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Snow/Wolf/Elk Interactions in Yellowstone National Park. Craig Anderson. Institute of Arctic and Alpine Research Department of Geography University of Colorado-Boulder Boulder, Colorado. Overview. Introduction Background History Winter Mortality

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Snow/Wolf/Elk Interactions in Yellowstone National Park

Craig Anderson

Institute of Arctic and Alpine Research Department of Geography University of Colorado-Boulder Boulder, Colorado


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Overview

  • Introduction

  • Background

    • History

    • Winter Mortality

    • Index of Winter Severity

  • Current Research

  • My Research

  • Summary


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Introduction

  • Reintroduction of grey wolves (Canis lupus) into Yellowstone National Park 1995

  • Provided new opportunities to study several aspects of wolf predation

    • Effects of winter severity on predation patterns

    • Specifically elk (Cervus elaphus)


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Introduction

  • Previous studies focused on long-extant wolf-prey systems

  • Reintroduction allowed for studies focusing on mutual development of learned wolf and elk behavior simultaneously


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Possible Questions

  • How would the winter severity affect wolf predation on a previously wolf-free elk herd?

  • Would introduced wolves tend to take older, malnourished or otherwise vulnerable elk?

  • What is the kill rate and amount of prey consumed?


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Possible Questions

  • Would reintroduced wolves find predation so easy that they would eat small amounts from each kill?

  • Finally, and perhaps most importantly, how would these relationships be affected by winter severity?

    Other questions ???


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Northern Rocky Mountain wolves native to Yellowstone in 1872

Predator control prominent in late 1800’s and early 1900’s

Between 1914-1926 at least 136 wolveskilled

Background


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Background

  • Yellowstone wolves believed to be extinct by 1940

  • Wolves persistent in lower 48 states only in Minnesota and on Isle Royal in Michigan

  • Early 1980’s, wolves began to reestablish near Glacier National Park in northern Montana

  • By 1996, estimated 75 wolves inhabited Montana


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Background

  • Wolves are listed as “endangered” throughout its historic range in lower 48 except Minnesota where it is threatened

  • NPS policy calls for restoring native species under certain circumstances:

    • Sufficient habitat exists

    • Management can prevent threats to outside interests

    • Restored species resembles extirpated species

    • Extirpation resulted from human activities


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Background

  • October 1991 EIS begun on restoring wolves to Yellowstone and central Idaho

  • Several years of study and near record number of public comments

  • Finally, two wolf packs released in 1995 and 1996


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Background

  • USFS and Canadian wildlife biologists captured the wolves in Canada

  • The release was successful and wolves seen preying on elk shortly thereafter


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Winter Mortality

  • The primary prey for wolves in YNP is ungulates, specifically elk

  • Until reintroduction, mortality of most ungulates in winter due to malnutrition


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Winter Mortality

  • At reintroduction, the YNP elk herd was near or at ecological carrying capacity

  • Herd contained high numbers of old and vulnerable individuals

  • Herd #’s estimated between 14,000-20,000


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Winter Severity

  • Widely accepted that severe winter conditions are the primary cause of elk mortality in YNP

  • Heavy snowpack, cold temperatures, and inadequate forage contribute to significant mortality


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Winter Severity

  • Large ungulates can travel and forage in deep snow, but it also limits their mobility and increases overall energy expenditures

  • Predation, locomotion, browsing strategies, thermodynamic regulation and herd distribution all affected by winter snowpacks

  • Snowpack properties can play a significant role: density, hardness, depth, stratigraphy, SWE


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Winter Severity

  • However, lacking a substantive definition of “winter severity”

  • Yet to be adequately quantified

  • “Its like porn, you can’t define it, but you know it when you see it”


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Current Research

  • Index of Winter Severity (Farnes et al., 1999)

    Snowpack Distribution Across Yellowstone National Park

    http://nrin.nbii.gov/climate/ynp_report.pdf

    • IWS intended to estimate animals’ response to climatic and vegetative conditions on the winter range

    • Obtained by combining snow water equivalent (SWE), cumulative minimum temperatures below the effective critical temperature and forage availability on the winter range


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Index of Winter Severity (IWS)

  • Snow Water Equivalent (SWE)

    • Amount of water produced by melting snowpack

    • Snow depth x (snow density/water density)

    • Obtained from SNOTEL, snow courses and CLIM stations

    • As SWE increases:

      • Foraging area decreases

      • Energy expended in locomotion and foraging increases

      • Competitionfor forage increase


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Index of Winter Severity (IWS)

  • Effective Critical Temperatures (ECT)

    • When air temps are below the threshold ECT, elk must increase basal metabolic rate to maintain body temperature

    • Must utilize energy from fat reserves to maintain adequate body temps

    • Cumulative losses thru the winter

    • Calculated by subtracting ECT from minimum temperature and accumulated over the winter


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Index of Winter Severity (IWS)

  • Forage production

    • Production of summer forage critical to winter survival

    • Amount produced usually a function of available spring moisture and temperature

    • Uses Keetch-Byram Drought Index (KBDI) to determine amount of annual forage produced


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Index of Winter Severity (IWS)

  • Combination of these three variables produces an IWS for elk

  • Values range from -4 to +4

  • Variables weighted as:

    • SWE = 45%

    • ECT = 35%

    • KBDI = 20%


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Current Research

  • Winter Severity and Wolf Predation on a Formerly Wolf-Free Elk Herd (Mech et al., 2001)

    http://www.npwrc.usgs.gov/resource/2002/severity/severity.htm

  • Studied wolf predation on elk in YNP in 1997-98 during severe and mild winter seasons

