Lecture 20

Question 1

What is the Isthmus of Panama?

Answer 1

Dry land connecting between North and South America.

First complete link between the Americas since the breakup of the Pangaea.

Question 2

How did the Isthmus of Panama get created?

Answer 2

Moving Caribbean Plate Tectonics.

Complex arrangement of multiple plates moving in different directions.

Question 3

What was the result of the tectonic events?

Answer 3

• mountains, volcanoes at plate boundaries.
• major topographic feature of isthmus.
• barrier to trans-oceanic circulation.

Question 4

What were the ocean circulation changes?

Answer 4

Previously, there was no oceanic circulation blockage.

then, circum tropical circulation of warm water is blocked and the warm water current is deflected north.

Question 5

What were the implications of the circulation changes?

Answer 5

Increased temperature difference between warm Caribbean/Gulf of Mexico and cool Pacific.

The deflection of Gulf Stream increases moisture in northern latitudes = snow and glaciation.

Question 6

What were the direct and indirect effects of Isthmus of Panama on the biological systems?

Answer 6

Direct effects:

• land bridge as a barrier to dispersal.
• land bridge as a corridor for dispersal.

Indirect effects:
- climatic changes, geological changes lead to subsequent changes in distribution, ecology.

Question 7

What are the lines of evidence for the closing of Isthmus?

Answer 7

• trade winds, upwellings and nutrients.
• fossils.
• shell formation.

Question 8

What was a consequences of the isolation of marine biota?

Answer 8

Speciation.

Question 9

What were the two types of environments created following the barrier?

Answer 9

1. Pacific:
   - deeper waters.
   - movement of nutrients, recycling of nutrients.
   - food chains due to energy sources.
   - high production due to high nutrients.
2. Caribbean:
   - shallow waters.
   - high diversity.
   - low nutrients.
   - construction = slow biological material created.

Question 10

Was was the fauna of North and South America before Isthmus?

Answer 10

Both continents had diverse fauna of large mammals, birds, etc filling all the usual terrestrial niches.

Question 11

What is convergent evolution?

Answer 11

Unrelated species subject to similar environmental and ecological conditions.

Selection pressures drive evolution in similar directions.

Species come to resemble each other - many examples in North and South America prior to connection.

Question 12

What are heralds and legions?

Answer 12

Successive waves of interchange.

Heralds: early colonizers - island hoping.
Legions: main invasive group - walkers and crawlers.

Question 13

What is the aftermath of the exchange of species between North and South America?

Answer 13

At least 50% of South American mammals are descendants of ancestors that came from North America.

Several extinction in South America mammal fauna.
- competition, predation.

Birds, reptiles, amphibians not as affected.

Question 14

What are new barriers between North and South America?

Answer 14

1. Replacement of the physical barrier (salt water) with an ecological barrier.

North and South America have very different vegetation patterns (rainforest, cloud forest vs grassland, desert or scrub forest).

2. Panama Canal = freshwater.