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Organisms and Populations ORGANISMS AND POPULATIONS Prerequisites For better understanding this chapter, the following are the prerequisites you need to know before starting this chapter. What is Diversity in organisms and how they are interacting? How Human beings are interacting with other animals in real life? How we as Humans are depending on other organisms for our survival? What is the population of India and what are its affects on our life style? How parasites are affecting our health and life style? Learning Objectives The following are the objectives for this lesson: Organisms and Factors affecting it. Major Biomes in India. Adaptations and kinds of adaptations. Populations and Population Attributes. Population Dispersal and Growth Models. Population Interactions. Parasitism and Types of Parasites. 1 www.sciencetuts.com Organisms and Populations Introduction Nature itself is a combination of living and non living components. The living component of the nature is highly complex and more diversified. The complexity of living world or living component shows various levels of hierarchy or organisations, starting from molecules to biomes. In the levels of organisations, organisms and populations are one level of organisations. ORGANISMS It is the one level of organisation in the nature. They perform various types of activities in the nature. When we observe every activity of the organism, we can understand the mechanism and significance of the activity. For e.g. when we consider the bird male crow, this bird during spring season gives a sweet melodious voice to the nature. The bird gives such voice due to the presence of voice box and vibrating bone. This voice is used to attract & communicate the Male and Female crows female crow to perform sexual reproduction. In this way when we want to study the every activity of an organism, with scientific approach, we can easily understand the operation or mechanism of the activity. The science ecology is basically concerned with four levels of biological organisations. They are Organisms, Populations, Communities, and Biomes. At present we can discuss about organisms and populations. Organism and Its Environment In the nature, different organisms adopted different environments for their survival and reproduction. Organisms in different Environments In the nature, earth is moving around the sun, tilt on its axis causes annual variations in the intensity, duration of temperature, resulting in the formation of different seasons. Solar system Rainy season Winter season 2 Summer season www.sciencetuts.com Organisms and Populations These variations along with annual variations in precipitation account for the formation of major biomes, such as deserts, rain forests, tundras. A wide variety of habitats are developed due to regional and local variations within each biome. On planet earth, life exists on favorable places, and also on extreme harsh habitats. Desert Tundras Rain forests Major biomes in India Scorching Rajasthan desert, Rain soaked Meghalaya forests, Deep ocean trenches, Permafrost polar regions, High mountain tops, Boiling thermal springs, Shrinking compost pits. Human intestine is a unique habitat for microbes. Deep ocean trenches Scorching Rajasthan desert Rain soaked Meghalaya forests High mountain tops Boiling thermal springs Permafrost polar regions The habitat or biomes are influenced by abiotic & biotic components. The key elements that bring so much variation in the physical, chemical constituents of different habitats are temperature, water, light and soil. Water Soil The characteristics of a habitat are also influenced by biotic components like pathogens, predators, parasitism, competitors etc. In the nature, in course of time organisms through natural selection undergo changes; develop new adaptations to optimise its survival and reproduction in its habitats. Pathogens Predators 3 Parasitism www.sciencetuts.com Organisms and Populations MAJOR ABIOTIC FACTORS TEMPERATURE It is the most ecologically relevant environmental factor. Average temperature on land varies seasonally. It decreases progressively from the equator towards the poles from plains to the mountain tops. It ranges from sub-zero levels in polar areas and high altitudes to more than 50oC in tropical deserts in summer. In some unique habitats, average temperature exceeds 100oCentigrade. E.g: thermal springs, Deep sea Thermal springs deep sea hydrothermal vents. hydrothermal vents Organisms which grow in habitats with definite temperature cannot grow in other habitats with different temperatures. E.g: a) Mango trees do not & cannot grow in temperate countries like Canada, Germany. b) Snow leopards are not found in Kerala forests. c) Tuna fish are rarely caught beyond tropical latitudes in the ocean. Mango trees Snow leopards Tuna fish Temperature affects the kinetics of enzymes. Organisms tolerate at a specific rate of temperature. Based on this, organisms are classified into two types, namely EURTYTHERMAL - Organisms can tolerate and thrive in a wide range of temperatures. STENOTHERMAL – Organisms can tolerate narrow range of temperatures. The levels of thermal tolerance of organisms determine to a large extent their geographical distribution. In recent years, there has been growing concern about the gradually increasing average global temperatures. If this trend continues, the distributional range of some species to be affected. WATER It is the second most important factor influencing the life of organisms. Living organisms cannot sustain without water. Life on earth originated in water. In deserts, availability of water is so limited, so plants develop special adaptations to survive in deserts. 4 Water Desert www.sciencetuts.com Organisms and Populations The productivity & distribution of plants is also heavily dependent on water. The important factors for aquatic organisms for their survival in water are quality of water, salt concentration of water. The salt concentration of water in which organisms grow is less than 5% in inland water, 30-35% in the sea water, more than 100% in some hyper saline lagoons. The tolerant capacity of organisms to the water is variable with one another. Based on this, organisms are classified into two types. EURYHALINE – organisms tolerant to a wide range of salinities. STENOHALINE – organisms are restricted to a narrow range of salinities. Many fresh water animals cannot live for long in sea water and vice versa, because of the osmotic problems, they would face. LIGHT In the nature, Sun is the source of energy to all living organisms. Autotrophs are mainly depends by a process called photosynthesis. In dense forests, small plants (herbs & shrubs) get low light intensity, because canopy is covered by trees. So the rate of photosynthesis occurs at optimum rate. Sun Dense forests Autotrophs Herbs and Shrubs Plants also depend on light for their flowering. Depending on the photoperiod required for their flowering, plants are categorised into three groups, they are Long day plants (LDP) – Plants which require more photoperiod or day length. Short day plants (SDP) – Plants which require short photoperiod or day length. Day neutral plants (DNP) – Plants which require average day length or photoperiod. Long day plants Short day plants Day neutral plants Animals also influenced by light intensity in their foraging, reproduction and migratory activities. Intensity of light is variable when diurnal & seasonal variations exists. Sun is the source of energy and temperature to the nature. So the availability of light on land is closely linked with that of temperature. 