 Basically, there are two types of populations, semiparous populations and atheropyrous populations. Semiparous populations, individuals, or organisms under this category, have only one reproductive period during their life cycle. So in one reproductive period, they produce large numbers of individuals, like thousands of individuals. So they do not exhibit age structure because individuals in the population are of the same ages. Examples of these are animal plants, like rice. Whenever, during rice-cropping season, the seeds are sown at the same time so that the seedlings, the flowering stage, would be of the same age. And so they do not exhibit age structures. Other examples would be insects. The adult insects lay in mass of eggs by the thousands. Then the adult dies. Then the eggs are hatched, produce larvae, and then transformed into pupa, and then to the adult. But all of these individuals in the population are of the same ages. So they do not exhibit age structure. The other type of population, the atheropyrous population, are the ones that exhibit age structure. These are organisms that have several reproductive periods in their life cycle. And in each reproductive period, they only have only few individuals, one or two, or at most ten. The examples of these are mammals. We humans are mammals, and we have several reproductive periods. So a woman give birth to one at most five quintuplets. But normally, we only have one newborn infant at each reproductive period. So that the individuals of our population belong to different ages. And so we exhibit age structure. So in this particular part of the lecture, we are going to show you the age structure of the Philippine population as of 2016. Our population is estimated to be 102,250,000. And the natural increase that is by birth would be 1,724,603 individuals per year. That is 4,396 new infants are born daily. The net migration is about negative 144,883 people. So these are our OFWs and all those that are migrating to different parts of the country, different parts of the world. There are, in the diagram of the age structure, you'll notice that you have the male and female segments of the population. And then the age structure would be divided into different ages. So at the bottom would be 0 to 4 and so on. And at the top would be our age and population, or the very old. Now there are three ecological periods. The first would be the pre-reproductive period, which is from 0 to 14 years old. And at present, there are about 35 million individuals of which 17.2 million are female. The rest would be male. And the median age would be about 24 years. The second ecological period would be the reproductive period, which would be from 15 to 49 years old. So this is a very important segment of the population because these are the ones contributing to population increase. Our density at the moment is 383.3 people per square kilometer. And that would be the average from different parts of the country. The third ecological period would be the post-reproductive. And that would be from 49 to over 49. It means that the individuals have already reached the period when they can no longer give birth. Now it's very important to understand the meaning of these ecological periods. It means that with the reproductive period from 15 to 49, there are about, at present, there are about 30 million women. And if this 30 million women are the ones that are responsible for increasing population. Now, in ecology, one way of effective way of decreasing population growth would be to increasing the age of women bearing children. We have mentioned that the start of the reproductive period is 15. If we increase 15 to 25 through education and counseling, we are actually lessening the period of reproduction from about, let's say, from 49 minus 15, or let's say 45 minus 15, that's 30. If we increase the age of women bearing children from 15 to 25, we actually subtracted 10 years of reproductive period. So that's a very effective way of decreasing population. Let's say, for example, in 10 years that has been removed from the reproductive period, a young woman can already give birth to three children. That is, if the birth would be every three years. Imagine that from 15 to 45, 30 years of reproduction, a woman can already give birth to about 10 children. But if you remove 10 years, that's already 10 minus 3. So the potential of the woman to give birth is only to give birth to seven children. That's how effective increasing the age of reproduction for women. Another important aspect that we can get from the age structure is what we call age dependency ratio. In the diagram, we can see that about 34.6% are young children aged from 0 to 15, and these 15 years old. And they constitute about 35 million. And those that are over 65 years old constitute about 4.3 million population. These two periods are the 0 to 15 years old, and over 65 years old are dependent on the productive period, the 16 to 64 years old, which is about 62 billion. These 16 to 64 years old are the productive sectors of the population. They are the labor force that support themselves, but also the expenditure of children and the aged person. In the Philippines, at now, half of the working population is only about 39.3 million. So these are the segment of the population that are supporting the very young, the children of school age and the old, who are already retired. Now, child dependency ratio in the Philippines is about 57%. To be exact, it's 56.7%. So it means that those in the productive period, about 62 million Filipinos, are supporting the children and the aged. That's on the part of the family. The Philippine government also has investments on this segment of the population that are dependent on the productive sector. In the case of the education, our government has