unit 2
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Study Guide: Jawed Fishes (Gnathostomes)
I. Introduction
• Gnathostomes = “jaw-mouth” (page 2)
o Jaws evolved from anterior gill arches (not for filter feeding)
o Pharyngeal slits → used only for gas exchange
o Lateral line system: sensory organ for detecting water movement
II. Anatomy & Adaptations
• Gill Arches (page 3)
o Bones or cartilage between gill slits → modified into jaws
• Lateral Line System (pages 4–5)
o Detects vibrations and movement in water
o Made of canals, sensory hairs, and mucus-filled cupulae
III. Evolutionary History
• First appeared ~440 million years ago (page 6)
o Placoderms (extinct by ~359 mya) → armored jawed fishes
• Three main extant lineages:
o Chondrichthyes (cartilaginous fishes: sharks, rays, skates)
o Osteichthyes (bony fishes)
▪ Ray-finned
▪ Lobe-finned
IV. Chondrichthyes (Cartilaginous Fishes)
• Traits (page 8–9)
o Cartilaginous skeleton, ventral mouth, gill slits, placoid scales
• Examples (pages 10–12)
o Sharks (diverse species list, e.g., great white, hammerhead, whale shark)
o Rays and skates (sting rays, manta rays)
• Internal Anatomy (page 20)
o Large liver for buoyancy
o Spiral valve in intestine for nutrient absorption
V. Respiration & Circulation
• Gills (pages 13–14)
o Gill arches support filaments for gas exchange
o Countercurrent exchange maximizes O₂ uptake
• Circulation (page 16)
o Single circulation: heart pumps blood → gills → body capillaries
VI. Osteichthyes (Bony Fishes)
• General Traits (page 22–25)
o Operculum covers gills (vs. open gill slits in sharks)
o Swim bladder for buoyancy (instead of liver reliance)
o Cycloid/ctenoid scales (vs. placoid)
• Ray-finned Fishes (page 26)
o 27,000+ species
o Bony rays support fins
o Extremely diverse body forms
• Lobe-finned Fishes (page 27–29)
o Sturdy, rod-shaped bones in fins
o Surviving lineages: Coelacanth, Lungfish, Tetrapods
o Important for evolution of terrestrial vertebrates (e.g., Tiktaalik, Acanthostega)
VII. Convergent Evolution
• Some ray-finned fish (e.g., climbing perch) developed fin-walking independently from
amphibians (page 30)
Review Questions
Basic Traits
1. From which anatomical structure did jaws evolve?
2. What is the function of the lateral line system in fishes?
Evolution
3. What were Placoderms, and when did they go extinct?
4. What are the three major lineages of gnathostomes alive today?
Chondrichthyes
5. How do cartilaginous fishes maintain buoyancy without a swim bladder?
6. Compare the scales of sharks and bony fishes.
Osteichthyes
7. How does the operculum aid respiration in bony fishes?
8. What key trait distinguishes ray-finned from lobe-finned fishes?
Evolutionary Significance
9. Which lobe-finned fish is considered a transitional form to tetrapods?
10. How did some ray-finned fishes independently adapt to walking on land?
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Study Guide: Tetrapods, Amphibians, and
Reptiles
I. Tetrapods
• Adaptations to Land
o Appeared ~365 mya (Devonian wetlands)
o Lobe-fins adapted for shallow, low-oxygen waters
o Innovations:
▪ Limbs to support body weight
▪ Digits for walking
▪ Neck (separate head movement)
▪ Pelvic girdle, wrists, shoulders
• Fossil Evidence
o Tiktaalik, Acanthostega, Tulerpeton → show intermediate traits
o Limbs with digits emerge before full terrestrial life
II. Amphibians
• General Traits
o Include frogs, salamanders, caecilians
o Life cycle: aquatic larvae (gills) → terrestrial adults (lungs, skin respiration)
• Adaptations
o Gills lost in adults (except in paedomorphy like axolotls)
o Moist skin for respiration
o Double circulation system (pulmocutaneous + systemic circuits)
• Examples
o Tadpoles
o Salamanders & newts
o Frogs
o Caecilians
III. Amniotes (Reptiles & Mammals)
• Key Adaptations
o Amniotic egg: protects embryo, prevents desiccation
o More efficient lungs (rib ventilation)
o Keratinized skin (less permeable, water conservation)
• Amniotic Egg Structure
o Chorion, yolk sac, amnion, allantois, albumen, shell
• Circulation
o Double circulation (pulmonary + systemic circuits)
o Seen in reptiles, birds, and mammals
IV. Reptiles
• Defining Traits
o Diapsids: two skull openings behind eye socket
o Mostly ectothermic (except birds)
• Phylogeny
o Major groups:
▪ Turtles
▪ Crocodilians
▪ Dinosaurs & Birds
▪ Tuataras
▪ Squamates (lizards & snakes)