5 www.sciencetuts.com Organisms and Populations In deep ocean (>500 meters) the environment is perpetually dark. The habitat of these regions is not aware of the existence of solar energy. The spectral quality of solar radiation is also important Deep ocean for life. The UV component of the spectrum is harmful to many organisms while not all the colour components of the visible spectrum are available for marine plants living at different depths of the oceans. Depth of oceans SOIL The nature and properties of soil differ from one another in different habitats or environments. The nature & properties of soils are depends upon the climate, the weathering process, formation of soils, development of soils etc. Soil The soil characteristics like soil composition, grain size, aggregation determine the percolation and water holding capacity of the soils. These characters along with PH, mineral composition and topography determine to a large extent the vegetation in any area. This is in turn dictates the type of animals that can be supported. In the aquatic environments, the sediment characteristics often determine the type of benthic animals that can thrive there. RESPONSE TO ABIOTIC FACTORS In the nature, abiotic factors are variable from time to time and area to area. These abiotic conditions influence the external and internal environment of living beings. Generally internal environment is stable in most of the organisms. It is called HOMEOSTASIS. E.g: Maintenance of optimum temperature & osmotic concentration of body. Internal environment of the living organisms is maintained by physiological & biochemical activities of the organisms. 6 www.sciencetuts.com Organisms and Populations External environment of the organisms is severally influenced by the habitat state. A person is able to form his/her best when the temp is 25oC and wishes to maintain it so, even when it is scorchingly hot or freezingly cold outside. Human beings Heater Conditioner It could be achieved at home/in the car while travelling/at work place, by using air conditioner in summer and heater in winter. Then his/her performance would be always maximal regardless of the weather around him/her. In these conditions homeostasis of the organisms is maintained by artificial methods. Living organisms core with the situations by means of various possibilities like Regulate, Conform, Migrate, and Suspend. REGULATE It is one of the important activities of organisms to survive in any external environment. Organisms are regulated in any type of environment by various activities. Some organisms regulate the homeostasis or internal environment by physiological conditions like regulation of the body temperature, constant osmotic concentration of body fluids, etc. All birds, mammals, and a very low vertebrates and invertebrates’ species are indeed capable of such regulations. E.g: Thermoregulation & Osmoregulation. Bird Mammal Vertebrate Invertebrate According to evolutionary biologists, the fitness of mammals is largely due to their ability to maintain a constant body temperature, and thrive to maintain or live in Antarctica or in the Sahara desert. Mammals Antarctica 7 Sahara desert www.sciencetuts.com Organisms and Populations The mechanism used by most mammals to regulate the body temperature is similar to the ones used by human beings. Human beings maintain constant body temperature 37o centigrade. In summer, the body temperature is maintained by profuse sweating, because outside temperature is more than that of inside temperature. Similarly in winter also body temperature is maintained by shivering, because external temperature is less than that of internal temperature. Shivering is a type of exercise which generates heat and raises the body temperature. Plants do not have such mechanism to maintain internal temperature. CONFORM Organisms which can change their internal environment, according to the ambient environment are called Conformers and the process is called Conform. In majority of animals and nearly all plants body temperature changes with the ambient temperature. In aquatic animals, the osmotic concentration of the body fluids changes with that of ambient water osmotic concentration. Aquatic Animals Organisms maintain constant internal environment cannot act as conformers. Conformers also act as regulators. In majority of conformers thermoregulation is energetically expensive process. It is based on heat loss/heat gain of surface area. The small animals like Shrew and Humming birds have a larger surface area relative to their volume. They tend to lose body heat very fast when it is cold outside. They have to spend much energy to generate body heat through metabolism. Due to this reason, very small animals are rarely found in Polar Regions. Shrew Humming bird During the course of evolution, the costs and benefits of maintaining a constant internal environment are taken into consideration. Some species have evolved the ability to regulate, but only over a limited range of environment conditions, beyond which they simply conform. If the stressful external conditions are localised or remain only for a short duration, the organisms has two other alternatives. They are Migrate and Suspend. 8 www.sciencetuts.com Organisms and Populations MIGRATE The movement of organisms temporarily form the stressful habitat to a more hospitable area and return when stressful period is over is called Migration. In terms of human analogy, during summer human beings move from Delhi to Shimla (hot place to cool place). Eg: Siberian Cranes – These birds migrate every winter season from Siberia to Keolado National Park, Bharatpur, Rajasthan, to avoid extreme cold. Siberian Cranes SUSPEND Temporary withstanding of organisms in different forms during stressful/unfavourable conditions is called Suspend. Bacteria, fungi, lower plants produce various types of thick walled spores to survive during unfavourable conditions. These spores germinate during favourable conditions. Higher plants survive during unfavourable conditions in the form of seeds & vegetative reproductive structures. These parts by reducing their metabolic activity survive during unfavourable conditions. It is called Dormancy. When favourable conditions prevailed, they germinate and develop into new plants. Higher plants also exhibit dispersal to avoid unfavourable conditions. Animals avoid/escape unfavourable conditions by escaping in time. Bear – These animals going into hibernation during winter. Snails & Fishes – these animals going into aestivation to avoid summer (heat & desiccation). Zooplanktons – these animals enter into diapause – a stage of suspended development. Bear Snail Fish Zooplanktons ADAPTATIONS Any attribute of the organisms that enables the organism to survive, reproduce in its habitat are called Adaptations. Many adaptations have evolved over a long evolutionary time and are genetically fixed. These adaptations are in morphological, physiological and behavioural. 