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Module 1: Introduction to Ecology and Evolution

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Introduction to the Course

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Namaste, and welcome to this course on Wildlife Ecology. I am Dr Ankur Awadhiya. Iam an officer in the Indian forest service of the Madya Pradesh Cadre. This course isgoing to have 12 modules, with 3 lectures in each module, we begin with the firstmodule, that is the Introduction to the course.(Refer Slide Time: 00:35)
This module will be having 3 lectures. First is introduction to the course; second is ahistorical overview of ecology and third is ecology and evolution.
(Refer Slide Time: 00:47)
Let us begin this course with a story. This story concerns a girl who lives in a village. Letus call this girl as Miss “X” and she is living in a village. This village is a very beautifulvillage. It is surrounded by some beautiful hills. It has a river that passes through it. Ithas some trees around, some grasslands, some fields and this girl is fond of looking atnature.She is very fond of looking at different kinds of birds that are found in this village. Thereare some flying birds, there are some water birds, there are some ground birds, there aresome parakeets that live on the trees and so on. But, this village also has a lot ofinfestation of mosquitoes and mosquitoes result in malaria, which is a major issue in thisvillage. So, one day the government decides to take a plane full of insecticides to thisvillage and spray this village with the insecticides to kill off the mosquitoes. A very fineidea; a number of people would say so, the chemical that is being sprayed here is aninsecticide, it only kills insects, that’s what the company claims.So, the village is sprayed with insecticides, and lo and behold the girl finds that after ashort while all her beautiful birds that were there in the village die. This story mightappear hypothetical, but we are observing such instances in a number of places aroundthe world. We have seen situations in which the spray of DDT has resulted in the deathof birds. Now, if you spray DDT at a very low concentration to kill mosquitoes, you donot require a very huge amount of DDT. So, you spray this insecticide at a very low
concentration. Still a number of birds die and when their bodies are autopsied, it is foundthat they have a very huge concentration of DDT that is found inside their bodies.(Refer Slide Time: 02:57)
Let us look at another story. This is a paper which says that high levels of PCBs inbreast milk of Inuit Women from Arctic Quebec.PCBs are polychlorinated biphenyls. These are chemicals that are added to a number ofplastics, Inuit women refers to women who have an eskimo lifestyle. Quebec is a placein Canada.So, there are eskimo women who are living in the arctic region of Canada. When theirbreast milk was analyzed, it was found that it had a very high concentration ofpolychlorinated biphenyl. Now, the question arises that arctic is a very serene place. Wedo not go there and dump these chemicals in the arctic, but still, in the human populationthere, we observe that there is a very huge concentration of a number of chemicals; anumber of which are toxic to the newborn babies. Some people have even argued that themost toxic food that a human being can eat is the breast milk of an Eskimo woman that isliving in the arctic regions.How do these chemicals reach there? and is it important for us? Well, it is importantbecause, if you have chemicals in the breast milk, invariably they are going to reachanother human, and in this case, the body of a human baby.
(Refer Slide Time: 04:21)
In certain instances, this may even result in very tragic consequences. For instance, therewas a case in which an infant was killed because it was breast-fed by its mother and themother of the baby was on some drugs. She was taking drugs and the baby died becausethe baby was getting a very high concentration of the drugs. Now questions such as theseare arising everywhere; they are arising anywhere and everywhere on this planet.(Refer Slide Time: 04:55)
And ecology deals with a number of these questions. So, if you look at the word roots,Ecology comes from the Greek words or Oikos and logos. Oikos means a household ;household where people live.(Refer Slide Time: 05:11)
When we say ecology; Oikos is home and logos is study. Now we can see eco as a wordroot also in things such as economics, in which “eco”, or “oikos” is home and “nomy” isto count.Now, ecology is the study of home; it could be my home, it could be your home, it couldbe somebody else’s home or it could be the home of other animals, it could be the homeof tiger, it could be the home of elephant, it could be a marine home and so, on.Because of these word roots, we can have a number of different kinds of ecologies. Forinstance, when we are looking at the population of humans, we can have a subject ofhuman ecology. If you are looking at different population, we can have populationecology. If we are looking at marine environment, we can have marine ecology; becausethe marine environment is also a home to a number of animals; we can have forestecology or we can even have lacustrine ecology, which is a lake ecology. In all of thesewhat we are doing is, we are studying the home of some organisms or some groups oforganisms. That is why it is called ecology.
