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Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:02.12,0:00:04.37,Default,,0000,0000,0000,,In our series on biology we\Nspent many weeks together,
Dialogue: 0,0:00:04.37,0:00:06.29,Default,,0000,0000,0000,,talking about the physiology\Nof animals and plants,
Dialogue: 0,0:00:06.29,0:00:08.33,Default,,0000,0000,0000,,and how cells work\Ntogether to make tissues,
Dialogue: 0,0:00:08.33,0:00:10.02,Default,,0000,0000,0000,,to make organs, to make organ systems.
Dialogue: 0,0:00:10.02,0:00:13.10,Default,,0000,0000,0000,,To make us the hunks of meat\Nand vegetables that we are.
Dialogue: 0,0:00:13.10,0:00:14.54,Default,,0000,0000,0000,,Understanding the whole organism.
Dialogue: 0,0:00:14.54,0:00:17.58,Default,,0000,0000,0000,,It's important to know what's\Ngoing on at all those levels.
Dialogue: 0,0:00:17.89,0:00:19.96,Default,,0000,0000,0000,,The same is true for ecology.
Dialogue: 0,0:00:20.25,0:00:23.81,Default,,0000,0000,0000,,Only, instead of zooming in and out on\Ndifferent levels within a living thing,
Dialogue: 0,0:00:23.81,0:00:25.87,Default,,0000,0000,0000,,we can zoom in and out on the earth.
Dialogue: 0,0:00:26.16,0:00:27.40,Default,,0000,0000,0000,,Depending on the power\Nof the magnification,
Dialogue: 0,0:00:27.40,0:00:30.42,Default,,0000,0000,0000,,we can understand a whole range\Nof things about our planet.
Dialogue: 0,0:00:30.42,0:00:32.90,Default,,0000,0000,0000,,For instance, we can look\Nat groups within a species,
Dialogue: 0,0:00:32.90,0:00:35.55,Default,,0000,0000,0000,,and how they live together\Nin one geographic area.
Dialogue: 0,0:00:35.55,0:00:37.07,Default,,0000,0000,0000,,That's population ecology.
Dialogue: 0,0:00:37.07,0:00:38.37,Default,,0000,0000,0000,,There's also community ecology,
Dialogue: 0,0:00:38.37,0:00:40.95,Default,,0000,0000,0000,,where you look at groups of\Ndifferent organisms living together,
Dialogue: 0,0:00:40.95,0:00:42.70,Default,,0000,0000,0000,,and figure out how they\Ninfluence each other.
Dialogue: 0,0:00:42.70,0:00:45.95,Default,,0000,0000,0000,,Then, the most zoomed out\Nwe get is ecosystem ecology.
Dialogue: 0,0:00:46.26,0:00:49.39,Default,,0000,0000,0000,,The study of how all living\Nand non-living things,
Dialogue: 0,0:00:49.47,0:00:51.48,Default,,0000,0000,0000,,interact within an entire ecosystem.
Dialogue: 0,0:00:51.70,0:00:54.62,Default,,0000,0000,0000,,Let's start by zooming in\Nwith population ecology.
Dialogue: 0,0:00:54.82,0:00:56.53,Default,,0000,0000,0000,,The study of groups within a species,
Dialogue: 0,0:00:56.53,0:00:58.87,Default,,0000,0000,0000,,that interact mostly with each other.
Dialogue: 0,0:00:59.31,0:01:00.61,Default,,0000,0000,0000,,To understand why these populations,
Dialogue: 0,0:01:00.61,0:01:03.65,Default,,0000,0000,0000,,are different in one time and\Nplace than they are in another.
Dialogue: 0,0:01:03.85,0:01:07.07,Default,,0000,0000,0000,,How, you may be asking yourself, is\Nthat in any way useful to anyone ever?
Dialogue: 0,0:01:07.44,0:01:09.89,Default,,0000,0000,0000,,Well, it's actually super\Nuseful to everybody always.
Dialogue: 0,0:01:09.89,0:01:13.19,Default,,0000,0000,0000,,Let's look, for instance, at\Nthe outbreak of West Nile Virus,
Dialogue: 0,0:01:13.19,0:01:16.33,Default,,0000,0000,0000,,that struck Dallas, Texas\Nin the summer of 2012.
Dialogue: 0,0:01:16.73,0:01:19.24,Default,,0000,0000,0000,,In Dallas County, twelve\Npeople died from the virus,
Dialogue: 0,0:01:19.24,0:01:20.57,Default,,0000,0000,0000,,as of the filming of this.
Dialogue: 0,0:01:20.74,0:01:22.74,Default,,0000,0000,0000,,Nearly three hundred\Npeople have been infected.
Dialogue: 0,0:01:22.90,0:01:24.81,Default,,0000,0000,0000,,In 2011 the whole state of Texas,
Dialogue: 0,0:01:24.81,0:01:28.04,Default,,0000,0000,0000,,reported only twenty seven cases\Nof West Nile and only two deaths.
Dialogue: 0,0:01:28.46,0:01:29.34,Default,,0000,0000,0000,,That seems kind of significant.
Dialogue: 0,0:01:29.34,0:01:30.04,Default,,0000,0000,0000,,So, what's up?
