 day about modern human ecology as a continuation of our look at the hominin record last time. We're bringing that into the present and looking at the dynamics of humans in more recent times, historical times, and then bringing that to today. And we'll finish on Friday and with a bit on Monday about looking forward and the role of ecology in present day science and politics and looking a bit toward what we can expect in coming years. So I'm going to step back and review a bit of what we talked about last time first here and then we'll get into human population growth, a focus on human demography and some details of the human demographic process, and then set human population dynamics into the context of resource consumption, which will be our avenue for talking about environmental problems today and the role of ecology in elucidating and helping to solve them. So last time we were talking about these guys as a transition to our discussion of early hominins, right? These are great apes. These are types of primate. These are types of primate that are particularly closely related to ourselves, orangutans, chimpanzees, bonobos, and gorillas. Where do these things live? People rainforests, someone said, what else might you answer to that? Where do they live? Central Africa. The orangutan is also in Southeast Asia, but the others are in Africa and particularly in the forest zone. And that's one thing that led Darwin to suggest that humans evolved in Africa because he and others recognized how close we were to them in so many respects anatomically. Most importantly, they recognized that, and he made the suggestion that humans probably evolved in Africa. Indeed, the three out of the four types are concentrated in Africa and in the forest. These move into the open country a bit, into the woodlands, into the rich savannas, savanna woodlands. What are they eating primarily? Chimps and gorillas and orangs? Chimps eat termites. They are famous for eating termites based on the studies of Jane Goodall. It's a very minor portion of their activities in terms of the time spent doing it, but it's potentially a major contribution in terms of nutrients because of some specific things that termites provide. What else do they eat? Fruit? Yeah, a lot of fruit, orangs and chimps. Grillas eat a lot of pith, the more woody parts of plants. They're primarily vegetarian, although there's considerable omnivory in the chimpanzees, and strict carnivory in the chimpanzees where they hunt monkeys. That's only a discovery of the last couple of decades, the sophistication with which chimps hunt monkeys. The traditional view is of these apes as fruit-eating forest dwellers. The interpretation of hominin ancestry has generally been in that context in relation to a group of ancestors that lived in the forests and ate fruit. The distinction with humans was that they at some point moved out into open country, went up on two legs, and started incorporating a broader menu into their diet, including much more reliance on meat. That has framed the discussion for anthropology and paleoanthropology for most of its history, a movement into open country and more and more incorporation of meat into the diet. There's much basis in fact for that type of interpretation. These forms, in earlier times, are considered to have been more vegetarian in this traditional approach, but incorporating more and more meat with time, becoming more omnivorous to the point of sophisticated hunting along with cultural advances like the domestication of fire in later stages. This is a cartoon version where they're all carrying spears and you get to this noble hunter type here toward the end of the line, standing perfectly straight, great posture there. But again, there is a lot of evidence for the incorporation of meat in the diet starting as early as 2.5 million years ago, the incorporation of large mammal meat, and a sophistication of hunting techniques in time. That led to the suggestion that humans, as they moved around the world, as they moved out of Africa and around the world, could have been partly responsible for the loss of the megafauna, the loss of vertebrates over about 100 pounds, because so many of those vertebrates were lost in different areas and the correlation was striking with the presence of humans, the arrival of humans into those areas. The traditional hypothesis related to this great extinction event, the loss of the megafauna, concerned active hunting by humans of these organisms, ground sloth up against the tree and human thrusts spear into ground sloth, that kind of hunting, direct predation dynamic. What are some other possible explanations if indeed humans had a role in these extinctions? What are some other possible ways in which these extinctions might have been unfolded that are not specifically direct hunting pressure? Yes, changing climates, yeah. We wouldn't think of humans having a role in that, but if there were general climate change occurring all around, then that could have an impact on the fauna, and perhaps there's some reason why a changing climate disproportionately affected the large fauna. How about some other anthropogenic explanations for why these losses might have occurred, yes. So a type, she said humans using up resources that the megafauna also used, so that would be a type of exploitative competition, right. Many of these creatures were herbivores, the carnivores were also lost in many cases, but