• Examples
o Lizards
o Snakes
o Turtles
o Crocodilians
Review Questions
Evolutionary Background
1. What structural innovations allowed lobe-finned fish to transition to land?
2. Which fossil species demonstrates both fish-like and tetrapod-like traits?
Amphibians
3. How do amphibians exchange gases, and why are they limited to moist environments?
4. What is paedomorphy, and which amphibian shows this trait?
Amniotes
5. What are the four membranes of the amniotic egg, and their functions?
6. How does reptile circulation differ from amphibians?
Reptiles
7. What does “diapsid” mean, and which groups fall under it?
8. How do reptiles adapt to conserve water in terrestrial environments?
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Study Guide: Birds – The Flying Reptiles
I. Introduction
• Birds are considered “flying reptiles” due to their evolutionary lineage.
II. Modifications for Flight
• Anatomical Adaptations (page 2)
o Forelimbs evolved into wings
o Bipedal locomotion
o Lightweight body
▪ Hollow bones
▪ Loss of teeth
▪ No bladder (uric acid excretion)
▪ Reduced reproductive organs
• Feathers
o Derived from scales (β-keratin protein)
o Two main types:
▪ Downy (insulation)
▪ Contour (aerodynamics)
III. Skeletal Changes
• Avian Skeleton Features (page 3)
o Hollow bones with crisscross struts
o Fusion of bones for rigidity
o Keeled sternum (attachment for flight muscles)
o Strong pectoral girdle and lightweight skull
IV. Feather Structure
• Components (page 4)
o Quill, rachis (shaft), barbs
o Barbules with hooks interlock for surface integrity
V. Other Bird Characteristics
• Behavioral
o Parental care (nesting, feeding young)
o Courtship displays (plumage, dances, vocalizations)
• Physiological
o High energy demand of flight
o Endothermic (warm-blooded)
o 4-chambered heart
o Highly efficient lungs with air sacs for continuous airflow
VI. Evolution
• Origins (page 8)
o Part of theropod lineage (saurischian dinosaurs)
o Feathers evolved before flight
▪ Possibly for insulation or display
o Archaeopteryx: transitional fossil
▪ Reptilian traits: toothed beak, wing claws, long tail with vertebrae
▪ Avian traits: contour feathers, airfoil wings
VII. Flight Diversity
• General
o Similar body structure adapted for flight
• Variation (page 9)
o Different styles of flight (hovering, soaring, flapping)
o Specializations in beaks and feet depending on lifestyle (e.g., seed-cracking, fish-
catching, perching, swimming)
Review Questions
Flight Adaptations
1. Which anatomical modifications reduce bird weight for flight?
2. What are the functional differences between downy and contour feathers?
Skeletal & Feather Structure
3. How do hollow bones help in flight?
4. What structural feature of feathers allows them to interlock and maintain smooth
surfaces?