Dialogue: 0,0:01:30.04,0:01:32.03,Default,,0000,0000,0000,,Turns out that this is a\Npopulation ecology problem.
Dialogue: 0,0:01:32.03,0:01:33.91,Default,,0000,0000,0000,,West Nile is a mosquito born illness,
Dialogue: 0,0:01:33.91,0:01:36.72,Default,,0000,0000,0000,,and the population of\Nmosquitoes in Dallas in 2012,
Dialogue: 0,0:01:36.72,0:01:39.11,Default,,0000,0000,0000,,busted through brick walls\Nlike the Kool-aid man,
Dialogue: 0,0:01:39.11,0:01:40.60,Default,,0000,0000,0000,,spreading West Nile like crazy.
Dialogue: 0,0:01:40.60,0:01:44.12,Default,,0000,0000,0000,,Why did this outbreak happen in\N2012 and not the year before?
Dialogue: 0,0:01:44.55,0:01:47.39,Default,,0000,0000,0000,,And why did it happen in\NTexas and not in New Jersey?
Dialogue: 0,0:01:47.39,0:01:49.38,Default,,0000,0000,0000,,The answer, is population ecology.
Dialogue: 0,0:01:49.38,0:01:59.64,Default,,0000,0000,0000,,(fast lively music)
Dialogue: 0,0:01:59.64,0:02:02.32,Default,,0000,0000,0000,,Before we start solving any\Ndisease outbreak mysteries,
Dialogue: 0,0:02:02.32,0:02:04.82,Default,,0000,0000,0000,,we got to understand the\Nfundamentals of population ecology.
Dialogue: 0,0:02:04.82,0:02:08.29,Default,,0000,0000,0000,,For starters, a population is\Njust a group of individuals,
Dialogue: 0,0:02:08.29,0:02:10.99,Default,,0000,0000,0000,,of one species who interact regularly.
Dialogue: 0,0:02:10.99,0:02:14.24,Default,,0000,0000,0000,,How often organisms interact\Nhave a lot to do with geography.
Dialogue: 0,0:02:14.24,0:02:16.54,Default,,0000,0000,0000,,You're going to have a lot more face\Ntime with the folks you live near,
Dialogue: 0,0:02:16.54,0:02:18.26,Default,,0000,0000,0000,,than those who live farther away.
Dialogue: 0,0:02:18.26,0:02:20.60,Default,,0000,0000,0000,,As a result, individuals\Nwho are closer to you,
Dialogue: 0,0:02:20.60,0:02:22.89,Default,,0000,0000,0000,,will be the ones that you compete\Nwith for food and living space,
Dialogue: 0,0:02:22.89,0:02:24.35,Default,,0000,0000,0000,,mates, all that stuff.
Dialogue: 0,0:02:24.35,0:02:26.35,Default,,0000,0000,0000,,In order to understand why\Npopulations are different,
Dialogue: 0,0:02:26.35,0:02:27.88,Default,,0000,0000,0000,,from time to time and place to place,
Dialogue: 0,0:02:27.88,0:02:31.10,Default,,0000,0000,0000,,a population ecologist needs to know\Na few things about a population.
Dialogue: 0,0:02:31.10,0:02:32.42,Default,,0000,0000,0000,,Like, it's density.
Dialogue: 0,0:02:32.42,0:02:34.60,Default,,0000,0000,0000,,In this instance, how\Nmany mosquitoes there are,
Dialogue: 0,0:02:34.60,0:02:37.74,Default,,0000,0000,0000,,in the greater Dallas area that might\Ncome into contact with each other.
Dialogue: 0,0:02:37.74,0:02:40.16,Default,,0000,0000,0000,,A population's density changes\Ndue to a number of factors,
Dialogue: 0,0:02:40.16,0:02:41.79,Default,,0000,0000,0000,,all of which are pretty intuitive.
Dialogue: 0,0:02:41.79,0:02:43.74,Default,,0000,0000,0000,,It increases when new\Nindividuals are either,
Dialogue: 0,0:02:43.74,0:02:46.02,Default,,0000,0000,0000,,born or immigrate, that is, move in.
Dialogue: 0,0:02:46.47,0:02:49.75,Default,,0000,0000,0000,,It decreases because of\Ndeaths or emigration,
Dialogue: 0,0:02:49.75,0:02:50.96,Default,,0000,0000,0000,,or individuals moving out.
Dialogue: 0,0:02:50.96,0:02:53.37,Default,,0000,0000,0000,,Simple enough, but as\Na population ecologist,
Dialogue: 0,0:02:53.37,0:02:55.100,Default,,0000,0000,0000,,you also need to know about\Nthe geographic arrangement,
Dialogue: 0,0:02:55.100,0:02:58.20,Default,,0000,0000,0000,,of the individuals within the population.
Dialogue: 0,0:02:58.71,0:03:00.12,Default,,0000,0000,0000,,This is their dispersion.
Dialogue: 0,0:03:00.12,0:03:01.84,Default,,0000,0000,0000,,Like, are the mosquitoes\Nall clumped together?
Dialogue: 0,0:03:01.84,0:03:03.69,Default,,0000,0000,0000,,Are they evenly spaced\Nthroughout the county?
