DO LEMMINGS COMMIT SUICIDE?

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DO LEMMINGS COMMIT SUICIDE?

• Beautiful Hypotheses and Ugly Facts

Dennis Chitty, 1996
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WHATS A LEMMING?

• KingdomAnimal
• PhylumChordata
• ClassMammalia
• OrderRodentia (gnawing teeth)
• FamilyCricetidae (mice, rats, voles)
• GeneraN about 7
• SpeciesN about 20

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Lemming habitat
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Brown lemming (Lemmus sibericus)
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Collared lemming (Dicrostonyx torquatus)
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Norway lemming (Lemmus lemmus)
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Wood lemming ( Myopus schisticolor)
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Bog lemming (Synaptomys borealis)
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Winter
Summer
Brown lemming
Molting
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WINTER LEMMING
SUMMER CLAWS
WINTER CLAWS
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What lemmings do.

• Eat green vegetation
• Dont hibernate active summer and winter
• Breed like rabbits!

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Lemming reproduction

• Average 4-6 young per litter
• Gestation 3 weeks
• Weaned at 3 weeks of age
• Can mature at 4 weeks of age
• Breed post-partum (on the day they give birth)
  simultaneously pregnant and lactating!

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Small mammals in general

• 20-50 gm as adults
• 2 gm at birth
• 10 gm at weaning
• Mature when 80 of adult size usually within
  weeks of weaning
• Breed repeatedly but usually only in summer

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A human perspective

• 130 lb mom
• Quintuplets
• Each baby 12 lb at birth
• Conceive again on day of birth
• Babies weaned at 60 lb each
• Give birth again next week

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How many lemmings?
Number of generations
Nt N0 Rg
Predicted number
Rate
Number to start
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• Number to start 2 (1 mom 1 dad)
• Rate babies per adult 6/2 3
• Generation time (weeks from mom giving birth to
  offspring giving birth) 7 weeks
• Number of generations in 5 month summer (20 wks/7
  2.9

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Number at the end of summerfrom 2 parents
2 X 32.9 48!
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BUT WAIT!
Snow is good insulation!
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Lemmings can breed in winter too!
52 weeks 7.4 generations!
2 lemmings become 6,788 lemmings in 1 year!
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In reality..
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Nevertheless..lemmings can be abundant, in a
cyclic sort of way.
Finerty, 1980
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Northern populations only
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Cycle characteristics.
Chitty, 1996
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Influences on populations
Chitty, 1996
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Influences on others.
Chitty, 1996
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WHAT ABOUT THOSE MYTHS?
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MYTH 1

• LEMMINGS RAIN DOWN FROM THE SKY!

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MYTH 2

• PEOPLE TOUCHING LEMMINGS BECOME POISONED!

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MYTH 3

• LEMMINGS UNDERGO MASS MIGRATIONS!

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MYTH 4

• LEMMINGS COMMIT SUICIDE!