[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:00.58,0:00:02.28,Default,,0000,0000,0000,,- [Voiceover] What I\Nwanna do in this video
Dialogue: 0,0:00:02.28,0:00:04.26,Default,,0000,0000,0000,,is think about how different populations
Dialogue: 0,0:00:04.26,0:00:06.30,Default,,0000,0000,0000,,that share the same ecosystem can interact
Dialogue: 0,0:00:06.30,0:00:08.24,Default,,0000,0000,0000,,with each other and actually provide
Dialogue: 0,0:00:08.24,0:00:10.12,Default,,0000,0000,0000,,a feedback loop on each other.
Dialogue: 0,0:00:10.12,0:00:11.53,Default,,0000,0000,0000,,And there's many cases of this,
Dialogue: 0,0:00:11.53,0:00:13.66,Default,,0000,0000,0000,,but the most cited general example
Dialogue: 0,0:00:13.66,0:00:15.52,Default,,0000,0000,0000,,is the case when one population
Dialogue: 0,0:00:15.52,0:00:18.03,Default,,0000,0000,0000,,wants to eat another population.
Dialogue: 0,0:00:18.03,0:00:21.19,Default,,0000,0000,0000,,And so you have the predator population
Dialogue: 0,0:00:21.19,0:00:23.99,Default,,0000,0000,0000,,that likes to eat the prey.
Dialogue: 0,0:00:23.99,0:00:27.77,Default,,0000,0000,0000,,So you have the predator\Nand prey interactions.
Dialogue: 0,0:00:27.77,0:00:29.51,Default,,0000,0000,0000,,I'm doing the prey in I guess\Na somewhat bloody color,
Dialogue: 0,0:00:29.51,0:00:31.76,Default,,0000,0000,0000,,I guess 'cause, well,\Nthey're going to be eaten.
Dialogue: 0,0:00:31.76,0:00:33.61,Default,,0000,0000,0000,,So let's just think about how these
Dialogue: 0,0:00:33.61,0:00:35.27,Default,,0000,0000,0000,,populations could interact.
Dialogue: 0,0:00:35.27,0:00:37.62,Default,,0000,0000,0000,,Let me draw a little chart\Nhere that you're probably
Dialogue: 0,0:00:37.62,0:00:39.33,Default,,0000,0000,0000,,familiar with by now where we show
Dialogue: 0,0:00:39.33,0:00:42.34,Default,,0000,0000,0000,,how a population can change over time.
Dialogue: 0,0:00:42.34,0:00:44.94,Default,,0000,0000,0000,,So the time, the horizontal axis is time.
Dialogue: 0,0:00:44.94,0:00:47.60,Default,,0000,0000,0000,,The vertical axis is population.
Dialogue: 0,0:00:49.34,0:00:50.26,Default,,0000,0000,0000,,Population.
Dialogue: 0,0:00:51.55,0:00:53.60,Default,,0000,0000,0000,,And so let's just, in our starting point,
Dialogue: 0,0:00:53.60,0:00:56.85,Default,,0000,0000,0000,,let's say that our prey is starting out
Dialogue: 0,0:00:58.26,0:01:00.40,Default,,0000,0000,0000,,at a relatively high point.
Dialogue: 0,0:01:00.40,0:01:02.17,Default,,0000,0000,0000,,Let's say we're right there in time,
Dialogue: 0,0:01:02.17,0:01:03.96,Default,,0000,0000,0000,,and let's say for whatever reason,
Dialogue: 0,0:01:03.96,0:01:07.48,Default,,0000,0000,0000,,our predator population is relatively low.
Dialogue: 0,0:01:07.48,0:01:09.82,Default,,0000,0000,0000,,So what do we think is\Ngoing to happen here?
