The mountain gorilla, spotted owl, giant panda, snow...

Key Concepts

r-selected Life History Traits

r-selected life history traits describe species that reproduce rapidly in large numbers with minimal investment in individual offspring. These traits are advantageous in unpredictable or unstable environments because the high reproductive output can quickly replenish populations after declines. However, r-selected species are less competitive in stable environments where resources are limited. When comparing with K-selected species, the rapid population growth of r-selected species provides a buffer against extinction in the face of high mortality rates.

Survivorship Curves

Survivorship curves are graphical representations that depict the number of individuals of a species surviving at each age. K-selected species typically exhibit a Type I survivorship curve, where most individuals survive early life and the majority of mortality occurs later in life. This contrasts with r-selected species, which often exhibit a Type III survivorship curve characterized by high mortality rates among juveniles, with survivors living much longer. The Type I curve of K-selected species further underscores their vulnerability to increased adult mortality, as loss of mature individuals can have a significant impact on the overall population regeneration.

K-selected Life History Traits

K-selected life history traits refer to strategies where species produce fewer offspring but invest significant resources in their development and parental care. This results in individuals that are highly competitive in stable environments, but their low reproductive rate makes populations more vulnerable to rapid environmental changes and human-induced pressures. In the context of endangered species, this trait means that recovery from population declines can be slow, as the species cannot quickly replace lost individuals.

Transcript

00:01 Hey there, this is a cool problem about k and r selected species.

00:07 It talks about gorillas, owls, pandas, leopards, and grizzly bears, and how they're all endangered because of human encroachment in their natural habitat.

00:21 They're all k -selected species, and you're trying to figure out why are they more endangered than our selected species, and what type of survivorship curb would you expect for each of these? okay, so first off we need to go over what r and k -selected species are.

00:41 So our selected species, here i'm going to do a little drawing over here.

00:47 They produce lots and lots of babies.

00:52 Usually some species that are selected are reptiles.

00:58 So let's do sea turtles.

01:03 Okay? so let's think about sea turtles really quick.

01:07 They lay like, i don't know, i think it's on average like 100, around 100 eggs.

01:14 That's a lot.

01:15 And you see on the documentaries and everything that there's a little nest, okay? you see that only like one survive, right? and you're like, why does that happen? why does only one survive? that seems crazy.

01:29 Well, the answer to that question is actually because it's an our selected species.

01:33 So basically what they do is our selected species produce a ton of babies.

01:40 However, they don't provide a lot of parental care because you basically are deciding, do you want to spend your energy raising that one child, putting all of your resources into that one child to make it the super seed turtle? you know what i mean? raise it, make sure it knows how to eat correctly, gets jellyfish, doesn't eat straws, you know, whatever.

02:03 Or do you want your probability to be higher by just having a ton of different eggs hoping that one of them survives from each clutch? this gives you a lot more options, right? if one of these eggs, one of these eggs dies, okay, gets cracked, whatever.

02:27 You still got this and there's more, really.

02:30 I just drawing a smaller amount.

02:33 You got this many options.

02:36 Accidents happen.

02:37 It happens quite frequently, actually.

02:39 So it's basically just based on where those animals live, what their environment selects for, on why they are and are selected species.

02:51 I basically draw on a survivorship curve over here.

02:56 I believe k -selected species are type 1.

03:00 And then r -selected are 3.

03:05 And then like a middle ground would be like birds who do like air right once use green which is type two go straight through the middle they have some parental engagement they but they do have multiple offspring right okay so on average if you have a doubt whether or not something that's an r or k selected species if it has scales assume that it's an r because reptile are usually what people think of when you are talking about our selected species because they produce a ton of different babies and then the majority of them die.

03:52 Lots of them are born without digestive systems or something.

03:56 Like they would never have survived.

03:58 But it's fine because there's so many of them that probability says that at least one will make it into a reproductive stage.

04:06 And that's how most biologists, by the way, measure like success of a species is reproductive success.

04:14 So how did it determine if an animal was successful in its lifetime is how many offspring they produce.

04:21 Okay? on the other hand, k -selected species, let's think.

04:27 Let's do, what's a cute animal? orangutans.

04:46 Okay, so orangutans are a case -elected species.

04:52 They produce one cute little baby.

05:02 Only one...