Bird Physiology & Behavior
5. Why do birds require a 4-chambered heart and efficient lungs?
6. Give an example of parental care and courtship display in birds.
Evolution
7. What evidence supports the idea that birds are descended from theropod dinosaurs?
8. What traits make Archaeopteryx a “transitional fossil”?
Flight Diversity
9. How do bird beaks and feet reflect their ecological niche?
10. Compare the flight style of a hummingbird with that of a hawk.
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Study Guide: Mammals
I. General Characteristics
• Mammary Glands (page 2, 5)
o Produce milk rich in fats, sugars, and nutrients
o Lactation supports high-energy demand in offspring
• Hair (pages 2, 7)
o Insulation, water conservation
o Fatty subcutaneous layer also helps regulate temperature
• Endothermy & High Energy Demand (page 2)
o Large brains (like birds)
o Require high parental care
• Circulatory & Respiratory Efficiency (page 2, 10)
o 4-chambered heart
o Efficient lungs, diaphragm for breathing
o Kidneys conserve water
• Skull & Jaw Adaptations (pages 2–3)
o Synapsids: one skull opening for jaw muscle attachment
o Jaw bones modified into middle ear bones (malleus, incus, stapes)
• Teeth Differentiation (page 4)
o Reptiles: simple, uniform teeth
o Mammals: specialized teeth (incisors, canines, premolars, molars) depending on
diet (carnivores, herbivores, omnivores)
II. Sensory Characteristics
• Nocturnality – many mammals are active at night (page 6)
• Olfaction – excellent sense of smell (page 8)
• Hearing – highly sensitive, aided by inner ear bones (page 9)
III. Major Mammal Groups
• Monotremes (page 12)
o Platypus, echidnas
o Lay eggs, have fur, produce milk but no nipples
• Marsupials (page 13)
o Kangaroos, opossums, koalas
o Short gestation → young develop in pouch
o Simple placenta
• Eutherians (Placental Mammals) (page 14)
o Most diverse group
o Complex placenta → longer gestation
o Embryo nourished directly by mother’s blood
IV. Primates
• Traits (page 15)
o Large brains
o Complex social behavior
o Forward-facing eyes (binocular vision)
o Short jaws, nails (not claws)
o Hands/feet adapted for grasping
V. Convergent Evolution
• Marsupials vs Placental Mammals (page 16)
o Evolved separately due to Pangea breakup
o Marsupials radiated in South America & Australia
o Placental mammals later outcompeted marsupials in South America
Review Questions
Mammalian Characteristics
1. What skeletal difference distinguishes mammal skulls from reptile skulls?
2. How did some jawbones in mammals evolve into ear bones?
Adaptations
3. Why is hair important for mammalian survival in extreme environments?
4. How do mammalian kidneys conserve water more efficiently than reptilian kidneys?
Diversity
5. What are the key differences between monotremes, marsupials, and eutherians?
6. Why do marsupials have shorter gestation periods compared to placental mammals?
Primates & Evolution
7. Which traits make primates well adapted for arboreal (tree-dwelling) life?
8. What happened to most South American marsupials after the arrival of placental
mammals?
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Study Guide: Animal Behavior
I. Types of Scientific Questions
• Proximate causation (page 2)
o What stimulus triggers behavior?
o What systems are involved?
o How does development influence it?
• Ultimate causation
o What advantage does the behavior provide (fitness)?
o How did it evolve?
o Genetic basis → evolution acts on behaviors that increase survival & reproduction
II. Stimuli & Migration
• Stimuli (page 3)
o Sources: environment, internal, other species, or conspecifics
o Can trigger and guide behaviors (e.g., migration)
• Migration (page 4)
o Arctic terns travel 50,000+ km/year
o Cues for timing: day length
o Navigation: sun, stars, magnetic fields, landmarks
III. Rhythms
• Behavioral cycles (page 5)
o Seasonal: breeding, hibernation, food storage
o Daily: circadian rhythms
o Internally controlled, calibrated with light/dark
IV. Communication
• Modes of communication (page 6)
o Visual (courtship displays, physical traits, etc)
o Sound (calls, songs)
o Pheromones (chemical signals, e.g., bees)
V. Learning
• Genetic & environmental interaction (page 7)
o Nature + nurture
• Examples:
o Bird songs (genetic template + practice)
o Social learning: tool use in chimps, vervet monkey alarm calls
VI. Evolutionary Basis of Behavior
• Behaviors persist if they increase fitness (page 8)
o Improve survival
o Improve mating success
VII. Foraging
• Optimal foraging theory (page 9)
o Maximizes energy gain vs. time/effort
o Example: crow experiment with dropping shells
VIII. Mating Strategies
• Types (page 10)
o Promiscuous: fruit flies
o Monogamous: many birds
o Polygamous:
▪ Polyandry: bees, primates, sandpipers
▪ Polygyny: lions, elk, elephant seals
• Sexual dimorphism (pages 11, 13)
o Monogamous: sexes look similar
o Polygamous: showy males, secondary sexual traits (antlers, plumage)
• Factors influencing mating systems (page 12)
o Parental care → favors monogamy
o Paternity certainty: mate guarding, sperm competition
IX. Complex Mating Strategies
• Side-blotched lizards (page 14)
o Orange-throated: aggressive, many mates
o Blue-throated: defend fewer mates
o Yellow-throated: sneaky strategy
X. Cooperation
• General cooperation (page 15) – benefits all members
• Cooperative breeding (page 16) – helpers increase reproductive success of group
XI. Altruism
• Problem: behaviors that reduce individual fitness but help others (pages 17–20)
o Examples: alarm calls, helpers, reciprocal altruism (bats)
• Kin selection (inclusive fitness) (pages 21–23)
o rB > C → altruism spreads if genetic benefit outweighs cost
o Examples: turkeys helping brothers, bee-eaters
XII. Maladaptive-Looking Behaviors
• Infanticide (page 24)
o Common in polygynous mammals (e.g., lions, primates)
