UNIT 1 EXAM
Introduction to Ecology
Ecology is the study of the relationships between organisms and their environment.
A fundamental aspect of ecology involves explaining the distribution and abundance of organisms.
Examples of ecological questions include understanding why elephants use specific watering holes, their distribution patterns, and population dynamics.
Specialist Herbivores: Swallowtail Caterpillars
Swallowtail caterpillars primarily consume Queen Anne's lace (Apiaceae family).
Apiaceae plants contain toxic secondary metabolites that deter most herbivores.
Some herbivores, like swallowtail caterpillars, have evolved adaptations to detoxify or utilize these compounds.
Swallowtail caterpillars sequester alkaloids from Queen Anne's lace, making them unpalatable to predators.
Their distinct coloration (black, yellow, and white stripes) serves as a warning signal to predators, a concept related to mimicry.
Most caterpillars are specialists, feeding on only one or two plant species. (Spongy moth caterpillars are an exception eating up to 200 species).
Caterpillar Food Plant Recognition
How do caterpillars identify their food plants? Potential factors include:
Visual recognition
Taste discrimination
Odor detection
Touch sensitivity
Combination of factors
Vincent's Experiment (1941): Do Caterpillars Discriminate by Smell?
Reference: American Naturalist, Vol. 75.
Research Question: Do caterpillars discriminate by smell?
Hypotheses:
Null Hypothesis: No difference in response to odors from different plants (randomness prevails).
Alternative Hypothesis: Different responses are elicited by different odors from different plants.
Experimental Design
Prediction: Caterpillars will be attracted to filter paper infused with Apiaceae odor.
Methodology:
Leaves from different plants were ground, blended with water, and filtered.
Extracts were applied to filter paper inside a petri dish.
A screen prevented caterpillars from directly touching or tasting the extracts.
Caterpillars were placed on the screen, allowing them to assess odors.
Result: Caterpillars congregated above the filter paper spots containing plant extract.
Conclusion: Caterpillars discriminate by odor.
Western Ragweed and Salt Tolerance
Western ragweed thrives in salty soil environments, common in the Great Plains.
High salt concentrations in soil can cause water to flow out of plant roots, leading to dehydration.w
Western ragweed has adapted to tolerate high salt concentrations.
Ragweed exhibits clonal growth, using rhizomes to produce clones (genetically identical offspring) some distance from the parent plant.
Clonal growth allows new clones to access the parent plant's resources during establishment.
Salzman's Experiment (1985): Microhabitat Selection via Clonal Growth
Hypothesis: Plants can select a microhabitat based on their clonal growth in response to salt concentration.
Null Hypothesis: No difference in clonal growth in response to different salt levels.
Alternative Hypothesis: Clonal growth occurs more in less salty areas.
Prediction: Plants grown in a salt gradient will exhibit greater clonal growth in the less salty areas.
Experimental Design
A rectangular box was filled with soil and a salt gradient (1% on one side, tap water on the other).
A clone was placed in the middle of the box.
Number of shoots in each end (salty vs. non-salty) was measured.
Six replicates per genotype were performed across nine different genotypes.
Importance of Replication
Replication is crucial for representing variation within a population and ensuring reliable results.
Insufficient replication can lead to inaccurate conclusions due to chance, genetic differences, or experimental errors.
The number of replicates should reflect the variation in the population.
Experimental Results
Analysis of nine genotypes showed that, on average, 67% of shoots grew in the non-salty end.
Conclusion: Western ragweed preferentially grows clones in less salty areas.
Field Experiment
Goal: To determine if lab results hold true in natural settings.
Plants grown in nonsalty areas should have their clonal growth or shoots nearby, while those in salty areas should be sending their clones farther away from the parent plant.
Clones were planted in salty and non-salty areas, and salt concentration was measured.
After several months, shoots were counted, and the distance from parent plants was measured.
Field Results
In non-salty areas, 97% of shoots grew less than 20 cm away from the parent plant.
In salty areas, 28% of shoots grew more than 20 cm away from the parent plant, while only 17% grew less than that.
Conclusion: Ragweed can select a favorable habitat through clonal growth, avoiding salty areas.
Elephant Waterhole Preference
Why do elephants prefer certain waterholes in a nature preserve?
Potential factors:
Availability of preferred food near waterholes
Presence of predators (human or non-human)
Salt attraction
Salt as an Attractant
Herbivores often seek out salt sources due to their diet being high in potassium but low in salt.
Marmots chewing car wires and hoses in Yosemite National Park were attracted to the salt from winter road treatments.
Elephant Experiment
Record waterhole usage of elephants
Assess salt availability differences between waterholes and correlate with waterhole usage to find relationship, but remember that correlation does not mean causation.
Experimentally add salt to a waterhole to see if usage increases
Experimentally remove salt from a waterhole to see if usage decreases.
Summary of Scientific Method
The lecture illustrates the scientific method:
Observations
Questions and hypotheses
Experiment/test design
Data collection and analysis
Comparison to a null hypothesis
If data deviates from randomness, a biological process is likely occurring.
Repeat until results can be trusted.
Light and Heat Effects on Ecosystems and Biomes
Introduction
Transition from the ecosystem level to the biosphere level.
Focus on the effects of light and heat from the sun on ecosystems, biomes, and biome placement through climate.
Hybrid lecture format: combination of ecosystem and biosphere levels.
Physics of Light
Light is a form of energy that travels in photons.
Photons act as particles and travel in waves.
Wave properties:
Wavelength.
Frequency.
Amplitude.
Energy of a photon determines its wavelength.
Wavelength and Energy
Long wavelength vs. short wavelength:
Wavelength is the distance between successive peaks or valleys.
Shorter wavelengths have more energy than longer wavelengths.
Speed of light is constant.
Photon energy:
Short wavelength: Photon travels up and down more frequently, requiring more energy.
Long wavelength: Photon travels up and down less frequently, requiring less energy.
