noc18-bt26-Lecture 05-Preliminaries

[Music] [Music] so let us now begin with our first lecture of the module which is preliminaries the first question that we need to ask is why do we need to assess the number of wildlife and there are a number of reasons for that one numbers are essential at every stage of management now classically management is said to follow the Deming cycle now Deming cycle consists of four stages it goes by the name of PD CA cycle which means P is for plan followed by du followed by check followed by Act and followed by plan again now what do we mean here plan means to take all the steps and the decisions beforehand on what we want to do why we want to do that and how are we going to do so when we answer all these three questions this is the planning stage the doing stage is the actual execution of work now to take an example suppose you have a forested area which also has a thick undergrowth of weed so one of our management interventions could be to remove these weeds so our aim is to remove weeds now why do we want to remove these weeds because these weeds are of a non palatable species and because the animals are not able to utilize this is peace now so what we want to do is to remove the weeds why we want to do it so that more animals can utilize this space and how are we going to do it maybe say using a manual labor to uproot all these weeds now once we have decided that once we have decided on how much amount of work is required at what rate we are going to pay these laborers and things like that will actually execute the work on the field now while doing this execution there might be some other impacts that we had not thought of beforehand so for instance when we went there with our laborers and we saw that most of the animals are just running away from the field now this is something that we had not expected beforehand so which is why we'll come to the checking stage so while we are doing our work will be checking our work again and again and again just to see whether we are able to to reach our outcome of the animals being able to utilize this space in a more effective manner now checking means that we are will look at how many animals are utilizing this area when we are doing this work and also after we are done with our work and then this check will be followed by act now act actually means that we'll utilize our knowledge of the checking stage to incorporate it into our next planning so for instance if you have a last chunk of forest maybe we are doing our weed removal in this a small patch and once we have we are done with the bead removal in this patch will utilize the knowledge that we gained from our exercise to plan the vida movin in summary some other area so which is the acting stage now numbers are crucial inputted all of these stages because when we said during our planning stage that we wanted to remove these weeds so that animals would be able to utilize this area in a more effective manner and because animals are not utilizing this area in an effective manner because of the presence of the weeds so in that case what we need as our baseline information is how many animals are there in this weed infested area say in a in a per hectare format while we are doing our work while we are executing our work will also incorporate data about the weeds that are being removed the rate at which we are removing the weeds the time it is going to take to remove these beads in a patch of area and we'll also need information about what the animals are doing in this period of time in the checking stage so once we are done with our weed removal we again required data was this patch once we have removed the weeds from there is this patch being utilized by the animals in a more effective manner so essentially if we said if we found out that our baseline with the presence of feeds was say 15 animals per hectare and after removal after we have removed all these weeds and after the animals have gotten inside and are utilized in this area this density moved up from 15 animals per hectare to say 100 animals per hectare now this is an information which will be extremely crucial when we are doing the next stage of planning so essentially wildlife numbers are required at every stage of Management now second point why we need to assess wildlife numbers is that numbers are crucial inputs for decision support now what does this mean suppose we are managing a tiger reserve and suppose we have the density of the herbivores at say 50 animals per square kilometers now is this 50 animals per square kilometer good for our tigers in the tiger reserve do we need more number of animals do we need less number of animals because if we have less number of herbivores - less prey population so our Tigers will not be able to reach their optimal density so we will need to increase the numbers of the herbivores on the other hand if we have a situation in which we have quite a lot of herbivores in our area so we already have a huge density of tigers which is leading to more and more fights between these tiles so we will need to reduce our prey density now do we need to increase our prey density or do we need to reduce our prey density or do we need to keep our prey density as constant will able to gather information about it only when we know their numbers so we need to know the numbers of the herbivores we need to know the numbers of the tigers at the same time numbers also help us assess the risk of a population decline or a crash so as we have seen beforehand in another lecture if we have a population that is very small will have a number of stochastic phenomena that will become dominant in that area now stochastic phenomena means chance events so a chance event essentially means that earlier if we had say 1,000 animals so suppose we had a huge population size of our animals suppose we had 10,000 animals and every year this pool of 10,000 animals is giving rise to say 1,000 young ones now considering a sex ratio of one male is to one female which is naturally found in most of the situations we can say that out of these 1,000 individuals see around 500 would be males and we'll be having 500 that are females and in in such a scenario all of these animals would be able to to mate properly because they have a nice sex ratio but considered we have only say 10 animals left in our reserve and these 10 