Field Research on Small Rodents - NorecopaField Research on Small Rodents orwayleming Root voleN /...
Transcript of Field Research on Small Rodents - NorecopaField Research on Small Rodents orwayleming Root voleN /...
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Field Research on Small Rodents
Root vole / Tundra voleNorway lemming Grey-sided vole
Torbjørn ErgonUniversity of Oslo / Finse Research Center
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Studies of population cycles dateback to the 1920’s
Charles Elton, 1924
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Field research on small rodents today
Population dynamics Life-history theory Ecophysiology Ecosystem functioning
Basic science questions
Studies of animals in their natural environment
Replacement (alternatives) not possible
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Field research on small rodents today
Population dynamics Life-history theory Ecophysiology Ecosystem functioning
Basic science questions
Studies of animals in their natural environment
Replacement (alternatives) not possible
Instrumental for otherfields of (applied)
ecology
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Rodent cycles and climate change
Hörnfeldt, 2004
Henttonen & Wallengren, 2004
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Rodent cycles and climate changeLargest change in spring densities:
Hörnfeldt, 2004
SPRING AUTUMN
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Rodent cycles and climate changeLargest change in spring densities:
SPRING
Indications that this is due to worsesnow conditions during winter
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Understanding population (andecosystem) dynamics requiresknowledge about:
Population size and structure Survival rates Recruitment rates Fecundity Age at first reproduction Movements ...etc.
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Field methods in populationecological studies Radio tracking – equipment with
radio collars Capture-mark-recapture –
individual identification marks
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Collecting Capture-Mark-Recapture Data
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Capture-Mark-Recapture Data
Captured NOT captured
Session 1 Session 2 Session 3 Session 4
Captured NOT captured
1 0 1 0Ind. 1:
1 1 0 1Ind. 2:
...
Ind. 1:
Immature Immature NOT Captured Mature Ind. 2:
I I 0 MInd. 1:
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Capture-Mark-Recapture Data
Captured NOT captured
Session 1 Session 2 Session 3 Session 4
Captured NOT captured
1 0 1 0Ind. 1:
1 1 0 1Ind. 2:
...
Ind. 1:
Immature Immature NOT Captured Mature Ind. 1:
I I 0 MInd. 1:
Statistical modeling allows estimation of: (Capture probability) – dealing with imperfect detection
Survival probabilities
Recruitment rates
Maturation rates
Age of reproduction
Timing of life-history events
Population size and structure
... (parameters needed to understand population dynamics)
Need to mark ahigh number of
individuals
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Live-trapping Food in trap (e.g., grain and
carrots)
Cotton bedding when cold
Traps checked every ~6 hours
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Methods for individual marking
Ear tags- May cause infection
- May cause ear to rip
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Methods for individual markingEar tags
Toe clipping
5 × 5 × 6 × 6 -1 = 899 combinations
Some argue better thanear tags:- Less risk of infection
- Ear tags are obstacles thatcan get caught in vegetation
...but:- may be painful
- may reduce function (dependson species)
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Methods for individual markingEar tags
Toe clipping
Transponders(PIT-tags)
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Methods for individual markingEar tags
Toe clipping
Transponders(PIT-tags)
Best alternative:- low impact on animal
- reliable, can use automatic readers
...but:- rather expensive
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Experimental treatments:
Treatments of individuals Anti-parasite treatment
Treatments of the local environment Predator exclusion Supplemental feeding Habitat characteristics (fragmentation, hides, ...)
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Physiological measurements:
Blood samples (tail tipping) Energetic measurements by use of
doubly-labeled water Measuring body composition by ‘total body
electrical conductivity’ (TOBEC)
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Thank you for the attention!