Dialogue: 0,0:03:03.69,0:03:05.63,Default,,0000,0000,0000,,Is there some kind of random spacing?
Dialogue: 0,0:03:05.63,0:03:07.41,Default,,0000,0000,0000,,The answers to these\Nquestions give scientists,
Dialogue: 0,0:03:07.41,0:03:09.79,Default,,0000,0000,0000,,a snapshot of a population\Nat any given moment.
Dialogue: 0,0:03:10.08,0:03:12.51,Default,,0000,0000,0000,,To figure out a puzzle like\Nthe West Nile outbreak,
Dialogue: 0,0:03:12.57,0:03:15.34,Default,,0000,0000,0000,,which involves studying how a\Npopulation has changed over time,
Dialogue: 0,0:03:15.34,0:03:19.08,Default,,0000,0000,0000,,you have to investigate one of\Npopulation ecology's central principles.
Dialogue: 0,0:03:19.51,0:03:20.82,Default,,0000,0000,0000,,Population growth.
Dialogue: 0,0:03:20.82,0:03:22.78,Default,,0000,0000,0000,,There are all kinds of factors\Nthat drive population growth,
Dialogue: 0,0:03:22.78,0:03:25.31,Default,,0000,0000,0000,,and they can vary radically\Nfrom one organism to the next.
Dialogue: 0,0:03:25.31,0:03:26.55,Default,,0000,0000,0000,,Things like fecundity.
Dialogue: 0,0:03:26.55,0:03:28.99,Default,,0000,0000,0000,,How many offspring an individual\Ncan have in a lifetime,
Dialogue: 0,0:03:28.99,0:03:31.52,Default,,0000,0000,0000,,make a huge difference in\Nthe size of a population.
Dialogue: 0,0:03:32.01,0:03:35.60,Default,,0000,0000,0000,,For instance, why do mosquito\Npopulations seem to grow so quickly,
Dialogue: 0,0:03:35.60,0:03:38.16,Default,,0000,0000,0000,,while, the endangered black\Nrhino may never recover,
Dialogue: 0,0:03:38.16,0:03:39.94,Default,,0000,0000,0000,,from a single act of poaching?
Dialogue: 0,0:03:39.94,0:03:42.47,Default,,0000,0000,0000,,For starters, mosquitoes can\Nhave two thousand offspring,
Dialogue: 0,0:03:42.47,0:03:44.12,Default,,0000,0000,0000,,in their two week lifetime.
Dialogue: 0,0:03:44.48,0:03:47.29,Default,,0000,0000,0000,,While the rhino can have\Nlike five in forty years.
Dialogue: 0,0:03:47.46,0:03:50.03,Default,,0000,0000,0000,,Still, a population doesn't\Nusually or even ever,
Dialogue: 0,0:03:50.03,0:03:53.10,Default,,0000,0000,0000,,grow to its full potential and it\Ncan't keep growing indefinitely.
Dialogue: 0,0:03:53.28,0:03:55.03,Default,,0000,0000,0000,,To understand how fast or slow,
Dialogue: 0,0:03:55.03,0:03:57.71,Default,,0000,0000,0000,,and high or low a\Npopulation actually grows,
Dialogue: 0,0:03:57.77,0:03:59.88,Default,,0000,0000,0000,,you need to focus on what's\Nkeeping growth in check.
Dialogue: 0,0:04:00.22,0:04:01.92,Default,,0000,0000,0000,,These factors are appropriately called,
Dialogue: 0,0:04:02.53,0:04:03.85,Default,,0000,0000,0000,,limiting factors.
Dialogue: 0,0:04:03.85,0:04:05.94,Default,,0000,0000,0000,,Say, you're a mosquito in Dallas in 2011,
Dialogue: 0,0:04:05.94,0:04:07.11,Default,,0000,0000,0000,,the year before the outbreak.
Dialogue: 0,0:04:07.39,0:04:10.43,Default,,0000,0000,0000,,Back then, the growth rate\Nwasn't what it was in 2012,
Dialogue: 0,0:04:10.43,0:04:12.34,Default,,0000,0000,0000,,so something was keeping you down.
Dialogue: 0,0:04:12.77,0:04:14.92,Default,,0000,0000,0000,,To figure out what your\Nlimiting factors were,
Dialogue: 0,0:04:14.96,0:04:17.14,Default,,0000,0000,0000,,you first have to narrow down\Nwhat you need as a mosquito,
Dialogue: 0,0:04:17.14,0:04:19.36,Default,,0000,0000,0000,,to live and reproduce successfully.
Dialogue: 0,0:04:19.59,0:04:20.74,Default,,0000,0000,0000,,First, you got to find your food.
Dialogue: 0,0:04:20.74,0:04:22.83,Default,,0000,0000,0000,,Now, you mosquitoes, you\Neat all kinds of things.
Dialogue: 0,0:04:22.83,0:04:25.33,Default,,0000,0000,0000,,But in order to reproduce,\Nassuming you're a female,
Dialogue: 0,0:04:25.33,0:04:26.73,Default,,0000,0000,0000,,you need a blood meal.