animals gave rise to say two young ones and these 10 animals are now growing old and so our population growth is only dependent on these two young ones now even though we say that our sex ratio of 1 is to 1 would mean that we would have on an average one male and one female but because here we have such a small population size it is also possible that we got two males or two females now if we have say two males and we do not have any more females then this population might be leading into a crash similarly if we have only females left if you do not have any means the population will not be able to grow so these kinds of phenomena are known as stochastic phenomena and at small population sizes we have different stochastic phenomena as you can see on your sites now so we have demographic stochasticity now the demographic stochasticity means demo is your people graffia is to write demographic stochasticity is a stochastic city at the level of your population numbers so here you can have chance variations in births and deaths leading to more deaths and less births for instance so in a very small population if more number of individuals died out so you will be having a population crash trans variations in sex ratios as we saw in a population with all males or all females or even environmental stochasticity such as draught flood famine or diseases now if we have a large population of animals then these stochastic these environmental stochastic phenomena like draught so floods do not have a major impact because if we have say 10,000 animals and the draught killed as many as say 5,000 animals we still have 5,000 animals left but if we had a very small population say of ten animals and if draught occurred and say nine of these animals died we'll be left only with one animal which will again not be able to breed and the population would be towards a crash another stochastic phenomenon as you can see on your sides now is genetic problems such as inbreeding depression now inbreeding depression occurs when your animals are meeting with their closest relatives so for instance if you have a very small population say you have only two individuals left now these two individuals after they have mated they would produce an offspring and because we have very less number of individuals left now the next level of mating would be say between the parents and and their children or maybe between those children themselves which would be a case of inbreeding which also leads to a number of genetic problems also genetic problems could include genetic drift of small populations so this is something that will can we'll discuss in more details in the conservation genetics module and also the loss of heterozygosity at the same time when you have very small populations you also have behavioral problems and ill effects so for instance consider the case of pack-hunting animals consider the case of wild dogs now in the case of wild dogs you have a large sized pack and say ten to fifteen animals go to hunt at the same time now in such a scenario if you have a population in which you have only five animals left and these animals are adapted to pack hunting so they required say 15 animals to hunt and you are left only with five animals so these five animals will not be able to hunt sufficiently or efficiently enough so that they would not be able to to gain enough amount of food so this is another stochastic phenomenon that will happen another thing that happens when you have a very small population size is that the animals are highly dispersed they are unable to find a mate so you have a large size forest and in this forest you have an a male here and you have a female here but just because their densities are so less they are not able to find each other and so they are not able to mate which generally have happens when your population densities are very less another situation when we are required to assess wildlife numbers is because numbers help us plan scenarios and take steps so if we know that our population is going down we can take steps and these steps could include adaptation steps and mitigation steps now the difference between adaptation and mitigation is that mitigation tries to remove the root cause of the problem whereas adaptation tries to acclimatize your population so that even that even when that root causes present you are able to cope with it to give an example from a very different field when we talk about climate change adaptation and mitigation so climate change mitigation would mean that we'd reduce the amount of carbon dioxide that we are putting into that maas field or we increase the amount of carbon dioxide that we are taking out of the atmosphere so that is mitigation because the root cause that is the presence of carbon dioxide in the air that is being addressed on the other hand adaptation would mean that even though we have carbon dioxide in the atmosphere even though we are having global warming we want our populations to adapt to it so that would include installation of say both number of air conditioners is construction of more number of dams so as to be able to cope with the situations of draughts and things like that so when we have numbers we can plan scenarios even for our by life and we can take steps for them another question that we need to answer is do we need numbers or do we need trends so what do we mean by numbers and trends so for instance in our Tiger Reserve suppose we have 50 Tigers so this number 50 would be and the number of Tigers but if we say that say 10 years back we were having 70 Tigers and now we are having 50 Tigers so we are having a downward trend so if we do the number of Tigers versus the years earlier we had 70 Tigers now we have 50 Tigers so this downward sloping graph would give us the trend that this is a decreasing trend on the other hand we could also have an increasing trend so earlier we had 70 Tigers now we have 90 Tigers at the same time we can also have a trend of status quo in which earlier also we had 70 Tigers now also we have 70 Tigers so do we need numbers or do we need trends so actually we need both of these why because in most of the situation's it is easier to find out trends and it is more difficult to find out numbers so trains help us gather information in a very short period of time but numbers are also important because they give us fine resolution