Ecology and Population Dynamics

Introduction to Ecology and Populations

• Topics Covered:

  • Origin of cranium, vertebrae, jaw, bony endoskeleton, lungs, lobed fins, limbs, and amniotic egg.

  • Chordate and vertebrate evolution.

  • Key innovations in vertebrates.

Key Innovations in Vertebrates

• Derived traits of chordates include:

  • Notochord

  • Hollow nerve cord

  • Post-anal tail

  • Pharyngeal slits

Learning Outcomes

• Define ecology and differentiate levels of ecological research.

• Define a population and describe key characteristics.

• Correlate life history traits and trade-offs.

• Calculate population size using the mark-recapture method.

• Describe life history strategies and their fitness trade-offs.

• Calculate population growth and factors affecting population size.

• Contrast exponential and logistic population growth.

Ecological Research Branches

• Ecology has various branches explained in the lecture video (15:48).

Characteristics of Populations

• Definition: A group of individuals of one species in a common area sharing resources and environmental factors.

• Key Questions:

  • How many individuals are present?

  • Where is the population located?

  • What is the distribution of individuals?

  • How many individuals of each age?

  • How many offspring do individuals have?

  • Is the population changing?

Geographic Distribution

• Typically shown as a range.

• Evaluated at different scales.

• Determined by various living and non-living factors.

Estimating Population Size for Immobile Species

• Use Quadrats (rectangular plots) and Transects (lines of known position).

• Set at random locations and extrapolate counts to the entire area.

Estimating Population Size for Mobile Species

• Use the mark-recapture method.

• Formula:

  • Let

  • M = ext{# frogs marked today}

  • N = ext{total population size}

  • m = ext{# marked frogs re-caught}

  • n = ext{total frogs caught today}

• Rearranging helps estimate population size.

Population Characteristics

• Distribution and density variability can inform biology.

• Examples:

  • Seagulls establish breeding territory.

  • Sea stars group where food is available.

  • Dandelion seeds disperse randomly.

Life Histories

• Life histories involve allocation of resources to growth, reproduction, and survival.

• Key factors: age of reproduction, number of young, reproductive events, lifespan, and mortality.

Life History Trade-offs

• Limited resources lead to trade-offs:

  • Large body size vs few young

  • Small body size vs many young

Population Dynamics

• Studies how populations change over time.

• Population Gains: B, Population Loses: D

• Population size (N) is determined by birth and death rates:

  • If B > D, population increases.

  • If B < D, population decreases.

  • If B = D, population size remains stable.

Population Growth Rate

• Formula:

  • rac{∆N}{∆t} = B - D

• Per capita growth rate r = rac{B}{N} - rac{D}{N}

• Thus, rac{∆N}{∆t} = N(r).

  • If r > 0, population grows.

  • If r < 0, population shrinks.

  • If r = 0, population remains stable.

Exponential Growth

• Characterized by a constant rate of increase.

• J-shaped curve: observed in favorable conditions (e.g., microorganism growth).

Logistic Growth

• Growth rate decreases as population approaches carrying capacity.

• S-shaped curve.

• Density-dependent factors begin to limit growth as population nears carrying capacity K.

Carrying Capacity

• Defined as the maximum population size an environment can support.

• Varies among species and habitats due to differing adaptations and resources available.

Summary on Population Growth Types

• Exponential growth occurs under plentiful resources.

• Logistic growth is more realistic, accounting for limited resources and competition.