polar bear pg(3-39)

Polar Bear Biology

  • Overview of Topics
      - Systematics & genetics
      - Habitat selection & space use
      - Physiology
      - Reproduction
      - Mating strategies & behavior

Classification and Evolution

  • Largest Terrestrial Carnivore

  • Species Information
      - One of 8 bear species globally
      - Closely related to brown bears
      - Divergence timeline: approximately 150,000 to 600,000 years ago

Genetic Relationships

  • Mitochondrial DNA Studies
      - Reference: Hailer et al. 2012, Science 336:344-347
      - Findings:
        - Brown bears are not a monophyletic group
        - Certain brown bears are more closely related to polar bears than to other brown bears

Genetic Markers and Analysis

  • Nuclear DNA Information
      - North American (N.Am): 0.74
      - Analysis from 125,000 (65,000-207,000) years ago
      - Genetic similarities across regions and species:
        - East brown bear: >0.99
        - West brown bear: 0.99
        - Polar bear: 603,000 (338,000-934,000) years ago
        - Black bear presence in analysis

  • Mitochondrial DNA Overview
       - Polar bears show evidence of introgressed brown bear mitochondrial DNA due to hybridization in the past
       - Utilizing multilocus genomic analysis is critical for accurately reconstructing evolutionary history
       - Low genetic diversity in polar bears indicates past population bottlenecks due to environmental changes

Habitat and Population Dynamics

  • Characteristics of Polar Bears
      - Ice-obligate species, distributed throughout the circumpolar region
      - Consist of 19 discrete subpopulations
      - Global population estimate: between 22,000 and 32,000 polar bears
      - Approximately 60-80% of the global polar bear population resides in Canada

  • Dietary Preferences
      - Primary consumption: Ringed seal (smallest seal species) and Bearded seal (largest seal species)
      - Focus on high-fat content for energy efficiency, as protein can produce nitrogenous waste
      - Efficient recycling of nitrogen aids survival in harsh environments

  • Habitat Selection
      - Influenced by prey availability and distribution, specifically regarding ringed seals
      - Seals tend to prefer landfast ice or areas with complete snow cover
      - Habitat Preferences:
        - High-quality foraging habitat: Polar bears prefer areas with significant snow cover and large deformation structures
        - They avoid wind-packed snowdrifts, areas without ice drifts, or heavily deformed ice structures

  • Home Range and Movement Patterns
      - Average female home range: 125,100 km²
      - Comparative ranges:
        - Grizzly bear: 70 km² (as per Jonkel & Cowan 1971)
        - Black bear: 5.2 km² (as per Pearson 1972)

  • Seasonal Behavior
      - Males tend to remain near the coast while females may move inland during seasons

Denning Habits

  • Polar Bear Den Potential
      - Wapusk National Park denning sites
      - Use of Random Forest probability maps from known denning sites and selected landscape features, with AUC=0.8909
      - Dens are often built in peat

Seasonal Feeding Patterns

  • Non-Pregnant Polar Bears (April to March)
      - Feeding patterns include periods of hyperphagia and fasting
      - Hyperphagia includes abundant food intake, while fasting results in loss of approximately 3 lbs/day during ice-free periods

  • Pregnant Polar Bears (Seasonal Cycle)
      - Important dietary need for 200 kg of fat to support breeding
      - Life cycle events: Fasting, Mating, Implantation, Birth (newborns weigh 0.6 kg)
      - Cubs stay with mothers for approximately 2.5 years, leading to a 3-year breeding cycle for females

Reproductive Ecology

  • Operational Sex Ratio (OSR)
      - Defined as the ratio of receptive males to receptive females
      - Mating patterns:
        - Females are a scarce resource for males
        - Investment in reproduction differs between sexes:
          - Females: higher investment
          - Males: lower investment
        - This asymmetry creates conditions for sexual selection

  • Sexual Selection
      - Definition: Selection for traits specifically aimed at increasing mating success
      - Types of Sexual Selection:
        - Intrasexual Selection: Male-male competition (includes fighting, defending territories, dominance hierarchies)
        - Intersexual Selection: Female choice (traits to appeal to the opposite sex)

Mating Characteristics

  • Sexual Dimorphism in Polar Bears
      - Adult male polar bears (150-300 kg) are approximately twice as heavy as females (350-550 kg)
      - Consequences of sexual selection lead to noticeable sexual size dimorphism.

  • Mating Strategies
      - OSR is heavily male-biased due to females breeding only every three years
      - This influences the competitive dynamics among males for access to females

  • Physical Traits
      - Patterns of aggression and injury in males, indicating male-male competition

Social Behavior

  • Interactions Among Polar Bears
      - Autumn interactions are generally non-aggressive with few injuries recorded outside of breeding times
      - Males may aggregate along coastal lines during specific seasons, showcasing social behavior

Research Methodologies

  • Data Collection and Individual Identification Techniques
      - The importance of identifying individual polar bears for behavioral studies
      - Methods used include photo-identification and whisker prints for recognizing individuals
      - The Polar Bear Photo-identification Library created by the University of Manitoba serves as a vital resource for tracking and analyzing polar bear encounters and populations.