Dialogue: 0,0:04:27.31,0:04:29.73,Default,,0000,0000,0000,,You have to find a vertebrate\Nand suck some of its blood out.
Dialogue: 0,0:04:29.73,0:04:32.43,Default,,0000,0000,0000,,Presumably there's no shortage of\Nvertebrates walking around Dallas,
Dialogue: 0,0:04:32.43,0:04:33.88,Default,,0000,0000,0000,,for you to suck blood out of.
Dialogue: 0,0:04:33.88,0:04:36.12,Default,,0000,0000,0000,,I have good friends who\Nare vertebrates in Dallas.
Dialogue: 0,0:04:36.61,0:04:38.57,Default,,0000,0000,0000,,You might even be able to\Nsuck some of their blood.
Dialogue: 0,0:04:38.78,0:04:39.50,Default,,0000,0000,0000,,Next, temperature.
Dialogue: 0,0:04:39.50,0:04:42.13,Default,,0000,0000,0000,,Because you mosquitoes are\Nectothermic, it has to be warm,
Dialogue: 0,0:04:42.13,0:04:43.98,Default,,0000,0000,0000,,in order for you to be active.
Dialogue: 0,0:04:44.01,0:04:48.30,Default,,0000,0000,0000,,Now, Texas is pretty warm and the winter\Nof 2011, 2012 was especially balmy.
Dialogue: 0,0:04:48.30,0:04:51.26,Default,,0000,0000,0000,,In fact, the summer of\N2012 was exceptionally hot,
Dialogue: 0,0:04:51.26,0:04:53.55,Default,,0000,0000,0000,,which helps speed up\Nthe mosquito life cycle.
Dialogue: 0,0:04:53.55,0:04:55.54,Default,,0000,0000,0000,,That's one limiting factor\Nthat's been removed,
Dialogue: 0,0:04:55.54,0:04:57.15,Default,,0000,0000,0000,,for Dallas area mosquitoes.
Dialogue: 0,0:04:57.15,0:04:58.62,Default,,0000,0000,0000,,Moving on to mates.
Dialogue: 0,0:04:58.62,0:05:01.32,Default,,0000,0000,0000,,If you're a female mosquito, you\Nneed to find a nice male mosquito,
Dialogue: 0,0:05:01.32,0:05:03.16,Default,,0000,0000,0000,,with a job and preferably his own car,
Dialogue: 0,0:05:03.16,0:05:05.68,Default,,0000,0000,0000,,because Dallas is a pretty\Nbig city, to mate with.
Dialogue: 0,0:05:05.68,0:05:07.50,Default,,0000,0000,0000,,This isn't actually all that hard\Nbecause the way that mosquitoes do it.
Dialogue: 0,0:05:07.94,0:05:10.32,Default,,0000,0000,0000,,Males just gather into a mosquito cloud,
Dialogue: 0,0:05:10.32,0:05:12.39,Default,,0000,0000,0000,,at dusk every night during mating season,
Dialogue: 0,0:05:12.39,0:05:15.10,Default,,0000,0000,0000,,and all the female has to do\Nis find her local dude cloud,
Dialogue: 0,0:05:15.10,0:05:17.06,Default,,0000,0000,0000,,and fly into it in\Norder to get mated with.
Dialogue: 0,0:05:17.66,0:05:18.27,Default,,0000,0000,0000,,Easy cheese.
Dialogue: 0,0:05:18.27,0:05:19.51,Default,,0000,0000,0000,,Finally, space.
Dialogue: 0,0:05:19.51,0:05:20.46,Default,,0000,0000,0000,,And, aha!
Dialogue: 0,0:05:20.46,0:05:22.71,Default,,0000,0000,0000,,Because here we have\Nanother important clue.
Dialogue: 0,0:05:22.71,0:05:25.18,Default,,0000,0000,0000,,Mosquitoes need to lay their\Neggs in stagnant water,
Dialogue: 0,0:05:25.58,0:05:26.97,Default,,0000,0000,0000,,if there's anything mosquito larva hate,
Dialogue: 0,0:05:26.97,0:05:29.20,Default,,0000,0000,0000,,it's a rainstorm flushing out\Nthe little puddle of water,
Dialogue: 0,0:05:29.20,0:05:30.11,Default,,0000,0000,0000,,they've been living in.
Dialogue: 0,0:05:30.11,0:05:32.94,Default,,0000,0000,0000,,Since Dallas saw a pretty severe\Ndrought in the summer of 2012,
Dialogue: 0,0:05:32.94,0:05:35.97,Default,,0000,0000,0000,,there were lots of pockets of\Nstagnant, nasty mosquito water,
Dialogue: 0,0:05:35.97,0:05:38.18,Default,,0000,0000,0000,,sitting around acting\Nas nurseries for many,
Dialogue: 0,0:05:38.18,0:05:40.38,Default,,0000,0000,0000,,many West Nile infected mosquitoes.
Dialogue: 0,0:05:40.88,0:05:42.03,Default,,0000,0000,0000,,When we look at this evidence,
Dialogue: 0,0:05:42.03,0:05:43.48,Default,,0000,0000,0000,,we find at least two limiting factors,
Dialogue: 0,0:05:43.48,0:05:45.88,Default,,0000,0000,0000,,for Dallas' mosquito population growth,
Dialogue: 0,0:05:45.88,0:05:48.08,Default,,0000,0000,0000,,that were removed in 2011.
