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Critical Thinking: Climate, Phenotypic Plasticity, and Dynamic Systems

Critical Thinking 6: Climate diagrams and growing season

  • Key idea: Plant growth is constrained by either temperature or precipitation depending on which resource limits production at a given time. If the temperature line falls below the precipitation line on a climate diagram, growth is limited by temperature; if the precipitation line falls below the temperature line, growth is limited by water (precipitation).

  • Task from Page 2: Identify climate diagrams where water has the potential to seasonally limit plant productivity.

Climate diagram for Miami, Florida (Part 2)

  • Monthly data (Temperature in °C; Precipitation in mm) from the transcript:

    • January: T=2\,^{\circ}\mathrm{C}, \quad P=45\,\mathrm{mm}

    • February: T=5\,^{\circ}\mathrm{C}, \quad P=50\,\mathrm{mm}

    • March: T=9\,^{\circ}\mathrm{C}, \quad P=104\,\mathrm{mm}

    • April: T=15\,^{\circ}\mathrm{C}, \quad P=100\,\mathrm{mm}

    • May: T=18\,^{\circ}\mathrm{C}, \quad P=120\,\mathrm{mm}

    • June: T=23\,^{\circ}\mathrm{C}, \quad P=110\,\mathrm{mm}

    • July: T=28\,^{\circ}\mathrm{C}, \quad P=88\,\mathrm{mm}

    • August: T=25\,^{\circ}\mathrm{C}, \quad P=100\,\mathrm{mm}

    • September: T=21\,^{\circ}\mathrm{C}, \quad P=140\,\mathrm{mm}

    • October: T=15\,^{\circ}\mathrm{C}, \quad P=98\,\mathrm{mm}

    • November: T=8\,^{\circ}\mathrm{C}, \quad P=100\,\mathrm{mm}

    • December: T=3\,^{\circ}\mathrm{C}, \quad P=65\,\mathrm{mm}

  • Climate diagram construction rules:

    • Axis labels: Temperature (°C) and Precipitation (mm).

    • Scaling rule: for every 10°C increase in temperature, precipitation increases by 20 mm.

    • Quantitative relation (scaling):\Delta P = 2\,\Delta T\quad(\text{mm per }^{\circ}\mathrm{C})

    • Title: something like "Climate Diagram for Miami, Florida"; you may draw by hand.

    • Grading rubric (as given):

    • 2 pts — the trend on the graph looks correct

    • 1 pt — axes are labeled with units specified

    • 1 pt — values on each axis are correct

    • 1 pt — graph has a title

  • Part 3 Interpretation tasks (based on your graph):

    • Identify the months when the growing season occurred.

    • Identify which months growth was limited by temperature.

    • Identify which months growth was limited by precipitation.

Critical Thinking 5: Air and water vapor (Fig 5.5) – True statements to evaluate

  • Which statements about air and water vapor are true? (refer to Fig 5.5; copy true responses onto submission file)

    • a. Hot air can hold more moisture than cooler air.

    • b. At 30°C, air can contain up to 30 g of water vapor per m³.

    • c. Cool air can hold more moisture than hotter air.

    • d. When air cools its saturation point decreases (and it holds less water).

    • e. Air that contains the maximum amount of water vapor has reached its saturation point.

    • f. When air heats, the excess water vapor in the air will undergo a phase change from gas to liquid producing clouds and precipitation.

    • g. The relationship between temperature and water vapor saturation affects patterns of evaporation and precipitation around the world.

  • Note: The true/false determinations depend on Fig. 5.5; refer to the figure when answering.

Critical Thinking 5: Conceptual questions involving adiabatic processes and rainshadows (Fig. 5.6)

  • Why are there rainforests at the equator? Use "adiabatic cooling" in your response. (Fig. 5.6 may help; 3 points)

  • Why do air cells move? (3 points)

  • Why are there deserts at 30° N and 30° S of the equator? Use "adiabatic heating" in your response. (Fig. 5.6 may help; 3 points)

  • Use adiabatic heating and adiabatic cooling to explain the rainshadow effect.

  • Why do the western side of the Sierra Nevada Mountains get more rain than the eastern side? (refer to the rainshadow figure below; 3 points)

Critical Thinking 4: Fig. 4.2 and phenotypic plasticity

  • 1. Refer to Fig. 4.2 to answer:

    • a) Describe what is happening in Fig. 4.2a & b. In your response, correctly use the terms: “phenotypic plasticity”, “environment”, and “fitness” (2 points).

    • b) Refer to Fig. 4.2c to explain why we need to consider the mean fitness across all environments when evaluating whether evolving a phenotypically plastic genotype will be favored over a non-plastic genotype? (1.5 points)

Critical Thinking 4: Classification of phenotypically plastic traits (1 point each)

  • Phenotypically plastic traits include behavior, physiology, morphology, and life history. Each type of trait differs in how fast it can respond to environmental change and whether the responses are reversible. Classify the following traits as behavioral, physiological, morphological, or life history:

    • a) In the warm wet season, when food and reproductive opportunities are abundant, the African savannah butterfly Bicyclus anynana lives short with fast growth and maximal reproduction, allocating fewer resources to body maintenance; in the cool dry season, adult food is limited and larval food is absent, and adults express inactivity traits, postponed reproduction and longer lifespan. → best fit: life history (reproduction strategy) and possibly behavior, but classify as Life history for the stated emphasis.