Electromagnetic Radiation
Wide range of energies from the sun is called electromagnetic radiation.
Different wavelengths are treated differently on Earth's surface.
Types of electromagnetic radiation (from long to short wavelengths):
Radio waves and microwaves: Long wavelengths, low energy.
Infrared radiation: Just below red light in energy.
Visible spectrum: Red to violet; wavelengths decrease and energy increases from red to violet.
Ultraviolet radiation: Just above violet light in energy.
Gamma rays and x-rays: Short wavelengths, high energy.
Visible Spectrum
Visible spectrum is the range of electromagnetic radiation that humans can see.
Different wavelengths trigger different sensors in our eyes, allowing us to see colors (red, yellow, green, etc.).
Combining all wavelengths of light results in white light.
Prism demonstration: Light separates into different wavelengths, showing a rainbow of colors.
Infrared and Ultraviolet Radiation
Infrared (below red):
Slightly less energy than red light.
Not enough energy to trigger eye sensors.
Adding energy would make it visible as red light.
Ultraviolet (above violet):
More energy than violet light.
Exceeds the threshold of what our eyes can detect.
Thermal Radiation
Everything above absolute zero (0 degrees Kelvin) emits photons (thermal radiation).
These photons often do not have enough energy to trigger the sensors in our eyes.
Objects are visible due to reflected light rather than emitted photons.
Heated iron bar example:
Initially, the bar is visible due to ambient light.
Heating the bar increases the energy of emitted photons.
Red light: Minimum threshold of photons our eyes are sensitive to.
Yellow light: Higher temperature emits photons corresponding to yellow light.
White light: High temperature emits photons covering all wavelengths simultaneously.
Sun's temperature emits visible light across the spectrum, resulting in white light, as well as infrared, radio waves, gamma rays, x-rays, and ultraviolet radiation.
Infrared Scopes and Cameras
Technology can receive and transform photons into visible pictures.
Infrared scopes/night vision: Capture photons emitted by objects and create an image.
Images are often displayed in shades of green.
Green filters are used in movies and TV to simulate night vision.
Black filters used in older movies to create the feeling of darkness; however, shadows reveal that filming wasn't actually at night.
Gamma Rays and X-Rays
Short wavelengths with high energy.
Can penetrate various objects.
Limited travel distance for accurate interpretation.
X-ray machine example: X-rays penetrate soft tissue and reflect off bones.
Person must be close to the machine for proper reading due to photon disintegration over distance.
Earth's Energy Budget
Sunlight as a heat source striking the planet: influx and income versus expenditures.
The Earth's energy budget is generally balanced (heat in equals heat out).
The atmosphere complicates this balance.
Troposphere
Bottom layer of the atmosphere.
Where most weather occurs (rain, snow, sunshine, clouds).
Temperature decreases with nutrie
Some weather impacts but not main weather systems.
Components:
Jet stream: Fast-moving air affecting surface weather systems; influences airplane travel.
Ozone layer: Absorbs sunlight energy, especially UV radiation; protects organisms from harmful radiation.
Ozone Layer
Ozone (O3) forms when oxygen gas (O2) molecules are broken apart into free oxygen atoms by sunlight.
Free oxygen atoms bind with oxygen molecules to form ozone.
Ozone layer in the stratosphere absorbs UV radiation.
Ozone depletion: Diminishes ozone layer, allowing more UVB radiation to strike the surface, causing skin and tissue problems in organisms.
Mesosphere and Thermosphere
Mesosphere: Separates the stratosphere from the thermosphere; relatively thin.
Thermosphere: Top layer of the atmosphere; very cold and very hot depending on sun exposure due to thinness of molecules.
Heat Influx vs. Heat Outflux
Earth's energy budget is generally balanced.
Heat coming in from sunlight equals heat released as thermal radiation.
Heat Sources
Earth's Surface:
Sunlight striking the earth: units.
Atmosphere radiating heat: units.
Heat Loss Methods
Evaporation: units (from open water, wet plants, wet soil).
Convection and Conduction: units (movement of air molecules and physical touch).
Thermal Radiation: units (photons liberating from the surface).
Balancing the Equation
Heat gained at the surface versus heat lost from the surface is balanced.
Heat coming in equals heat going out.
Atmospheric Balance
Solar radiation strikes Earth; some is reflected back from the atmosphere.
Some is absorbed by the atmosphere and clouds, eventually radiating into space.
Total heat coming in from the sun into Earth and its atmosphere equals heat radiated away into space.
Climate Change and Greenhouse Effect
Problem: Humans are altering the atmosphere by adding greenhouse gases (carbon dioxide, methane).
This causes the atmosphere to absorb and hold more heat, preventing it from radiating into space.
Altered convection and conduction: Surface loses less heat; may even gain some.
The equation is thrown off: 51 + 96 > 23 + 117
Greenhouse Effect
Natural warmth of Earth due to the atmosphere holding in heat.
Without the atmosphere, average temperature would be degrees Celsius.
With the atmosphere, average temperature is around degrees Celsius.
Climate change: Occurs when the atmosphere holds onto more heat due to human activities.
This affects ecosystems, communities, populations, and individuals.
Conclusion
Future lectures will cover climate formation relative to light and heat from the sun and Earth's movement around the sun.
Also, how biomes are placed around the globe because of light, heat, and climate.
Sunlight and Climate
Sunlight interacts with the Earth's surface differently due to its spherical shape, tilt, and revolution around the sun.
These interactions influence climate patterns, which in turn affect the distribution of biomes.
Climate vs. Weather
Weather: Short-term atmospheric conditions (e.g., daily rain or snow).
Climate: Long-term, annual expectations for temperature and rainfall in a region (e.g., predictable seasonal changes).
Biomes
A biome is a collection of similar ecosystems.
Classifying regions into biomes is useful because similar environmental conditions lead to similar evolved adaptations in organisms across different locations.