9 www.sciencetuts.com Organisms and Populations MORPHOLOGICAL ADAPTATIONS XEROPHYTES: These plants have a thick cuticle on their leaf surfaces and have their stomata arranged in deep pits to minimise water loss through transpirations. They also have a special photosynthetic pathway (CAM) that enables their stomata to remain closed during day time. Xerophytes Opuntia – Leaves are reduced to spines, stems are modified into phylloclade to perform photosynthesis. Mammals – Mammals from colder climates generally have shorter ears and limbs to minimise heat loss (Allen’s rule). AQUATIC MAMMALS – SEALS – These animals have a thick layer of fat (bubber) below their skin that act as insulator and reduces the loss of body heat. Opuntia Seals PHYSIOLOGICAL ADAPTATIONS Some organisms exhibit physiological adaptations to tide over unfavourable conditions. ALTITUDE SICKNESS It is the most important adaptation experienced by the people who move to the high altitudes. When the people move to the high altitudes (more than 3,500 meters) like Rohtang pass near Manali, Manasarovar, in China occupied Tibet. Rohtang pass Manasarovar In the high altitudes low atmospheric pressure exists. So body does not get enough oxygen. The symptoms like Nausea, Fatigue, heart palpitations develop. But these symptoms gradually decrease and the organism gets acclimatised to the conditions, finally altitude sickness stops. The body compensates the low availability of oxygen by increasing RBC production, decreasing the binding capacity of haemoglobin and by increasing breathing rate. 10 www.sciencetuts.com Organisms and Populations ANIMALS – In majority of animals, all metabolic reactions/physiological functions proceed optimally in a narrow temporary range. ARCHAEBACTERIA – They flourish in hot water springs, deep sea hydrothermal vents, and temperature exceeds 100oC. FISHES – Many fishes thrive in Antarctic water, temperature below zero. MARINE INVERTEBRATES- FISHES – These organisms live at great depth in the ocean where the pressure could be >100 times the normal atmospheric pressure that we experience. These organisms show a fascinating array of biochemical adaptations. Fig 13.61 Animals Fig 13.62 Archaebacteria Fig 13.63 Fishes Fig 13.64 Marine Invertebrates Fishes BEHAVIOURAL ADAPTATIONS Some organisms show behavioural responses to cope with variations in their environment. DESERT LIZARD – These organisms maintain the constant body temperature by behavioural means. They bask in the Sun & absorb heat when their body temperature drops below the comfort zone, but move into shade when the ambient temperature starts increasing. Some species are capable of burrowing into the soil to hide & escape from the above ground heat. Desert lizard Populations A group of organisms of similar species belongs to same locality is called Population. Every population is confined to a well defined area, share or compete for similar responses, potentially interbred or reproduce by vegetative & sexual methods. LOCAL POPULATIONS or DEME – A group of interbreeding individuals of a species found in a space or geographical area at a particular time is called Local populations or Deme. METAPOPULATIONS – A complex of local populations connected by dispersing individuals is called Metapopulations. Population gives various meanings in different areas of study. They are HUMAN DEMOGRAPHY – According to human demography population means number of human beings in a given area (School, Village, Town etc.) GENETICS – According to Genetics, Population is a group of interbreeding individuals of the same species which live in semi isolation from other such groups. 11 www.sciencetuts.com Organisms and Populations ECOLOGY – According the Ecology, population is a group of individuals of the same species living in the same area which functions as a unit of biotic community. The parameters used for describing a population are a) Total number of individuals or population size. b) Kind and ratio of individuals like male and female and pre-reproductive and post-reproductive. c) Space or area. d) Time. Natural selection plays an important role to produce the desired traits in populations. Population ecology, an important area of ecology because it links ecology to population genetics & evolution. POPULATION ATTRIBUTES Every population expresses certain attributes to survive in the environment. They are 1) Birth & Death rate. 2) Sex ratio. 3) Age of the organisms. 4) Population size/ Population density. Birth And death rate In a population birth and death rates refer to per capita birth & deaths respectively. These rates hence are expressed is change in numbers with respect to members of populations. Eg: In a pond 20 Lotus plants are present in last year, by reproduction 8 new plants are added. Current population reaches 28. Example of Birth Rate Then the birth rate is 8/20 = 0.4 that means 0.4 off-springs per Lotus plants per year are added. If 4 individuals in laboratory populations of 40 fruit flies are died during a specified time interval (week), the death rate in the population during that period is 4/40=0.1 individuals per fruit fly per week. Died 40 4 40 0.1 Example of Death Rate 12 www.sciencetuts.com Organisms and Populations SEX RATIO It is the number of individuals of a particular sex out of total populations. 60 60 40 40 Females males Images showing Sex ratio Eg: In a population 60 females and 40 males are present. That means 60% of females, 40% males are present. AGE DISTRIBUTION Ecologically a population has three age groups. They are pre-reproductive, reproductive and postreproductive. Their comparative abundance determines the reproductive status of population. A population having larger number of young individuals will show rapid increase. It will have a slow increase or become static in various age groups are evenly balanced. A population with larger number of post-reproductive or older individuals and less number of pre reproductive individuals will show a negative growth etc. The graphic representation of different age groups found in a population with pre-reproductive groups at the base, reproductive ones in the middle and post-reproductive groups at the top is called Age pyramid. A population at any given time is composed of individuals of different ages. A graph is made by plotting number of individuals in a population on one axis and