(Refer Slide Time: 06:47)
Ecology is the study of life at home; at the home of you, me or some other organism. So,if you have to define ecology; ecology can be defined as the scientific study ofinteractions among organisms and their environment.(Refer Slide Time: 06:59)
Essentially, lets say we have a forest and we have some animals here in the forest. Let ussay that we have an elephant in the forest. This elephant would be deriving its nutrientsfrom these trees, or maybe from the grasses below. So, they also act as food; when thisanimal is living in the forest there might also be some other animals in this forest. So, let
us have another animal. Let us say that this animal is a sambar; and this sambar also eatsthis grass. So, we could have competition between both of these animals. The animal,elephant, is interacting with the trees. it is interacting with the sambar, it is interactingwith the number of other organisms and it is also dependent on the environment that ishere.For instance, it would depend on the amount of sunlight that is there. If it is very hot or ifit is very cold, then probably this animal might not be able to live in that area, probablythis animal might have to migrate from this area. Or for instance, if we have a river thatis passing through this area and if this river dries out, this animal is now not gettingenough water so, it might have to move out. Ecology is the study of all of these. Ecologyis the scientific study of interactions among organisms and their environment. In thissystem we have the organisms, we have the environment and we are studying all of theseinteractions.Another definition could be that, ecology is the scientific study of interactions thatdetermines the distribution and abundance of organisms. What we are looking here is thedistribution of animals or organisms and the abundance of organisms.(Refer Slide Time: 09:09)
Now let’s take another example; suppose we have this mountain and in this mountain, atthis level, we have an average temperature of say around 20 degree celsius and as wemove up the temperature reduces.
In this region, we have around 15, 10, 5, 0 and this area has an annual averagetemperature of minus 5 degree celsius. Now, the organisms that are found in this zone,let us call it zone 1, will be very different from the organisms that are found in zone 2and extremely different from the organisms that are found in zones 3, 4, 5 and 6. Now, ifyou look at the definition again, Ecology is the scientific study of the interactions thatdetermine the distribution and abundance of organisms.Now, what we will be asking here in the case of ecology is: What organisms are found inone zone? What organisms are found in the other zones? and so on. And if they aredifferent, why are they different? Is it because of the temperature? Is it because of wind?Is it because of less amount of sunshine that this region gets? or Is it because of lessamount of moisture or differences in moisture that are there in different areas? So, whatare these factors that are determining the distribution of these organisms? and secondly,what are the factors that are determining the abundance of these organisms?(Refer Slide Time: 10:49)
When we say abundance, what we are referring to is that, if we take any of theseparameters; let us say temperature, and we look at the number of organisms per squarekilometer, that is, the number of organisms of species “x” per square kilometer. Now,what we will observe is that there would be a set of temperature in which theseorganisms find it very easy or very congenial to survive. For instance, in the case of us
human beings, if our surrounding temperature is around 25 degree celsius, we will feelextremely comfortable. So, this is the most comfortable zone.But, if we increase this temperature from 25 degree celsius to say 40 degree celsius, alarge number of us might not be able to feel very comfortable. So, there would be somepeople who would find it comfortable, but there would be a very huge number of peoplewho would find it relatively uncomfortable. Less number of organisms would be foundin this region. Let us increase the average temperature to say 60 degree celsius andprobably one or none of us human beings would be found in that region, in thattemperature range.Now, similarly if we reduce the temperature to say 10 degree celsius, you would find thatless number of people are able to do to find this temperature to be congenial. If youreduce it to even less to say zero degree celsius probably very few of us would be able tolive there. So, we can now draw a curve that is something like this (refer slide). Now,this curve is telling us the abundance of human beings that would be found at differenttemperatures. So, there is this zone we are arbitrarily dividing the curve into 3 regions.So, in this zone we will have less number of animals; in this zone we will be havingmore number of animals; in this zone will be having less number of animals; and in thesezones will probably be having zero number of animals. Now, similarly for everyorganism, so for elephant there would be a certain range of temperature in which it willfind congenial to survive. For the case of tigers, there would be a very different range oftemperatures. For polar bears it will be a very different zone. So, in the case of polarbears we could even have a situation in which we have a maximum, somewhere here.Polar bears would probably prefer to live somewhere say around 1 or 2 degrees averagetemperature or maybe even lesser.When we look at ecology, what we are asking are the interactions that are determiningthe distribution and abundance of organisms. So, distribution refers to what are the areasin which these organisms are able to live and abundance refers to what are their numbers.Now, these are physical factors, but we could also have a number of biological factors.For instance, in a forest in which you have ample number of prey animals. So, if youhave a forest in which you have a substantial population of chital or sambar, you wouldfind tigers that are living in that area. But if you have another forest in which we have