Dialogue: 0,0:01:09.82,0:01:12.69,Default,,0000,0000,0000,,Well, at this point, with\Na low density of predators,
Dialogue: 0,0:01:12.69,0:01:15.25,Default,,0000,0000,0000,,it's gonna be much easier\Nfor them for find a meal,
Dialogue: 0,0:01:15.25,0:01:18.01,Default,,0000,0000,0000,,and it's gonna be much easier\Nfor the prey to get caught.
Dialogue: 0,0:01:18.01,0:01:20.75,Default,,0000,0000,0000,,So since it's more easy,\Nit's easier for the predators
Dialogue: 0,0:01:20.75,0:01:23.07,Default,,0000,0000,0000,,to find a meal, you can\Nimagine their population
Dialogue: 0,0:01:23.07,0:01:25.60,Default,,0000,0000,0000,,starting to increase.
Dialogue: 0,0:01:25.60,0:01:26.75,Default,,0000,0000,0000,,But what's going to happen is
Dialogue: 0,0:01:26.75,0:01:28.20,Default,,0000,0000,0000,,their population is increasing.
Dialogue: 0,0:01:28.20,0:01:30.20,Default,,0000,0000,0000,,Well, it's gonna be more\Nlikely that they're gonna,
Dialogue: 0,0:01:30.20,0:01:32.31,Default,,0000,0000,0000,,they prey is gonna get caught.
Dialogue: 0,0:01:32.31,0:01:34.16,Default,,0000,0000,0000,,There's gonna be more\Nof their hunters around,
Dialogue: 0,0:01:34.16,0:01:35.35,Default,,0000,0000,0000,,more of their predators around.
Dialogue: 0,0:01:35.35,0:01:39.05,Default,,0000,0000,0000,,So that population is\Ngoing to start decreasing
Dialogue: 0,0:01:39.05,0:01:42.40,Default,,0000,0000,0000,,all the way to a point\Nwhere if the population
Dialogue: 0,0:01:42.40,0:01:44.21,Default,,0000,0000,0000,,of the prey gets low enough, the predators
Dialogue: 0,0:01:44.21,0:01:45.92,Default,,0000,0000,0000,,are gonna have, they're gonna start having
Dialogue: 0,0:01:45.92,0:01:49.36,Default,,0000,0000,0000,,trouble finding food again,\Nand so that their population
Dialogue: 0,0:01:49.36,0:01:51.98,Default,,0000,0000,0000,,might start to decrease,\Nand as their population
Dialogue: 0,0:01:51.98,0:01:53.97,Default,,0000,0000,0000,,decreases, what's gonna\Nhappen to the prey?
Dialogue: 0,0:01:53.97,0:01:56.47,Default,,0000,0000,0000,,Well, then, there's gonna\Nbe less predators around,
Dialogue: 0,0:01:56.47,0:01:59.16,Default,,0000,0000,0000,,so they might be able to, their population
Dialogue: 0,0:01:59.16,0:02:00.80,Default,,0000,0000,0000,,might start to increase.
Dialogue: 0,0:02:00.80,0:02:02.72,Default,,0000,0000,0000,,And so I think you see what's happening.
Dialogue: 0,0:02:02.72,0:02:05.96,Default,,0000,0000,0000,,The predator and prey,\Nthey can kind of form
Dialogue: 0,0:02:05.96,0:02:08.53,Default,,0000,0000,0000,,this cyclic interaction with each other.
Dialogue: 0,0:02:08.53,0:02:10.01,Default,,0000,0000,0000,,And what I've just drawn,\Nthis is often known
Dialogue: 0,0:02:10.01,0:02:12.26,Default,,0000,0000,0000,,as the predator-prey cycle.
Dialogue: 0,0:02:13.56,0:02:16.10,Default,,0000,0000,0000,,And I just reasoned through\Nthat you can imagine
Dialogue: 0,0:02:16.10,0:02:17.59,Default,,0000,0000,0000,,a world where you can\Nhave the cycle between
Dialogue: 0,0:02:17.59,0:02:19.69,Default,,0000,0000,0000,,predator and prey populations.
