Prepare for the Ice Age

Question 1

Millankovitch cycles

Answer 1

Schematic of the Earths orbital cycles, results in ice ages (Rhamstorf & Schellnhuber, 2006)

Question 2

Eccentricity

Answer 2

96,000 year periodicity – more elliptical orbit- greater seasonal contrasts in solar radiation

Question 3

Obliquity

Answer 3

42,000 year periodicity – when the angle is greater, seasons are more marked; summers in both hemispheres receiving more energy from the Sun, and the winters less.

Question 4

Precession

Answer 4

‘Wobble’ – 21,000 year periodicity

Again affects strengths of seasons – from similar in both hemispheres to more marked in one or the other.

Question 5

Role of Antarctica?

Answer 5

Drakes Passage opened 34 Million years ago (Livermore, 2005) Between the Eocene & Oligocene

South America and Antarctica split apart very rapidly. This formed the Drake Passage and resulted in a major global cooling. Weddel Sea

Profound effect on Southern Ocean circulation and subsequently climate

Question 6

Role of the Tibetan Plateau?

Answer 6

India collides with Asia ca. 45 MYA

Tibetan Plateau is uplifted, particularly in last 10 MY

Tibetan Plateau disrupts global air circulation

Question 7

The role of the Isthmus of Panama?

Answer 7

Atlantic and Pacific became isolated as the isthmus closed

Closure of isthmus ca. 3 MYA results in current global ocean circulation pattern – the conveyer

Gulf stream moves warm waters north….more ice and snow in arctic, Global Ocean Conveyer, 100 year

Question 8

What are the ecological and evolutionary consequences of Pleistocene ice ages?

Answer 8

The latitudinal gradient in species richness (see Mittelbach et al., 2007)

Extinctions at high latitudes – greatest impact in Northern Hemisphere

Narrow-range endemics are not evenly distributed – concentrated in the tropics

Pleistocene glaciations may have driven diversification – refuge hypothesis (see Knapp & Mallet, 2003 & Mittelbach et al., 2007)

Question 9

What is Rapoport’s rule, Stephens, 1989

Brown, 1995; Gaston, 2003

Answer 9

The latitudinal gradient in species richness is paralleled by a latitudinal gradient in geographical-range size

Question 10

Why are very few endemics at high latitudes?

Answer 10

Communities in formerly glaciated areas assembled recently

It is certain that the fauna of any such region is qualitatively poorer than that of warm temperate and tropical areas of comparable effective precipitation. It is probably considered to be intuitively obvious that this should be so, but on analysis the obviousness tends to disappear. If we can have one or two species of a large family adapted to the rigors of Arctic existence, why can we not have more?

Hutchinson (1959)