Population Dynamics of Voles

16.2.2015

Population dynamics of voles

Janne Sundell Lammi Biological Station University of Helsinki

Konnevesi 15.2.2015

Outline

• Introduction: Northern voles • Monitoring methods • Introduction: cycles • Overview of hypotheses

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Voles • Subfamily; Arvicoline rodents • Appr. 70 species living in northern hemisphere • Includes species like muskrats and lemmings • Common, exhibit wide variation in abundance • Some, mainly northern populations, cyclic • Important part of the community – Common and numerous – Effect on vegetation – Support large number of predators • Important to us – Pests in forestry and agriculture – Vectors of many diseases

Voles of northern Europe • Two species of lemmings (Lemmus, Myopus) • Four species of ‘field voles’ (Microtus) • Three species of ‘forest voles’ (Myodes) • Water vole • Muskrat

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Voles of northern Europe • Two most common ones are: – The bank vole (Myodes glareolus) • Common, almost everywhere in Finland • Mainly granivorous • Habitat generalist living mainly in forests • Females territorial –limits density

Voles of northern Europe • The field vole (Microtus agrestis) • Common, almost everywhere in Finland • Mainly herbivorous • Lives mainly in fields and meadows • Young females live and breed close to their mothers – high densities possible

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Voles of northern Europe

1.0 Forest Microtus agrestis Forest linear regr. Clear-cut Clear-cut linear regr. 0.8 Field Field linear regr.

0.6

0.4

0.2

0.0

1.0 Myodes glareolus

0.8 Relative use of habitat

0.6

0.4 Henttonen & Hansson 1984

0.2

0.0 0.00 0.05 0.10 0.15 0.20 Density Sundell et al. 2012 JAE

Voles of northern Europe • The bank vole is partly replaced by the grey-sided vole (M. rufocanus) and the red vole ( M. rutilus) in the north • The sibling vole (M. levis) locally abundant e.g. western Finland

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Voles of northern Europe

• The field vole is partly replaced by the root vole (M. oeconomus) in the north

Voles of northern Europe

• Due to species’ distribution the most vole species rich area in Finland is Lapland – Nine species – Why?

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Relationship between vole species • Generally larger species dominate smaller species • Competition ‘severe’ during population highs – Dynamics generally synchronous • Competition leads to slightly asynchronous dynamics? • Habitat selection reduces competition: – Wood lemming; old growth forests – Norwegian lemming; tundra – Muskrat and water vole; wet habitats

Relationship between vole species

Henttonen et al. 1977 Henttonen & Hansson 1984

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Vole monitoring

• Necessary for study of dynamics • In Finland Finnish Forest Research Institute monitors vole populations with biannually in +20 sites • Additionally, some amateur ornithologists and researchers monitor voles (<10 sites)

Vole monitoring: methods

• Snaptraps • Systemically – Density index • E.g. Small Quadrat Method, trap lines – Ind./100 trap nights

15 m

2 m

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Vole monitoring: methods

• Live trapping • Systemically in small area; a grid – Density estimates (CMR) • Additional data on many variables; survival, behaviour • Does not remove ind. from pop. • Too laborious for large areas

Vole monitoring: methods

• Indirect methods – Tracks • Snow • Foraging • Burrows, nests • Pellet counts – Predator abundance/breeding success – Predator diet • Only abundance indices

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Vole monitoring: time series

• Regular monitoring yields time series of abundance = population dynamics • Lots of statistical tools to detect density dependence, periodicity, trends, synchrony etc.

Population cycles

• ’Regular’ multiannual fluctuations, not seasonal fluctuations – Period: cycle length – Amplitude: difference between min and max density

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Population cycles • Density dependence: delayed vs. direct

– 2nd order autoregressive model: xt=β0+β1xt−1+β2xt−2+εt – Royama triangle • Autocorrelation functions (ACF)

Ims et al. 2008 TREE

Population cycles

• Divided into different phases

Peak Density

Low

Years

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Vole cycles: brief history

• The Bible and historical writings on periodic mass occurrences • Collett 1911-1912: Norges pattedyr; fluctuations of lemmings and other mammals • Hewitt 1921: fluctuations of wildlife in Canada

Vole cycles: brief history

• Elton 1924: Periodic fluctuations in numbers of animals: their causes and effects • Elton 1942: Voles, mice and lemmings: problems in population dynamics • Oxford: Bureau of Animal Population • 1960-1980; dispute on cycles, different schools • Hundreds of papers and more than 20 reviews