Dialogue: 0,0:05:48.08,0:05:50.17,Default,,0000,0000,0000,,The constraints of temperature and space.
Dialogue: 0,0:05:50.35,0:05:51.92,Default,,0000,0000,0000,,It was plenty hot and there were lots,
Dialogue: 0,0:05:51.92,0:05:55.91,Default,,0000,0000,0000,,of egg-laying locations so\Nthe bugs were free to go nuts.
Dialogue: 0,0:05:55.91,0:05:58.15,Default,,0000,0000,0000,,Population ecologists group\Nlimiting factors like these,
Dialogue: 0,0:05:58.15,0:05:59.67,Default,,0000,0000,0000,,into two different categories.
Dialogue: 0,0:05:59.67,0:06:02.44,Default,,0000,0000,0000,,Density dependent and density independent.
Dialogue: 0,0:06:02.44,0:06:03.68,Default,,0000,0000,0000,,They do it this way\Nbecause we need to know,
Dialogue: 0,0:06:03.68,0:06:05.56,Default,,0000,0000,0000,,whether a population's growth\Nrate is being controlled,
Dialogue: 0,0:06:05.56,0:06:07.05,Default,,0000,0000,0000,,by how many individuals are in it,
Dialogue: 0,0:06:07.05,0:06:08.91,Default,,0000,0000,0000,,or whether it's being\Ncontrolled by something else.
Dialogue: 0,0:06:08.91,0:06:10.21,Default,,0000,0000,0000,,The reason these limitations matter,
Dialogue: 0,0:06:10.21,0:06:12.83,Default,,0000,0000,0000,,is because they affect what's\Nknown as the carrying capacity,
Dialogue: 0,0:06:12.83,0:06:14.52,Default,,0000,0000,0000,,of the mosquitoes' habitat.
Dialogue: 0,0:06:14.97,0:06:17.78,Default,,0000,0000,0000,,That's the number of individuals\Nthat a habitat can sustain,
Dialogue: 0,0:06:17.78,0:06:19.03,Default,,0000,0000,0000,,with the resources that it has available.
Dialogue: 0,0:06:19.03,0:06:22.13,Default,,0000,0000,0000,,So, density dependent limitations\Nare factors that inhibit growth,
Dialogue: 0,0:06:22.13,0:06:25.26,Default,,0000,0000,0000,,because of the environmental\Nstress caused by a population size.
Dialogue: 0,0:06:25.72,0:06:27.82,Default,,0000,0000,0000,,For example, there may\Nsimply not be enough,
Dialogue: 0,0:06:27.82,0:06:29.97,Default,,0000,0000,0000,,food, water, and space\Nto accommodate everyone.
Dialogue: 0,0:06:29.97,0:06:31.82,Default,,0000,0000,0000,,Or maybe because there\Nare so many individuals,
Dialogue: 0,0:06:31.82,0:06:34.49,Default,,0000,0000,0000,,a nearby predator population explodes,
Dialogue: 0,0:06:34.49,0:06:36.69,Default,,0000,0000,0000,,which helps keep the population in check.
Dialogue: 0,0:06:36.69,0:06:39.18,Default,,0000,0000,0000,,Things like disease can also be\Na density dependent limitation.
Dialogue: 0,0:06:39.44,0:06:41.08,Default,,0000,0000,0000,,Lots of individuals\Nliving in close quarters,
Dialogue: 0,0:06:41.08,0:06:42.91,Default,,0000,0000,0000,,can make infections spread like crazy.
Dialogue: 0,0:06:42.91,0:06:44.28,Default,,0000,0000,0000,,Now, I don't think that\Nthe Dallas mosquitoes,
Dialogue: 0,0:06:44.28,0:06:46.26,Default,,0000,0000,0000,,are going to run out of vertebrates\Nto dine on any time soon,
Dialogue: 0,0:06:46.26,0:06:50.97,Default,,0000,0000,0000,,but let's say hypothetically, that the\Nexplosion of local mosquito populations,
Dialogue: 0,0:06:50.97,0:06:52.26,Default,,0000,0000,0000,,caused a similar explosion,
Dialogue: 0,0:06:52.26,0:06:54.15,Default,,0000,0000,0000,,in the number of Mexican free tailed bats,
Dialogue: 0,0:06:54.15,0:06:56.68,Default,,0000,0000,0000,,the official flying mammal\Nof the state of Texas.
Dialogue: 0,0:06:56.68,0:06:58.61,Default,,0000,0000,0000,,They eat mosquitoes.
Dialogue: 0,0:06:58.61,0:07:01.40,Default,,0000,0000,0000,,That would be a limiting factor\Nthat was density dependent.
Dialogue: 0,0:07:01.40,0:07:03.25,Default,,0000,0000,0000,,More mosquitoes leads to more bats,
Dialogue: 0,0:07:03.25,0:07:04.93,Default,,0000,0000,0000,,which leads to fewer mosquitoes.