o Male kills offspring → female returns to estrus
o May promote female promiscuity to confuse paternity
Review Questions
Proximate vs. Ultimate
1. What is the difference between proximate and ultimate causation in behavior?
2. Give an example of each type of question applied to bird song.
Stimuli & Rhythms
3. What environmental cues help animals navigate during migration?
4. How are circadian rhythms controlled and calibrated?
Communication & Learning
5. Name three modes of animal communication and give examples.
6. How do young birds learn their songs?
Mating & Evolution
7. Why do monogamous species often lack sexual dimorphism?
8. What factors can increase paternity certainty in males?
Cooperation & Altruism
9. How does kin selection explain altruistic behaviors?
10. What is reciprocal altruism, and how is it different from kin selection?
Complex Cases
11. What are the three throat color strategies in side-blotched lizards, and how do they differ?
12. Why might males commit infanticide in polygynous species?
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Study Guide: Population Ecology
Bio 415
I. What Is a Population?
• Definition (page 2):
o All members of the same species within a defined area
o Area can be natural (lake, mountain, forest) or arbitrary (research-defined)
• Population size
o Described by density (number per area) and dispersion (spacing)
II. Estimating Population Size
• Challenges: difficult to count every individual
• Mark–Recapture Method (page 3):
o Formula:
[
\frac{x}{n} = \frac{s}{N}
]
▪ x = marked in 2nd capture
▪ n = total captured 2nd time
▪ s = number marked 1st time
▪ N = total population size (to solve for)
III. Dispersion Patterns
• Clumped: grouped individuals (resources, social behaviors)
• Uniform: evenly spaced (territoriality, competition)
• Random: independent spacing (uniform resource distribution)
o See diagrams on page 4 for examples like sea stars, penguins, and dandelions
IV. Population Dynamics
• Key Processes: births, deaths, immigration, emigration (page 7)
• Life Table: tracks a cohort from birth to death
o Survivorship (lx): proportion alive at each age
o Fecundity (mx): offspring per female at each age
o lx × mx gives contribution to next generation
V. Survivorship Curves
• Type I: high survival → rapid decline at old age (e.g., humans)
• Type II: constant mortality (e.g., rodents)
• Type III: high early mortality → survivors live long (e.g., oysters)
VI. Reproduction
• Fecundity: number of female offspring per female (page 9)
• Varies by species:
o Elephants: 1 calf every 2–3 years
o Birds/mammals: few offspring per season
o Invertebrates: millions at once
• Age effect:
o Some species increase reproduction with age (fish)
o Others decline (humans, squirrels)
VII. Population Growth Models
A. Basic Equation
[
\text{Population Change} = B + I - D - E
]
Simplified to:
[
\frac{dN}{dt} = rN
]
• r = intrinsic rate of increase
• r > 0: growth | r = 0: stable | r < 0: decline
B. Exponential Growth Model (pages 11–12)
• J-shaped curve
• Occurs under ideal, unlimited conditions
C. Logistic Growth Model (pages 13–14)
[
\frac{dN}{dt} = rN \left(1 - \frac{N}{K}\right)
]
• K = carrying capacity
• Growth slows as N → K
• S-shaped curve (realistic)
VIII. Regulation of Population Growth
• Density-independent factors:
o Affect population regardless of size (e.g., weather, natural disasters)
• Density-dependent factors:
o Regulate population near K
o Negative: competition, disease, limited space, waste accumulation
o Positive (Allee effect): group protection, increased reproduction at higher
densities
IX. Life History Traits
A. Key Characteristics (page 17)
1. Age at first reproduction
2. Number of offspring per attempt
3. Frequency of reproduction
B. Age at First Reproduction (page 18)
• Loggerhead turtle: 30 years
• Guppies: ~1 year
• Trade-off between growth and reproduction
C. Frequency of Reproduction (page 19)
• Semelparity: reproduce once → low survival (salmon, agave)
• Iteroparity: reproduce multiple times → higher survival (oak tree, mammals)
D. Number of Offspring (page 20)
• Trade-off: number vs. size vs. care
• r-selected species: many small offspring, little care (weeds, insects)
• K-selected species: few large offspring, high care (elephants, trees)
X. Population Fluctuations
• Non-regular fluctuations: weather, disasters
• Regular fluctuations: predator-prey cycles (e.g., lynx–hare, wolf–moose data on page
21)
