ESS Topic 2.1-2.5 Notes

2.1 Species and Populations

  • Introduction

    • Species interact with their environment.
    • Ecological niches define species' roles.
    • Populations respond to environmental factors.
    • Understanding these concepts is important for ecosystem analysis and ecological studies.

  • Key Terminology

    • Species: A group of organisms that share common characteristics and can interbreed to produce fertile offspring.
    • Population: Organisms of the same species living in the same place at the same time and interacting with one another.
    • Habitat: The environment where a species normally lives (its physical home).
    • Ecological Niche: The specific role an organism plays within its habitat (where, when, how it lives, what it feeds on, and its interactions).

  • Defining a Species (3 Key Criteria)

    • Common characteristics.
    • Ability to interbreed.
    • Production of fertile offspring.
    • Example: Dogs
      • All dog breeds share common characteristics.
      • They can interbreed and produce fertile puppies.
      • Therefore, they are all members of the same species (Canis familiaris).
    • Example: Horses and Donkeys
      • They share common characteristics and can interbreed.
      • However, their offspring (mules) are infertile.
      • Therefore, horses and donkeys are different species.
    • Example: Lions and Tigers
      • They can produce hybrid offspring (ligers).
      • However, these hybrids are typically sterile.
      • The inability to produce fertile offspring indicates different species.

  • Habitat

    • The environment where a species normally lives, an organism’s address or physical location.
    • Example: A woodpecker's habitat is the forest, with adaptations like a strong beak for finding insects.
    • Habitats can be:
      • Terrestrial (land-based): deserts, mountains, grasslands.
      • Aquatic (water-based): oceans, ponds, estuaries (freshwater and marine ecosystems).
    • Each habitat type has unique environmental conditions that support specific species.

  • Ecological Niche

    • Describes the abiotic and biotic conditions and resources to which an organism or population responds.
    • Abiotic Factors: Physical elements like temperature, water, salinity, and soil characteristics.
    • Biotic Factors: Interactions with other organisms such as food sources, predators, competitors, and beneficial organisms.
    • Example: Warbler Species
      • Five different warbler species share the same habitat (coniferous trees) but occupy different niches.
      • Each species feeds at a different height and portion of the tree, reducing direct competition.
    • Example: African Savannah
      • Zebras eat the tall grass first.
      • Wildebeests consume what’s left.
      • Gazelles eat the new sprouts.
      • This staggered feeding strategy reduces direct competition and allows coexistence.

  • Fundamental vs. Realized Niche

    • Fundamental Niche: The full range of conditions and resources in which a species could potentially survive and reproduce.
    • Realized Niche: The actual conditions and resources in which a species exists due to biotic interactions, particularly competition.
    • Example: Barnacles
      • Chthamalus can physically survive in both deep and shallow intertidal zones (fundamental niche).
      • Balanus outcompetes it in the deeper zone, restricting Chthamalus to the drier upper portion of the intertidal zone (realized niche).

  • Abiotic vs. Biotic Factors

    • Abiotic Factors: Non-living physical elements that influence organisms and ecosystems.
      • Temperature, sunlight, pH, salinity, precipitation.
      • These factors are interdependent (e.g., sunlight influences temperature and evaporation rates).
    • Biotic Factors: Interactions between organisms.
      • Predation: One organism hunts and eats another (e.g., owl and mouse).
      • Herbivory: The consumption of plants, putting selection pressure on plants to develop defenses (e.g., caterpillars consuming leaf tissue).
      • Parasitism: One species depends on another for nutrition and harms the host (e.g., aphids feeding on a plant).
      • Mutualism: Each species benefits from the relationship (e.g., moth pollinating a flower).

  • Population Dynamics

    • Populations change in response to interactions with their environment.
    • Example: Geographic isolation leading to speciation in amphibians.
    • Interactions between species influence population dynamics and carrying capacity.
    • Predator-Prey Relationships: Classic example with wolves, moose, and lynx.
      • Cyclical patterns and time lags in population graphs.
      • Prey increase→Predator increase→Prey decrease→Predator decreasePrey \,increase \rightarrow Predator \,increase \rightarrow Prey \,decrease \rightarrow Predator \,decrease

  • Population Definition Revisited

    • Organisms of the same species living in the same time and place, capable of interbreeding.
    • Example: Elephant Populations
      • Elephant populations in Tanzania are separated by human settlements and minimal habitat.
      • Different Asian elephant populations are isolated by geographic barriers and human development, preventing genetic exchange.
      • Isolation can amplify genetic abnormalities due to limited gene flow.
      • Asian elephants (Elephas maximus) are divided into separate populations that rarely interbreed.
      • Asian elephants and African elephants are different species.