of data so for instance in our Tiger Reserve we have tigers and we also have herbivores in the case of herbivores it does not matter much whether we have say 10,000 herbivores or we have 10,000 100 herbivores because the purpose of having a large population of herbivores in our Tiger Reserve is to act as a pre population so in the case of herbivores it would be worthwhile just to know their trends whether this figure is close to ten thousand or whether this figure is going down drastically or whether this figure is increasing drastically so that course level of information is good for us but for other animals such as Tigers which are already in a very small numbers we need to know the actual number of tigers that are there in that area similarly with other animals such as the Dewgong or the sea cow we or we have only a few scores of sea cows left in our ocean and so it is extremely crucial that we know the correct numbers and even a single individual counts in that scenario another point to keep in mind between numbers and trends is that with the numbers you can always figure out the trends but not vice versa so for instance if I say that my trend has been increasing for the last 20 years and now I have say 20 thousand animals it is very difficult to to to use just this data of an increasing trend without knowing the actual numbers to back calculate the number of animals that were there beforehand but on the other hand if we knew that the number of animals in different years was say five thousand five thousand five hundred six thousand and say year 2000 2005 and 2010 so if we have these numbers where you can very easily see that we are having an increasing trend so it is very easy to find out the trends from the numbers and not vice-versa now the next question is what are the kinds of demographic information that we are trying to get from our counting of animals just a mere count of the number of animals is not enough we also need to know a number of other demographic parameters one is the population size or the number of individuals that are there in the population and this is one figured that we directly get out of our counts from the population size if you divide the size by the area you will get the population density so it is generally in per unit per hectare or per square kilometer or in some animals which have an even lesser density we we generally make use of per hundred square kilometers next is the H pyramid so the H pyramid tells us the distribution of various age groups in the population which also tells us whether our population is young population whether it's an old population whether it consists of a number of adults because if our population consists of mostly old animal spin it might suffer a crash in the near future then we have the crude birth in death rates which tells us the number of life or death or dead birth the the number of live births or the number of deaths per 1000 individuals of the population we also need to know the general fertility rate so general fertility rate tells us the the annual number of live births per 1000 females of reproductive age in the population then we also need to know the age specific fertility rate which is the the annual number of live births per 1000 females of a specific age class in the reproductive age so in this case we can say for instance what is the age specific fertility rate for females of ages between 5 and 7 years in a tiger population then next we have the total fertility rate which is the average number of live births per female individual completing her reproductive age if she followed the current age specific fertility rate of the population so essentially we are integrating the age specific fertility rate data to get the total fertility rate the next very important information is the replacement level fertility now replacement level fertility means that when you have a male and a female that have mated how many offsprings are do they need to produce so that they are adequately replaced by the next generation so the average number of offsprings that a female individual must produce such that the population is completely replaced for the next generation and the replacement level of fertility is generally greater than or equal to 2 now what this means is if you have a male and a female and throughout their lifetime they are only producing one offspring so in that case if our population in this generation as 1000 individuals in the next generation it will become 500 individuals because out of every 2 individuals there there is only one individual that is being produced on the other hand if you have a replacement level of fertility which is equal to two so that means that every for every Bale and female they are producing two offsprings so they are getting completely replaced in the next generation but then why do we say that the replacement level of fertility is greater than or equal to two now this is because a number of offsprings will die before reaching their reproductive age so if you have juvenile mortality or infant mortality so this number would be greater than two now juvenile mortality rate is the annual number of deaths of juveniles per 1000 live births now here it is important to note that this is one thousand live births and not one thousand births life expectancy is the number of years that an average individual in the population at a given age could expect to live at the present age specific mortality levels other information include immigration which is how many individuals are coming from outside into our population emigration which is the number of individuals that are going out from our population into some other population net migration which is emigration - emigration naturally increase which means in the case of national increase we do not consider migration into account so naturally an increase is the number of births minus the number of deaths population growth which is births minus deaths plus immigration minus emigration so it's births plus immigration minus deaths minus emigration so essentially how does our population grow our population will grow if we have any births in the population or if there are more animals that are coming from outside now our population would reduce if there are deaths in the population or when the animals are moving outside so when we considered all of these four together