Review Questions
Basics
1. Define a population and list two ways its boundaries may be determined.
2. What does “density” vs. “dispersion” describe?
Methods
3. Explain how the mark–recapture method estimates population size.
4. Which type of dispersion pattern is most common and why?
Growth & Dynamics
5. How do Type I, II, and III survivorship curves differ?
6. What assumptions are made in exponential growth?
7. How does logistic growth differ from exponential growth?
Regulation
8. Distinguish between density-dependent and density-independent factors.
9. What is the Allee effect?
Life History
10. Compare semelparity and iteroparity with examples.
11. How do r-selected and K-selected species differ in reproduction and survival strategies?
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Study Guide: Community Ecology
Bio 415
I. Community Basics
• Community Definition (page 2)
o All interacting populations of species within a given area.
o Influenced by:
▪ Biotic factors: species interactions.
▪ Abiotic factors: weather, resources, disturbances.
II. Interspecific Interactions
• Types of interactions (pages 3–4)
o Competition (-/-) – both species harmed.
o Mutualism (+/+) – both species benefit.
o Commensalism (+/0) – one benefits, other unaffected.
o Antagonism (+/-) – one benefits, other harmed.
o Each affects fitness differently.
III. Niches and Competition
• Ecological Niche (page 5)
o Organism’s role and use of resources (space, time, food, interactions).
o Fundamental niche: potential range.
o Realized niche: actual range (limited by competition).
• Competition (pages 6–8)
o Occurs when species share limited resources.
o Outcomes:
1. Competitive exclusion: one species outcompetes the other.
2. Resource partitioning: species evolve to use different resources or times.
3. Character displacement: traits diverge to reduce overlap (e.g., Darwin’s
finches).
IV. Positive Interactions
• Mutualism (+/+) (pages 9–12)
o Examples:
▪ Ants & acacia trees
▪ Pollinators & flowers
▪ Mycorrhizae & plants
▪ Coral & zooxanthellae
▪ Animal gut microbiomes
o Cheating & Sanctions: fig–wasp example—trees abort unpollinated figs to
punish cheaters.
• Commensalism (+/0) (page 13)
o Examples:
▪ Birds on herbivores
▪ Plants growing in shade
▪ Animals using trees for shelter
V. Antagonistic Interactions
• Predation, Herbivory, Parasitism (+/-) (pages 14–15)
o Predation: prey killed outright.
o Herbivory: plant damaged but not killed.
o Parasitism: host harmed, not killed.
o Parasitoidism: host eventually killed.
o Leads to coevolutionary arms races.
VI. Predator–Prey Adaptations
A. Defensive & Offensive Traits (pages 15–22)
• Sensory Adaptations: enhanced vision, hearing, smell.
• Behavioral Adaptations: speed, size, defense postures.
• Morphological Defenses: armor, spines, horns.
• Chemical Warfare:
o Predators use toxins to subdue prey.
o Prey produce toxins to deter predators (e.g., rough-skinned newt vs. garter snake).
• Aposematic Coloration:
o Bright colors warn predators (e.g., poison dart frogs).
• Mimicry:
o Müllerian mimicry (+/+) – toxic species resemble each other to reinforce
avoidance.
o Batesian mimicry (+/-) – harmless species mimic toxic ones, harming the
model’s effectiveness.