  • Carrying Capacity

    • The maximum population size that can be sustainably supported by available resources.
    • Populations fluctuate seasonally, kept below carrying capacity by various factors.
    • When populations exceed carrying capacity, resources become scarce, leading to increased mortality.

  • Population Growth Curves

    • J Curve (Exponential Growth): Occurs when resources are abundant and few limiting factors exist.
      • Corresponds with very high reproductive potential.
    • S Curve (Logistic Growth): Initially rapid growth, but the growth rate levels off as the population approaches carrying capacity.
    • Abiotic factors: temperature, water, space.

  • Limiting Factors

    • Slow population growth as it approaches carrying capacity.
    • Starvation, disease, parasites, accidents, weather, hunting, and predation.

  • Graphical Representations of Ecological Relationships

    • Example: Population cycles of snowshoe hares and Canadian lynx over 80 years.
      • Lynx population closely follows the hare population with a time lag.
      • Hare: abundant food supply, Lynx populations increase, less hares, allows hares to recover.

  • Population Growth Curves Explained

    • Consider both absolute numbers and rates of change.
    • Exponential Growth: Continuously accelerating growth rates, J-shaped curve.
    • Logistic Growth: Begins exponentially but slows as the population approaches carrying capacity, S-shaped curve.
    • The carrying capacity is the maximum sustainable population size.

  • International Perspective: The Butterfly Effect

    • Changes in one ecological community can impact others.
    • Small changes can cascade through interconnected systems.
    • Environmental issues require international cooperation; ecological studies must consider systems at different scales.

2.2 Communities and Ecosystems

  • Communities

    • A group of populations living and interacting with each other in a common habitat.
      • Example: Zebras, elephants, and antelope at a watering hole in Africa.

  • Ecosystems

    • Include both the community and the physical environment with which the communities interact.
      • Example: Coral reef ecosystem including turtles, fish, coral organisms, water, sunlight, density of salt in the water, and ocean currents.

  • Ecosystem Complexity

    • Temperate forest food web demonstrating multiple interconnected feeding relationships.
    • Organisms participate in different food webs simultaneously.
    • Photosynthesis and respiration play important roles in energy flow through communities.
    • Energy flows through an ecosystem, matter cycles within it.

  • Photosynthesis and Respiration

    • Essentially opposite reactions.
    • Photosynthesis: Plants convert carbon dioxide and water into glucose and oxygen using light energy.
    • CO<em>2+H</em>2O+Light→C<em>6H</em>12O<em>6+O</em>2CO<em>2 + H</em>2O + Light \rightarrow C<em>6H</em>{12}O<em>6 + O</em>2
    • Respiration: Organisms break down glucose with oxygen to release energy, producing carbon dioxide and water.
    • C<em>6H</em>12O<em>6+O</em>2→CO<em>2+H</em>2O+EnergyC<em>6H</em>{12}O<em>6 + O</em>2 \rightarrow CO<em>2 + H</em>2O + Energy

  • System Analysis of Photosynthesis

    • Inputs: Light energy, carbon dioxide, and water.
    • Outputs: Glucose and oxygen.
    • Transformation: Chloroplasts convert light energy to chemical energy (glucose).

  • System Analysis of Respiration

    • Inputs: Glucose and oxygen.
    • Outputs: Carbon dioxide, water, and energy.
    • Transformation: Cellular mitochondria.

  • Energy Flow and the Second Law of Thermodynamics

    • During respiration, energy is dissipated as heat.
    • This increases entropy (disorganization) in the ecosystem.
    • However, this energy release enables organisms to maintain organized structures with low entropy.
    • Follows the second law of thermodynamics: entropy in a system tends to increase over time.

  • Trophic Levels

    • Primary producers (plants and algae): Convert light energy into chemical energy via photosynthesis.
      • Some bacteria produce food through chemosynthesis without sunlight.
    • Feeding relationships: Producers, consumers, and decomposers.
    • Modeled using food chains, food webs, and ecological pyramids.

  • Trophic Levels Explained

    • First level: Primary producers (plants).
    • Second level: Primary consumers (herbivores).
    • Third level: Secondary consumers (omnivores).
    • Fourth and above level: Tertiary consumers, carnivores (that eat herbivores).
    • Decomposers: Break down organic matter from all trophic levels, recycling nutrients.

  • Energy Transfer and the 10% Rule

    • As energy moves through trophic levels, significant amounts are lost as heat.
    • Only about 10% of the energy that's available is transferred to the next level.
      • 90% is lost through metabolic processes, movement, and heat production (respiration).
    • This inefficiency limits food chains to typically four or five trophic levels.