Sunrise and Sunset at the Poles on March 20/21
March 20/21 marks sunrise at 90 degrees north latitude (North Pole) and sunset at 90 degrees south latitude (South Pole).
This is significant because it indicates the first sunlight in six months for the North Pole and the last sunlight for the South Pole.
Seasons
Question: Why do we have seasons?
Common misconceptions:
Earth's orbit: Sometimes Earth is closer/farther from the sun.
Earth's tilt: Some places are closer/farther from the sun.
Shape & tilt: Some places get less sunlight per unit area.
Earth's Orbit
Earth's orbit is an ellipse, not a perfect circle.
The distance between Earth and the sun varies by about 3 million miles annually.
Reality: Earth is farthest from the sun in July (Northern Hemisphere summer) and closest in January (Northern Hemisphere winter).
This contradicts the idea that distance causes seasons.
Earth's Tilt
Earth is tilted at 23.5 degrees from vertical.
Even with an extreme hypothetical tilt of 90 degrees, the change in distance to the sun is minimal.
\frac{7926 \text{ miles (Earth's width)}}{93,000,000 \text{ miles (Avg. distance to sun)}} < 0.0001 (less than 0.01%)
This small difference cannot explain seasonality.
Shape and Tilt: Sunlight Distribution
The curvature of the Earth spreads out sunlight.
Sunlight striking the Earth perpendicularly (e.g., at the equator) is concentrated over a smaller area compared to sunlight striking at an oblique angle (higher latitudes).
Less sunlight per unit area results in less heating.
Differential Heating: The variation in solar energy received at different latitudes due to Earth's shape and tilt.
Seasonal Migration of Sunlight
Spring: Concentrated sunlight at the equator.
Summer (Northern Hemisphere): Concentrated heating migrates to 23.5 degrees north latitude (Tropic of Cancer).
Fall: Heating migrates back toward the equator.
Winter: Concentrated rays at 23.5 degrees south latitude (Tropic of Capricorn).
This migration causes seasonal changes due to differential heating.
Wind
Wind is moving air.
Question: What causes wind?
Uneven heating of the Earth is the primary driver.
Hot air rises because its molecules move faster, decreasing density. Less dense air rises among denser air.
This creates air movement or wind.
Cloud Formation and Rain
As warm air ascends, it cools due to:
Increasing distance from the warm Earth.
Decreasing atmospheric pressure.
Cooling causes water molecules to slow down and stick together (cohesion), forming clouds.
Further cooling causes water droplets to merge, becoming heavier and falling as rain.
Air Movement and Pressure
Air moves from areas of high pressure to areas of low pressure.
Rising hot air creates a low-pressure area, drawing in air from surrounding high-pressure zones.
Intertropical Convergence Zone (ITCZ)
The Intertropical Convergence Zone (ITCZ) is a region of intense heating and rising air near the equator.
Surface winds converge underneath the rising air.
The ITCZ is a significant rain-making system.
Surface winds are drawn in toward the equator underneath that rising air.
It oscillates annually between 23.5 degrees north and south latitude, bringing rain to different regions. The Intertropical Convergence Zone travels to the north, bringing more rain up, then travels to the south, bringing more rain down to the Tropic of Capricorn and then back up, bringing rain to the equator again.
Keys from the Lecture
The Intertropical Convergence Zone oscillates between the equator and the Tropics of Cancer and Capricorn annually.
This oscillation explains how biomes are placed around the globe.
Intertropical Convergence Zone (ITCZ)
The ITCZ is a rain-making machine that shifts throughout the year.
During the spring and fall, the ITCZ is at the equator, causing intense heating from the sun.
The heated air ascends into the atmosphere, creating a low-pressure zone. This zone is filled by surface air from the north and south, leading to surface winds.
As the air mass rises, water condenses, forming clouds and resulting in rainfall.
The ITCZ migrates due to the Earth's tilt:
Spring: Equator
Summer: 23.5 degrees north latitude
Fall: Equator
Winter: 23.5 degrees south latitude
The ITCZ is quite broad, spanning several degrees north and south of its center, distributing rain over a large area depending on the time of year.
Tropical Rainforests
Warm and wet year-round with minimal temperature variation.
Constant warmth and wetness promote continuous and rapid growth.
High and consistent rainfall due to the ITCZ, even during dry seasons.
Located near the equator in South America, Africa, and Malaysia.
The ITCZ spends most of its time between 23.5 degrees north and south latitude, leading to consistent rainfall in these areas.
Misconceptions about tropical rainforests:
They are not always as dense as imagined; the intense canopy cover limits sunlight penetration to the forest floor.
The forest floor is usually dark with sparse growth.
Species richness:
Tropical rainforests host approximately 80% of the world's species.
Medicinal resources:
About 25% of the world's medications originate from tropical rainforests.
Approximately 12% of all medications can only be sourced from plants in these rainforests, which cannot be manufactured in labs, emphasizing the importance of preservation and further research.
Soil fertility:
Contrary to popular belief, tropical rainforests have nutrient-poor soils.
Rapid plant growth and decomposition quickly recycle nutrients, leaving very little in the soil.
Nutrient distribution:
Temperate deciduous forests: About 90% of nutrients are in the soil, less than 10% in vegetation.
Tropical rainforests: About 90% of nutrients are in the vegetation, less than 10% in the soil.
Savannas
Characterized by alternating wet and dry seasons, each lasting about half the year.
The wet season is not as wet as in tropical rainforests.
Temperature variation is more pronounced compared to tropical rainforests.
Located away from the equator, such as in the Serengeti in Africa, northern South America, and parts of Australia.
The ITCZ influences savanna weather patterns:
As the ITCZ moves toward 23.5 degrees north latitude, it brings rain, but leaves areas south of the equator dry.
When the ITCZ shifts back towards and crosses the equator, it leaves areas like the Serengeti dry, creating distinct wet and dry seasons.
The acacia trees are well-adapted to the long dry periods.