very less number of chitals and sambars, then probably tigers will not survive in that areabecause they are not getting enough food. So, you can even have a number of biologicalfactors; or for instance, if you have a forest in which you have a very huge density oftigers, then probably leopards will not be able to live in that area, because they cannotcompete with tigers. Leopards would be found in an area where you do not have a verysubstantial number of tigers. So, you can have physical factors that determinedistribution and abundance or you can have biological factors that determine thedistribution and abundance.(Refer Slide Time: 15:15)
Now, let us recount some of the physical factors. Physical could be things liketemperature or rainfall, or humidity, or wind speed, or the depth of soil that is found inthat area or the amount of sunshine that the area gets, or in the case of marineenvironments we could even have things like the amount of salinity, that is there in aparticular segment of water or things such as the amount of sediment load that is there inwater or in the case of rivers we could even have things such as the speed of water.So, for instance in the case of a river, the central region that has greater speeds would beused by certain organisms and the surrounding regions that have lesser speeds would beutilized by some other organisms. These are all different physical factors that woulddetermine the distribution and abundance of different organisms and ecology would ask
the question, what are these interactions that are driving the abundance and distributionof these animals? Now, let us look at some biological factors or the biotic factors.(Refer Slide Time: 16:49)
Biotic factors could include things such as food. Food could include things like theamount of grass or vegetation that you have or the amount of prey that you have in thisarea. It would also be another biotic factor that would determine distribution, andabundance would be the presence or absence of predators in the area. So, if an area ishaving a very huge population of tigers, then probably chital and sambar would notprefer to live in that area, because they will get eaten if they live there; or you can alsohave things such as parasites or you can have things like diseases.So, a number of these factors play a role in determining the abundance and distributionof the annuals and ecology is the scientific study of all these different factors and theirinteractions that are determining the distribution and abundance of organisms. So, whatdo we actually study in ecology? So, this was the theoretical basis, but what do weactually look at in ecology.
(Refer Slide Time: 18:07)
Well, we look at habitats. Habitat is the home of an animal; the natural home, or theabode of the animal. So, for instance this is the Indian wild ass and this lives in thesesorts of habitats. So, we have this Indian wild ass sanctuary in Gujarat and as you can seethis is a very plain topography area. It hardly has any vegetation in most of the areas.There are some hills that have slight amount of vegetation, then this is a very dry area; ithas a lot of saline soil.So, ecology would go out and study what are the kinds of habitats that are there indifferent areas and how are these different habitats determining whether this organism isable to survive in that area or not. So, for instance we find Indian wild ass only inGujarat, we do not find it in, say, West Bengal, because the habitats that are provided orthat are available in West Bengal are very different from the habitats that are available inGujarat. And similarly, we have the royal bengal tiger that is found in West Bengal, butit is not found in Gujarat. So, ecology would go out and ask the question what are thedifferent kinds of habitats that the organisms get in different areas?
(Refer Slide Time: 19:21)
Then it would go out and ask, what is the amount of biodiversity that we have? Forinstance in the previous image, we saw that we have this Indian wild ass and there arehardly any other animals that are seen here and also the kind of grasses that we have, allthe kinds of vegetation that we have here is very different from say something that wewill find in Bharathpur.Now, Bharathpur is a bird sanctuary and in this area, we will find a number of birds andthis area is regularly inundated with water. So, in this area we will be having a number ofwater birds, we will be having ground dwelling birds, we will be having a number ofbirds that live on these trees, even the vegetation in this area will be very different,because this area has ample amount of water.So, the kinds of trees that will live here will be very different from what we are findingthere in Gujarat. So, the next question that ecology would try to study is the level ofbiodiversity that we have; what are the different kinds of species that are found in eacharea? what is their abundance and distribution? For instance if we look at this area, do wehave, say 1000 birds of this species and say only 10 birds of some other species or do wehave equal number of birds of all of these different species. So, that is also another topicthat is studied in ecology.
(Refer Slide Time: 20:49)
Next, we look at population interactions. Population is a group of animals that are livingtogether and they belong to the same species. So, for instance, in this image we can see atroop of macaques. We have these macaques. And if you look at these two animals, thefirst animal is grooming the second animal. What are the kinds of populationinteractions? How do they behave together? Why do they behave in this manner? Forinstance, What is the profit or loss, or the gain or loss that is being provided to thisanimal by grooming the other animal? ; because in the first instance it might seem thatthis is an act of altruism; this animal is only grooming this animal and not gettinganything in return.Now, such a system might not work in practice. In any case, this animal should givesomething back to the animal that was grooming it. So, how do these interactions workin these populations how is this animal able to give back to the first animal, are the kindsof things that we will study in ecology.
