3: Elevational Gradients

Question 1

Describe the climatic variation along a tropical mountain

Answer 1

• Lapse rates - air cools at c. 3oC/300m when saturated & 1.5oC/300m when unsaturated
• Cooling condenses water vapour → precipitation → drier air on leeward (sheltered) side of mountain

Question 2

Mountains generate strong gradients in ______ and ___________. What is this equivalent to?

Answer 2

temp and precipitation. This is equivalent to large scale latitudinal variation

Question 3

Due to _____ diversity, some people argue that the amazon basin has a lower biodiversity compared to montane regions e.g the Andes.

Answer 3

Beta diversity = how species composition changes across diff locations
- Much higher residual richness in montane areas

Question 4

Most of variation in climate is in montane environs, relatively low in lowland areas (e.g Amazonia and Cerrado).
→ Why does this mean there are more species in montane environs?

Answer 4

because there’s a bigger temp range = more specialist species

Question 5

Describe Janzen (1967) study into why mountain passes are higher in the tropics?

Answer 5

→ barriers to species dispersal greater on tropical mountains, i.e mountain passes are higher (= harder to cross) in the tropics
- At a given elevation tropical mountain species experience less variation than temperate species
- Physiological tolerances thus reduced and species have narrower elevational distributions that increase β diversity
- Altitudinal equivalent of Rapoport’s rule

Question 6

What can quaternary climatic shifts lead to?

Answer 6

lead to periods of isolation of biota on mountain tops - may promote more speciation

Question 7

Define Inversion layer refugia, how does this relate to speciation?

Answer 7

= small valleys at high elevations have caps of cold air that trap very stable warm air beneath for extremely long periods.
This stability has been hypothesized to promote speciation

Question 8

What does the study on Kilimanjaro show about patterns across taxa?

Answer 8

Looked at
- temp
- Precipitation
- NPP
- land area

Some groups show evidence for classic predictions based on temp, others for mid domain models

BUT, if you group together (e.g all plants, all animals) get clear evidence for negative relationships between no. of species and elevation

Question 9

Describe the mid-domain model

Answer 9

If a species richness is randomly distributed, ranges overlap increasingly in the centre
= controversial

Question 10

What are the 2 main reasons hypothesised as why species richness varies with elevation

Answer 10

• Some studies/taxa show support for mid domain, but not perfect predictions
• At larger taxonomic scales, at least some studies provide strong evidence for climatic factors, especially temperature

Question 11

Why are there more niches in mountain habitats?

Answer 11

Due to elevation creating climate variation, there is high vegetation differentiation = more niches