Chapter Review on Predation, Symbiosis, and Evolution

Introduction to Predator-Prey Dynamics

• Cost of Defense Mechanisms

  • Predator’s choice to attack or not involves energy allocation for fighting or fleeing.

  • Results in the potential for energy loss and risk of injury.

Escape Strategies

• Running Away

  • Animals utilize unpredictable movement patterns when escaping predators.

  • Notable examples:

  • Grasshoppers: Jumping high with erratic movements.

  • Rabbits: Zigzag patterns to evade foxes or dogs.

  • Antelope and Cheetahs: Cheetahs must adjust their approach as antelopes change direction rapidly.

  • Cephalopods: Ink release enables an escape by obscuring their presence.

Physical Defenses

• Armor

  • Turtles have shells providing protection for soft body parts.

  • Triceratops: Fossils show adaptation in neck protection through thick shields.

  • Armadillo: Keratinized skin resembles a shell, enhancing protection.

  • Beetles: Thick protein-based shells can deter predation without calcification.

Mass Production as Defense

• Semelparity and Nesting

  • Release large quantities of offspring simultaneously to overwhelm predators.

  • Two primary advantages:

  • Confuses predators regarding which offspring to attack.

  • Can satiate predators quickly, allowing some offspring to survive.

  • Examples include:

  • Cicadas: Emerge en masse every 17 years.

  • Lobsters: Release hundreds of thousands of larvae overnight.

Combination of Defense Techniques

• Examples in Lobster Defense:

  • Weapons such as claws and spiny structures act as physical deterrents.

  • Use of sound to repel predators and bright colors signaling unpalatability.

Specific Examples of Defensive Strategies

• Camouflage:

  • Example: Flounder blending into the sand.

• Schooling:

  • Safety in numbers helps deter predators.

• Intimidation and Weaponry:

  • Porcupines using quills to threaten predators.

Inducible Defenses

• Efficiency in Defense Mechanisms

  • Costs incurred to create defenses mean they are only activated when predators are present.

  • Mussels Example:

  • Increase shell thickness and thistle thread strength when sensing predators.

  • Data Comparison Experiment:

  • Without predators: Shell strength ~15-16 newtons.

  • With predator scent: Shell strength increased to over 40 newtons.

Comparative Physiology of Inducible Defenses

• Shell thickness changes based on predator presence incorporate protein links and calcification.

• Volume and surface area considerations illustrate significant changes due to increased thickness.

Evolutionary Implications in Defensive Strategies

• Symbiotic Relationships

  • Three main types:

  1. Mutualism: Benefits both organisms. E.g., plants with nitrogen-fixing bacteria.

  2. Commensalism: One benefits, the other is unaffected. E.g., clownfish and anemone.

  3. Parasitism: One benefits at the expense of another. E.g., heartworms in pets.

• Types of Mutualism:

  • Facultative: Both can live independently but thrive together.

  • Obligate: Species cannot survive without each other.

Types and Mechanisms of Predation

• Ectoparasites vs Endoparasites

  • Ectoparasites: External feeders; e.g., mosquitoes.

  • Endoparasites: Internal feeders; can be dangerous if populations grow too large, potentially causing starvation of hosts.

The Arms Race Metaphor in Evolution

• A constant evolutionary battle between predator adaptations and prey defensive techniques resulting in varying success rates for each side.

• Honest Signals:

  • Example: Monarch butterflies ingesting toxic cardiac glycosides from milkweed, retaining toxins to protect from predators.

Historical Perspectives in Evolutionary Theory

• Aristotle: Early classification of organisms, linked to biblical perspectives.

• Linnaeus: Developed binomial nomenclature, recognized some species could change; influenced modern taxonomic methods.

• Nicholas Steno: Father of stratigraphy; introduced fossil record principles and layering.

• Georges Cuvier: Established extinction concepts, studied fossil layers; catastrophism theory.

• William Smith: Created first geological maps connecting fossils to specific rock layers across ages.

• Charles Lyell: Influenced Darwin with the concept of gradual change in geological processes.

• Jean-Baptiste de Lamarck: Proclaimed ideas of adaptation and species change due to environmental alterations.

Closing Remarks and Transition to Evolution

• Understanding the dynamics of predator-prey relationships highlights broader principles of evolution and adaptation in ecological contexts.

🧩 COMMUNITY ECOLOGY

⭐ What is a Community?

A community = all interacting populations (different species) in a defined area.

• Focuses on interactions between species

• Includes plants, animals, microbes, fungi, etc.

⭐ Emergent Properties of Communities

Community-level characteristics that arise from interactions among species.

⭐ Biodiversity

Biodiversity = number AND variety of organisms in a region.

Can be measured at:

• Genetic level (variation within species)

• Species level (richness/diversity)

• Ecosystem level (variety of habitats)

Importance

• Increases ecosystem productivity, resilience, and stability

• Maintains nutrient cycling, pollination, food webs, disease resistance

Productivity relationship

• Higher ecosystem productivity → higher biodiversity

• Why? More resources → more niches

Measuring diversity

• Species richness + evenness

• Indices (Shannon Index, Simpson Index) used to compare communities over time or across sites

⭐ Niche Concepts

Competitive Exclusion Principle

Two species cannot occupy the exact same niche indefinitely.