things like elephants, camels, it's possible that exploitative competition could explain some of this, but certainly not all of it because of the diversity of ecological types that did go extinct. What else? Pathogens, the possibility that humans transported pathogens or diseases with them as they went. We know that's the case, that that does happen in recent times, that's well documented, perhaps it happened in ancient times too. Yeah, and that's argued as an alternative possibility. What else? How about invasive species that we might bring along with us, where we go? Commensals to humans or organisms that are hitchhiking with humans that themselves alter ecosystems anew and disrupt them. That's a possibility. What else? I can think of another major force that humans would carry with them that could alter ecosystem structure and possibly lead to catastrophic changes in ecosystem structure around the world and cascading effects throughout these systems. Fire, it's a major factor here and it's one that's so often overlooked in the whole discussion about these events. Ecosystems evolve in relation to fire and areas that are fire prone, ecosystems are well attuned to those fires. Communities are adapted to those fire regimes, if we can speak of community adaptation. When you alter those fire regimes, it can have major effects on the existing forms of life. Humans bringing in their fire kits, their sophisticated means of creating fire and distributing it and we know that people do this a lot to assist them in their hunts, to assist them in their foraging. If those regimes are altered intentionally by humans, that can have major effects on community structure and ecosystem dynamics and perhaps lead to the shortening of these catastrophic chains and disruptive effects on whole communities. So when you encounter this whole debate and it's an old debate, it goes back to the 1800s. If you can mark a point where this debate was launched in, you probably can. The historical work, the history of science work on this hasn't been done yet, but Richard Owen in the 1800s, this was a contemporary of Darwin's, found he was a describer of fossils such as the giant extinct moas of New Zealand, but also the Australian megafauna. From the earliest days, he suggested that maybe humans had a role in these extinctions. He was focused on Australia. He even suggested that bringing dingos in might have led to the loss of some of the megafauna. Dingos being these derived dogs that are sort of wolf-like and pack hunters. Within a few years after Owen's suggesting this, someone else suggested as a counter proposal, well maybe climate change was actually the major factor. That individual pointed to some botanical information that suggested maybe climate had changed during this period. Off we were running with this debate between an overkill idea of human hunting versus a climate change idea related to the loss of the megafauna. But that's the simple dichotomy. Human predation perhaps assisted with a commensal or a climate. There's a lot of other possibilities including disease and alterations in fire regimes. What about the climate data? Here is an example of the estimation of global temperatures through time. In this case based on ice cores taken from glaciers where cores are taken deep into glaciers where bubbles of air that are trapped are analyzed for their gas content. The concentrations of carbon dioxide contained in those gas bubbles through time. By those means you can get very detailed records of how much carbon dioxide there was in the atmosphere based on those trapped air bubbles. You can see that carbon dioxide levels fluctuated cyclically through time over the last 400,000 years. This is known to be closely correlated with temperature changes. So we see that this occurred cyclically. These extinction events we're talking about, the extinction events of the megafauna are occurring in here. This is the end of the last ice age in here. Each of these is an ice age. We had cyclical ice ages going back a million years on earth. The dynamics in here sure, this is an ice age and then a rapid warming trend. But it's no different than what happened here or happened here or happened here really. So at least this dynamic, there's nothing unusual about this period of time in terms of the global climate based on the data from these ice cores in terms of global temperatures. Maybe there are other climate changes that haven't been documented that are specific to this time period that could explain the concentration of extinctions just in this time. Those extinctions happened for the most part incredibly rapidly and concentrated in this time and again correlated with human appearance. So for a lot of people the correlation is so stunning that it suggests causation but this is a great debate. This is one of the great contemporary debates. It started in the 1800s but it's really hot right now. A place like Australia, the debate will be differently structured than it is in a place like America or Europe. The African data is so interesting too, largely for the lack of clear megafaunal extinctions in Africa. You go to Africa, you're looking at a place to see in fauna really. You're seeing elephants and hippopotamuses and all these large fantastic creatures that went extinct in other places. So you're getting a window into the deep past if you go there. Why didn't they get knocked off in Africa? Anyone want to make