• Camouflage: concealment for both predators and prey.
VII. Host–Parasite Interactions
• Endoparasites: live inside host (tapeworms, flukes, pathogens).
• Ectoparasites: live on host (fleas, ticks, leeches).
• Parasitic plants: mistletoe, ghost plant (page 23).
VIII. Community Structure
A. Diversity
• Species Richness: number of species in a community.
• Relative Abundance: distribution of individuals among species.
• Shannon Diversity Index (H):
[
H = -\sum (p_i \ln p_i)
]
o Higher H → greater diversity, resilience, and invasion resistance (page 25).
B. Trophic Structure (pages 26–28)
• Trophic Levels: producers → consumers → decomposers.
• Food Webs: show energy flow (arrows point direction of energy).
• 10% Rule: only ~10% of energy passes to next trophic level (limits food web length).
C. Top-Down vs. Bottom-Up Control (page 29)
• Bottom-Up: resource availability limits upper levels.
• Top-Down: predators regulate lower levels; removing top predators creates trophic
cascades.
IX. Key Species Roles
• Foundation Species: abundant or large species structuring habitat (corals, kelp).
• Keystone Species: not abundant but critical to ecosystem stability (e.g., otters, elephants,
beavers).
o Beavers and elephants = ecosystem engineers—create or modify habitats.
X. Disturbance & Diversity
• Disturbance: changes in community structure due to events (fires, storms, human
activity).
• Intermediate Disturbance Hypothesis (page 32):
o High disturbance: favors r-selected colonizers.
o Low disturbance: favors K-selected competitors.
o Intermediate disturbance: highest diversity.
XI. Succession
• Primary Succession: starts from lifeless areas (volcanic rock, glacier retreat).
• Secondary Succession: occurs after disturbance (e.g., fire, flood).
• Stages:
o Pioneer species: fast colonizers, tolerate harsh conditions.
o Intermediate species: improve environment.
o Climax community: stable, long-term equilibrium.
XII. Latitudinal Diversity Gradient
• Diversity increases toward equator (page 36)
o Environmental factors: more sunlight, rainfall → higher productivity.
o Community age: less disturbance, more speciation near equator.
o Area effect: larger tropical zones support more species.
Review Questions
Basic Concepts
1. Define a community and describe two major factors that shape it.
2. What distinguishes fundamental from realized niches?
Interactions
3. Compare mutualism, commensalism, and antagonism.
4. Explain how competition can lead to resource partitioning or character displacement.
Adaptations
5. Give examples of aposematic coloration and mimicry.
6. How does chemical warfare contribute to coevolution?
Community Structure
7. What does the Shannon Diversity Index measure?
8. Compare bottom-up and top-down control of food webs.
9. Why are keystone species vital despite low abundance?
Succession & Diversity
10. Contrast primary and secondary succession.
11. Summarize the intermediate disturbance hypothesis.
12. Why does species diversity tend to increase near the equator?
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Study Guide: Ecosystems
Bio 415
I. What Is an Ecosystem?
• Definition (page 2)
o All biotic (living) and abiotic (nonliving) factors interacting in an area.
o Can range in size: lake, forest, backyard, or even a decomposing log.
• Two Key Properties of Ecosystems:
0. Energy Flow – moves in one direction.
1. Nutrient Cycling – matter is recycled.
II. Energy Flow
• Energy Laws (page 3)
o Cannot be created or destroyed (First Law of Thermodynamics).
o Enters as sunlight → converted to chemical energy (photosynthesis).
o Lost as heat during transfers – energy is not recycled.
III. Matter Cycling
• Mass Conservation (page 4)
o Elements cycle, not energy.
o Ecosystem mass is constant overall (Earth = closed system).
• Detritivores (decomposers): fungi, bacteria – recycle nutrients between organic and
inorganic forms.
• Diagram on page 4 shows fungi and prokaryotes decomposing a dead tree.
IV. Ecosystem Flow Diagram
• Page 5 diagram:
o Energy: sun → producers → consumers → decomposers.
o Nutrients: cycle between producers, consumers, and detritus.
o Heat is lost at each step.
V. Primary Production
• Definition (pages 6–7):
o Conversion of solar → chemical energy by producers.
o Gross Primary Production (GPP): total energy captured.
o Net Primary Production (NPP): energy available to consumers.