The Serengeti supports a variety of herbivores and bird species.
Deserts
Defined by evaporation and transpiration rates exceeding precipitation.
Significant temperature variation within 24-hour periods and across the year due to low moisture content.
Located approximately at 20-25 degrees north and south latitude, influenced by the ITCZ.
The Sahara Desert in Africa and deserts in Australia are examples.
The ITCZ brings limited rainfall to these areas, resulting in prolonged dryness.
Descending dry air masses at around 30 degrees north and south latitude contribute to desert formation.
Deserts at the poles (90 degrees N/S latitude) are desert-like, with very little rainfall or snow due to descending air masses, but minimal evaporation due to extreme cold.
The Sonoran Desert is known for high species richness due to its two distinct rainy seasons, influenced by hurricanes and Pacific Ocean storms.
Not all deserts are piles of shifting sand; many support plant and animal life.
Airflow and Desert Formation
Air rises at the equator, loses moisture as rainfall, and then travels north or south. The air then descends around 30 degrees latitude, warming up but remaining dry, creating deserts by absorbing surrounding water vapor.
Hadley Cell: This is the name we give to the circular motion of the air around the equator.
Deserts form at 30 degrees north and south latitude due to descending dry air masses; the deserts in Australia exemplify this.
Rain Shadow Effect: Occurs when warm, wet air is forced over mountains, cools, and releases moisture on the upwind side, while the descending air on the downwind side is warm and dry, creating deserts.
Examples:
The Cascades in Washington, where the western side receives significant rainfall (over 180 inches per year), while the eastern side is very dry (under 10 inches per year).
The Sierra Nevadas in California, with similar effects.
Global Air Circulation
Hadley Cell: Air rises at the equator, travels to 30 degrees N/S, descends, and returns to the equator. Air cycles in a counterclockwise manner in the northern hemisphere and in a mirror image in the southern hemisphere.
Ferrel Cell: Driven by the Hadley cell between 30 and 60 degrees latitude.
Polar Cell: Located between 60 and 90 degrees latitude.
Air ascends at the equator and 60 degrees latitude, leading to precipitation.
Air descends at 30 and 90 degrees latitude, creating deserts.
Constant air flow takes place, with winds in the upper atmosphere flowing north and a southerly flow of air along the surface of the planet itself.
Coriolis Effect
Surface winds and objects in motion deflect to the right in the northern hemisphere and to the left in the southern hemisphere.
Northeast Trade Winds: Between 30 degrees north and the equator, winds travel southward and bend to the right (east to west), creating winds from the northeast to the southwest.
Westerlies: Between 30 and 60 degrees north latitude, winds travel northward and bend to the right (west to east), creating winds from the southwest to the northeast.
In the Binghamton area, the prevailing wind direction is from the west.
Tundra
Located in Arctic areas not covered by ice.
Very low temperatures with high annual variation due to long periods of sunlight in summer and darkness in winter.
Low precipitation but high moisture due to minimal evaporation, dominated by cold-tolerant plants and animals.
Permafrost: A permanently frozen layer below the surface that limits tree growth.
Found across the top of Russia and Europe as well as the tops in North America.
Boreal Forest
Found in Canada, Alaska, Russia, and Northern Europe.
Low temperatures and relatively high temperature variation across the year.
Low precipitation but high moisture due to minimal evaporation.
Dominated by cold-tolerant shrubs, trees, and evergreens such as spruce and pine.
Conifers dominate over deciduous trees in boreal forests because:
They can start photosynthesizing sooner in the spring when soils thaw.
Boreal forest soils are acidic and nitrogen-poor; conifers are more efficient at using limited nitrogen to maintain their needles.
Temperate Forests
Widespread in eastern North America, Western Europe, and Asia.
Moderate temperature and precipitation variations.
Dominated by deciduous trees (trees that lose leaves in winter).
Biome Placement on Continents
Australia: Deserts in the middle (at 30 degrees south latitude), savannas around the deserts, tropical rainforests along the northern peninsula, and temperate deciduous forests in the southeast.
Considerations for Explaining Biome Placement:
Differential heating, tilt of the earth, and shape of the earth.
Elevation and large landmasses.
Summary Points
Biomes are not randomly distributed; they are shaped by the Earth's physical conditions and differential heating.
Organisms evolve to fit available niche spaces within these biomes.
Differential heating sets up precipitation patterns, which position climates.
Seasonality is caused by the tilt of the earth and curvature of the Earth.
Wind is caused by the ascension of warm air masses and the filling of low-pressure systems.
Large continents and elevation changes can create smaller, different biomes.
The Hydrologic Cycle
Almost all organisms rely on water.
The hydrologic cycle involves:
Ascending warm air masses containing water molecules.
Water molecules sticking together and falling as rain.
Rainfall striking the earth.
Interception
Intercepted water: Water that doesn't reach the ground directly.
Examples: water striking roads, roofs, or vegetation without soaking in.
Infiltration
Infiltrated water: Water that seeps into the soil.
Available for plant growth.
Plant roots absorb infiltrated water.
Percolation
Percolated water: Water that seeps through the soil into bedrock and aquifers.
Can remain underground for centuries.
May emerge as groundwater or be accessed via wells.
Groundwater
Groundwater: Water that has percolated below the soil surface into the bedrock layer.
Seeps out, often on exposed hillsides.
Slower movement to bodies of water compared to intercepted or infiltrated water.
Water Movement
All water eventually flows toward larger bodies of water (rivers, streams, lakes, oceans).
Intercepted water moves fastest, followed by infiltrated water, then percolated water (as groundwater).
Runoff
Excess intercepted water leads to runoff.
Runoff can cause erosion and damage to ecosystems.
High-powered water movement can lead to flash floods.
Evapotranspiration
Evapotranspiration: Water returning to the atmosphere.
Evaporation: Water from soil, lakes, and oceans evaporating.
Transpiration: Water moving through plants and then released into the atmosphere.