to build more classrooms. We can see that here in this figure, we have a crowded classroom in public schools. You can hear from the news every start of June of this year that we lack classrooms and that there are some classrooms here in Metro Manila where in one classroom or one class has 65 pupils or students. That's very crowded and that's an implication of high population growth. So it's both on the part of the family supporting the young children and on the part of the government and that's what we call age dependency ratio. Now, high population growth is also closely linked with economic development. There is the issue of unemployment and high dependency ratio, which I just discussed, but this is also related to exploitation of our natural resources. Now, Porter and Ganapin in 1998, it's a world research paper number four. In 1998, Porter and Ganapin stated that in the 70s to 80s, which are actually the martial law years, there was rapid population growth and the type of governance that we have is what was described by the authors as elite-centered political system. And the development strategy is what is known as ecologically and socially flawed. Now, why is this so? Because the people who do not find employment are dependent for livelihood on the natural resources, which are our forests, our agricultural lands, and our coastal marine ecosystems. And the result of this is massive deforestation and destruction of the coastal marine resources. So environmental degradation hurts more the rural poor because they are the ones that are dependent on natural resources for livelihood. So let's go back to the 1970s. At that time, we have only 35,680,000 population. But if you look at the age structure, notice that it has a very, very broad base. And then the rate of increase is about 2.98% or r is equal to 0.0298. That's a very high population growth. And the median age at that time was 17. So we have a very young population at that time. And most of this, those who are entering the labor force cannot find jobs. And so they have to depend on natural resources for their livelihood. In 1996, from 1970 to 1996, our population doubled. From 35 million, it ballooned to 71,437,000. So the doubling time was only 26 years. And at that time, the rate of population growth was 2.43% or r is equal to 0.0243. And the median age was 20 years old. The fertility rate is 4.14. We'll discuss the fertility rate in a few minutes. Now notice also, again, that the base of the population, especially those belonging to the reproductive age from 0 to 14, is still very broad. And we experience rapid population growth. So that here in this slide, we'll see the rate of deforestation as pictured in the Philippine Forest Covert, as cited by Suarez and Sahise 2010. But it was from the article of Moya and Malayang in 2004. Notice that the forest cover in 1900 was about 30 million hectares. We have a total of 30 million. The forest cover in 1900 was 20 million. Now, in the 1960s to about 1990, from about 18 million that was in 1960s, the forest cover dropped in 1990 to only about 5 million hectares. So this is what we mentioned earlier as massive deforestation. And why? Because our destruction, the destruction, was primarily due to conversion of the forest cover to agricultural lands, because there is a need to raise more food for increasing number of mouths to feed. At the same time, our lugs were exported to generate foreign exchange. You have the forest also converted to residential areas. So you have agricultural lands that were converted to housing, to subdivisions. And then the people have to open up the forest to in exchange for the agricultural lands that have been converted to subdivisions. At the same time, mining operations, again, to raise foreign exchange and also to generate jobs, are contributing to deforestation. So notice that here, the livelihood of our people because of lack of employment, they are dependent on the natural resources, one of which would be the forest. Now deforestation has many ecological consequences. One of that would be habitat destruction that leads to loss of biodiversity. The Philippines is one of the mega-diverse countries in the world, but we are losing such biodiversity. Now one important consequence of this high-population growth and flawed economic development is the destruction of fishery resources and marine environment. Primarily due to increasing pressure, as more and more people use this as livelihood. And that's the reason why in the next segments, we featured the echo-tipping point of the Apo Island fish sanctuary, how we are able to reverse this kind of destruction of fishery resources. Now not only that, environmental degradation led to pollution of air, water, and land. Now there are many contributing factors to environmental degradation. We have population pressure, I keep on mentioning that, high-population growth, poverty, lack of livelihood opportunities, and what is known as open access of bio-resources. Now open access means there is very poor regulation in the use of natural resources. Almost everybody can exploit the resources. There is very weak governance in the use of these natural resources. This resulted in over-harvesting of commercially timber species. That's the reason why we are losing our endemic dipterocarp trees. We have lost much of our mangrove ecosystem. The mangrove timber has been used for fuel wood. There is over-collection of our orchids. By the way, we have 95% endemism in terms of orchids. We have over-collection of ferns, insects, birds, mammals, the shellfishes, and destruction of our coral reef ecosystem. Animal products are also over-exploited. They are gathered such as the verseness, the guano, the honey, the beeswax, and even the animal skin. Aquarium fishes, these are the ones that we usually