National Geographic
Strange Days on Planet Earth
Name ________KEY___________
Episode 3: PREDATORS!
These are some things to think about while you watch the movie – jot down some notes/answers to
these questions, and you may use this sheet to help you when you are asked to do a writing
assignment next class!
1. What are the biologists in the motor boats in Venezuela doing in the first part of the video?
What cause this flood?
They are trying to save the animals that are now marooned due to a flood caused by a hydroelectric plant
2. What is going on a few miles north at Lake Guri, Venezuela? A dam has caused man-made
islands where a big lake used to be, the plants (trees) are dying…only the toughest plants
survive, animal wildlife has disappeared to a great extent (howler monkeys, etc)
3. What is happening with the animals on Iguana Island? (think of the iguanas and howler
monkeys…)
Iguanas are many times their normal densities, and the howler monkeys are anti-social,
displaying bizarre behaviors… Another island has an obscene # of leaf-cutter ants…decimating
the plant life…
4. What do the scientists hypothesize for all of these changes that are taking place on these and
other related islands? How does the research with tortoises help support this hypothesis?
Predators fled the region
Tortoise rings show a babyboom after the flood?
5. How does this same idea affect areas like the one in which we live?
Termites, raccoons….we are fragmenting habitats and taking out top predators, which is
allowing lower trophic levels (many times, pests) to accumulate to high population numbers.
6. Why can’t we just put the predators back? They are dangerous, and we have changed the
environment so much that they may not even be able to survive in the “new” environments.
Yellowstone
1. What is wrong with the river? How is it different from pictures that we have of these stream
banks from the past? Much less vegetation now and much more barren landscape
2. What kinds of organisms used to be in Yellowstone (or used to be there in far greater numbers)?
Bison, beavers,
3. In trying to figure out why the aspen trees are disappearing so rapidly, what factors did the
scientists originally suspect to be the cause of this ecological disaster? Why did they reject these
ideas? Climate change, but then all surrounding areas would be affected. Forest fires, but….?
4. What did the scientists find when they took core samples of the trees and counted up with
growth rings? That there are no middle-aged trees or old trees – they are all from after 1930’s
5. How does the proposed explanation for these changes tie in to something that we studied much
earlier this year? Reintroduction of Yellowstone wolves
6. What are some positive effects that the wolves have on the ecosystem?
When they kill an organism, it is a beginning of other decomposer/detritivore activity. Provides
food and micro-ecosystems for hundreds of other organisms within the ecosystem.
KILLING elk controls the massive herbivory of the grasses and plants in the park. . Beavers
came back…has willows to feed off of…have materials to build their dams.
7. What are some negative effects or repercussions of reintroduction of the wolves? The issue with
the ranchers.
Coral Reefs – Discovery Bay, Jamaica
1. What kinds of organisms are the top predators in the sea, surrounding many coral reefs? (Back
before they disappeared in some ecosystems…) sharks, bass, etc (large fish)
2. How do they “look at the fossil record” of a coral reef? What did they discover?
Take a core sample down into the layers since the bottom layers of the reef are dead remains of
older coral. It’s only been within the past 20 years or so that there has been such a decline in
species diversity and health.
3. What clues does the fish market provide to help explain the destruction of the coral reefs? ‘
There are no more big fish being sold…
a. What does “fishing down the food web” mean, and how does this affect the reef? Being
forced to catch smaller fish and sell these because now the bigger fish are gone… these
fish are herbivorous, so they are now unable to control algae growth.
4. What happened when large predators were taken out of the system, and how did this affect the
coral? (There are several steps in the “chain” that contributed to this topple of the coral reef
ecosystems…what are they?) Big fish eat herbivorous fish, so now noone is controlling algae
growth, and then reef coral starts to die…
5. How has this impacted St. Lucia and the economics and cultural traditions there? Prayer for the
fishermen…people dying out there because their livelihood depends on fishing…
6. How have the Caribbean Islands attempted to “solve” the problems of overfishing and coral reef
decimation? Marine reserves…has made an impact – some big fish are beginning to return…