Dialogue: 0,0:02:19.69,0:02:22.23,Default,,0000,0000,0000,,But you can also run computer simulations
Dialogue: 0,0:02:22.23,0:02:24.63,Default,,0000,0000,0000,,that will show this,\Nand even observational
Dialogue: 0,0:02:24.63,0:02:27.19,Default,,0000,0000,0000,,data out in the field also shows this.
Dialogue: 0,0:02:27.19,0:02:29.77,Default,,0000,0000,0000,,One of the often cited examples
Dialogue: 0,0:02:30.95,0:02:35.11,Default,,0000,0000,0000,,is interactions between,\Nbetween the snowshoe hare,
Dialogue: 0,0:02:37.67,0:02:41.09,Default,,0000,0000,0000,,which would be the prey in this situation,
Dialogue: 0,0:02:41.09,0:02:45.56,Default,,0000,0000,0000,,and the Canadian lynx,\Nwhich would be the predator,
Dialogue: 0,0:02:45.56,0:02:48.15,Default,,0000,0000,0000,,the predator in this situation.
Dialogue: 0,0:02:49.62,0:02:52.84,Default,,0000,0000,0000,,And you see a very similar\Ncycle to what I just drew,
Dialogue: 0,0:02:52.84,0:02:54.26,Default,,0000,0000,0000,,kind of just reasoning through it,
Dialogue: 0,0:02:54.26,0:02:56.50,Default,,0000,0000,0000,,and this, right here, is actual data.
Dialogue: 0,0:02:56.50,0:02:58.76,Default,,0000,0000,0000,,You see the passage of time here,
Dialogue: 0,0:02:58.76,0:03:00.55,Default,,0000,0000,0000,,and this is a long passage of time.
Dialogue: 0,0:03:00.55,0:03:02.30,Default,,0000,0000,0000,,We're starting in the early 1800's
Dialogue: 0,0:03:02.30,0:03:06.55,Default,,0000,0000,0000,,going all the way to the early-mid 1900's.
Dialogue: 0,0:03:06.55,0:03:08.72,Default,,0000,0000,0000,,So it's roughly 100 years\Nof data that we're showing,
Dialogue: 0,0:03:08.72,0:03:11.16,Default,,0000,0000,0000,,and in the vertical axis,\Nyou have thousands of animals
Dialogue: 0,0:03:11.16,0:03:13.13,Default,,0000,0000,0000,,and we're plotting both the population
Dialogue: 0,0:03:13.13,0:03:16.68,Default,,0000,0000,0000,,of snowshoe hares and Canadian lynx
Dialogue: 0,0:03:16.68,0:03:19.25,Default,,0000,0000,0000,,in a certain area on this chart.
Dialogue: 0,0:03:19.25,0:03:22.59,Default,,0000,0000,0000,,And as you see, when the prey population
Dialogue: 0,0:03:23.60,0:03:26.44,Default,,0000,0000,0000,,is high, when the prey population,
Dialogue: 0,0:03:27.50,0:03:29.75,Default,,0000,0000,0000,,sorry, when the predator\Npopulation is high,
Dialogue: 0,0:03:29.75,0:03:32.34,Default,,0000,0000,0000,,when we have a lot of\Nthe Canadian lynx around,
Dialogue: 0,0:03:32.34,0:03:35.59,Default,,0000,0000,0000,,that we see a lower, a lower population
Dialogue: 0,0:03:37.70,0:03:40.60,Default,,0000,0000,0000,,of the prey, of the hare.
Dialogue: 0,0:03:40.60,0:03:44.08,Default,,0000,0000,0000,,But then as, since you\Nhave a low population
Dialogue: 0,0:03:44.08,0:03:46.48,Default,,0000,0000,0000,,of the food in this situation,
Dialogue: 0,0:03:46.48,0:03:49.68,Default,,0000,0000,0000,,the predator population\Nstarts to decrease.