  • Bioaccumulation and Biomagnification

    • Bioaccumulation: Persistent pollutants (DDT, mercury) build up within an individual organism over time.
      • Occurs when the intake rate exceeds the elimination or degradation rate.
    • Biomagnification: The increase in concentration of these pollutants as pollutants move up the food chain.
      • Consumers accumulate pollutants from many prey organisms, leading to dangerous concentrations at higher trophic levels.

  • Examples of Biomagnification

    • PCB concentrations increase dramatically from seawater to marine mammals.
      • 0.00002mgL→160mgkg0.00002 \frac{mg}{L} \rightarrow 160 \frac{mg}{kg}
      • Doctors advise pregnant women and nursing mothers to avoid eating tuna and other top marine predators due to high toxin concentrations.

  • Ecological Pyramids

    • Quantitative models that visually represent trophic structure.
    • Show a decrease in numbers, biomass, and energy as we move up the chain.

  • Pyramid of Numbers

    • Counts organisms at each trophic level.
    • Can be inverted (e.g., one tree supports thousands of insects).

  • Pyramid of Biomass

    • Represents the total mass of organisms at each trophic level (grams per square meter).
    • Typically decreases at higher levels but can occasionally show greater quantities at higher trophic levels during winter if measured at one single point in time.
    • Can appear inverted during certain seasons, especially in aquatic ecosystems.
    • If measured over an entire year, the pyramid would show the 'normal' decreasing pyramid shape.

  • Pyramid of Productivity

    • Shows the flow of energy through each trophic level.
    • Units include a time component: kilos per hectare per year or grams per square meter per year.
    • Always shows a decrease along the food chain.
    • Calculate efficiency by dividing energy at two adjacent levels.
      • Producer productivity 1575gm2⋅ year1575 \frac{g}{m^2 \cdot \,year}, herbivore productivity 235gm2⋅ year235 \frac{g}{m^2 \cdot \,year}. That is approximately 15% efficiency.
      • Efficiency generally declines at higher trophic levels.

  • Laws of Thermodynamics

    • Govern energy flow in ecosystems.
    • First Law: Energy is neither created nor destroyed, but transformed.
    • Second Law: Energy becomes less available with each transfer because much of it is lost as heat.

  • Modeling Feeding Relationships

    • Constructing models from data.
    • Build food chains, food webs, or ecological pyramids.
    • Include components flows, inputs, outputs, transfers, transformations, and storages.

  • Energy vs Matter

    • Energy flows through a system.
    • Matter cycles within it.
    • Energy: sunlight, transfers, transforms, exits.

2.3 Flows of Energy and Matter

  • Ecosystem Connections

    • Ecosystems are connected by energy and matter flows.

  • Energy Flow vs. Chemical Cycling

    • Food webs illustrate energy flow from producers to consumers and decomposers.
    • Chemical cycling (blue arrows): Matter cycles through the ecosystem repeatedly.
    • Energy flow (red arrows): One-directional; enters, transfers, transforms, and exits.
    • Sun's energy drives these flows and humans impact them.

  • Solar Energy Distribution

    • Only a tiny fraction (0.08%) is captured by photosynthesis.
    • Most becomes thermal energy.
    • Human use taps into fossil fuels (ancient solar energy stored for millions of years).

  • Earth's Energy Budget

    • Incoming solar radiation:
      • Reflected by atmosphere, clouds, and Earth’s surface.
      • Absorbed by land, oceans, and atmosphere.

  • Radiation Pathways

    • About 31% of incoming solar radiation is reflected and not absorbed.
      • Cloud reflection, ground reflection, atmospheric scattering.
    • About 69% is absorbed by Earth.
      • Land, water, atmospheric molecules, and clouds.

  • Energy Pathways through Ecosystems

    • Light energy is transformed into chemical energy through photosynthesis.
    • Chemical energy transfers between trophic levels with varying efficiencies.
    • Eventually, all energy is transformed to heat and reradiated into the atmosphere.

  • Energy Transfer and Transformation

    • Only about 10% of energy moves from one trophic level to the next; the rest is lost as heat.
    • Energy pyramid shows primary producers capturing 100% of available energy, with subsequent levels retaining progressively less.
    • A significant portion of solar energy is converted to heat which is eventually reradiated as infrared energy.

  • Reradiation of Heat

    • Heat is reradiated to the atmosphere.

  • Productivity Measures

    • Measures the conversion of energy into biomass over time.
    • Measured in: grams per square meter per year or kilos per hectare per year.

