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    Optimal Width of Movement Corridors for Root Voles: Not Too Narrow and Not Too WideAuthor(s): Harry P. Andreassen, Stefan Halle and Rolf Anker ImsSource: Journal of Applied Ecology, Vol. 33, No. 1 (Feb., 1996), pp. 63-70Published by: British Ecological SocietyStable URL: http://www.jstor.org/stable/2405016.

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    Journal f

    Applied cology

    1996, 3,

    63-70

    Optimalwidth fmovementorridors or ootvoles:

    nottoo narrow ndnot oo wide

    HARRY P. ANDREASSEN, STEFAN HALLE and

    ROLF

    ANKER

    IMS

    Division fZoology,Department fBiology,Universityf Oslo, PO Box 1050

    Blindern, -0316 Oslo,

    Norway

    Summary

    1. The

    characteristics

    f male root vole movements

    s a

    function

    f

    corridorwidth

    were ested

    n

    a

    310

    m

    ong

    habitat orridor

    onnecting

    wo habitat atches.Detailed

    observations

    f movements eremade by means of radiotelemetrynd recording f

    footprints.

    2. The highest onnectivity,

    n

    terms

    f

    transferenceate

    f ndividuals

    n

    the

    orridor

    system,

    as observed

    n the

    ntermediate

    f three orridorwidths ested

    3 m,

    1

    m and

    0

    4

    m).

    3. The behaviouralmechanism ehind

    he

    owerconnectivity

    f the narrowest or-

    ridorwas a reluctance fvoles to enter t,while inearprogressnthewidest orridor

    was

    hampered y

    a

    high

    frequency

    f

    cross-directional

    ovements.

    4. The relationship etween

    orridorwidth nd movement ehaviourwas unaffected

    by

    the imulated

    resence

    f competitors

    nd

    predators.

    5. Our results

    hallenge

    he the-wider-the-better'

    rinciple

    f

    movement

    orridor

    design,

    nd

    provide

    lements

    or n

    understanding

    f the behaviouralmechanisms

    underlying

    hemovement

    cology

    f ndividuals

    n

    inearhabitats.

    Key-words:onnectivity,

    orridor

    esign,Microtus,

    movement

    cology.

    Journal

    fApplied cology

    1996) 33,

    63-70

    Introduction

    Habitat ragmentationasbeen ecognizeds a major

    threato wildlifeopulationsDiamond 976;Gilpin

    & Diamond 980;Higgs& Usher 980; oule 1986;

    Lande 1988; ms & Stenseth 989).As continuous

    habitats ecome ragmented,n immediateonse-

    quence

    s that he

    mobility

    f

    organisms

    ecomes

    restrictedFahrig& Merriam 985; Stamps t al.

    1987a,b; ahrig& Paleheimo 988;Burkey 989).

    This n turn ecreaseshe ffectiveize, nd, onse-

    quently,

    he

    viability

    f

    populationsSoule 1986;

    Boyce1992). t has been laimed hat henegative

    effectsf habitat ragmentationan be reduced y

    connecting

    solated

    ragmentsy

    narrow

    trips

    f

    habitat,ermed ovementorridorsWilson Willis

    1975;Harris 984;Bennett 990; aunders Hobbs

    1991). n the resentaperwe

    will

    dhere

    o the

    trict

    definitionf movementorridorss linear abitats

    allowingormovements,ut ot or ermanentettle-

    ment.

    The establishmentf movementorridorss cur-

    rentlymplementeds an expensive

    onservation

    strategy

    orld-wide

    Simberloff

    t

    al. 1992;

    Mann&

    Plummer 993). As very

    few tudieshave been able

    to obtain data about animalmovements

    n corridors

    (Hobbs 1992), heempirical asis for orridor esign

    is poor Simberloff& ox 1987; imberlofft al. 1992;

    Mann & Plummer 993).