Properties of Water
Water is a polar molecule with positive and negative sides.
Acts like tiny magnets, influencing its properties.
Specific Heat
Specific heat: Energy required to raise 1 cubic centimeter of a substance by 1 degree Celsius.
Water has a high specific heat.
Takes a lot of energy to heat up.
Takes a long time to cool down.
Impact on local climate:
Areas near large bodies of water have more moderate temperatures.
Winds shift direction near large lakes and oceans due to differential heating.
Latent Heat
Latent heat: Energy needed to free water vapor or water molecules from ice.
Water holds onto its heat.
Cohesion & Adhesion
Cohesion: Water molecules sticking to each other.
Adhesion: Water molecules sticking to other substances.
High surface tension results from these properties.
Water bubbling over the top of a filled glass.
Water forming bubbles on oily surfaces.
Surface Tension
Surface tension is important for organisms living on or near water surfaces.
Water striders:
Live on the surface of ponds due to surface tension.
Cannot get underwater.
Use modified front legs to vibrate the water surface and communicate through wave patterns.
Territorial signals, mating signals, danger signals.
Tim Wilcox: A researcher who studied water strider communication.
Used a water tank suspended from the ceiling to minimize vibrations.
Used an electronic robotic arm to create vibrations and communicate with water striders.
Viscosity
Viscosity: Measurement of the force it takes to move through water.
Water has a relatively high viscosity.
Requires more energy to swim through water compared to substances with lower viscosity.
Density & Buoyancy
Density: Mass per unit volume.
Buoyancy: Ability to float in water based on density.
Objects less dense than water float.
Fish utilize swim bladders to control buoyancy.
Swim bladder: An air-filled chamber inside the fish.
Relaxing muscles expands the swim bladder, decreasing density, causing the fish to float.
Contracting muscles reduces the size of the swim bladder, increasing density, causing the fish to sink.
Deep-water fish and swim bladder issues when rapidly brought to the surface.
Refraction
Refraction: Bending of light as it moves from one medium to another.
Light bends toward the normal when moving from less dense to more dense medium (air to water).
Light bends away from the normal when moving from more dense to less dense medium (water to air).
Implications for organisms:
Objects underwater appear higher and closer than they actually are.
Great blue herons and kingfishers must compensate for refraction when hunting.
Archer fish spits water at insects, compensating for the refraction of light.
Light Absorption
Pure water absorbs sunlight.
Absorption increases with depth.
Infrared and ultraviolet light are absorbed rapidly.
Red light is absorbed within 5-7.5 meters.
Blue light penetrates deepest.
Plants can't grow very deep because of light limitations.
75% of light is absorbed in the first 10 meters.
Shallow coral reefs have a variety of colors, while deeper waters become monochromatic.
Standing Bodies of Water
Freshwater Lakes
Littoral zone: Area where plants grow attached to the bottom.
Limnetic zone: Open water area where plants don't grow at the bottom.
Vertical layers:
Epilimnion: Upper layer, warm with most oxygen during summer.
Thermocline: Layer of rapid temperature transition.
Hypolimnion: Coldest layer at the bottom.
Stratification: Layers don't mix during summer.
Turnover: Mixing of layers in fall and spring.
Fall: Surface water cools, thermocline disappears, nutrients cycle up, oxygen cycles down.
Spring: Ice melts, surface water reaches 4 degrees Celsius, another turnover occurs.
Late spring: Ice covers the lake longer than average, can lead to fish die-offs due to lack of oxygen.
Oceans
Intertidal zone: Area between high and low tide.
Neritic zone: Extends out to the continental shelf.
Oceanic zone: Rest of the ocean.
Plants grow in the intertidal and shallow neritic zones.
Organisms classified as benthic (living on the substrate) or pelagic (living in the water column).
Stratification: Layers stratified by temperature and salt.
Colder water sinks.
Warmer water rises.
Saltwater is denser than freshwater.
Ocean currents are affected by these factors.
Melting glaciers release freshwater, slowing the descent of cold, dense saltwater, affecting climate.
Water as a Solvent
Water dissolves various substances, primarily salt in oceans.
Dead Sea: High salt concentrations allow for easy floating.
Adaptations for osmoregulation:
Freshwater organisms prevent water from diluting their internal salt concentrations.
Saltwater organisms prevent salt from entering their bodies.
Euryhaline species: Fish that can live in both freshwater and saltwater (e.g., Pacific and Atlantic salmon).
Estuaries: Areas where freshwater meets saltwater, require adaptations to handle both conditions.
pH Levels
Water has a pH of 7.
Organisms have varying tolerances for pH levels.
Bacteria, plants, and algae have broader tolerances than fish.
Acid rain: Can lower pH levels, leading to die-offs of sensitive organisms.
Runoff from land can carry various substances into the water, impacting aquatic environments.
The Terrestrial Environment: Physical Characteristics
Introduction
This lecture focuses on the physical characteristics of the terrestrial environment and the adaptations organisms have developed to live on land.
It contrasts with the aquatic environment discussed earlier.
The primary challenge of terrestrial life is the limited availability of water.
The Problem of Drying Out
The central issue for terrestrial organisms is avoiding desiccation or drying out.
This applies to plants, animals, and other organisms.
The lecture will discuss how organisms prevent water loss, the problems they face, and their solutions.
Water Loss in Animals
Animals primarily lose water through two surfaces:
Outer surface (skin)
Respiratory surfaces (lungs)
Respiratory surfaces need to be wet for gas exchange (oxygen in, carbon dioxide out).
Breathing with lungs leads to moisture loss during exhalation, posing a challenge.
Strategies to Avoid Water Loss in Animals
Behavioral Adaptations:
Avoiding hot, dry parts of the day (middle of the day).
Seeking shade, burrows, or forests with leaf cover.
These locations are cooler, reducing moisture loss.
Warm air causes faster evaporation compared to cool air.