Dialogue: 0,0:07:04.93,0:07:05.69,Default,,0000,0000,0000,,It's pretty simple.
Dialogue: 0,0:07:05.69,0:07:07.54,Default,,0000,0000,0000,,When density dependent\Nlimitations start to kick in,
Dialogue: 0,0:07:07.54,0:07:09.51,Default,,0000,0000,0000,,and start to limit a population's growth,
Dialogue: 0,0:07:09.51,0:07:12.37,Default,,0000,0000,0000,,that means that the habitat's\Ncarrying capacity has been reached.
Dialogue: 0,0:07:12.37,0:07:15.41,Default,,0000,0000,0000,,The other type of limiting factor,\Nthe density independent ones,
Dialogue: 0,0:07:15.41,0:07:17.44,Default,,0000,0000,0000,,have nothing to do with how\Nmany individuals there are,
Dialogue: 0,0:07:17.44,0:07:19.46,Default,,0000,0000,0000,,or how dense the population is.
Dialogue: 0,0:07:19.46,0:07:21.49,Default,,0000,0000,0000,,A lot of times, these\Nlimitations are described,
Dialogue: 0,0:07:21.49,0:07:22.84,Default,,0000,0000,0000,,in terms of some catastrophe.
Dialogue: 0,0:07:23.24,0:07:25.44,Default,,0000,0000,0000,,A volcanic eruption, a\Nmonsoon, a Chernobyl.
Dialogue: 0,0:07:25.44,0:07:28.68,Default,,0000,0000,0000,,In any case, some crucial aspect\Nof the population's lifestyle,
Dialogue: 0,0:07:28.68,0:07:31.22,Default,,0000,0000,0000,,changes enough that it\Nmakes it harder to get by.
Dialogue: 0,0:07:31.22,0:07:32.98,Default,,0000,0000,0000,,These factors don't have\Nto be super dramatic.
Dialogue: 0,0:07:32.98,0:07:36.76,Default,,0000,0000,0000,,Going back to mosquitoes, say, in\N2013 there's a huge thunderstorm.
Dialogue: 0,0:07:36.78,0:07:39.98,Default,,0000,0000,0000,,A really gully washer in Dallas\Nevery day for three months.
Dialogue: 0,0:07:39.98,0:07:41.90,Default,,0000,0000,0000,,That's going to disturb the\Nclutches of mosquito eggs,
Dialogue: 0,0:07:41.90,0:07:43.35,Default,,0000,0000,0000,,hanging out in the stagnant water.
Dialogue: 0,0:07:43.35,0:07:46.43,Default,,0000,0000,0000,,So the number born that year\Nwould be substantially smaller.
Dialogue: 0,0:07:46.43,0:07:48.17,Default,,0000,0000,0000,,By the same token, if the\Ntemperature swung the other way,
Dialogue: 0,0:07:48.17,0:07:49.94,Default,,0000,0000,0000,,and it was unseasonably cold all summer,
Dialogue: 0,0:07:49.94,0:07:51.67,Default,,0000,0000,0000,,the bugs' growth rate would drop.
Dialogue: 0,0:07:51.67,0:07:54.34,Default,,0000,0000,0000,,Now, the truth is, there are a\Nbillion and a half situations,
Dialogue: 0,0:07:54.34,0:07:57.08,Default,,0000,0000,0000,,both big and small that\Ncould lead to a population,
Dialogue: 0,0:07:57.08,0:07:58.73,Default,,0000,0000,0000,,either reaching its carrying capacity,
Dialogue: 0,0:07:58.73,0:08:00.69,Default,,0000,0000,0000,,or collapsing because of external factors.
Dialogue: 0,0:08:01.14,0:08:04.80,Default,,0000,0000,0000,,It's a population ecologist's job to\Nfigure out what those factors are.
Dialogue: 0,0:08:05.26,0:08:07.12,Default,,0000,0000,0000,,That is what math is for.
Dialogue: 0,0:08:07.26,0:08:10.41,Default,,0000,0000,0000,,Our friend math says that\Nany population of anything,
Dialogue: 0,0:08:10.41,0:08:12.38,Default,,0000,0000,0000,,anything, will grow exponentially,
Dialogue: 0,0:08:12.38,0:08:13.97,Default,,0000,0000,0000,,unless there's some reason that it can't.
Dialogue: 0,0:08:14.38,0:08:16.40,Default,,0000,0000,0000,,Exponential growth means\Nthat the population grows,
Dialogue: 0,0:08:16.40,0:08:19.31,Default,,0000,0000,0000,,at a rate proportional to\Nthe size of the population.
Dialogue: 0,0:08:19.71,0:08:21.12,Default,,0000,0000,0000,,Here at the beginning of 2012,
Dialogue: 0,0:08:21.12,0:08:23.26,Default,,0000,0000,0000,,we might only have had a\Nthousand mosquitoes in Dallas,
Dialogue: 0,0:08:23.30,0:08:25.80,Default,,0000,0000,0000,,but then after, say, one\Nmonth we got three thousand.