their age is on another axis, the resulting graph/structure is called AGE PYRAMID. For human population, the age pyramid generally show age distribution of males & females in a combined diagram. The shape of the age reflects the growth status of the population. They are a) Growing/Expanding b) Stable and C) Declining 13 Age Groups AGE PYRAMID Post reproduction Reproduction Pre-reproduction Population Age Pyramid Graphic Representation of Different age groups in a population www.sciencetuts.com Organisms and Populations TYPES OF AGE PYRAMIDS Post-reproduction Reproduction Pre-reproduction negative growth Triangular Bell shaped Turn shaped Types of Age Pyramid TRIANGULAR AGE PYRAMID In this, the number of pre-reproductive individuals is very large. The Number of reproductive individuals is moderate. The number of post-reproductive individuals is less. Population growth depends upon the comparative size of pre-reproductive population. BELL SHAPED AGE PYRAMID In this, the number of pre-reproductive and reproductive individuals is almost equal. Post reproductive individuals are comparatively fewer. The population size remains stable. TURN SHAPED AGE PYRAMID The proportion of reproductive age group is higher than individuals in pre-reproductive age group. The number of post–reproductive individuals is also sizeable. Population shows negative growth. POPULATION SIZE (OR) DENSITY The number of individuals confined to a particular habitat is called Population size. Population size is more technically described as population density. It is designated as D. Population Density = (Number of Individuals (N) or Space (S) D= N S Population size It always indicates the nature or status of the habitat. The population size/density of a habitat depends upon the outcome of the various ecological processes or associations like competition, predation, mutualism etc. In the nature, size could be as low as less than 10 (Siberian Cranes at Bharatpur wetlands in any year) or go into millions (Chlamydomonas in a pond). Siberian Cranes 14 Chlamydomonas www.sciencetuts.com Organisms and Populations Generally population density can be calculated by knowing the total number of individuals of a particular area irrespective of their role in that area. In some cases it is meaningful and difficult to estimate. For eg: In an area 200 Parthenium plants and one Banyan tree is present. As per our observations, population density of Banyan tree is less than that of Parthenium plants. In such cases, the percent cover of biomass is a more meaningful measure of the population size. The contribution/rate of Banyan tree in that area is more than that of Parthenium plants. Parthenium plants Banyan tree When the population is huge and counting is impossible and time taking, then total number is again not an adoptable measure. Culture media Fishes For eg: culture media in a petridish is completely filled with bacteria. The total number of bacteria in the culture cannot be countable. In such cases relation densities serve the purpose equally well than absolute population densities. For instance, the population density of fish in a lake is determined by number of fish caught per trap. It is better to understand the population density/size of a habitat or area indirectly without actually counting them/ seeing them. For eg: the tiger census in our national parks & tiger reserves is often based upon on pug marks & faecal pellets. In case of aquatic habitat, the space is measured in three dimensions, while the space in terrestrial habitat is measured in two dimensions. Unit of area depends upon the size and number of individuals. For plants and animals, density is known by counting individuals in sampling units of predetermined sizes randomly in an area. Density of a population may vary from time to time and area to area. Eg: Density of small plants in rainy season and dry season. Population density is also depends upon availability of nutrients and other resources for it. 15 www.sciencetuts.com Organisms and Populations POPULATION GROWTH The population growth in any area is based on population density. Population growth is not a static parameter. It keeps on changing in time, depending on various factors including food availability, predation pressure and reduced weather. The population density in a given habitat during a given period fluctuates due to changes in four basic processes, in which two processes contribute an increase in populations, they are natality & immigration. The remaining two processes contribute in declining the population number, they are mortality & emigration. Immigration Nalality Population density(N) Mortality Emigration NATALITY (B) It refers to the number of births during a given period in the population that are added to the initial density or the rate of production of new individuals per unit of population per unit time through birth, hatching, germination or vegetative propagation. Biotic potential – The maximum natality or birth rate achieved under ideal conditions is called Biotic potential. It can be realised only when environmental resources are non-limiting and conditions favour for minimum mortality. Realised natality – The actual birth rate found under existing conditions is termed as realised natality. In Human beings, natality is calculated per thousand per year. Natality 16 www.sciencetuts.com Organisms and Populations MORTALITY (D) It refers to the number of deaths in the population during a given period or it is the rate of loss of individuals per unit time due to death. Maximum mortality occurs in egg/larval/seeding and old age. Specific mortality – it is the theoretical, minimum death rate that occurs under ideal conditions due to natural processes or senescence. Realised mortality – The actual rate of death occurring in a unit population due to environmental changes, nutritional deficiency, disease, competition, predation etc. is called realised mortality. Mortality VITAL INDEX The percent ratio of natality in relation to mortality. It indicates the normal rate of growth of population. Vitality index= n/m x 100 IMMIGRATION(I) It refers to the number of individuals of the same species that have come into the habitat from elsewhere during the time period under consideration. Immigration EMIGRATION(E) It refers to the number of individuals of the population who left the habitat and gone elsewhere during the time period under consideration. 