Desert organisms are active early in the morning, at dusk, or at night to conserve moisture.
Obtaining Water
Eating wet foods and drinking water.
Metabolic Water:
Some organisms, like kangaroo rats, can create water through metabolic processes.
They oxidize dry food items like seeds.
They break down fats and proteins to obtain hydrogen and oxygen, which they combine to create water ().
This allows them to survive in environments without readily available water sources.
Concentrating Waste Products
Efficient water balance involves concentrating waste products (urine and feces) to extract water.
Kangaroo rats produce extremely dry feces and highly concentrated urine.
Feces are almost 150 times drier than those of a typical lab rat.
Urine is 10 to 20 times more concentrated.
Boundary Layer
The boundary layer is central to minimizing water loss through the outer body surface.
It's the space between the skin and the outside air.
Without a boundary layer, wind velocity decreases linearly towards the skin surface, reaching zero at the skin.
Water evaporates from the skin surface at a rate proportional to the dryness of the outside air.
Moving air carries away water molecules accumulating near the skin, making the area drier and increasing evaporation.
Hair, scales, and feathers disrupt wind flow, creating a boundary layer.
Wind velocity is reduced more quickly, allowing water molecules to build up.
This reduces the difference in water concentration inside and outside the body.
Water loss is slowed down.
Smooth scales (e.g., on Tegu lizards) create a tight boundary layer.
They're dry, contrary to common misconceptions about reptiles.
Air and gases move in and out of the boundary layer more easily than water.
Insulation
Boundary layers provide both insulation and moisture retention.
In the summer, birds lay their feathers flat to hold onto moisture.
In the winter, birds puff up their feathers to increase the boundary layer thickness and retain heat.
Water Reclamation in the Lungs
Lungs contribute significantly to water loss.
Mammals (e.g., camels), some reptiles, and many birds have a water reclamation process involving the sinuses.
Sinuses have a wavy structure that increases surface area.
Inhalation:
Dry air passes across the wavy structure, picking up moisture and body temperature.
Cooling hot air and warming cool air before reaching the lungs.
Exhalation:
Damp breath passes across a different set of turbinates, causing cooling.
Cooled air condenses water, which sticks to the surfaces.
Drainage systems return the water to the body.
Camels can reclaim about 90% of the water they would otherwise lose through their sinuses.
Example: A runny nose on a cold day is often due to water condensing in the sinuses.
Water Loss in Plants
Plants also face the problem of water loss on land.
They need to lose some water for proper function (water moves from roots to leaves for photosynthesis and sugar transport).
However, they need to regulate the amount and location of water loss.
Plant Adaptations to Prevent Water Loss
Thick, Waxy Cuticle:
Covers the leaf surface.
Prevents moisture loss.
Protects against harsh sunlight.
The top cuticle is thicker than the bottom cuticle.
Boundary Layers:
Formed by structures like trichomes (spiky structures on the leaf surface).
Trichomes slow down airflow across the leaf surface, reducing water loss.
Trichomes can be physical or chemical.
Stomata:
Openings on the undersides of leaves for CO2 intake and water evaporation.
Plants can open and close their stomata.
Open stomata for photosynthesis and CO2 intake.
Close stomata to prevent excess water loss, especially at night.
Plants in wetter areas have more exposed stomata, while those in drier areas have stomata flush with the leaf surface to minimize moisture loss.
Photosynthesis Adaptations
C-3, C-4, and CAM plants are different ways of performing photosynthesis to maximize water efficiency.
CAM plants collect at night and close their stomata during the day to prevent water loss while still performing photosynthesis.
Buoyancy
Buoyancy is another challenge for terrestrial organisms compared to aquatic organisms.
Water is dense, providing buoyancy.
Air is much less dense, requiring organisms to support themselves.
Aquatic mammals have reduced bone structure compared to terrestrial mammals.
Aquatic plants have less biomass than terrestrial plants since they float easily in water.
Trees have extensive structures to support their mass and reach the canopy for photosynthesis.
Light Intensity
Terrestrial ecosystems have high light intensity, but not all light is used for photosynthesis.
Scientists refer to Photosynthetic Active Radiation (PAR), which is the sunlight plants use for photosynthesis.
PAR is similar to the visible part of the spectrum.
Photosynthetic Efficiency
Most terrestrial ecosystems absorb sunlight through plant structures before it hits the soil.
Photosynthetic efficiency is the percentage of light that strikes a plant and is used for photosynthesis.
This percentage is very low, typically between 0.3% and 10%, with most studies showing around 1%.
Reasons for low efficiency:
Not all sunlight is PAR (some is UV, gamma rays, or infrared).
Not all photons strike chloroplasts.
Environmental conditions may not be appropriate for photosynthesis.
In forest ecosystems:
About 79% of incoming PAR is absorbed by the canopy.
7% by mid-story plants.
Only 2% reaches the forest floor.
Forest Structure and Light Penetration
Tropical rainforests are relatively barren on the forest floor due to the lack of light.
Thick ground cover is found near the edges of the forest where there is exposed sunlight.
Leaf Area Index (LAI) is the ratio of the surface area of leaves above relative to the surface below.
A healthy ecosystem usually has an LAI greater than two, as leaves can overlap and still photosynthesize.
Life in the Shade
Life in the shade involves tolerating low levels of light and being able to photosynthesize.
Compensation intensity is the value where photosynthesis and respiration are equal.
At compensation intensity, the production of carbohydrates equals the breakdown of carbohydrates by the plant.
Sun vs. Shade Leaves
Sun leaves are smaller and thicker, adapted for maximum sunlight exposure.
Shade leaves are broader and thinner, designed to capture the relatively few photons available.
Some species have both sun and shade leaves.
Oak trees may have broader leaves lower down and smaller leaves higher up due to different light conditions.
Shade Tolerance
Shade-tolerant species can handle a good deal of shade and tend to have more accessory pigments, which allow them to capture a broader range of light.