Dialogue: 0,0:08:25.80,0:08:27.56,Default,,0000,0000,0000,,Now, with three times as\Nmany reproducing mosquitoes,
Dialogue: 0,0:08:27.56,0:08:29.60,Default,,0000,0000,0000,,the population grew three times as fast,
Dialogue: 0,0:08:29.60,0:08:30.90,Default,,0000,0000,0000,,as when there were a thousand.
Dialogue: 0,0:08:30.90,0:08:32.24,Default,,0000,0000,0000,,Then there are nine thousand,
Dialogue: 0,0:08:32.24,0:08:34.43,Default,,0000,0000,0000,,at which point it's growing\Nthree times as fast,
Dialogue: 0,0:08:34.43,0:08:35.87,Default,,0000,0000,0000,,as when there were three thousand.
Dialogue: 0,0:08:35.87,0:08:37.54,Default,,0000,0000,0000,,And on and on into infinity.
Dialogue: 0,0:08:37.54,0:08:39.73,Default,,0000,0000,0000,,And in this scenario,\Nthe mosquitoes are all,
Dialogue: 0,0:08:39.73,0:08:41.92,Default,,0000,0000,0000,,carrying capacity my chitin-covered butt!
Dialogue: 0,0:08:41.92,0:08:43.63,Default,,0000,0000,0000,,There's no stopping us!
Dialogue: 0,0:08:43.63,0:08:44.66,Default,,0000,0000,0000,,But you know what doesn't really happen?
Dialogue: 0,0:08:44.67,0:08:46.46,Default,,0000,0000,0000,,I mean, it can happen for a while.
Dialogue: 0,0:08:46.46,0:08:48.83,Default,,0000,0000,0000,,Humans have been on an\Nexponential growth curve,
Dialogue: 0,0:08:48.83,0:08:51.44,Default,,0000,0000,0000,,since the Industrial\NRevolution, for example.
Dialogue: 0,0:08:51.44,0:08:54.92,Default,,0000,0000,0000,,Eventually something always knocks\Nthe population size back down.
Dialogue: 0,0:08:54.92,0:08:56.94,Default,,0000,0000,0000,,That thing might be a\Ndensity dependent factor,
Dialogue: 0,0:08:56.94,0:08:58.84,Default,,0000,0000,0000,,like food scarcity or an epidemic.
Dialogue: 0,0:08:58.84,0:09:00.27,Default,,0000,0000,0000,,Or a density independent one,
Dialogue: 0,0:09:00.27,0:09:02.66,Default,,0000,0000,0000,,like an asteroid that takes\Nout the whole continent.
Dialogue: 0,0:09:03.09,0:09:06.74,Default,,0000,0000,0000,,Regardless, this exponential\Ngrowth curve can't go up forever.
Dialogue: 0,0:09:06.74,0:09:08.02,Default,,0000,0000,0000,,When those factors come into play,
Dialogue: 0,0:09:08.02,0:09:11.07,Default,,0000,0000,0000,,a population experiences\Nonly logistic growth.
Dialogue: 0,0:09:11.07,0:09:12.63,Default,,0000,0000,0000,,This means that the population is limited,
Dialogue: 0,0:09:12.63,0:09:14.94,Default,,0000,0000,0000,,to the carrying capacity\Nof its habitat, which,
Dialogue: 0,0:09:14.94,0:09:17.43,Default,,0000,0000,0000,,when you think about it,\Nain't too much to ask.
Dialogue: 0,0:09:17.43,0:09:19.40,Default,,0000,0000,0000,,See how this graph flattens up at the top?
Dialogue: 0,0:09:19.40,0:09:22.58,Default,,0000,0000,0000,,The factor that creates that\Nplateau is almost always,
Dialogue: 0,0:09:22.60,0:09:24.26,Default,,0000,0000,0000,,a density dependent limitation.
Dialogue: 0,0:09:24.26,0:09:27.14,Default,,0000,0000,0000,,As you add mosquitoes, eventually\Nthe rate of population growth,
Dialogue: 0,0:09:27.14,0:09:30.04,Default,,0000,0000,0000,,is going to slow down because\Nthey run out of food or space.
Dialogue: 0,0:09:30.29,0:09:31.80,Default,,0000,0000,0000,,When we get to where\Nthat number levels off,
Dialogue: 0,0:09:31.80,0:09:33.77,Default,,0000,0000,0000,,that number is the carrying capacity,
Dialogue: 0,0:09:33.77,0:09:36.12,Default,,0000,0000,0000,,of the mosquito population\Nin that particular habitat.
Dialogue: 0,0:09:36.52,0:09:38.10,Default,,0000,0000,0000,,Now, let's apply all of these ideas,
Dialogue: 0,0:09:38.10,0:09:40.58,Default,,0000,0000,0000,,using a simple equation\Nthat will allow us,
Dialogue: 0,0:09:40.58,0:09:43.45,Default,,0000,0000,0000,,to calculate the population\Ngrowth of anything we feel like.
Dialogue: 0,0:09:43.64,0:09:46.96,Default,,0000,0000,0000,,I know it's math, but wake\Nup because this is important.
Dialogue: 0,0:09:46.96,0:09:48.93,Default,,0000,0000,0000,,The city of Dallas is depending on you!