culture in aquarium. They are collected from the wild in the marine ecosystem. And destructive method, just like the use of cyanide, was used to collect these aquarium fishes that led to exploitation and degradation of our marine ecosystem. There was no control on logging, and there was over-harvesting. Of course, you have the illegal fishing, such as I mentioned, cyanide fishing, in order to capture the aquarium fishes. As a result of the massive forest destruction, there is severe erosion that results to landslides and many other catastrophic events that we experience and witness in the recent years, especially with climate change. So we have flash floods and the rain events as a result of climate change. Now, what are the government actions? I just would like to point out two important government actions. In 1995, during the presidency of President Fidel V. Ramos, we adopted the Sustainable Economic Development. And then very recently, during the term of President Aquino, the third, there is the passage of the Reproductive Health Law in 2014. Now, let's move to TFR. TFR means total number of children completed by a woman over her reproductive years. And the TFR, or total fertility rate, is highly influenced by social factors, such as women literacy and economic well-being. There is a study that educated women have less children than those with women in low educational attainment. And women that are gainfully employed and therefore would have high economic well-being would tend to bear also less number of children. In 2016, our TFR is 3.1. That means that on the average, a Filipino woman bears about three children. That's on the average. Of course, there are those that would bear six or more, but there are also those who would have only one child. And 3.1 children remains one of the highest TFR in all of Southeast Asia. So we really have a very high population growth. Now, take note that in 1996, the fertility rate is 4.14. It means on the average, a Filipino woman at that time would have four children. But in the 1970s, which I have pointed out earlier, the fertility rate was very high. On the average, at that time, a Filipino woman has 6.5 children. And that's because our population growth at that time was about 3%, 2.98%. Now, we have already our reproductive health law. We are aiming for ZPG. And what is ZPG? Zero Population Growth, where TFR, Total Fertility Rate, is about 2.2. It means that on the average, a couple will have only two children. OK? In based on our current population growth, which is about 0.07%, R is equal to 0.074, by 2050, we'll be able to attain ZPG. And the population at that time is predicted to be 148,264,778. So when we say TFR, 2.2, it does not mean that there will be no new infants born. There will still be new individuals. But this is what we call replacement fertility level. Because two children would mean that they will only be replacing their parents, the father and the mother. So this is ZPG because there will be very minimal increase. The population will be maintained. 2050 is 148,260,478. Our population would be maintained around that number. But at that time, 2050, the population density will already be 497 people per square kilometer. Remember, in the previous slide, our population density is only around 393. So by 2050, it's almost 500 people per square kilometer. That is what it means with increasing population and moving towards CPG. Now, so this is the age structure when we, by 2050, notice that there is the, I have been pointing the bars at the pre-reproductive age. Notice that in this particular age structure, the base is more or less the same, or even. Starting from about 25 years going down, the bars are more or less the same. It means that the number of people added would be just the same as in the previous year. That's why it's CPG. The number of individuals moving to the reproductive period will be equal to the number of individuals that are born, or the newborn individual. Now, with the reproductive health law properly implemented, we have sexual education already taught in our elementary and high school or secondary education. The curriculum for sexual education will be appropriate for the ages of the few pills. There will be access to family management methods available to almost everybody. We will be able to reach CPG at a much shorter period, and the population may be lower than 148,260,000. So hopefully, our reproductive health law will be properly implemented. We move to the next topic, which is a characteristic of population. We call it survivorship curve. This applies to all types of populations. There are three different curves as shown in the diagram. We have type one, which is the convex, wherein the individuals of the population are able to reach the total lifespan of the individual. So mortality increases as the individuals reach the lifespan. So they are able, there is minimal mortality at a very young age. So most individuals of the population are able to reach the reproductive period. So that is type one or convex. Type two would be the straight line. It means that mortality is the same at almost all stages. Now type three is the concave, wherein you have a very high mortality at young age. Here, the environment, the physical environment, the habitat of the organisms would be very unfavorable. That causes high mortality of the young. And the surviving population would be able, only a small segment of the surviving population will reach the reproductive age. That's why it's called concave. We humans belong to type one survivorship curve with very good health care system. Most of the children, the infant mortality has been lowered. So you have most of the individuals of the population reaching the reproductive age. And mortality increases as an individual reaches the lifespan.