They also have a lower compensation intensity, meaning they can photosynthesize at lower light levels.
Shade-intolerant species require higher light intensity for photosynthesis and have a higher maximum rate of photosynthesis.
Shade-tolerant plants also tend to have lower respiration rates, as they have evolved to use minimal energy in low-light conditions.
Graph Explanation
Two lines, A and B, represent different kinds of plants.
The graph shows light intensity on the x-axis.
The y-axis shows net carbon dioxide production or absorption, which measures the balance of photosynthesis and respiration.
Zero represents compensation intensity.
The positive side indicates photosynthesis is greater than respiration.
The negative side indicates respiration is greater.
Saturation intensity is the amount of light at which a plant will not photosynthesize more, even with more light.
Conclusion
This concludes the lecture on the terrestrial environment.
The next lecture will cover climate change.
This also concludes the Unit One lectures.
Introduction
Climate change is a critical and complex topic, driven largely by increased carbon dioxide levels.
The lecture aims to provide essential information, acknowledging the limited time available for such a significant issue.
The Carbon Cycle
The carbon cycle is closely linked to climate change due to the impact of carbon dioxide levels on the atmosphere.
Review the carbon cycle through the provided link in the post-lecture assignment if needed.
The carbon cycle itself won't be directly tested, but understanding it is beneficial.
Early Life and Oxygen
Early Earth (3.7 billion years ago) had an anaerobic atmosphere, where oxygen was toxic to existing organisms (oxygen toxicity).
Example: Coral Reefs:
Coral polyps host algae (zooxanthellae) in a mutualistic relationship.
Algae photosynthesize, slowly releasing oxygen that coral polyps use.
Climate change warms oceans, increasing algal blooms due to fertilizer runoff.
Warmer temperatures cause algae to photosynthesize faster, producing excess oxygen.
Excess oxygen leads to coral bleaching, where coral polyps eject algae and eventually die due to lack of carbohydrates.
Evolution of Photosynthesis
Around 2.8 billion years ago, organisms evolved to use CO2 and produce O2 as waste.
This was detrimental to anaerobic organisms, described as the "most severe pollution episode" by ecologist Walker in 1986.
Atmospheric Composition
Current atmospheric composition:
78% Nitrogen
20% Oxygen
0.93% Argon
0.03% Carbon Dioxide
Trace amounts of Ozone (O3)
The Natural Greenhouse Effect
The atmosphere functions like a blanket, trapping heat and keeping the Earth warm.
The Earth's surface is warmed by direct sunlight and heat radiating from the atmosphere.
The greenhouse effect is beneficial, maintaining an average temperature of 15 degrees Celsius instead of -18 degrees Celsius.
Climate change results from disrupting the natural greenhouse effect.
Global warming refers to the increase in the planet's temperature, but scientists now use the term climate change to account for increased variability in weather patterns.
Carbon Reservoirs
Carbon reservoirs are sources that exchange carbon with other parts of the globe.
Examples:
Atmosphere: An active reservoir where CO2 cycles in and out regularly.
Terrestrial Ecosystems: Plants act as carbon sinks, but overall, these ecosystems are reservoirs due to respiration and decomposition.
Oceans: Surface layers exchange CO2 with the atmosphere actively, while deeper layers are relatively inactive carbon storage areas.
Sediments: Accumulation of carbon-based molecules, including fossil fuels.
Fossil fuels are becoming an active reservoir due to human extraction and combustion.
Earth's Energy Budget
Incoming solar radiation: 100%.
30% is reflected away by the atmosphere, clouds, and Earth's surface.
70% is absorbed by oceans, land, atmosphere, and clouds, then radiated back into space.
Climate Change and the Atmosphere
Climate change is primarily impacting the atmosphere's ability to retain heat.
Increased greenhouse gases (CO2, methane) enhance the atmosphere's heat-trapping capacity.
The atmosphere has shifted from being a regular blanket to an electric blanket,radiating heat back to the surface.
Temperature Increases Observation
Since the late 19th century, the average global temperature has increased by nearly 2 degrees Fahrenheit.
Most of the increase has occurred in the last 35 years.
18 of the 19 warmest years on record have been since 2000.
Oceans have absorbed much of the heat, with ocean temperatures increasing by almost a half-degree since 1970.
Greenhouse Gases
Greenhouse gases trap heat by absorbing energy and re-emitting it back into the environment.
Common greenhouse gases include:
Water Vapor (H2O)
Carbon Dioxide (CO2)
Methane (CH4)
Ozone (O3)
Nitrous Oxide (N2O)
Chlorofluorocarbons (CFCs)
CFCs, once widely used, have been phased out due to their ozone-depleting effects but persist in the atmosphere for 75-100 years.
Ozone Depletion vs. Climate Change
Ozone depletion and climate change are distinct issues.
Ozone depletion does not cause global warming.
Ozone is a greenhouse gas, and its decrease would slightly cool the Earth.
The ozone hole is a localized area of ozone thinning, allowing more UV radiation to penetrate, but it doesn't cause overall warming.
CO2 and Temperature Correlation
Analysis of ice cores reveals a strong correlation between CO2 concentrations and temperature over the past 160,000-200,000 years.
Increased CO2 levels correlate with increased temperatures, and vice versa.
The data indicates a link, though not necessarily a direct cause-and-effect relationship in the past, but with the evidence we have now it is clear that causes temperature increase
Current CO2 Levels
CO2 levels have increased dramatically since the early 1700s.
Current CO2 concentrations are the highest in the last 160,000-200,000 years.
Causes of Increased CO2 Levels
Multiple correlations point to human activities as the primary cause of increased CO2 levels.
Increased industrial activity.
Continuous CO2 increase interrupted only by human events (wars, economic depressions).
Decline in radioactive carbon in the atmosphere (the Suess effect).
Historical CO2 Trends
For approximately 500,000 years, CO2 levels remained below 300 parts per million (ppm).