we get the population growth from population growth we can also figure out the population growth rate when we divide it by the size of the population over a fixed time period it is generally expressed this percent per annum now the next concept when we are estimating animal numbers is absolute and relative estimates of animal numbers now absolute estimates of animal numbers the size of the population or its density by actually looking at the animals or their cues such as nest so examples include point counts and discipline sampling and they generally require more effort than relative estimates and relative estimates on the other hand do not count the actual population rather they utilize proxies to estimate animal densities in unknown units so essentially what we want to say in this case is that suppose you wanted to figure out how many fishes are there in a pond now absolute estimate of the animal number or the number of fishes would actually involve taking a sample of fishes from that area and counting the number of pitches that are there in the sample and then extrapolating it to the whole of the area on the other hand a relative estimate of the number of fishes would include just say going into that that pond fishing for say two words and if I did a fishing now and suppose I caught hundred fishes now I do this experiment again I go to the pond again and then I again fish for the same amount of time and in pace of 100 individuals I gots a hundred in ten individuals so a relative estimate of animal numbers would say that the number of animals in pond two is greater than the number of animals in point one so relative estimates permit comparisons over space and time they're useful when doing extensive works when actual number of individuals in the population are not required and rather trends are all that we are looking after so let us now have a look at some of the common techniques of estimating population abundance so some common techniques are complete census now in a complete census you count each and every individual of the animal species that is present in your area so this is generally utilized for those animals that are already in very small numbers so for instance in the case of dugongs or the sea cows will have a complete census of the number of individuals that are there plot sampling now in the case of a plot sampling what we do is that out of our complete forest we take some small plots so they can be rectangular plots or they could be circular plots or they could be even be our strip plots so we take some plots suppose the areas are a1 a2 a3 and a4 and the total area of our region is capital a now the number of animals that we have in a1 as n1 here we have n2 here we have n3 here we have n4 so we did not count the total number of animals in our complete forest but we only counted it in four of the sample plots in that case the total number of animals in the sample plot which is n will be n1 plus n2 plus n3 plus n4 the total area a of all the four sample plots would be e 1 plus a 2 plus a 3 plus a 4 in which case we'll get the density of animals which is the number of animals per unit area is given by sum of Ni divided by sum of AI and then we'll extrapolate this density to the whole area so we'll say that the density of animals that we have found using our 4 sample plots is the same as the density of the animals and our complete forest so we will have D is equal to D now this small D we can calculate because we have the n values and we have the AI values and we have this assumption that capital D which is the density of animals and our complete forest is the same as the density of animals in the 4 sample plots in which case to find out the total number of animals in our forests we'll multiply this capital T with the total area e to get the number of animals so this is plot sampling now distance sampling is another technique in which which takes a modification of a plot sampling and also in suits the data that not all the animals are counted so there could be some animals that we melt out during our counting's and when we incorporate that data in in our formula we get into the distance sampling next we have the capture mark recapture method sometimes we cut curly Yampa so let us now understand the capture mark recapture technique by doing the small experiment so in this jar we have some chickpeas and we do not know the number of these chickpeas so we'll perform the the capture mark recapture method and I will show you all the steps to to make an estimate of the number of chickpeas that are there in the jar so we first begin by doing a capture of some animals so we took out some animals these chickpeas and here we have 1 2 3 4 5 10 15 20 so we have 20 animals here let's take a few more so we now have 25 animals so we have captured these 25 animals next we mark these animals so let us mark them with a filter pin so I am marking them with a black color so in the field what we do is this marking say in the case of birds would be done by putting small bands into their feet in the case of butterflies it would be done by putting small stickers on their wings in the case of ants it would be done by spraying them with some colored dyes and so on now the important thing to note here is the number of animals that we have captured if the number of animals that we have captured is very less then our errors in the estimate would be great whereas if the number of animals is more then we'll have a much more correct estimate of the total number of animals in the forest so now that we have marked all our 25 animals we now release them back into the forest so we put them back into the jar remember we had 25 animals so 25 marked animals and then we let them roam freely and make sure that the mix with the other animals so now that we have mixed these animals now let us take out a sample so we do a recapture of the enemies and now let us count the number of animals that we have 5 6 7 8 9 10 15 20 25 30 35 40 45 47 50 54 now out of these 54 animals we have 5 5 10 13 animals so we took out these samples of 54 animals and out of these 54 animals we have 13 animals that are marked so now let us do the calculations so let us now look at the experiment again so in the first case we took out n1 number of animals which were 25 animals and we marked these animals in the next stage we took out into animals