17 www.sciencetuts.com Organisms and Populations Emigration If N is the population density at time (t), then its density at a given time (t+1) is Nt+1 = Nt + [(B+I) – (D+E)] Then Nt+1 = population density at a given time Nt= Population density at a time ‘t’ B = Natality I = Immigration D = Mortality E = Emigration From the above equation, population density increases, if number of births plus number of immigrants is more than the number of deaths and number of emigrants. Otherwise it will decrease. Under normal conditions, for an existing habitat, the most important factors, influence the population density are Natality & Mortality, where as Immigration & Emigration are special factors, which influence the population density. For instance, for a newly formed habitat immigration may contribute more significantly to the population growth than other factors. POPULATION DISPERSAL It is the movement of individuals or propagules into or out of population for preventing overcrowding, obtaining food, avoiding predators and other adverse conditions is called population dispersal. It affects the size of the population. Emigration, Immigration, Migration together called Population dispersal. Population Dispersal 18 www.sciencetuts.com Organisms and Populations GROWTH MODELS In the nature, the growth of a population with time show specific & predictable pattern of population growth. When plotting of population growth against time in the form of graph, the resulting structure/graph is called growth model. Growth models are useful to understand the growth pattern of the organisms and the application of controlling factors. Population (bn) 1.5 1.4 1.3 1.2 1.1 2000 10 20 30 40 Time Graph Showing growth of population with time There are two types of growth models explained below to understand the population growth. They are 1) EXPONENTIAL GROWTH 2) LOGISTIC GROWTH The growth of population is unlimited when the resource availability is unlimited. The graph which shows this type of growth is called Exponential growth. When resources in the habitat are unlimited, each species has the ability to release fully its innate potential to grow in number as Darwin observed while developing his theory of natural selection. Then the population grows in an exponential or geometric fashion. Population EXPONENTIAL GROWTH Exponential growth Time Graph Showing Exponential growth In a population of size N, the birth rates are represented as b and death rates are represented as d, then the increase or decrease in population size (N) during unit time period t(dN) will be (dt) dN = (b-d) x N dt Let (b-d) = r then dN = rN dt r = Intrinsic rate of natural increase. r is an important parameter chosen for assessing impacts of any biotic or abiotic factors on population growth. 19 www.sciencetuts.com Organisms and Populations The above equation describes the exponential or geometric growth pattern of population growth, and results in J-shaped curve. When we plot N in relation to time, the magnitude of r value is variable between the organisms. For eg: r value of Norway is 0.015 Flour beetle is 0.12 Human beings in 1981 is 0.025. The integral form of exponential growth equation can be derived by using calculus Nt = N0 ert Nt = population density after time t. N0 = Population density at time zero. r = Intrinsic rate of natural increase. e = the base of natural logarithm (2.71828) Under unlimited resource conditions, any species grown exponentially and it can reach enormous population densities in a short time. Darwin showed how even a slow growing animal like elephant could reach enormous number in the absence of checks. Darwin Population growth in which the growth rate decreases with increasing number of individuals until it becomes zero when the population reaches a maximum state. When the population density increases exponentially, competition develops between the organisms. Finally fittest individual will survive & reproduce. Population LOGISTIC GROWTH Logistic growth Exponential growth Time Graph Showing Logistic growth In the nature in a given habitat every species shows carrying capacity. CARRYING CAPACITY (K) – A species with maximum limited number of individuals in a given habitat, which has enough resources to support them, is called carrying capacity (K) for that species in that habitat. The maximum number of individuals of a population which can be provided with all the necessary resources for their healthy living in a habitat/locality/environment is called carrying capacity. 20 www.sciencetuts.com Organisms and Populations Carrying capacity(K) dN = rN (K-N) dt K Population When carrying capacity of habitat/locality/ environment is exceeds the limit, the size of the population begins to decrease due to lower natality, higher mortality and emigration. A population growing in a habitat with limited resources show initially lag phase, followed by phases of acceleration and deceleration and finally an asymptote when the population density reaches the carrying capacity. Logistic growth Exponential growth Time Graph Showing Carrying Capacity A plot of N in relation to time (t) results in a sigmoid curve. This type of population growth is called VERHULST – PEARL LOGISTIC GROWTH. This is described by the following equation dN (K-N) = rN dt K Where N= population density at time t, e = Intrinsic rate of natural increase, K = carrying capacity. Since growth resources for most of the animal populations are limited and becoming limiting factor gradually, the logistic model is considered as more realistic one. ENVIRONMENTAL RESISTANCE The sum of abiotic and biotic factors which checks the rise in population size and prevents the species to realise its biotic potential is called Environmental resistance. It is inversely related to difference between carrying capacity (K) and number of existing population (N). Environmental resistance rises as the population size approaches the carrying capacity of the habitat. It helps in limiting population size to below the carrying capacity. Carrying capacity(K) Population Environmental resistance rN Logistic growth (K-N) K Exponential growth Time Graph Showing Environment Resistance The effect of environmental resistance on biotic potential is denoted by the following formula. Where r is reproductive rate and N is the population. 21 www.sciencetuts.com Organisms and Populations LIFE HISTORY VARIATIONS The life history of an organism depends upon the abiotic & biotic factors available in that particular habitat. It is variable from one species to another species. Life history of an organism mainly depends on reproductive fitness of that organism. It is also called DARWINIAN FITNESS. Reproductive fitness of an organism depends on the nature of habitat in which they live. In a particular habitat, organisms evolve towards the most efficient reproductive strategy under a particular set of selection pressures. According to reproductive strategy of the organism, some organisms breed only once in their life time. Eg: Pacific fish, Bamboo, while some other organisms breed many times during their life time. Eg: most of the birds and mammals. Pacific fish Mammals Birds Some produce a large number of small sized offsprings (Oysters, Perlagic fishes) while others produce a small number of large sized offsprings (Birds, mammals). Oysters Perlagic fishes Ecologists suggest that life history traits of the organism have evolved in relation to the constraints imposed by the abiotic & biotic components of the habitat in which they live. Evolution of life history traits in different species is currently an important