    For instance, he effects f

    structural spects

    of habitat

    corridors,

    uch as cor-

    ridorwidth nd continuity, n movement ates are

    poorly known. Still, specificrecommendations n

    optimal orridor esignmay

    be found n the iterature

    (Noss 1987; Harrison

    1992; Merriam & Saunders

    1993). The urgent eed

    for mpirical tudies ddress-

    ingbasic questionsregardingmovement cology

    of

    individuals in linear habitats, has recentlybeen

    stressed

    see

    Hobbs 1992; nglis

    & Underwood

    1992;

    Simberlofft al.

    1992;

    Lindenmayer Nix 1993).

    We here

    resent

    ata from

    study

    wheremovement

    behaviour of

    the

    root vole Microtus oeconomus

    (Pallas)

    in

    corridors f varying idthwas subject o a

    detailed

    nalysis.

    We usedcorridorwidths themain

    treatment

    ariable,

    ecause

    t

    s themostbasic struc-

    tural haracteristic

    f

    inear abitats pon which rac-

    tical corridor

    design nevitably equires

    decision.

    Root voles were selected s the

    studyorganisms

    s

    they

    have

    proved

    to be veryusefulmodels forfield

    63

    ?

    1996

    British

    Ecological

    Society

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    64

    Optimalwidth f

    movement

    corridors

    experimentsnvolving abitatmanipulationsIms &

    Stenseth1989; Ims et al.

    1993;

    Wiens

    et

    al.

    1993).

    Moreover, lthoughweprimarily esigned his tudy

    to serve s an empirical

    model system sensu

    ms

    &

    Stenseth 989) for

    ddressing

    asic

    biological

    mech-

    anisms that mpinge n

    corridor esign e.g.

    move-

    mentbehaviour), ur results

    may

    have some direct

    implications or he onservation fremnant ootvole

    populations nEurope van Apeldoorn

    t

    al. 1992).

    We show hat ptimalwidth fmovementorridors

    in terms f habitat

    connectivity

    or root voles is

    a

    compromise

    betweennot too

    narrow and

    not too

    wide. Hence, our results hallenge he commonpre-

    sumption hatwider orridors ecessarilyre better

    corridors Noss 1987; Harrison

    1992;

    Merriam &

    Saunders

    1993).

    Methods

    STUDY PLOT AND MANIPULATIONS

    The study ookplaceatEvenstad ieldStation, outh-

    east

    Norway uring ugust-October

    992.The move-

    ment behaviourof

    individualmale root voles

    was

    studied n a fenced

    ystem

    onsisting

    f two habitat

    patches

    onnected

    y

    a 310

    m

    long

    corridor

    Fig. 1).

    The

    length

    f the

    corridorwas about one order

    of

    magnitude onger than the diameter f an

    average

    male rootvole homerange

    n

    non-linear abitatsIms

    et

    al.

    1993,

    nd

    unpublished).

    The twohabitat

    atches

    sed as release

    oints size:

    5

    x

    5 m) and the

    corridor onsisted f dense,homo-

    geneous

    meadow

    vegetation,

    nownto be

    preferred

    habitat

    by

    root voles

    (Ims et

    al.

    1993).

    An

    artificial

    runway ystemFig. 1)

    was established

    s

    0

    1

    m

    wide

    vegetation-freeaths

    long

    and acrossthe orridor o

    facilitatemovements

    n

    theotherwise

    ery

    ense

    grass

    carpet:

    one 310m

    long mid-runway

    nd cross-run-

    ways

    t

    1

    -m ntervals. hese

    runways

    ended o direct

    movements cross footprint lates see below).

    The

    area between he fences nd thecorridorwas cleared

    of vegetative over by means of herbicides Fig.

    1).

    The fenceswere established o hinder he intrusion

    of othervoles and mammalian redators uring he

    experiment.We expected hat the absence of female

    voles should motivate xploratorymovement Ims

    1988) or breedingdispersal Kawata 1989) in the

    experimentalmales. To ensure that the olfactorial

    environmentn the orridor t the tart fthe

    xperi-

    mentwas not very ifferento the situation ateron,

    some adult males were temporarily eleased

    n

    the

    corridor few

    days

    before he

    first

    xperimental

    rial

    was executed.

    We tested hreedifferentorridorwidths

    n

    com