a suggestion? If you're wedded to the idea that humans had a role in this, what might be an explanation for getting out of the counter data in Africa that there really weren't any concentrated megafaunal extinctions in here? How might you explain that away? Humans might not have been an invasive species. Humans were evolving there for millions of years. Perhaps there was a co-evolution that allowed them to coexist. It was a more gradual process. You arrive in the Americas at 13,000 years with a sophisticated tool and fire kit and explode in the terms of population numbers. Perhaps that has a different effect than an evolution over millions of years. So let's focus on some new slides here and think about the numbers of humans on Earth. Humans started to expand their range as early as two million years ago out of Africa, but this was all hunter-gatherer times, living off of the land in without large sedentary populations for the most part. You had some great civilizations, many of most of which are lost to history, but for the most part you didn't have the metropolises that we see in more recent times. And population numbers on Earth in total were fairly steady up through relatively recent times. Now this is sort of a funny depiction, but year 2000, relative to year zero and then before the common era. So minus 4,000 years ago is 6,000 years from earlier than today. And you can see an increase in numbers. Populations were expanding in terms of geography and increasing in numbers with steadier increases in more recent times, blips related to major diseases. Some one fourth of Europeans, I think, were in this plague in particular, fully a quarter of the European population, but it just shows up really as a blip in this whole dynamic. And then a really steep increase starting with industrialization. And then an even greater than exponential increase in starting in the 1900s with further advances in medicine and science, leading to longer life spans and reduced infant mortality. Steeper than exponential. For a big organism like ourselves, this is incredible growth. I don't think there's certainly not anything documented like this for any other organism of our size and our capacity for resource consumption. So here we are today at some approaching 7 billion, 7 billion strong on planet Earth. Just a finer and finer detail, if you want, in billions. Major crises in human populations, major diseases don't even show up in this trend in these data. This steady, seemingly inexorable increase in numbers to today. And this was quite alarming. This alarmed people long ago when they were recognizing trends in population growth. And you'll learn about Thomas Malthus in the evolution section and his influence on Darwin. He was one of the early scientists' thinkers to point out the potentially catastrophic consequences of growth such as this for human well-being. And in the 60s and 70s, ecologists and sociologists and many others started to really try to draw attention to the potential consequences of this greater than exponential increase phenomenon. So you can go to the web and check the population on Earth today, updated every, I don't know how often, every 30 minutes or something like that. But you can just watch the numbers tick forward this morning. We were at about 6.8 billion on Earth, 310 million in the U.S. and increasing rapidly. One of the interesting trends in population growth in different countries as they develop, and we'll speak of developing and developed countries following your book, is that in their history, a declining death rate related to better sanitation and better hospitals and advances in medicine precedes any decline in birth rate. And this gap created between a declining death rate and a steady and later declining birth rate is what's referred to as the demographic transition, this period of time, when there's a strong gap formed between these dynamics. So your birth rates remain high and your death rates are plummeting. And this is a time of wildly expanding population growth as you can understand from your study of organismal demography earlier in the semester. The larger this gap, the greater potential there is for population growth. And this is Mexico showing the same data, death rate versus birth rate, and the height of this gap is fantastic. This is kind of a crappy graph, and I borrowed it from another professor, not to say that they produce a crappy graph. It's just that I couldn't find a better one, a more up-to-date one or less fuzzy one. But it gives you the idea that in relation to gross national product or some estimate of income or wealth, rates of birth and death rates seem to decline. And this is supported by data from all over the world. As populations and families garner more resources, become more wealthy themselves, they tend to have fewer children. And we're not going to get into the sociology of all of this, but please do think about it a bit. And one of the simple ways of interpreting this is in the context of communities and societies where children are the wealth in certain respects, particularly in agricultural communities where, or communities relying on manual labor and more hands, more resources, more hands, more wealth. And as wealth becomes derived from different sources, the importance of children in terms of generating wealth becomes reduced. But there are other factors. I'll mention a couple more, and it's a very complex circumstance