    • b) In the presence of a predator, bluegill sunfish, freshwater snails (Physa virgata) make their shell shape more rotund and reduce growth. → Morphological

    • c) Cephalopods, which can rapidly change color to communicate, warn predators, camouflage, or avoid predation. → Physiological

    • d) The thermal tolerances, metabolic rate, and oxygen consumption of fish, reptile, and amphibian species in temperate climates change over the year to reduce energy consumption in winter. → Physiological

Critical Thinking 4: Plant responses to stressful environmental conditions (a–e)

  • For each scenario, give an example of phenotypic plasticity in a plant, classify the trait, indicate reversibility, and estimate time to respond.

    • a) Low water availability → example: deeper root growth or reduced leaf area; classification: morpho- logical/physiological depending on trait chosen; reversibility: generally reversible; time to respond: days to weeks.

    • b) Low light availability → example: increased chlorophyll concentration or leaf angle adjustment; classification: physiological (or morphological; here call it physiological); reversibility: reversible; time: days to weeks.

    • c) Low nutrient availability → example: enhanced root proliferation into nutrient patches; classification: morphological (root architecture); reversibility: reversible; time: days to weeks.

    • d) Being eaten by an insect or animal → example: production of defensive chemicals (phytoalexins) or tougher tissues; classification: physiological (or morphological if thorns develop); for this entry, classify as morphological/chemical defense depending on example; reversibility: often reversible after herbivore pressure ends; time: hours to days.

    • e) Pesticide application → example: upregulation of detoxification enzymes; classification: physiological; reversibility: reversible after exposure ends; time: hours to days.

Critical Thinking 3: Plant and animal adaptations to hot and dry climates

  • 1) Define photorespiration and explain why it is a problem for plants.

    • Photorespiration occurs when Rubisco fixes O2 instead of CO2, producing 2-phosphoglycolate and leading to energy loss and reduced net carbon gain; it is problematic especially at high temperatures and low CO2 when stomata are partially closed.

  • 2) How do C4 plants solve the problem of obtaining CO2 for photosynthesis while minimizing water loss?

    • C4 plants concentrate CO2 in bundle sheath cells via the Hatch–Slack pathway: CO2 is initially fixed in mesophyll cells by PEP carboxylase into a four-carbon acid (e.g., oxaloacetate), transported to bundle sheath cells where CO2 is released for the Calvin cycle, reducing photorespiration and allowing stomata to remain less open, saving water.

  • 3) In addition to having highly efficient kidneys, what behaviors do desert animals use to reduce water loss? (Refer to Fig. 3.10, 3.11, 3.14 for guidance)

    • Nocturnal activity to avoid heat, burrowing or seeking shade, retreating during the day, producing concentrated urine or dry feces, and obtaining water from food when possible.

Critical Thinking 2: Osmoregulation in fish and mangrove salt balance

  • 1) Define the mechanism for maintaining water and salt balance across external surfaces in aquatic vertebrates (use correct terms: osmosis, osmoregulation, diffusion, active transport).

  • 2) Freshwater fish: describe their osmotic challenges and the three primary mechanisms to balance solutes in tissues.

    • Freshwater fish are hyperosmotic to their surroundings (their body fluids have higher solute concentration than the surrounding water), so water tends to enter their bodies and salts tend to diffuse out. Primary mechanisms to balance solutes include:

    • Active uptake of ions (Na+, Cl−) across the gills and gut.

    • Production of large volumes of dilute urine to excrete excess water while conserving salts.

    • Limited drinking and selective ion transport to minimize salt loss; and sometimes dietary salt uptake helps.

  • 3) How do mangrove trees maintain salt balance?

    • Salt balance is managed via multiple strategies: leaf salt glands or salt-secreting structures to excrete excess salt; sequestration of salt in vacuoles or old leaves; exclusion of salt uptake at the roots; and adjustments in water use efficiency and ion transport.

Critical Thinking 1: Dynamic steady state (Fig 1.4)

  • 1) Define: dynamic steady state is a condition where inputs and outputs balance over time, keeping a system approximately constant despite ongoing fluxes.

  • 2) Give an example of a dynamic steady state at any biological level (e.g., cellular homeostasis, body temperature regulation in mammals, or population-level regulatory balances).

  • 3) At the population level, what would happen to a population of animals that was not in a dynamic steady state over long time periods? (Use Fig 1.4 as a guide)

    • Without a dynamic steady state, populations may grow unchecked, collapse due to resource depletion, or experience oscillations and eventual extinction or instability; long-term trajectories depend on resource limits and environmental feedbacks.

Endnotes on terms and concepts used in these notes

  • Phenotypic plasticity: the ability of a genotype to change its phenotype in response to environmental conditions.

  • Dynamic steady state: a state where flows of matter/energy into and out of a system balance over time, allowing the system to stay near a characteristic state.

  • Adiabatic cooling/heating: air cools as it rises and expands without heat exchange with surrounding air; conversely, it heats as it sinks and compresses.

  • Rainshadow effect: moist air rises on the windward side of mountains, leading to precipitation, and descends on the leeward side, causing aridity.

  • Photorespiration: a process in plants where Rubisco oxygenates RuBP, reducing photosynthetic efficiency, especially under high temperature and low CO2.

  • C4 photosynthesis: a carbon-concentrating mechanism that minimizes photorespiration by spatially separating initial CO2 fixation from the Calvin cycle.

  • Osmoregulation: regulation of water and ion balance across membranes, essential for maintaining cellular and bodily function across aquatic environments.

  • Salt balance in mangroves: strategies to manage excess salt through secretion, sequestration, and selective uptake.

  • All mathematical expressions used here are in LaTeX and are denoted with double dollar signs for clarity, e.g.:

    • Climate diagram scaling: \Delta P = 2\ \Delta T\quad(\text{mm per }^{\circ}\mathrm{C})

    • Dynamic steady state (population level): \frac{dN}{dt} \approx 0