Dialogue: 0,0:09:49.36,0:09:52.71,Default,,0000,0000,0000,,So, let's calculate the growth\Nof Dallas' mosquito population,
Dialogue: 0,0:09:52.71,0:09:54.08,Default,,0000,0000,0000,,over a span of two weeks.
Dialogue: 0,0:09:54.33,0:09:57.37,Default,,0000,0000,0000,,All we have to do to get the\Nrate of growth, that's R,
Dialogue: 0,0:09:57.68,0:09:59.100,Default,,0000,0000,0000,,is take the number of births.
Dialogue: 0,0:10:00.100,0:10:03.94,Default,,0000,0000,0000,,Births minus the number of deaths.
Dialogue: 0,0:10:05.47,0:10:08.88,Default,,0000,0000,0000,,Then divide that all by the\Ninitial population size.
Dialogue: 0,0:10:11.52,0:10:14.33,Default,,0000,0000,0000,,Which we generally just call N.
Dialogue: 0,0:10:14.33,0:10:16.16,Default,,0000,0000,0000,,So, let's say we start\Nwith an initial population,
Dialogue: 0,0:10:16.16,0:10:18.30,Default,,0000,0000,0000,,of a hundred mosquitoes.
Dialogue: 0,0:10:18.30,0:10:20.78,Default,,0000,0000,0000,,Each of those mosquitoes\Nlives an average of two weeks.
Dialogue: 0,0:10:20.78,0:10:24.40,Default,,0000,0000,0000,,Our deaths, over a span of two\Nweeks, will be one hundred.
Dialogue: 0,0:10:24.40,0:10:27.13,Default,,0000,0000,0000,,Half of these mosquitoes are going\Nto be female, so fifty of them.
Dialogue: 0,0:10:27.62,0:10:30.12,Default,,0000,0000,0000,,They can produce about two\Nthousand babies in their lifetime,
Dialogue: 0,0:10:30.12,0:10:31.95,Default,,0000,0000,0000,,so that's times two thousand.
Dialogue: 0,0:10:31.95,0:10:32.78,Default,,0000,0000,0000,,Ugh!
Dialogue: 0,0:10:32.78,0:10:36.28,Default,,0000,0000,0000,,Fifty mommy mosquitoes times\Ntwo thousand babies per mommy.
Dialogue: 0,0:10:36.28,0:10:41.71,Default,,0000,0000,0000,,You get births equaling one hundred\Nthousand little baby mosquitoes.
Dialogue: 0,0:10:41.71,0:10:43.36,Default,,0000,0000,0000,,Once we plug in all the\Nnumbers into this equation,
Dialogue: 0,0:10:43.36,0:10:44.76,Default,,0000,0000,0000,,even though this is\Ntotally a hypothetical,
Dialogue: 0,0:10:44.76,0:10:47.70,Default,,0000,0000,0000,,we will see the true scope\Nof Dallas' mosquito problem.
Dialogue: 0,0:10:48.23,0:10:51.12,Default,,0000,0000,0000,,Blink, in two weeks the population\Nhad a hundred thousand babies,
Dialogue: 0,0:10:51.12,0:10:53.36,Default,,0000,0000,0000,,and only a hundred of them died.
Dialogue: 0,0:10:53.36,0:10:55.84,Default,,0000,0000,0000,,This is a population growth\Nrate, if you do the math,
Dialogue: 0,0:10:55.84,0:10:57.85,Default,,0000,0000,0000,,of nine hundred and ninety nine.
Dialogue: 0,0:10:57.85,0:10:59.49,Default,,0000,0000,0000,,This means, that for\Nevery mosquito out there,
Dialogue: 0,0:10:59.49,0:11:00.36,Default,,0000,0000,0000,,at the beginning of two weeks,
Dialogue: 0,0:11:00.36,0:11:03.22,Default,,0000,0000,0000,,there will be ninety hundred\Nand ninety nine more,
Dialogue: 0,0:11:03.22,0:11:04.35,Default,,0000,0000,0000,,at the end of two weeks.
Dialogue: 0,0:11:04.35,0:11:08.00,Default,,0000,0000,0000,,That is a ninety nine thousand,\Neight hundred percent increase.
Dialogue: 0,0:11:08.00,0:11:09.50,Default,,0000,0000,0000,,By Thor's hammer!
Dialogue: 0,0:11:09.50,0:11:10.94,Default,,0000,0000,0000,,Again, these are hypothetical numbers,
Dialogue: 0,0:11:10.94,0:11:13.68,Default,,0000,0000,0000,,but it gives you a sense\Nof how a population,
Dialogue: 0,0:11:13.68,0:11:15.09,Default,,0000,0000,0000,,can just go out of control,
Dialogue: 0,0:11:15.09,0:11:17.69,Default,,0000,0000,0000,,when all the factors we\Ntalk about go in its favor.
Dialogue: 0,0:11:17.69,0:11:19.62,Default,,0000,0000,0000,,You guys haven't even seen\Ntrouble until you see,
Dialogue: 0,0:11:19.62,0:11:22.20,Default,,0000,0000,0000,,what the graph of human\Npopulation looks like,
Dialogue: 0,0:11:22.20,0:11:24.00,Default,,0000,0000,0000,,over the last couple millennia.