The Effects of Ski Areas on the Population Dynamics of the Pacific - - PowerPoint PPT Presentation

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The Effects of Ski Areas on the Population Dynamics of the Pacific Marten in the Lake Tahoe Region Preliminary Results Keith Slauson and William Zielinski U.S. Forest Service, Pacific Southwest Research Station Marten Life History

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The Effects of Ski Areas on the Population Dynamics of the Pacific Marten in the Lake Tahoe Region

Keith Slauson and William Zielinski U.S. Forest Service, Pacific Southwest Research Station Preliminary Results

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Marten Life History Characteristics

Mating System: Polygamous, females solely responsible for raising young Total Length: 500-680 mm Weight: 500-1400 g Sexually dimorphic: adult males 40% larger than females Reproduction: ≥2 year-old females 1-3 kits / litter Longevity: Most individuals 5 years Diet: Varies seasonally, dominated by Squirrels, Voles & Birds

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Marten Population Responses to Habitat Fragmentation

Bissonette et al. 1997 Potvin et al. 2000

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Potential Effects of Ski Areas to Martens

Negative: Habitat Fragmentation

movements energy loss reproduction and /or survival risk of predation survival prey species or abundance reproduction and/or survival

Positive: Anthropogenic sources of Food

extrinsic sources

  • f food

direct energy gain reproduction and/or survival populations

  • f prey

energy gain reproduction and/or survival

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Research Questions

  • 1. Are population sizes reduced on ski areas?
  • 4. What is the net effect of ski resort development on

marten population persistence?

  • 3. Are reproductive females affected by ski area

fragmentation?

  • 2. Is marten survival lower on ski areas?

Response variable: marten abundance Response variable: survival estimates (MARK) Response variable: distribution of females relative to remnant forest fragments

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Study Design: Treatment vs Control

Treatment: Ski Areas Controls

Potential Marten Habitat Heavenly Ski Area Sierra At Tahoe Ski Area Homewood Ski Area Pre-development Marten Habitat Topography Elevation Range Macro Aspect Proximity

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100 ha

Study Area Sampling Design

Example: Sierra At Tahoe Ski Area Every selected point was sampled for 15 consecutive days during winter of 2009 & each spring 2009-2011

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Capture Methods

Winter 2009 Spring 2009-2011

15-day Station Durations Bait: Chicken Lure: Gusto Age 1st premolar

January-March May-July Winter 5-day Visits Spring daily Visits

Protocol

Spring: PIT tag

Individual ID

Winter: DNA

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Ski Areas Controls Males Females 9 11 8 11 P > 0.05

Marten Captures: Winter 2009 Marten Captures: Spring 2009-2011

Ski Areas Controls Females 30 31 14 13 P > 0.05 Males

Marten Abundance Does Not Differ Between Ski Areas & Controls

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Survival Modeling in Program Mark

Pradel Model: Survival and Seniority Robust Design Closed Population

Model Parameters

Survival (S) ‘Seniority’ (G) probability that if alive and in the population at time i (this year), that you were also alive and in the population at time i-1 (last year) Capture Probability (P) Recapture Probability (C) Population Size (N)

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Parameter

Survival (Spring-Spring)

Covariate Effect

Seniority (Winter-Spring) Seniority (Spring-Spring) Control

Estimate (95% CI)

Survival (Winter-Spring) 0.60 (0.44-0.75) 0.38 (0.28-0.49) 0.79 (0.11-1.69) 0.56 (0.40-0.71) 0.49 (0.35-0.64) Control 1.67 (0.51-2.82)

Marten Survival and Seniority Estimates

Marten Survival is Significantly REDUCED on Ski Areas Turnover Rates are Significantly HIGHER on Ski Areas

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Reproductive Females Captured More Often on Edges of Ski Areas than Controls

Captured on Edge Captured in Core Ski Areas Controls Total 14 12 10 5 4 7 Proportions Test Z-value P = 0.06

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Reproductive Female Capture Locations Sierra At Tahoe 2009-2011

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Female-13 Capture Locations on Heavenly Ski Area 2009-2011

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Reproductive Females On Ski Areas Use the Largest Remnant Forest Patches

Sierra At Tahoe

Homewood: 1 residual patch >20 hectares No reproductive females within

  • perations area

0.0% 20.0% 40.0% 60.0% 80.0% 100.0%

<10 10-20 20-40 >40

Available Used

Heavenly

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Preliminary Conclusions

  • Marten abundance is not affected by ski resorts
  • Marten survival is reduced by ski resorts
  • Fragmentation from resorts negatively affects

the distribution of reproductive females

  • Reduced Survival and Reproduction have created

population ‘sink’ conditions on all (Homewood) or portions of resorts (Heavenly & Sierra At Tahoe)

Next Steps

  • Parentage analysis to determine recruitment
  • Apply female reproductive habitat model to pre-resort

development conditions

  • Population modeling to quantify magnitude of affects
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Acknowledgements

Lake Tahoe Environmental Improvement Program Sierra Nevada Land Management Act Tahoe Science Consortium Field Crews: Mark Linnell, Matt Delheimer, Pete Lundberg,

Nathan Shea, Katlin Mansfield, Katie Greller, Dustin Marsh, Devin Crenshaw, Natalie Craven, Michelle Rann, Tim Sichmeller, Wes Watts, Conor MacNamara, Natalie Mesce, Kathleen Sholty, Kirsty Lawson

Lake Tahoe Basin Management Unit El Dorado National Forest Tahoe Region Planning Agency Heavenly Resort Sierra At Tahoe Resort Homewood Mountain Resort Pacific Southwest Research Station