Lesson 5.3 - Population Factors

Lesson Overview

Population Factors

  • Understanding factors affecting populations

  • Inter- and intraspecific relationships affecting populations

Learning Goals

  1. Population Factors: Understand and explain factors affecting populations.

  2. Relationships: Understand inter- and intraspecific relationships affecting populations.

Success Criteria

  1. Density-independent vs. density-dependent factors

  2. In-depth explanation of competition

  3. Identification and examples of defense mechanisms

  4. Examples of symbiotic relationships

  5. Explanation and examples of keystone species in ecosystems

Factors Affecting Natural Populations

Classifications

  1. Density-Independent Factors

    • Not influenced by population density

    • Often abiotic (e.g., weather events, floods, droughts, pollution)

    • Can cause minor or major changes in population numbers.

  2. Density-Dependent Factors

    • Often biotic factors

    • Greater effect at high population densities

    • Minimal effect if population is below carrying capacity.

Density-Dependent Factors

Competition

  • Individuals compete for limited resources:

    • Water, food, breeding sites, shelter, etc.

    • Intraspecific Competition: competition within a single population (same species).

    • Interspecific Competition: competition between different species for the same resources.

Interspecific Competition

  • Species that thrive in given conditions outcompete others

  • Competitive Exclusion Principle: one species outcompetes another for resources.

    • Example: zebra mussels outcompeting young fish for plankton.

  • Resource Partitioning: species utilize different resources to reduce competition, increasing survival.

Relationships in Populations

Predator-Prey Dynamics

  • Producer-Consumer interactions (e.g., grass-deer) and Predator-Prey cycles (e.g., coyote-lynx).

  • Population cycles produce sinusoidal growth patterns.

Defense Mechanisms

  • Purpose: Protection against predators.

  • Examples: porcupine quills, cactus thorns, bitter-tasting chemicals.

  • Co-evolution: predators and prey evolve mechanisms and tactics against each other.

  • Protective Coloration strategies:

    • Mimicry (Mullerian and Batesian), Camouflage, and Aposematic (warning coloration).

Symbiotic Relationships

  • Close interactions between species (Symbiont + Host).

  1. Parasitism: one organism is harmed while the other benefits (e.g., salmon + sea lamprey).

  2. Mutualism: both organisms benefit (e.g., anemone + clownfish).

  3. Commensalism: one benefits, other unaffected (e.g., orchids + trees).

Keystone Species

  • Read and explain significance in ecosystems, with examples.

Homework Assignments

Textbook Readings

  • Pages 520-533

Textbook Questions

  • Page 533: #7, 9-14, 16

  • Page 541: #1-14