of population of species present in
geographical area interacting with themselves.5. Ecosystem: Ecosystem is a functional unit of nature, where living
organisms interact among themselves and also with the surrounding physical environment.
6. Environment: Sum total of biotic and abiotic factors.7. Biome: The large unit of environment consisting of major type of
flora or vegetation and associated fauna( animals) in specific climatic zone is called biome.
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Annual variations in the intensity and duration of temperature and precipitation are responsible for the formation of major biomes.
• The major biomes are:
1. Arctic & alpine tundra
2. Coniferous forest
3. Temperate forest
4. Grasslands
5. Tropical Forest
6. Desert.
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• Abiotic factors :The most important abiotic factors of the environment are temperature, water, light and soil.
• Biotic factors: Biotic factors are pathogens, parasites, predators, competitors etc.
• Temperature: The physiological functions and geographical distribution of organisms is governed by temperature.
• Temperature affects the kinetics of enzymes, BMR (Basic Metabolic Rate) and other physiological actions in organisms.
• Eurythermal: A few organisms which can tolerate wide range of temperatures are called eurythermal organisms.
• Stenothermal: Many organisms which can tolerate narrow range of temperatures are called stenothermal organisms.
• Water: Important factor influence the life of organisms.• The productivity and distribution depends on water.• For aquatic organisms, chemical composition , pH, salinity and temperature
of water are important.• Euryhaline: The organisms which can tolerate wide range of salinity are
called euryhaline organisms.• Stenohaline: The organisms which can tolerate narrow range of salinity
stenohaline organisms.
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• Light: light is important abiotic factor bcoz the autotrophsprepares its food by photosynthesis.
• sciophytes : Small herbaceous plants and some shrubs live under the canopy forest trees are adapted to photosynthesis under very low light intensities. These are called sciophytes
• Animal use the seasonal variations in the light intensity and photoperiod as cues for timing of forage, reproduction and migration.
• The distribution of red, green and brown algae at difference depths of water depends on the light, red algae can live in very deep water.
• Soil: Nature and properties of soil depends on climate, weathering process.
• The physical and chemical properties of soil determine the type of plants that can grow in a particular habitat.
• The characteristics of the bottom sediments of aquatic environment determine type of benthic animals that can live there.
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• Organisms responses to environment:
• Regulation: Organisms maintain homeostasis in constant body temperature and osmotic concentration.
• Conformation: Majority (99%) of animals and plants cannot maintain a constant internal environment. Such animals and plants are simply called as conformers.
• Their body temperature varies according to ambient temperature.
• In aquatic animals the osmotic concentration of body fluid varies with ambient water osmotic concentration.
• Thermoregulation is energy-expensive process. Heat loss or gain is a function of surface area. therefore small animals are not found in polar region.
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• Migration: Organisms can move away temporarily from stressful conditions to another habitat is called migration.
• Suspension: Organisms that cannot migrate , suspend their metabolic functions during stressful period. It is called suspension.
• E.g. Hibernation, aestivation, Diapuse.
• Hibernation: Hibernation is a process by which the animals avoid the stress and become inactive during winter.
• Ex: Polar bear, Frogs, Lizards
• Aestivation: Aestivation is a process by which the animals avoid the stress and summer related problems and become inactive during summer.
• Ex: snails and fishes
• Diapause: It is a stage of suspended development seen in many zooplanktons to avoid unfavorable conditions.
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• Adaptation: Adaptation is any changes of the organism (morphological, physiological, and behavioral) that enables to survive and reproduce in its habitat.
• Adaptations have evolved over a long period of time and are genetically controlled
• Examples:• Desert Plants: have thick cuticle on leaf surface.• Sunken stomata.• leaves modified into spines. • Due to CAM pathway photosynthesis the stomata remain closed
during the day.• Ex: Opuntia, cactus etc.
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• Aquatic Plants: Have evolved aerenchyma for buoyancy and floating. leaves have waxy covering.
• Desert animal: Kangaroo rat living in the desert of North America never drink water. The water requirement is by internal fat oxidation (in which water is the by product).
• It is also able to concentrate its urine so that the minimal volume of water is lost during excretion
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• Allen’s rule: Allen’s rule states that, animals from colder climates generally have Shorter ears and limbs to minimize the heat loss.