Dialogue: 0,0:03:49.68,0:03:51.15,Default,,0000,0000,0000,,So let me draw an arrow here.
Dialogue: 0,0:03:51.15,0:03:53.62,Default,,0000,0000,0000,,The predator population starts to decrease
Dialogue: 0,0:03:53.62,0:03:56.49,Default,,0000,0000,0000,,and, let me do that same blue color.
Dialogue: 0,0:03:56.49,0:03:59.54,Default,,0000,0000,0000,,And so the predator population decreases,
Dialogue: 0,0:03:59.54,0:04:01.82,Default,,0000,0000,0000,,and as that predator population decreases,
Dialogue: 0,0:04:01.82,0:04:04.54,Default,,0000,0000,0000,,well then the prey population increases
Dialogue: 0,0:04:04.54,0:04:08.33,Default,,0000,0000,0000,,'cause there's less folks\Naround to hunt them.
Dialogue: 0,0:04:08.33,0:04:10.52,Default,,0000,0000,0000,,So the prey population increases,
Dialogue: 0,0:04:10.52,0:04:12.14,Default,,0000,0000,0000,,and you see that the other way around.
Dialogue: 0,0:04:12.14,0:04:15.17,Default,,0000,0000,0000,,When the prey population\Nis really is, well maybe
Dialogue: 0,0:04:15.17,0:04:16.95,Default,,0000,0000,0000,,we'll show it right over\Nhere, and this is real data.
Dialogue: 0,0:04:16.95,0:04:18.87,Default,,0000,0000,0000,,That's why it's not always super clean.
Dialogue: 0,0:04:18.87,0:04:22.90,Default,,0000,0000,0000,,But when the prey population\Nis really, really high
Dialogue: 0,0:04:22.90,0:04:26.83,Default,,0000,0000,0000,,and the predator population\Nis relatively low,
Dialogue: 0,0:04:26.83,0:04:29.41,Default,,0000,0000,0000,,well, then, the predators\Nsay, "Hey, it's really
Dialogue: 0,0:04:29.41,0:04:31.56,Default,,0000,0000,0000,,"easy for us to find meals right now."
Dialogue: 0,0:04:31.56,0:04:33.17,Default,,0000,0000,0000,,That's kind of that\Nstarting point in that,
Dialogue: 0,0:04:33.17,0:04:34.88,Default,,0000,0000,0000,,when I was just reasoning through it.
Dialogue: 0,0:04:34.88,0:04:37.43,Default,,0000,0000,0000,,And so their population starts to.
Dialogue: 0,0:04:37.43,0:04:38.54,Default,,0000,0000,0000,,Oh, oops, what did I do?
Dialogue: 0,0:04:38.54,0:04:39.63,Default,,0000,0000,0000,,There, there.
Dialogue: 0,0:04:40.95,0:04:42.27,Default,,0000,0000,0000,,Let me make sure.
Dialogue: 0,0:04:42.27,0:04:45.36,Default,,0000,0000,0000,,So their population starts to increase,
Dialogue: 0,0:04:45.36,0:04:48.04,Default,,0000,0000,0000,,and as the predator population increases,
Dialogue: 0,0:04:48.04,0:04:51.76,Default,,0000,0000,0000,,well the prey population,\Nthe prey population
Dialogue: 0,0:04:51.76,0:04:53.51,Default,,0000,0000,0000,,is going to decrease.
Dialogue: 0,0:04:54.46,0:04:57.67,Default,,0000,0000,0000,,So this is real data\Nshowing the snowshoe hare,
Dialogue: 0,0:04:57.67,0:05:00.58,Default,,0000,0000,0000,,the prey, and the Canadian\Nlynx, the predator,
Dialogue: 0,0:05:00.58,0:05:03.31,Default,,0000,0000,0000,,on over many, many decades to show
Dialogue: 0,0:05:03.31,0:05:05.39,Default,,0000,0000,0000,,this predator-prey cycle.