(Refer Slide Time: 21:59)
Next, we look at community interactions. Now community is a group of organisms thatbelong to different species and they are living together. So, for instance in this imagefrom Kaziranga, we can see we have a buffalo, we have some scavengers in the form ofvultures and then we have a number of different trees here of different species.Now, community interaction means, what are the kinds of interactions that are being heldbetween say this buffalo and the scavengers or between the buffalo and the trees and soon. For instance, in a number of trees, we have a phenomena that is known as zoophily.(Refer Slide Time: 22:41)
Now in zoophily. “zoo” is animal and “philly” is love. Now zoophily is a situation inwhich you have a tree and this tree bears fruits and then these fruits are eaten up by abird and when this bird eats up this fruit, it gets nutrients; but at the same time the seedsalso get inside the bird.So, now the seeds of the tree are inside this bird and then this bird moves to some otherlocation. Let us say there is an electricity line, and this bird goes there and then itdefecates these seeds out here. When it defecates, you have all these seeds that havefallen onto the ground and then after a while after the next rains, we will have somesmall plants of this tree that grow up in this area.In this case this tree is using the bird as a vehicle to transport its feeds. So, “zoo” isanimal, so it is using this animal which is the bird to transport its seeds. So, again in thiscase we can see that there is a one to one interaction or a give and take relationshipbetween both of these organisms. The tree is giving food to the bird and the bird isgiving a transport mechanism to the tree.So, here we have organisms that belong to two different species and they are interactingin a way that is mutually beneficial to both of these. Similarly in this situation, if we havethe buffalo, is it helping the trees? or is it harming the trees? or some other vegetation.Similarly, if you look at these vultures, are they helping the system? Or are theyharming the system? and how are they doing that? These are the kinds of interactionsthat we observe in a community and this is also a topic of study in ecology.
(Refer Slide Time: 25:07)
Now, ecology also looks at the impacts or the effects of different changes that arehappening on our earth. For instance, this is an image again from Gujarat and here wecan observe a number of goats and as you can observe, here we have these sand dunesand we also have very scanty vegetation.Now, if you have vegetation somewhere, the roots of the plants are able to bind the soilor are able to bind the sand in this region. Now, if you have goats and if you have a largenumber of goats that are growing there and eating away these plants, what will happen ina short while is that, after these plants get removed the sand will be able to move freely.Because it is now unbound, you will have a situation in which the amount of erosionwould increase in the system, or for instance earlier this area was having some vegetationand so, we had a situation in which this area is a semi-arid area. But once you haveremoved all of these plants, you do not have any further seeds that remain in this area,this area will become completely barren. It will become a complete desert.So, things such as these; things such as desertification that have been brought about bysome human activities are also topics that we study in ecology. Effects of changes; theseare also topics that we study in ecology, but how do we study them?
(Refer Slide Time: 26:41)
There are three approaches to ecology. The first approach is called the theoreticalapproach. In the theoretical approach, we use equations and models in an ab-initiomanner to understand what is going on in the system.(Refer Slide Time: 26:59)
For instance, to give an example, you have a predator and you have a prey population.Now, if the number of prey increases, then we will observe that the number of predatorswould also increase because they are getting more amount of food, and because they aregetting more amount of food they will be able to devote more resources to reproduction.
So, an increase in the prey population would increase the predator population. But, if youhave more number of predators, because of this increase, it would provide a negativefeedback. So, a negative feedback to the prey population will be seen, because you havemore number of predators.These predators would be again preying upon the prey population and would reduce theirnumbers. So, this would reduce it down. Now if this number reduces, if the number ofprey animals reduce, that would again go back and reduce the population of the predatorsand when that number reduces that would again give a feedback that would increase theprey population.(Refer Slide Time: 28:17)
To put it in other words, if you have more prey that would give you more predators.Now, if you have more predators that will result in more number of prey animals beingeaten up, which would result in less prey. Now, if you have less prey, you will have lessamount of food that is available to the predators. That would result in less number ofpredators, because less number of prey population is able to support a lesser number ofpredator population. Now, if you have less number of predators, the prey would be ableto increase. So, then we would be having more number of preys. Now this is somethingthat we can understand intuitively.
Now, if you go to the theoretical approach, it would begin with such a framework andwould then go on and define different equations and different models through which wecan understand the system.For instance, if you have prey population that is represented by “p” and predatorpopulation that is represented by “P”, theoretical approach would ask that, if you havethis prey population, it would be a function of the predator population and the existingprey population, and what would be the equation through which we can model this
system. We will have an example. This system is governed by what we call as the Zotka-Volterra equations and we will have a greater look at this system in more detail in one of
the later lectures.Now, the second approach to ecology is the laboratory approach. Laboratory approachuses the scientific method of formulating hypotheses and testing them throughexperiments.(Refer Slide Time: 30:21)
To give an example; suppose we have this area. Suppose this is a pond. In this pond weare having very less amount of algae. Now the question that we could ask here is, Whatare the factors that are limiting the algae population in this pond? Here again we arelooking at the abundance and distribution of an organism, in this case, the organism isalgae. Now we are asking the question, What are the limiting factors in this pond becauseof which the population is less?
What we can do in this case is that we can divide this pond into different regions; we canset up curtains. Once we have set up these curtains we have these different regions