Tundra, a simple ecosystem

Question 1

tundra

Answer 1

• simple ecosystem with global importance
• type of plant community that grows in extreme environmental conditions
• 5% of global cover but 1/3 of global soil carbon
• stable store of carbon but threatened by global warming
• very cold and dry environment
• short growing season, ~3months 24hr sun
• high wind chill, no tree cover

Question 2

arctic amplification

Answer 2

• loss of albedo creating a positive feedback effect
• Arctic is warming at a faster rate than anywhere else

Question 3

vegetation in northern tundra

Answer 3

• no trees
• dwarf shrub and herb vegetation

Question 4

permafrost

Answer 4

• kilometres deep
• never thaws
• currently receding from climate change

Question 5

migratory birds

Answer 5

• snow geese in summer, maximum temperature less than 10C

Question 6

polygons

Answer 6

landscape features from annual freezing and thawing

Question 7

point Barrow, Alaska

Answer 7

• shallow pools and marshes
• 3-4m above sea level
• simple ecosystem, ~100 vascular plant species, 10 dominant species ~90% of vegetation biomass

Question 8

predators at point Barrow

Answer 8

• long tailed skuas and other skua species and snowy owls
• prey mainly on lemmings

Question 9

observations of predatory birds

Answer 9

• dramatic fluctuations in predatory bird populations
• McIlhenney (1897) visited & saw large number of predatory birds
• Anderson (1913 & 1915) visited but could not confirm McIIhenney’s earlier observations - very few skuas and snowy owls to be seen
• Pitelka (1952) took systematic observations in a permanent recording area (standardised data collection, only recorded birds occupying territories) but saw very few
• returned in 1953, dramatic increase

Question 10

lemmings at point Barrow

Answer 10

• collared and brown lemming species
• do not migrate at times of high numbers
• populations can fluctuate dramatically
• many predators including skuas, snowy owls, arctic foxes, weasels etc

Question 11

lemming habitats

Answer 11

• not evenly distributed, tend to occur in specific locations
• live in ice polygon depressions and burrow underground in better drained ramparts and slopes of troughs
• live in snow tunnels in winter

Question 12

plant consumption by lemmings

Answer 12

• perpetually night in winter so no vegetation growth
• high lemming numbers in winter eat everything leaving sparse plants for spring growth
• low lemming numbers in winter means there is plenty of vegetation cover left for spring growth

Question 13

experimental approach, lemming exclusion

Answer 13

• fenced off vegetation to create ‘exclosure’
• surrounding area grazed by lemmings, lemmings inside exclosure removed, so vegetation is left ungrazed
• vegetation inside exclosure relatively constant, control vegetation outside declined in years with large lemming numbers

Question 14

phosphorous

Answer 14

• phosphorous (P) is important in the diet of breeding mammals
• P is concentrated in the top 3-4cm of soil

Question 15

experimental approach, lemmings and quality of vegetation

Answer 15

Pitelka already shown a correlation between levels of phosphorous in vegetation and lemming numbers
Schulz (1960s) experiment:
- added P to soil as a fertiliser in the exclosure to see if lemmimg numbers were enhanced in non-lemming years
- density of nests were much larger inside the exclosure

Question 16

phosphorous levels when there has been heavy lemming grazing

Answer 16

• roots are mainly in active layer where P is concentrated
• bare soil absorbs more solar energy and vegetation holds snow and absorbs solar energy
• heavy lemming grazing leads to warming of soil, lowering the permafrost
• the roots can then grow past the P active layer in the surface soil
• this lowers the P content of the plant material
• lemming populations decline
• skua and other predator populations decline