Cannibalism in the animal kingdom - Bill Schutt
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0:07 - 0:10In the deserts of the American Southwest,
-
0:10 - 0:14spadefoot toad tadpoles
hatch in tiny oases. -
0:14 - 0:19Until they develop into toadlets,
they can’t survive outside of water, -
0:19 - 0:22but these ponds are transient
and quickly evaporate. -
0:22 - 0:25The tadpoles are
in a race against the clock -
0:25 - 0:28to grow up before
their nurseries disappear. -
0:28 - 0:32So nearly overnight,
some of the brood explode in size. -
0:32 - 0:36They use their jack-o-lantern teeth
and huge jaw muscles -
0:36 - 0:39to devour their smaller pond mates.
-
0:39 - 0:41Nourished by this extra fuel,
-
0:41 - 0:46they develop quicker,
leaving the pond before it can dry out. -
0:46 - 0:49The spadefoot toad
is far from the only animal -
0:49 - 0:54to eat members of its own species
as a normal part of its life cycle. -
0:54 - 0:56All of these animals do.
-
0:56 - 0:59If that surprises you,
you’re in good company. -
0:59 - 1:02Until recently, scientists
thought cannibalism -
1:02 - 1:06was a rare response to starvation
or other extreme stress. -
1:06 - 1:08Well-known cannibals,
-
1:08 - 1:10like the praying mantis
and black widow spider, -
1:10 - 1:13were considered bizarre exceptions.
-
1:13 - 1:17But now, we know they more
or less represent the rule. -
1:17 - 1:19While it may seem counterproductive
-
1:19 - 1:22for members of the same species
to eat each other, -
1:22 - 1:25cannibalism can promote the survival
of the species as a whole -
1:25 - 1:27by reducing competition,
-
1:27 - 1:28culling the weak,
-
1:28 - 1:30and bolstering the strong.
-
1:30 - 1:32Some species, like the spadefoot toad,
-
1:32 - 1:36cannibalize in response
to environmental pressures. -
1:36 - 1:38Their situation is precarious,
-
1:38 - 1:42but cannibalism for them isn’t
a last-ditch attempt to avoid starvation. -
1:42 - 1:45Rather, it’s a way to more quickly
outgrow a stage -
1:45 - 1:48where they’re especially vulnerable
to predation -
1:48 - 1:50or dangerous environmental conditions.
-
1:50 - 1:52Other species, including many fish,
-
1:52 - 1:57indiscriminately cannibalize each other
during foraging behavior. -
1:57 - 1:59Fish produce large numbers of tiny young,
-
1:59 - 2:04and adults exhibit about as much
individual recognition of their offspring -
2:04 - 2:07as humans do for a handful of raisins.
-
2:07 - 2:12Fish eggs, larvae, and juveniles
are easily available, nutrient-rich meals, -
2:12 - 2:14and with thousands of eggs in a clutch,
-
2:14 - 2:19plenty are still available to hatch
after the adults have snacked. -
2:19 - 2:23Baby fish aren’t just at risk of being
cannibalized by adults— -
2:23 - 2:26siblings eat each other too.
-
2:26 - 2:28Sand tiger shark eggs develop and hatch
-
2:28 - 2:32inside their mother’s oviducts
at different times. -
2:32 - 2:34When the hatchlings run out of yolk
from their own eggs, -
2:34 - 2:37they eat the other eggs and hatchlings
-
2:37 - 2:41until one baby shark
from each oviduct remains. -
2:41 - 2:45When they emerge, the young sharks
are well-nourished, experienced predators -
2:45 - 2:47who stand a better chance of surviving.
-
2:47 - 2:49Even when they aren’t consumed
for nutrition, -
2:49 - 2:53young animals are especially
vulnerable to cannibalism. -
2:53 - 2:54Hamsters,
-
2:54 - 2:54rats,
-
2:54 - 2:56and other rodent mothers
-
2:56 - 2:58will eat some of their young
if they’re sick, -
2:58 - 2:59dead,
-
2:59 - 3:02or simply too numerous to feed.
-
3:02 - 3:05In other mammals,
including bears and lions, -
3:05 - 3:08males will kill offspring
sired by another. -
3:08 - 3:13That’s because childless females become
receptive to mating more quickly -
3:13 - 3:15than if they were caring for a cub.
-
3:15 - 3:20Rather than waste nutritious meat,
the males then eat the dead cubs. -
3:20 - 3:24Meanwhile, cannibalism is less common
in birds than in other groups, -
3:24 - 3:28but certain species will eat diseased
or dead hatchlings -
3:28 - 3:33as a way of disposing of the
bodies before they can attract maggots. -
3:33 - 3:37When adults eat each other, males are
cannibalized more often than females, -
3:37 - 3:41usually during mating
and generally because they’re smaller. -
3:41 - 3:47Male Australian redback spiders
mate with much larger females. -
3:47 - 3:51Rather than scrambling away after mating,
the tiny male does a somersault, -
3:51 - 3:55bringing his abdomen into contact
with his mate’s mouthparts. -
3:55 - 4:01The female showers him with enzyme-rich
gut juice and consumes his abdomen. -
4:01 - 4:04Males not killed in the initial mating
crawl back into the fray, -
4:04 - 4:06often half-eaten,
-
4:06 - 4:10to mate again, after which they’re
dispatched to the spider pantry. -
4:10 - 4:13So not only does the male provide
the female with his sperm, -
4:13 - 4:16but he also provides her with
a nutritious meal -
4:16 - 4:21to better ensure that she’ll
survive to pass on his genes. -
4:21 - 4:23All in all, it’s clear
that cannibalism is -
4:23 - 4:26as much a part of life
in the animal kingdom -
4:26 - 4:29as other, better-recognized behaviors.
-
4:29 - 4:32As we sink our teeth into the evidence
of cannibalism in nature, -
4:32 - 4:34we might ask ourselves,
-
4:34 - 4:39what else have we missed by applying
human standards to the natural world?
- Title:
- Cannibalism in the animal kingdom - Bill Schutt
- Description:
-
View full lesson: https://ed.ted.com/lessons/cannibalism-in-the-animal-kingdom-bill-schutt
Until recently, scientists thought cannibalism was a rare response to starvation or other extreme stress. Well-known cannibals like the praying mantis and black widow were considered bizarre exceptions. But now, we know they more or less represent the rule. Bill Schutt shows how cannibalism can promote the survival of a species by reducing competition, culling the weak, and bolstering the strong.
Lesson by Bill Schutt, animation by Compote Collective.
- Video Language:
- English
- Team:
- closed TED
- Project:
- TED-Ed
- Duration:
- 04:58
Michelle Mehrtens edited English subtitles for Cannibalism in the animal kingdom - Bill Schutt | ||
Michelle Mehrtens edited English subtitles for Cannibalism in the animal kingdom - Bill Schutt | ||
Michelle Mehrtens approved English subtitles for Cannibalism in the animal kingdom - Bill Schutt | ||
Michelle Mehrtens accepted English subtitles for Cannibalism in the animal kingdom - Bill Schutt | ||
Michelle Mehrtens edited English subtitles for Cannibalism in the animal kingdom - Bill Schutt | ||
Jennifer Cody edited English subtitles for Cannibalism in the animal kingdom - Bill Schutt | ||
Jennifer Cody edited English subtitles for Cannibalism in the animal kingdom - Bill Schutt |