Around 1950, CO2 levels surpassed 300 ppm and have been increasing rapidly ever since.
Current CO2 levels exceed 400 ppm.
The rate of increase is about ten times greater than any previous period.
Correlations: Industrial Revolution
The industrial revolution, starting in the early 1800s, led to increased burning of fossil fuels (coal, gasoline, oil).
This resulted in a dramatic increase in atmospheric CO2.
Decreases in CO2 emissions during World War I, World War II, and the Great Depression indicate the impact of industrial activity on CO2 levels.
The COVID-19 pandemic may result in a temporary dip in CO2 levels due to reduced driving and industrial activity.
The Suess Effect
Carbon-12 and carbon-14 occur naturally in the atmosphere.
Carbon-14 is radioactive with a half-life of approximately 5,700 years.
Fossil fuels contain little or no carbon-14, as it has decayed over millions of years.
Burning fossil fuels releases carbon-12 into the atmosphere, diluting carbon-14 concentrations.
The Suess effect refers to the decrease in the ratio of carbon-14 to carbon-12 in the atmosphere due to fossil fuel combustion.
Consequences of Temperature Increase
The planet's temperature is increasing at an unprecedented rate.
The temperature increase in the past 50 years is equivalent to that since the last ice age (10,000 years ago), but occurring 10-40 times faster.
Rapid temperature changes may exceed the ability of organisms to adapt and evolve.
Soil quality and food production are at risk as optimal crop-growing regions shift.
Observed Climate Change Effects
Global weather patterns are changing, with more extreme weather events.
Record-warm temperatures are increasing in the winter and summer.
Severe storms and rainstorms are becoming more frequent.
Ecosystems are being disrupted due to species' intolerance of changes.
Ice sheets and glaciers are melting, causing ocean currents disruption and sea-level rise.
Sea Level Changes
Sea levels have risen approximately 10 inches in the past 150 years.
Since 2000, sea levels have increased by about 40 millimeters (4 centimeters).
Sea-level rise is due to:
Melting glaciers and ice sheets.
Thermal expansion of warming oceans.
Even small increases in sea level can lead to coastal flooding during storms.
Conclusions
CO2 concentrations have varied over the past 560,000 years, paralleling global temperature changes.
Increased CO2 leads to increased temperatures.
Current CO2 levels are the highest ever measured and are strongly influenced by burning fossil fuels.
Future Temperature Predictions
Models from the 1990s predicted a temperature increase of 1.5 to 5.5 degrees Celsius by the end of the 21st century.
Revised models now predict an increase of 3.5 to 7 degrees Celsius by 2100 if current trends continue.
Potential for massive die-offs of populations if significant temperature changes occur by 2050.
Call for Action
Changes are needed now to mitigate climate change.
Solutions will be discussed later in the semester.
Acknowledges the slow pace of change and human resistance but emphasizes the potential for future solutions. #Unit 1 Conclusion
This concludes the Unit 1 lecture material.
The post-lecture assignment focuses on balancing energy sources for global energy demands.
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Toward the end of summer, a moderately deep freshwater lake exhibits distinct horizontal and vertical zones. Horizontally, the littoral zone extends from the shore, characterized by rooted plants, to the limnetic zone, which is the open water area where plants do not grow on the bottom. Vertically, the lake is stratified into three layers: the epilimnion, a warm upper layer rich in oxygen; the thermocline, a zone of rapid temperature change; and the hypolimnion, a cold bottom layer. During the spring turnover, as ice melts and
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Toward the end of summer, a moderately deep freshwater lake presents a complex profile both horizontally and vertically.
Horizontally, the lake is divided into:
Littoral Zone: This zone is nearest to the shore and is characterized by shallow water, abundant sunlight, and rooted aquatic plants. The littoral zone is a highly productive area, supporting a diverse community of organisms, including algae, invertebrates, amphibians, and fish.
Limnetic Zone: Extending from the littoral zone into the open water, the limnetic zone is the region where rooted plants no longer grow. This zone is defined by its depth and distance from the shore, with phytoplankton serving as the primary producers that support the aquatic food web.
Vertically, the lake is stratified into distinct layers:
Epilimnion: This is the warm, upper layer of the lake that receives ample sunlight. Due to its exposure to sunlight and wind mixing, the epilimnion is typically oxygen-rich and supports photosynthetic activity.
Thermocline: Below the epilimnion lies the thermocline, a zone characterized by a rapid change in temperature with increasing depth. The thermocline acts as a barrier, preventing mixing between the warm epilimnion and the cold hypolimnion.
Hypolimnion: The hypolimnion is the cold, bottom layer of the lake. It is isolated from surface mixing and sunlight, resulting in low oxygen levels and a relatively stable temperature.
Spring Turnover: In the spring, as ice melts and surface waters warm to 4 degrees Celsius (the temperature of maximum density for water), the thermal stratification weakens. The lake undergoes a mixing process called spring turnover, during which surface and bottom waters mix, redistributing nutrients and oxygen throughout the water
Photosynthetic efficiency refers to the percentage of light energy that a plant captures and converts into chemical energy through photosynthesis. However, this conversion is quite low, typically ranging from just 0.3% to about 10%, with many studies converging around 1% efficiency.
Several biotic and abiotic factors influence photosynthetic efficiency:
The type of plant species, as shade-tolerant plants have different photosynthetic pathways than shade-intolerant species
The availability of key resources, such as water, nutrients, and carbon dioxide
Environmental conditions such as high or low temperatures
The Leaf Area Index (LAI), defined as the ratio of the surface area of leaves to the ground area, significantly affects photosynthetic efficiency within ecosystems. Ecosystems with LAI values greater than two typically support overlapping leaves that continue to photosynthesize, thereby enhancing overall photosynthetic efficiency. However, ecosystems with extremely high LAI, such as dense tropical rainforests, often exhibit diminished photosynthetic efficiency at the forest floor due to light limitations.