area of research being conducted by ecologists. POPULATION INTERACTIONS In the nature, in any natural habitat, a group of different species or populations exists together. When they exist together, they interact with one another in various ways and form into a biological community. Biological community 22 www.sciencetuts.com Organisms and Populations Even in minimal communities, many interactive linkages exist, although all may not be readily apparent. For example, when we observe plants regularly interacting with microbes and animals, microbes involve in breakdown of complex organic materials into simpler ones. Plants absorb these simple inorganic substances to prepare biomolecules. Simultaneously animals also interact with plants for pollination, dispersal of fruits and seeds. microbes Pollination In every biological community, interactions arise among the different species or populations. These are called Interspecific interactions. Interspecific interactions These interactions are either beneficial or detrimental or neutral. Beneficial interactions are designated as + Detrimental interactions are designated as – Neutral interactions are designated as 0 (Zero) Different types of population interactions are explained below Beneficial (+ve) Interactions are mutualism, Detrimental (-ve) interactions are Competition, Predation, Parasitism and Neutral interactions are commensalism, amensalism. PREDATION The association, in which one organism kills the other organism, is called Predation. The organism which killed the other organism is called Predator and other organism is called Prey. These are carnivorous organisms. It is a mechanism of biological control that helps in keeping the population of various organisms under check. Predation is one of the nature’s ways of transferring energy from higher trophic level to lower trophic level. So predators act as ‘conducts’ for every transfer across trophic levels. E.g: Herbivores eating the plants. 23 Predation Predation Herbivores eating the plants www.sciencetuts.com Organisms and Populations Predators plays an important role in the nature. Predator keeps prey population under control. Without predators, prey species could achieve very high population densities and cause ecosystem instability. When certain exotic species are introduced into a geographical area, they become invasive and start spreading fast because the invaded land does not have its natural resources. In the early 1920’s a prickly pear cactus is introduced into Australia. It causes havoc by spreading rapidly into million hectares of rangeland. Biological control methods adopted in agriculture pest control based on the ability of the predator to regulate prey population. Prickly pear cactus The invasive prickly pear cactus in Australia was brought under control only after a cactus feeding predator (a moth) from its natural habitats into the country. Predators also help in maintaining species diversity in a community, by reducing the intensity of competition among competing prey species. feeding predator In the rocky intertidal communities of the American pacific coast, the star fish Piaster is an important predator. In a field experiment, when all the Starfish were removed from an enclosed intertidal area, more the 10 species of invertebrates become extinct within a year, because of interspecific competition. star fish Piaster If a predator is too efficient and over its prey, then the prey might become extinct and following it, the predator will also become extinct for the lack of food. This is the reason why predators in nature are prudent. Some species of insects and frogs are cryptically coloured to avoid being detected easily by the predator. Some are poisonous and therefore avoided by the predators. The monarch butterfly is highly distasteful to its predator (bird) because of a special chemical present it its body. Interestingly, the butterfly acquires this chemical during its caterpillar stage by feeding on a poisonous weed. butterfly 24 caterpillar www.sciencetuts.com Organisms and Populations Herbivores are the predators for plants. Nearly 25% of the all insects are known to be phytophagous. The problem is particularly severe for plants, because unlike animals, they cannot run away from their predators. Therefore plants have an astonishing variety of morphological and chemical defences against herbivores. E.g: Thorns are the most common morphological means of defence Many plants produce & store chemicals that make the herbivore sick when they are eaten, inhibit feeding/digestion, disrupt its reproduction or even kill it. CALOTROPIS – This is mostly growing in abandoned fields. The plant produces highly poisonous cardiac glycosides. Due to this reason cattle or goats will not eat this plant. Thorns cattle goats A wide variety of chemical substances that we extract from plants on a commercial scale (nicotine, caffeine, quinine, strychnine, opium, etc.) are produced by them actually as defences against grazes & browsers. nicotine caffeine quinine strychnine opium A rise in predator population will reduce prey population, which in turn will cause reduction in the population of predators due to starvation and emigration. A rise in herbivore population will result in overgrazing, shortage of herbage and ultimately reduction in herbivore population. Eg: Insectivorous plants – Drosera, Nepenthes, Utricularia. Drosera Nepenthes 25 Utricularia www.sciencetuts.com Organisms and Populations COMPETITION Charles Darwin was first convinced that interspecific competition is a potent force in organic evolution. Competition exists between either related or unrelated species for the same resource. Eg: Flamingos & resident fishes present in some shallow South American lakes compete for their common food, the zooplankton in the lake. Charles Darwin Flamingos Interference is another important factor in competition of different species, which compete for the same resource of food. It is called Interference competition. In the inference competition, the feeding efficiency of one species might be reduced due to interference & inhibitory presence of the other species, even if the resources are abundant. So competition is best defined as a process in which the fitness of one species is significantly lower in the presence of another species. Gause & other experimental ecologists demonstrated in laboratory experiments that when resources are limited the competitively superior species will eventually eliminate the other species, but evidence for such competition exclusion occurs in nature is not always conclusive. Strong & Persuasive circumstantial evidence does exist however in some cases. Competitive release is another important evidence for the occurrence of competition in nature. A species, whose distribution is restricted to a small geographical area because of the presence of competitively superior species, is found to expand its distributional range dramatically when the competing species is experimentally removed. Connell’s elegant field experiment showed that the larger and competitively superior barnacle Balanus dominates the intertidal area and excludes the smaller Barnacle chathamalus from that zone. In general, herbivores are plants appear to be more adversely affected by competition than carnivores. GAUSE’S COMPETITION EXCLUSION PRINCIPLE It states that two closely related species competing for the same resources cannot co-exist indefinitely and the competitively inferior one will be eliminated eventually. This may be true if resources are limiting, but not otherwise. These generalizations are not supporting competition completely. It is called RESOURCE PARTITIONING. 