that I'm simplifying greatly. But let's look at changing human birth rates from the late 60s to the early 21st century. In the world, birth rates have, average number of children per female have dropped quite a lot in these past 30 years. In Africa, they've dropped quite a lot also, but they remain extremely high relative to this, quote unquote, replacement rate at 2.1 children per female. That's roughly the replacement rate of replacing two parents. If you have 2.1 kids, you are roughly replacing yourselves in the sense that factoring in mortality, infant mortality, and also the fact that male children are born more frequently than female children, a disparity in the number of male births relative to female births, very slight difference, but a real difference. That's about 2.1 for replacement, so that's what this dotted line represents, and that'll produce zero population growth over time. Each of these areas exceeds zero population growth. Putting developed countries all together, I don't know how many are in these bins, I think probably some 40 countries, you can see that these are below replacement levels indicating declines in numbers over time, suggesting future declines in population numbers. More specific breakdown by particular countries, you can see dramatic declines in India, much more dramatic in China still, just in the last 40 years. That's a stunning drop. The U.S. sits right at replacement by many estimates today, right at about 2.1 kids per family, Canada below Australia, below replacement, and yet our population numbers are increasing a lot in this country, even though we're at replacement. Why? Immigration, of course, capital I, you got a factor in immigration and emigration into these equations too, and this is based on females from these countries that are born in those countries. It's not taking into account fertility rates of migrants, and that can differ. Someone moving into China might be very different in their fertility than someone native born there. Is there a question in the back? Yeah, that takes into account all the females. Yeah, his question was, for those of you watching at home, whether the calculation of that replacement rate value takes into account only the breeding females or all females, and it would be all females. So, look at this annual percent increase of the human population over time. I believe this is related to famine and disease dynamics in that period. Not quite remembering what that someone else maybe knows offhand. It was China, right? Yeah. So, in spite of that, you have this heightening of the annual percent increase in the population around 2.2 percent, which is massive given how many people you're starting with. Remember the compounding of growth here. N is increasing dramatically, so 2.2 percent is a huge increase in numbers. It's declining. It's seen to be declining relatively steeply, but still N is increasing a lot. So, this means the addition of huge numbers of individuals per day, per year, but it is decreasing, strikingly, and this has only been occurring since what? The 1970 or so. So, during this period, this is when, during the 60s, when academics were going nuts to try to draw attention to the reality of the problems of human population growth. No one was really projecting this type of trend, I don't think. I haven't read much of this literature, but I know that even, you know, I'm old enough to know that in this period, the alarmism was still quite striking for the trends not projected to go in this direction at all. An incredible turn of events. Still, we have a huge number of additional individuals per day. You can go to that website and just, you know, you're really stunned yourself by how many hundreds of thousands are added every day on earth, but this is, this is in many ways good news from an ecological standpoint. And if you follow these projections, you start, you start to have this problem, you know, New York Times in 1997, population explosion is over, they say. Economists, how to deal with a shrinking population, that's our new problem. Right? Maybe and not in all parts of the world. Things are happening in different ways in different places. And who knows? I mean, maybe this projection is not how we should follow it. Maybe we're going to spike in the other direction for some reason. These are just predictions. We're predicting the future here. It's always a difficult thing to do. But these are real problems in some countries where, where population numbers are seen to be decreasing. Let's just look at one example. This has come to my attention a couple of times. The possible role for television and soap operas in declining fertility rates around the world. I mean, we saw the role of just increases in wealth that that plays. The education of women plays a tremendous role in declining fertility rates, as most of you are probably aware. Countries where women receive an education or an advanced education, they tend to focus on other things in life in addition to having families. And something to be encouraged for so many reasons. Also for the ecological impacts that societies have on the environment. For TV, there are studies suggesting a pretty strong link between watching TV and watching soap operas in particular. And how often do you see kids, babies and parents raising kids in soap operas? It doesn't happen very much. It's usually about man and woman and woman and woman and man and man and