[
NPP = GPP - R_a
]
(Rₐ = energy used by producers in respiration).
o Expressed as g/m²/year.
o Global map (page 7): highest NPP in tropical regions.
• Net Ecosystem Production (NEP) (page 8):
o Includes heterotroph respiration (R).
o Negative NEP → ecosystem releasing CO₂ faster than absorbing.
VI. Limits to Primary Productivity
• Light & Nutrient Limitation (page 9):
o Light limits aquatic systems; nutrients often limit both aquatic and terrestrial.【
68†source**
VII. Aquatic Ecosystems
• Light Penetration (page 10):
o Productive zone: 15–50 m deep.
o Red light (680 nm) absorbed first.
• Nutrient Limitation & Eutrophication (pages 11–12):
o Nitrogen and phosphorus are primary limiting nutrients.
o Mismatch: nutrients sink; light only penetrates top layers.
o Eutrophication: excess nutrients → algal blooms → oxygen depletion (hypoxia).
• Upwelling (page 13):
o Brings nutrients to surface via thermohaline circulation.
o Productivity highest in upwelling zones.
VIII. Terrestrial Ecosystems
• Key Factors: precipitation & temperature (page 14).
o Biomes differ in NPP (rainforests = highest).
o Nutrient limitation can still occur.
• Global Patterns: (pages 15–16)
o NPP increases with temperature & rainfall.
o Tropical and temperate zones = high productivity.
• Plant Adaptations for Nutrient Uptake (page 17):
o Nitrogen-fixing bacteria.
o Mycorrhizal fungi (phosphorus uptake).
o Phosphatases & chelating agents to increase nutrient solubility.
IX. Secondary Production
• Definition: conversion of NPP to new consumer biomass (page 18).
o Only ~1/6 of plant material eaten.
o Production efficiency: proportion used for growth (not respiration).
▪ Mammals/Birds: 1–3%
▪ Fish/Reptiles: ~10%
▪ Insects/Microbes: ~40%
X. Trophic Efficiency & Biomass
• Trophic Efficiency (page 19):
o % of energy transferred between levels (~10% on average, range 5–20%).
o Explains fewer top predators.
• Biomass Pyramid (page 20):
o Usually upright (less mass at higher levels).
o Inverted in aquatic systems due to high turnover in producers (phytoplankton).
XI. Nutrient Cycling
• Role of Decomposers (page 21):
o Return nutrients to inorganic form.
o Influenced by temperature & moisture – faster in warm, wet climates.
• Reservoirs in Biogeochemical Cycles (page 22):
o A: Living organisms.
o B: Waterlogged sediments (peat).
o C: Water/air/soil.
o D: Rocks (released slowly via weathering).
XII. Major Biogeochemical Cycles
A. Water Cycle (page 23)
• Driven by solar energy.
• 97% ocean, 2% glaciers, 1% freshwater (rivers, lakes, groundwater).
B. Carbon Cycle (page 24)
• Photosynthesis & respiration balance carbon flux.
• Main reservoirs: sediments, soil, fossil fuels, oceans.
• Human impact: fossil fuel combustion increases atmospheric CO₂.
C. Nitrogen Cycle (page 25)
• N₂ gas in atmosphere → unusable to plants.
• Steps:
1. Fixation: lightning/bacteria → NH₃/NH₄⁺
2. Nitrification: → NO₂⁻/NO₃⁻ (usable form).
3. Denitrification: returns N₂ to atmosphere.
• Human fertilizer & runoff → eutrophication.
D. Phosphorus Cycle (page 26)
• Main reservoir: rocks.
• Released by weathering & erosion.
• Often limiting nutrient in ecosystems.
Review Questions
Basics
1. What are the two emergent properties of ecosystems?
2. Explain why energy flows but nutrients cycle.
Primary Productivity
3. Differentiate between GPP, NPP, and NEP.
4. What factors limit NPP in aquatic vs terrestrial ecosystems?
Energy & Matter
5. Why are decomposers essential to ecosystem stability?
6. How does energy efficiency vary across trophic levels?
Biogeochemical Cycles
7. Describe one major human impact on the nitrogen and carbon cycles.
8. Why is phosphorus often limiting in ecosystems?
9. What role does upwelling play in oceanic productivity?