26 Resource Partitioning www.sciencetuts.com Organisms and Populations Many ecologists in more recent studies observed that in the inter-specific competition when species facing competition they might evolve mechanisms that promote co-existence rather that exclusion. RESOURCE PARTITIONING If two species compete for the same resource, they could avoid competition by choosing, different times for feeding or different foraging patterns. McArthur showed that five closely related species of Warblers living on the same tree were able to avoid competition and co-exists due to behavioural differences in their foraging activities PARASITISM Warblers The association, in which one organism obtains nourishment from another organism, is called Parasitism. The organism which obtains food is called Parasite and the organism which supply food is called Host. In this association, parasites also obtain shelter from their host. In this association, host becomes weak with reduced life cycle and reduced reproduction often leading to sterility. Parasites reach the host through contact with infected hosts, contaminated food and water, animal bites and direct entry. Parasites reach the host by developing different types of adaptations. They are a) Holdfast, Haustoria, Suckers (ectoparasites) b) Suckers, hooks and spines (endoparasites) ectoparasites endoparasites c) Resistant covering, resistant eggs or cysts, formation of antienzymes, anaerobic respiration, degeneration of unwanted organs. Parasitic mode of life ensures free lodging and meals of a person in a host family. Parasitism has evolved in so many taxonomic groups from plants to higher vertebrates. Many parasites have evolved to be host specific in such a way that both host & parasitic tend to co-evolve, that is if the host evolves special mechanisms for rejecting or resisting the parasite, the parasite has to evolve mechanisms to counteract & neutralise them in order to be successful with the same host species. In accordance with their life styles, parasites evolved special adaptations such as the loss of unnecessary sense organs, presence of adhesive organs or suckers to clings on to the host, loss of digestive system & high reproductive capacity. The life cycles of parasites are often complex, involving one or two intermediate host or vectors to facilitate parasitisation of its primary host. Eg: The human lever fluke (a trematode parasite) depends on two intermediate host (a snail and a fish) to complete its life cycle. 27 www.sciencetuts.com Organisms and Populations The human lever fluke host The malaria parasite needs a vector, to spread to other hosts. Majority of parasites harm the host. They reduce the survival growth and reproduction of the host, reduce its population density. They might render the host more vulnerable to predation by making it physically weak. host malaria parasite TYPES OF PARASITES a) Non pathogenic – eg: Entamoeba coli b) Pathogenic – eg: Entamoeba histolytica, Taenia solium, Ascaris, Vibrio cholrae c) Temporary parasites – eg: Female mosquito, Leech, bed bugs d) Permanent parasites – eg: Entamoeba, Ascaris Entamoebacoli Entamoebahistolytica Female mosquito Taenia solium Leech Vibrio cholrae bed bugs Ascaris Entamoeba 28 www.sciencetuts.com Organisms and Populations e) ECTOPARAISTES - Parasites that feed on the external surface of the host organism are called ectoparasites. They attach to skin, hair and other surface features of the host. They have suckers, camps adhesive surface, cutting, biting or sucking mouth parts or root. Lice, ticks, mites, leeches, mosquitoes feed on body fluids Example: Lice on humans, Ticks on Dogs, Copepods on marine fish, Cuscuta on Hedge plants. Female mosquito is not considered as parasite, but it needs our blood for reproduction. Lice Ticks on Dogs tick mite leeche Copepods on marine fish mosquitoe Cuscuta on Hedge plants f) ENDOPARASITES- Parasites that live inside the host body at different sites (liver, kidney, lungs, RBC, etc. are called endoparasites. The lifecycles of these parasites are more complex because of their extreme specialization. Their morphological & anatomical features are greatly simplified while emphasising their reproductive potential. eg: Intracellular Plasmodium, Tissue parasite - Trichinella,Body fluid parasite Trypanosoma,Gut parasite - Taenia liver kidney lungs RBC Intracellular Plasmodium Trichinella Trypanosoma Taenia 29 www.sciencetuts.com Organisms and Populations g) Holoparasite – These are also called complete parasites eg: Animal parasite, Cuscuta, Rafflesia h) Semi parasite – These are also called Incomplete parasites eg: Visum, Loranthus i)Hyperparasite – Parasite over parasite. Cicinnobolus cesatii on Powdery mildew. Animal parasite Cuscuta Rafflesia Loranthus BROOD PARASITISM It is fascinating examples of parasitism in which the parasitic bird lays its eggs in the nest of its host and lets the host incubate them. It is called Brood parasitism. During the course of evolution, the eggs of the parasitic bird have evolved to resemble the host’s egg in size & colour to reduce the chances of the host bird detecting the foreign egg and ejecting them from the nest. Example: Cuckoo (Koel) and Crown relation. Cuckoo Crown relation COMMENSALISM In this type of interaction, one species benefits and the other is neither harmed nor benefited. It is of two types: a) periodic contact and b) continuous contact. Periodic contact a) Fierasfer in Cloaca of Cucumaria is able to obtain shelter and food. b) Polynox in the burrow of Chatopterus is able to obtain shelter and food. c) Clone fish is able to protect itself by living in the company of Sea Anemones. d) Naucrates, Remora (Pilot fish) accompanies shark without getting attached to the shark. Fierasfer Polynox Clone fish 30 Remora www.sciencetuts.com Organisms and Populations e) Echeneis (Sucker fish) has a holdfast or sucker which is a modified dorsal fin. It attaches to the underside of shark and therefore remains protected. The fish obtain food from small pieces of left over when shark is feeding on its prey. f) Jackal and Hyena accompany Tiger or Lion for eating over small bits of prey. Echeneis Jackal and Hyena Continuous contact a) Barnacles are often attached to the surface of whales for shelter and obtaining more food. b) Escherichia coli in human intestine. c) Climbers and twiners over other plants for exposing their foliage. d) Epiphytes perched on other plants for space only e) Adamsia pallicata (Sea Anemone) is commensal over Eupagurus prideauxi (Hermit crab). The latter gets protection in a small shell. Barnacles Epiphytes perched Escherichia Adamsia pallicata Sea Anemone attaches to the surface of shell. Hermit crab carries it from place to place. This provides otherwise sedentary Sea Anemone with food. MUTUALISM It is an interaction in which both species get benefited with one another. Eg: Lichens, Mycorrhizae, Plant-animal associations. It is considered to be obligatory. Lichens Mycorrhizae a) Association between an alga and fungus in lichen b) Rhizobium and root in nodular roots of leguminous plants c) Fungus and root in mycorrhiza. d) Bacteria present in the stomach of ruminants help in the digestion of cellulose. 