their dynamics. It's not about raising kids. And so the focus is shifted from the family dynamic and having babies perhaps. I don't know. But these are good sociologists and workers publishing material in good places and who knows, maybe there's something to it. Age structure pyramids. A way of looking at a population in an area by distribution of individuals in these different age groups and seeing at a glance and being able to predict at a glance the nature of population change in those communities. Taking Afghanistan as an example here, this is probably data from around 2000 or 2004 or something like that. A bottom heavy pyramid like this suggests a lot of individuals coming into reproductive age. And you can imagine what that means for population growth dynamics. The United States with I guess a baby boomer bulge in here but a mostly evenly distributed population across these age classes. And this is a place where you have for the most part replacement levels of growth compared to a European country and several of the European countries are like this, where you're top heavy. And the majority of your population is entering post reproductive periods. Humans are a weird beast where we live a long time after reproductive capacity. It would be interesting to talk about that phenomenon and the role that the grandmother effect, the grandfather effect in human populations is something that anthropologists study quite a lot. But we're a unique creature in many ways in that regard. There was a slide I skipped over before. Anyway, we should keep our focus because there's a lot of interesting tangents to go into. Anyway, so you can see at a glance from these types of distribution the likely dynamics in the near future of these populations. So setting these growth dynamics into an environmental context. And if I finish up early, I'll try to finish up early. Keep this a bit short. Your book covers this well. Just to show you a video at the end that's for your viewing pleasure only. It won't be on the webcast partly because I don't have any legal rights to show it on the web, I don't think. But I think you'll find it really interesting. So what is the Earth's carrying capacity? We have these wild increases in numbers. Well, how many people can Earth sustain? What is K for human beings on this planet right now? People have been, scientists, thinkers have been thinking about this for a long time. So in the literature, if you mind the literature, this is a figure from Krebs 2009, based on a study of Cohen's from the 90s. Just mind the literature and looked at different people's estimates of what the carrying capacity is. You can imagine there's many ways of trying to determine that. From the earliest estimates, Levenhook's estimates from the 1600s put it around 10 or 11 billion or something like that. And I don't know if everyone was just influenced by those first publications, but they've tended to hover. Estimates have tended to hover around that median of around 11 billion with a lot of variation. This is on a logarithmic scale. So here's a thousand billion estimates of what maybe Earth could sustain given no doubt assumptions about technological advances or somewhat dire forecasts of how few human beings Earth could sustain made in the 50s. So lots of variation, but a suggestion, this long-term scientific suggestion of some 11 billion as a carrying capacity on Earth. A moving target, of course. A carrying capacity is always a moving target and no less so for human beings given cultural change. And here we are today somewhere around approaching 7 billion. So if you want to think about that, you can. You should think about it in terms of how we consume resources. So here's human consumption of the products of photosynthesis. We saw the diagrams of net primary productivity around the world. This is how much humans consume of those products of photosynthesis, estimated in grams of carbon per year. And this is related to how many people are there. So it's how much people are consuming related to how many are there in the first place. There are a lot higher densities of people in some of these areas than there are in some of these areas, but still these are very hot spots. The hotter red, the greater consumption. And that's as a result of the higher consumption rates by people in these areas compared to these areas. You can see all of Europe's pretty hot. Consuming a lot, even though densities are much less than they are, say, in here, where people are consuming much less, but there's so many more people. We can look at something called the ecological footprint. We all have heard about carbon footprints now. An ecological footprint is just a per capita estimate of the impact of a person on available resources. Relative to the capacity of these various countries, you can graph the ecological footprint of a person, its impact on the environment, relative to the ecological capacity of the place they live in. And so individuals in these countries are suggested to fall below their line of carrying capacity, whereas we, for example, are living far above our carrying capacity because we consume so much and not just that we eat so much, although if you go somewhere else in the world, you will find a much smaller plate of food in front of you. Now, this takes into account the products of photosynthesis in general, so our total consumption, including electricity and fossil fuel consumption and so forth.