which is 54 animals and out of these 54 animals we found that 13 animals were marked now if we have 13 marked in 54 animals this ratio would be same as 25 marked in the total n animals that we have in our forest because we are taking the assumption that these animals have mixed up completely they have not lost any marks and we were able to see all these marks very clearly so from this let us find out what is n so n is equal to 54 into 25 divided by 13 so from here we get the value of 103.8 animals so this is the estimate of number of animals in the forest which in our case means the total number of these chickpeas that were there in the jar now I asked my associate to count the number of chickpeas in the jar and he came up with the figure of 100 chickpeas so there were actually 100 chickpeas and our estimate is one hundred and three point eight which is a very close estimate so coming back to the slides captured mark-recapture method is a very fast method of knowing the total number of animals that are there in our forest now another method is the removal method now removal method is not generally used in our country but it is generally used in those countries which perform hunting operations so essentially if we take the data from hunting and over the years the number of hunts if it has remained constant so we would say that our population has remained constant but if with the same amount of hunting effort our number of hunts is going down then we would say that the actual population is also going down because of which we are getting a lesser density of the animals so which is briefly about the removal method but it is not quite applicable to our country because we do not permit hunting so there are ways and means to decide which technique to deploy in different scenarios which is something that you might have a look at but it is not extremely crucial for this particular course now the next concept is what is the difference between precision and accuracy so for instance if we are doing any experiment if we repeat that experiment again and again we'll be getting different figures from that experiment from those figures we can figure out two things one is precision one is accuracy and to understand that let us look at the results of this experiment so we have a shooter and we have this bullseye and these dots represent where these bullets meant into the into the board now if we look at this shooter so she fired five shots all these five shots are centered at the bullseye and all these five shots are together now if we know the correct value now the correct value in this case should be the bullseye if the average of our values is close to the correct value we will see that the results are accurate so here the results are accurate here even though the shots are very far off but still we can say that the results are accurate because the average of these five would fall somewhere here but in this case the results are not accurate because they are at a quite a distance from the actual correct figure which should be this and in this case also the the results are not accurate because we will be seeing it at a distance so accuracy is how close our result is to our correct figure so basically in the case of our capture mark-recapture experiment we had the correct figure of hundred animals but we got a figure of 103 point eight animals from our experiment so our figure is less than four percent away from the actual correct figure so we would say that our results are pretty accurate now the next thing is about precision precision is how close are our values to each other so essentially if you look at these values even though these values are not accurate all these five values are close together similarly here also the five values are close together so we will say that both of these are precise results on the other hand these values are very far off from each other these values again are very far off from each other so we would say that both of these results are not precise now coming back to our experiment suppose we did this capture mark-recapture experiment again and in place of 103.8 we got a figure of say 102 or say 105 so we are doing these experiments again and again and we are getting these values of the first value was 100 and 3.8 the second value was say hundred and to 105 say 98 and 99 we did this experiment for five times on the other hand we did this experiment again in another scenario the first figure 100 in 3.8 the second was say 150 then 250 and say 100 now in this case all these values are close together the lowest values 98 the highest value is 105 which is a difference of only 7 points in the second case our lowest value is 50 our highest value is 200 so the difference here is 150 the difference here is 7 so we would say that these values are more precise as compared to these values and coming to the accuracy if we take the average of all these five values if they are close to hundred we would say that these values are accurate else not so this is the difference between precision and accuracy another concept that we need to know is bias so what is bias bias is the difference between the mean of the measured values and the reference value or the true value so if the if the reference value is the true value then the bias would indicate the error of measurement so in this case let us again go back to our shooter example so our shooter shot five shots these shots are very precise because they are all close together but they are not accurate they have a difference be between them and the correct value so this difference B would be called the bias now whenever we have a bias in our results so in those situations what we do is we calibrate our instrument or we calibrate our method so in this particular case the shooter might be having a bend in her in her gun so if and that bent in this case is towards the right and towards the upside so even though she was targeting this point the results came here because the gun had a bend like this so when we calibrate our instrument we counter for this bias and we ask our shooter to shoot somewhere here so if she took a target here she would come to the correct value and similarly with all our methods of measurement we would be having some or the other bias which would need to be calibrated so that's all for today thank you for your attention [Music] [Music]