• In Polar seals have a thick layer of fat below the skin that acts as insulator.
• It reduces loss of body heat. Short ears and limbs minimize heat loss.
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• Desert Lizards keep their body temperature constant by behavioral adaptation. They bask in the sun and absorb the heat when their body temperature decreases below the comfort zone.
• Burrowing habit also helps to protect desert animals from high temperature
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• Population attributes: Population is a group of individual living in a perticular geographical area.
• It has certain attributes, they are:• Birth rate.• Death Rate.• Sex Ratio.• Population density.• A population at any given time is composed of
individuals of different age group. As,• Pre-reproductive, Reproductive and Post- reproductive.• Age pyramid: If the age distribution is plotted for the
population, the resulting structure is called as age pyramid.
• For human population, the age pyramids show the age distribution of males and females in a combined diagram.
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• The shape of pyramids reflects the growth status of the population i.e. an expanding/ growing population, a stable population, a declining population.
• Population Growth: The size of population keeps changes with the time, depending on the factors like:
1. Food available;
2. weather,
3. predator pressure and
4. Competition.
• The density of a population in a given habitat during a given period changes due to four basic
• Natality (N), Mortality (M), Immigration (I) and Emigration (E).
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• The natality and immigration contribute to increase in the size and density of a population.
• Mortality and emigration contribute to a decrease in population
• So the equation for the population growth is;
• Nt = N0+[(B+I)- (D+E)]
• Nt = Population density at time.
• N0 = Population in beginning.
• B = Birth rate.
• I = Immigration.
• D = death rate.
• E = emigration.
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• Population Growth Models:
• There are two models of population growth:
• Exponential Growth Model: When the resources availability is unlimited in the habitat, the population grows in an exponential or geometric fashion,
• The equation is: dN/dt= (b-d)*N
• Let (b-d)= r,
• then the equation is,
• dN/dt= rN
• N=population density at time
• r= intrinsic rate of natural increase
• When a population shows exponential growth, the curve plotted with N in relation to time assume J shape.
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• Logistic growth Model: No population can continue to grow exponentially, as the resource availability become limiting at certain point of time.
• It is described by the equation:
• dN/dt = rN(K-N/K)
• N=population density at time
• r= intrinsic rate of natural increase
• K= carrying capacity
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• Life History Variations: Evolution of populations aims at improving the reproductive fitness to the maximum in their habitats.
• Most birds and mammals breed many times during their life time.
• According to ecologists life history traits of an organism have evolved in relation to the constraints imposed by the biotic and abiotic factors in their habitats.
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• Population Interactions:• Living organisms interact in various ways to form biological communities.• Interspecific interactions: It is the interactions of population of two
different species.• Interaspecific interactions: : It is the interactions of individuals of the same
species.• The interactions are following types:
Interaction Species A Species B
Predation + -
Competition - -
Parasitism + -
Commensalism + 0
Ammensalism. - 0
Mutualism. + +
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• Predation: It is an interspecific interaction in which predator(strong animal) kills and consumes prey (weak animal). Therefore one species is benefit and other is harmed.
• Predation is a way to transfer the energy from lower trophiclevels to higher trophic levels.
• Predator keep the prey population under control. Otherwise prey reach very high population density and cause imbalance in the ecosystem.
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• Sometimes predators are used as biological control for pests.
• Example:
• The Ladybird are useful to control aphids and Dragonflies for mosquitoes.
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• Prey species have evolved various defence mechanisms to reduce the impact of predation.
• Example:
• Certain insect species and frogs have camouflage (Cryptic coloration).
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• Monarch Butterfly is very distasteful to its prey bird. It has a special chemical in its body. This chemical is produced during its caterpillar stage by feeding on poisonous weeds.
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• Herbivores are the predators for plants.
• The problem of predation is more severe for plants than animals as they cannot move.
• About 25% of the known insects are the Phytophagus and feed on the plant sap.
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• Plants have developed certain morphological and chemical defence mechanism against herbivores. E.g. Thorns in Bougainvillea and Spines in Acacia
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• Certain chemicals produced by the plants act for defense.
• Calotropis produces a highly poisonous Glycoside that is a cardiac poison.