  • Examined carcasses for age, sex, estimated amount eaten

  • Collected bone marrow samples and mandibles

  • Concluded that the effect of wolves on elk herd numbers is related to the magnitude of winter severity


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Current Research

  • Others:

    • Density dependence modeling (Lora Ballinger 1999)

    • Bioenergetics/Spatial modeling (Dr. Monica Turner – University of Wisconsin at Madison

    • Several others


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My Research

  • Complexity Across Boundaries – Coupled Human and Natural Systems in the Yellowstone Northern Elk Winter Range

    • NSF funded under Biocomplexity program

    • Develop a Multi-Agent Simulation Model (MAS) that explores NEWR vulnerability to environmental stressors

    • Understanding ecological systems where humans are significant factors

    • http://gis.iowa.uiowa.edu/private/yellowstone/


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Biocomplexity Website

http://gis.iowa.uiowa.edu/private/yellowstone


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Objectives

  • Investigate snow/elk interactions while focusing on snow component by characterizing spatial and temporal distribution of snowpack properties

  • Use a combination field data, model evaluation and model development to make contributions in snow hydrology and ecology

  • To provide snowpack properties as input into the elk bioenergetics model


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Questions

  • Which snow parameters are significant with respect to elk bioenergetics?

    • Depth, density ,SWE, hardness

    • Snowfall and snowmelt magnitude and timing

  • Which elk energetic expenditures are significant components?

    • Forage, locomotion, winter survival

  • What is winter severity?

  • Model Resolution?

    • Spatial and temporal

  • What level of complexity is needed for most robust model?

    • Parameter selection and estimation

  • Deterministic and Stochastic modeling approaches


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Site Description

  • Spans ~80,000 hectares

  • Lands managed by

    • NPS, USFS, MFWP, private ownership, others

  • Contentious land management issues

  • Characterized by elevation, precipitation and temperature gradients

  • Inverse relationship b/t precip and forage


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Evaluation of NREL Yellowstone Snow Model

  • Snow Model for Yellowstone National Park developed by Francis Singer, Gary Wockner, Mike Coughenour of the Natural Resource Ecology Lab (NREL) and Phil Farnes of Snowcap Hydrology in 2001

  • Purpose: To produce prediction maps of snow water equivalence (SWE) in Yellowstone National Park (YNP)

  • Snowpack influences the feeding habitat, locomotion, migration timing, vulnerability to predation and overall energy expenditures of elk


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Field Work to Date

Field Methods:

  • Snow Probe

    • snow depth measurements at 50-m grid spacing

    • GPS point location

  • Snow Pits

    • Depth, density, temperature, hardness, grain size, grain shape and stratigraphy

    • GPS point location


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Field Work to Date

Yellowstone National Park

NEWR

Crystal Creek Drainage


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Field Work to Date

  • Crystal Creek Snow Survey

  • January 15-17, 2003

  • 1200 GPS depths

  • 21 reference snow pits

  • Crystal Creek Snow Survey

  • April 1-4, 2003

  • 300 GPS depths

  • 6 reference snow pits


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Field Work to Date

Sample snow pit profile from Crystal Creek April ‘03

crusts


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Additional Field Data (YERC)

  • Lamar Valley - 31 additional snowpits dug early and late season ’03

  • Blacktail Plateau – 30 additional snowpits dug early and late season ‘03


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CurrentStatus

  • Evaluation

    • NREL model evaluation and validation

    • Running model for days with corresponding field data

    • 24 days/119 snow pits

    • Measured vs. Modeled


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SNTHERM Overview

  • Process driven, one-dimensional energy and mass balance model

  • Developed by Rachel Jordan at CRREL in 1991

  • Models changes in snowpack properties through time

  • Model driven by first principles not empirical relationships


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SNTHERM Overview

  • Explicitly distributes energy, mass and momentum on a layer-by-layer basis throughout the snowpack

  • 14 constant parameters

    • Elevation, slope, aspect, surface roughness, etc.

  • 20 state variables

    • Snow density, temperature, depth, grain size, SWE, etc.

  • Driving Variables

    • Air temp, relative humidity, wind speed, incoming/outgoing shortwave radiation and incoming longwave radiation


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Geostatistical Overview

  • Understanding spatial distribution of snowpack properties challenging problem in snow hydrology

  • Past and current spatially distributed snow models differ in the process representation they involve

  • Use geostatistical techniques to spatially distribute measured snowpack properties


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Summary

  • Reintroduction of wolves in YNP contentious issue

  • Provides the opportunity to study the effects of wolves on a previously wolf-free elk herd

  • What are the effects of winter severity on elk/wolf/snow relationships?


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Summary

  • What is winter severity and what role does it play in elk-wolf interactions?

  • Current research efforts

    • Index of Winter Severity (Farnes et al)

      • intended to estimate animals’ response to climatic and vegetative conditions on the winter range

      • SWE, ECT and KBDI

    • Winter Severity and Wolf Predation on a Formerly Wolf-Free Elk Herd(Mech et al., 2001)


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Summary

  • Mech et al

    • Concluded that the effect of wolves on elk herd numbers is related to the magnitude of winter severity

  • Complexity Across Boundaries – Coupled Human and Natural Systems in the Yellowstone Northern Elk Winter Range

    • Develop a Multi-Agent Simulation Model (MAS) that explores NEWR vulnerability to environmental stressors


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Summary

  • Biocomplexity continued

    • Understanding ecological systems where humans are significant factors

    • Investigate snow/elk interactions while focusing on snow component by characterizing spatial and temporal distribution of snowpack properties

    • Use a combination field data, model evaluation and model development to make contributions in snow hydrology and ecology