31 www.sciencetuts.com Organisms and Populations e) Trichonympha (cellulose digesting flagellate) in intestine of Termite. f) Coelentarates and alga in coral reefs. Hydra and zoochlorellae. g) Insects obtain nectar and perform pollination in flowers h) Some ants take shelter and food from fruit trees. They protect the trees from other animals. This phenomenon is called Myrmecophily. lichen Trichonympha Rhizobium mycorrhiza Bacteria Hydra Insects ants PLANT – ANIMAL ASSOCIATION It is a classical example of mutualism. Eg: Ficus – Wasp association Ficus Ficus – Wasp association In this type of interaction plants need the help of animals for pollinating their flowers and dispersing their seeds. Plants reciprocate to the animals by offering the rewards in the form of pollen, nectar or juicy nutritious fruits. This system should also safe guard against ‘cheaters’. Ficus – Wasp Plant animal interactions often involve co-evolution of the mutualist, that is the evolution of the flower and pollinating agent. In Ficus trees, there is a tight one to one relationship with plant & pollinator agent WASP. This relationship explains that for very Ficus tree, the pollinating agent is WASP only, no other insect involve in it. 32 www.sciencetuts.com Organisms and Populations The female WASP uses the fruit not only as an opposition site but uses the developing seeds within the fruit for nourishing its larvae. The WASP pollinates the Ficus inflorescence while searching for suitable egg laying sites. In return, for the flavour of pollination, the Ficus offer the WASP some of its developing seeds as food for the developing WASP larvae. ORCHID- HONEY BEE ASSOCIATION Orchids show bewildering diversity of floral patterns, which are meant for attraction of suitable pollinating agent and ensure guaranteed pollination by them. They are Bees & Bumble bees. In this relation, only few orchids offer rewards, not all. The Mediterranean Orchid Ophrys employs sexual deceit, to get pollination by the Bee species. In the plant, one petal of its flower resembles the female bees, in its size, colour and markings. The male bee is attracted by this petal during reproduction by perceiving as a female bee. The male bee pseudo copulates with the flower. During this process, pollen of this flower falls on male bee body. male bee pollen When the same male bee wants to pseudocopulate with another flower, pollen is transfered to the stigma of that flower. It leads to the occurrence of pollination. Here we can observe the co-evolution of partners. If the female bee’s colour pattern changes for any reason during evolution, pollination success rate will be reduced unless the orchid flower co-evolve to maintain the resemblances of its petal to the female bee. PROTOCOOPERATION It is non-obligatory mutually beneficial relationship which develops when two different organisms get associated. a) Bubalcus ibis (Cattle Egret) feeds on lice and ticks of cattle. b) Buphagus(Ox pecker) on skin parasites of Rhino. c) Pluvianis (Crocodile Bird) rids Crocodile of leeches sticking inside its mouth while Shrimp eats up the parasites on the body of fish. Bubalcus ibis Buphagus 33 Pluvianis www.sciencetuts.com Organisms and Populations AMENSALISM It is the association in which one inhibits the growth of other by secreting chemicals. This phenomenon is called ANTIBIOSIS. The process of preventing growth of other organisms through secretion of toxic chemicals is called ALLOPATHY. a) Smoother crops do not allow weeds to grow. Eg: Sorghum, Sunflower, Barley, Sacred Basil does not allow other plants to flourish nearby. Convolvulus arvensis inhibits the germination of wheat seeds. Sorghum Barley Sunflower Sacred Basil Trichoderma checks the growth of Aspergillus, Chlorella inhibits the growth of Nitzschia frustrulum. Tagetus kills soil nematodes. Juglans regia (Walnut) produces allochemic juglone for preventing growth of Apple, Tomato, Alfa alfa, etc. Chlorella Nitzschia frustrulum Juglans regia AUTOPATHY The process of inhibition of their own organisms by an oraganism is called Autopathy. Eg: Grevillea robusta (Silver oak) does not allow its own seeds to germinate. Grevillea robusta (Silver oak) 34 www.sciencetuts.com Organisms and Populations SUMMARY 1. In the nature, different organisms adopted different environments for their survival and reproduction. 2. MAJOR ABIOTIC FACTORS: TEMPERATURE, WATER, LIGHT and SOIL. 3. Generally internal environment is stable in most of the organisms. It is called HOMEOSTASIS. 4. Homeostasis of the organisms is maintained by artificial methods. Living organisms core with the situations by means of various possibilities like Regulate, Conform, Migrate, and Suspend. 5. Adaptations are in morphological, physiological and behavioural in nature. 6. XEROPHYTES: These plants have a thick cuticle on their leaf surfaces and have their stomata arranged in deep pits to minimise water loss through transpirations. 7. ALTITUDE SICKNESS - It is the most important adaptation experienced by the people who move to the high altitudes. 8. DESERT LIZARD – These organisms maintain the constant body temperature by behavioural means. They bask in the Sun & absorb heat when their body temperature drops below the comfort zone, but move into shade when the ambient temperature starts increasing. 9. A group of organisms of similar species belongs to same locality is called Population. 10.Every population expresses certain attributes to survive in the environment. They are: Birth & Death rate, Sex ratio, Age of the organisms and Population size/ Population density. 11. The number of individuals confined to a particular habitat is called Population size. 12.In the nature, the growth of a population with time show specific & predictable pattern of population growth. 13.The sum of abiotic and biotic factors which checks the rise in population size and prevents the species to realise its biotic potential is called Environmental resistance. 14.The life history of an organism depends upon the abiotic & biotic factors available in that particular habitat. It is variable from one species to another species. 35 www.sciencetuts.com