• Nicotine, Caffeine, Quinine, Strychnine, Opium etc are the chemicals produced by the plants against herbivores.
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• Competition:
• Competition is an interaction among the individuals of same species (Intraspecific ) or between individuals of different species (Interspecific).
• Competition between the individuals of same species is for same resources that are limited.
• In some case, resources need not be limiting for competition to occur, the feeding efficiency of one species might be reduced due to the interfering of the other species.
• E.g. Abingdon tortoise in Galapagos Island became extinct within a decade after goats were introduced into the island.
• It was due to the fact that the goats had greater browsing efficiency than the tortoise.
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• Unrelated species also compete for same resources.
• Ex:- flamingo & fish compete for zooplankton
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• Competitive release:
• "A species, whose distribution is restricted to a small geographical area because of the presence of a competitively superior species is called competitive release.
• These species is found to expand its distributional range dramatically when the competing species is experimentally removed
• Gause’s Competitive Exclusion Principle : It states, ‘that two closely related species competing for the same resources cannot exist together and the competitively inferior will be eliminated by superior’.
• Resource Partitioning: It is the mechanism meant for co-existence of species to face competition .
• According to this, if two species compete for the same resource, they could avoid competition by choosing different times for feeding or different foraging patterns.
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• E.g.
• MacArthur showed that five closely related species of Warbles living on the same tree were able to coexist and avoid competition by having behavioraldifferences in their foraging( hunting) activities.
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• Parasitism:• Parasitism is the interspecific interaction where one of
the species (Parasite) depends the other species (Host)for food and shelter.
• Host gets harmed and parasite gets benefitted.• Parasites are host-specific and parasite and its host
tend to co-evolve.• Co-evolve: It means that if the host evolves a special
mechanism to reject or resist the parasite, the parasite has to evolve the mechanisms to neutralize them.
• Parasites adaptations:• Parasite tends to co-evolve.• It may loss of sense organs.• Presence of suckers or hooks. • Loss of digestive system.• High reproductive capacity.
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• Some parasites have complex life cycle and generally have one or two intermediate host.
• Intermediate hosts act as vectors which facilitates parasitisation of host.
• Human liver fluke has two intermediate hosts: a snail and a fish
• Malaria Parasite has one intermediate host (mosquito) to spread to other host.
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• Human lice and ticks are ectoparasites
• Copepods are the ectoparasites on some marine fish.
• Cuscuta is a parasitic plant that grows on the trees or shrubs.
• It lost its chlorophyll and leaves during evolution.
• It gets its nutrition from the host plants by haustoria.
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• Commensalism:• It is the interspecific interaction in which one species benefits and the other
is neither harmed nor benefitted.• Ex: Epiphytes i.e Orchids growing on a tree branch.• Barnacles growing on the back of whales.• Association between Egret and grazing cattle. Egrets always forage close to
cattle are grazing because they easily get insects. • The Clown fish living along with sea anemones. Clown fish get protection
from predators. • Sucker fish on the back of shark
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• Mutualism: It is the interspecific interaction in which Both the species interact gets benefit.
• E.g. Lichens are relationship between Fungus and Algae/ Cyanobacteria• Mycorrhiza – an association of Fungus with roots of higher plants. Fungi
help to absorb nutrients from the rocks and plants provide energy yielding carbohydrates to fungi.
• Plants depend on insects for pollination and in return they give them nectar or pollens to eat.
• Animals help the plants in seed dispersal and in return they give fruits to animals as food.
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• fig tree and pollinator species of wasp. Fig species can be pollinated by its partner wasp only.
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• Amensalism: It is the interspecific interaction in which one is harmed and the other is neither benefited nor harmed.
• E.g: Penicillium secretes chemical penicillin kills bacteria. Name the interaction in each of the following:
• a) Cuscuta growing on a shoe flower plant.
• b) Mycorrhizaa living on the roots of higher plants.
• c) Clown fish living among the tentacles of sea anemone.
• d) Koel laying her eggs in crow's nest.
• e) Five closely related species of warblers living on the same tree
• a. Parasitism
• b. Mutualism
• c. Commensalism
• d. Brood parasitism
• e).Competition with resource partitioning.