Outcomes:

• Extinction of one species

• Niche differentiation (Resource partitioning)

• Character displacement (evolution of traits to reduce competition)

Examples:

• Darwin’s finches evolving different beaks for food sources

⭐ Energy Flow & Trophic Levels

Key rule: Energy flows one way; nutrients cycle

10% rule

• Only ~10% of energy moves up a trophic level (5-20% range)

• Most lost as heat/respiration

Top-down control

• Predators regulate lower levels (keystone species)

• Removing wolves causes elk explosion → tree decline

Bottom-up control

• Productivity (# of nutrients, sunlight) limits food web size

⭐ Species Interactions

Ways to avoid predation

• Camouflage, mimicry, schooling, warning coloration, chemical defense, armor, speed, spines

🌍 EVOLUTIONARY IDEA FOUNDATIONS

⭐ Geological Influence & Age of Earth

Big shift

• Earth = old (millions+ years, not 6,000)

• Slow gradual changes allow evolution time

⭐ Early Biological Thinkers (Pre-Darwin)

⭐ Lamarck’s Theory (First Evolution Model)

Key principles:

1. Organisms seek complexity/perfection

2. Use & disuse alters organs

3. Inheritance of acquired traits

4. Changes accumulate → new species

Examples he used:

• Giraffe neck stretches → longer neck in offspring

• Snakes lost limbs from disuse

• Cave animals losing eyes

Incorrect aspects

• Acquired traits aren't inherited genetically
  (except limited epigenetic cases — gene expression changes, not DNA sequence)

⭐ Darwin & Wallace’s Theory of Natural Selection

Observations

• More offspring produced than survive

• Variation exists within populations

• Variation is heritable

Inferences

• Some variations give survival/reproduction advantages

• Advantageous traits increase in population over generations

• Leads to adaptation & eventual speciation

Key Influences:

• Malthus: human population growth → competition & struggle for existence

⭐ Key Differences: Darwin vs Lamarck

✅ NS 201 Exam 2 Master Notes — Part 2

🧬 Darwin, Wallace, Malthus, Lamarck & Evolution Theory

⭐ Thomas Malthus

• Wrote Essay on the Principle of Population

• Observed:

  • Human population grows geometrically

  • Food production grows arithmetically

  • Population > resources → competition, struggle

  • Influenced Darwin & Wallace: not all survive → selection pressure

⭐ Lamarck's Evolution Theory

Mechanisms he proposed:

1. Organisms strive toward complexity

2. Use & disuse

   • Frequently used structures strengthen & increase

   • Unused structures shrink

3. Inheritance of acquired characteristics

   • Traits gained during lifetime passed to offspring

4. Accumulation leads to new species

Examples Lamarck used:

• Giraffes stretch necks → longer neck offspring

• Snakes lost limbs via disuse

• Cave animals lose eyes

Why Lamarck is wrong

• Acquired physical traits don’t change DNA

• But partly revived now via epigenetics (environment can alter gene expression, not DNA sequence)

⭐ Darwin & Wallace Theory of Natural Selection

Observations

• More offspring produced than survive

• Populations show variation

• Traits are heritable

Conclusions

• Individuals with advantageous heritable traits survive & reproduce more

• Over many generations → adaptations accumulate

• Population evolves, not individuals

⭐ Key Definitions

⭐ Differences: Lamarck vs Darwin

✅ Evidence for Evolution

⭐ 1) Artificial Selection

• Humans choose traits (dogs, crops)

• Shows heritable variation can rapidly shape species

⭐ 2) Fossil Record

• Older → simpler organisms

• Transitional fossils show gradual change

  • Tiktaalik: fish → tetrapod

  • Horses: many toes → 1 toe, teeth change, taller

⭐ 3) Comparative Anatomy

⭐ 4) Embryology

• Early embryos similar across vertebrates

• Pharyngeal arches → fish gills / human ear & throat bones

⭐ 5) Biogeography

• Island species resemble nearby mainland species

• Continental drift explains fossils matching separated continents

• Adaptive radiation (ex: Darwin’s finches)

⭐ 6) Molecular Genetics

• DNA sequences diverge over time → molecular clock

• Hox genes control body plans in animals — highly conserved

✅ Phylogeny & Systematics

⭐ Terms

⭐ Trait Types

✅ Speciation Concepts

• Disruptive selection increases divergence → speciation

• Allopatric = geographic barrier

• Sympatric = speciation without physical separation (ex: niche partitioning, polyploidy in plants)

✅ Part 3 — Genetics, Cell Theory, Chromosomes

🧬 Cell Theory

⭐ Mendel’s Work

Key conclusions

• Traits controlled by heritable factors (genes)

• Each individual has two alleles

• Alleles segregate during meiosis

• Alleles assort independently (unless linked)

• Dominant vs recessive traits

⭐ Terms

⭐ Chromosome Theory

• Sutton & Boveri: chromosomes carry genes

• Behavior of chromosomes in meiosis = Mendel's laws

⭐ Morgan’s Experiments (Fruit Flies)

• Discovered sex-linked traits

• White-eye mutation only in males → X-linked

• Showed genes on chromosomes

• Linked genes deviate from independent assortment

• Crossing over produces recombinants

⭐ Types of Mutations

⭐ Nondisjunction (Calvin Bridges)

• Chromosomes fail to separate in meiosis

• Results: XO, XXY, XXX, etc.

• Confirmed chromosomes carry heredity

⭐ Sex Determination

• Y chromosome has SRY gene → testes development

• Hormones influence external development

• Genetics + environment = phenotype variation