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Nature of northern vole cycles • 3-5 year population cycles in voles – Gradient in cycle length and amplitude • Large-scale spatial synchrony • Temporal synchrony between many species • Phase-related changes in life history characteristics • Summer declines • Winter breeding

Cycle length

• Gradient in cycle length: 4-5 years in northern and 3-4 years in southern Finland, more south mainly seasonal fluctuations, occasional outbreaks Hansson & Henttonen 1988

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Turchin & Hanski 1997 Cycle length

Hanski et al. 1991 D

Hansson & Henttonen 1988

5 5 5 4 5 5 5 5 4 4 5 5 5 4 4 5 5 5 5 5 5 5 2 2 5 5 5 5 3 3 5 6 3 3 3 6 4 3 3 3 4 4 3 3 3 3 4 4 3 3 3 3 4 2 3 3 3 4 3-4 4 3 3 3 3 3 3 3 3 4 3 3 3 3 3 3 3 4 ) S - N s 5 r S - N a 3 3 3 3 3 4 4 4 5 4

e W - E y

( W - E

3 3 3 3 3 4 3 3 0 5 h t 4 g 3 3 3 3 3 3 7 3 3 3 3 n e l 3 3 3 3 3 3 3 3 3 3 e l 3 c y 3 3 3 3 3 3 3 3 4 4 3 C 3 3 3 3 3 3 3 3 4 4 2 Latitude 660 685 710 735 760 785 3 3 3 3 3 3 3 3 3 Longitude 15 40 65 90 4 3 3 3 3 3 3 Sundell et al. 2004

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Turchin & Hanski 1997 Hanski et al. 1991

Hanski & Korpimäki 1995

Vole cycles • 3-5 year population cycles in voles – Gradient in cycle length and amplitude • Large-scale spatial synchrony • Temporal synchrony between many species • Phase-related changes in life history characteristics • Summer declines • Winter breeding

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1.0 Cluster 1 0.8 Cluster 2 Cluster 3

t Cluster 4 n All

e 0.6 i c i f f e

o 0.4 c n o i t 0.2 a l e r r o 0.0 C

-0.2

-0.4 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 Distance (km) Sundell et al. 2004 Hellstedt et al. 2006

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Hanski & Henttonen 1996 M. agr Synchrony between M. oec species Myo rut

25 s t

h Bank voles Microtus voles g i n 20

p Myo gla a r t

0 15 0 1 / s l a 10 u d i v i

d 5 n

I Myo ruf

0 1984 1986 1988 1990 1992 Year Sundell & Norrdahl 2002

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Sundell & Norrdahl 2002 180 150 Increase 120 Chitty effect 90 60

0 • Voles are larger in 5 11 17 23 29 35 41 47 53 59 s l

a 180 u

increase and peak d i 150 v i

d 120 Peak n

phases than in decline i

f 90 o

r 60 (or low) phase e b 30 m u 0 • Phase-dependent N 5 11 17 23 29 35 41 47 53 59 changes also in 70 60

50 reproduction and Decline 40 survival (proportion of 30 20 mature voles, breeding 10 0 5 11 17 23 29 35 41 47 53 59 season length…) Body mass (g)

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Hanski & Henttonen 1996

M. agr Summer decline M. oec

Myo rut

Spring

Autumn Myo gla

Myo ruf

Hanski & Henttonen 1996

M. agr Winter breeding M. oec

Myo rut

Spring

Autumn Myo gla

Myo ruf

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Hypotheses on cycles

Olaus Magnus 1555

Hypotheses on cycles • Many different hypotheses to explain the phenomenon >20 – Abiotic factors: weather, sun spots – Intrinsic biotic factors: changes in quality of individuals during the cycle, density induced stress – Extrinsic biotic factors: food quality/quantity, parasites, diseases and predation – Multifactorial hypothesis; necessary and sufficient factors

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Take home messages • Vole populations fluctuate strongly • Periodic fluctuations, cycles, are common in northern populations • Characteristics for cycles are: – Periodicity of 3-5 years – High amplitude – Geographical trends in period and amplitude – Extensive synchrony over space and species – Summer decline and winter breeding

Take home messages • Explanations for cycles are numerous • No consensus about factors behind cycles • You will hear more about some of them

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