  • Gross vs. Net Productivity

    • Gross Primary Productivity (GPP): Total biomass produced through photosynthesis.
    • Respiration (R): Energy used by producers to maintain their living function.
    • Net Primary Productivity (NPP): What remains; actual growth available to other organisms.
      • NPP=GPP−RNPP = GPP - R

  • Gross vs. Net Secondary Productivity

    • Gross Secondary Productivity (GSP): Food eaten minus fecal loss. Total energy assimilated by consumers.
    • Net Secondary Productivity (NSP): GSP minus respiratory losses. New biomass created (consumer growth).
      • NSP=GSP−RconsumerNSP = GSP - R_{consumer}

  • Maximum Sustainable Yields

    • Equivalent to the net productivity of a system.
    • Sustainable yield: amount of biomass that can be removed without diminishing regeneration.
      • Example: if 1,000 lions exhibit a birth rate of 78 and a death rate of 48, you have a natural income of 30 lions annually
      • Theoretically, you sustainably harvest 30 lions but, accounting for a possibility of a new disease (etc.), the number would be approximately 50% of that to account. That means approximately 15 lions.

  • Carbon and Nitrogen Cycles

    • Illustrate matter flows.
    • Diagrams that show storages/sinks and flows.

  • Carbon Cycle

    • Carbon transfers location and transforms state.
    • Moves from gaseous CO2CO_2 to solid biomass or fossil fuels.
    • Storages: Organic forms in organisms and forests, inorganic forms in atmosphere, soils, fossil fuels, and oceans.
    • Flows: consumption/feeding, death/decomposition, photosynthesis, respiration, dissolving, and fossilization.

  • Nitrogen Cycle

    • Organic storages in organisms and inorganic storages in soil, fossil fuels, the atmosphere, and bodies of water.
    • Most nitrogen exists as atmospheric nitrogen gas.
    • Flows: nitrogen fixation by bacteria and lightning, absorption, assimilation, consumption, excretion, death, decomposition, and denitrification.

  • Human Impacts on Energy Flows and Biogeochemical Cycles

    • Consider agriculture, fossil fuel use, and deforestation.
    • Analyze impacts through inputs, outputs, and storage changes.
    • Harvesting biomass removes stored energy.
    • Fossil fuel extraction rapid.
    • Nitrogen removed from crop depletes nutrients unless amended or fertilized.

  • GPP, NPP, GSP, NSP Formula Summary

    • Gross productivity represents gain of energy/biomass.
    • Net productivity represents difference between total gain an losses during respiration etc.
      • NPP=GPP−RNPP = GPP - R
      • GSP=Food Eaten−Fecal LossGSP = Food \,Eaten - Fecal \,Loss
      • NSP=GSP−RconsumerNSP = GSP - R_{consumer}

2.4 Biomes, Zonation, and Succession

  • Key Concept: Climate Determines Biome Distribution

    • Climate sets the stage; local abiotic and biotic factors cause variations.
    • Graph showing average annual temperature and precipitation. It shows how different biomes are assigned in different climate spaces.

  • Biomes

    • Collections of ecosystems sharing similar climatic conditions.
    • Five major classes: Aquatic, forest, grassland, desert, and tundra.

  • Aquatic Biomes

    • Water-based ecosystems.
    • Include freshwater and marine ecosystems.
    • Limiting factors: Light penetration, available nutrients.
    • Has specific limiting factors, productivity levels, and biodiversity characteristics.

  • Terrestrial Biomes

    • Land-based ecosystems.
    • Similar biomes often occur at similar latitudes (distance from the equator).

  • Forests

    • Dominated by trees.
    • High primary productivity.
    • Limited by nutrient availability.

  • Grasslands

    • Characterized by grass.
    • Few trees.
    • Moderate productivity.
    • Limited by seasonal temperatures and slower nutrient cycling.

  • Deserts
    *Little precipitation.
    *Extreme temperature fluctuations.
    *Water is limiting.
    *Soil can be nutrient rich.

  • Tundra

    • Extremely cold temperatures.
    • Short growing seasons.
    • Often permafrost (permanently frozen ground).
    • Limiting factors: Short days, low temperatures.

  • Limiting Factors by Biome Type

    • Aquatic: Light absorption.
    • Forests: Nutrients locked in biomass.
    • Grasslands: Precipitation amount and temperature (extremes).
    • Deserts: Water.
    • Tundra: Short days and frozen conditions.

  • Productivity Across Biomes

    • Tropical coral reefs and rainforests show high productivity.
    • Deep oceans and deserts have low productivity.
    • Tropical rainforest are Earth's most biodiverse ecosystems.

  • What Creates Biome Distributions?

    • Insolation, precipitation, and temperature.
    • Insolation: Solar radiation reaching Earth’s surface.

  • Climate by Latitude

    • Due to Earth's tilt, differences in isolation can differ temperatures.
    • Creates the temperature patterns we observe globally.

  • Interaction of Temperature, Precipitation, and Evapotranspiration

    • Defines biome development.
    • Temperature, precipitation, and evapotranspiration are factors that create particular environments.

  • Tricellular Model of Atmospheric Circulation

    • Explains the distribution of precipitation and temperature globally.
    • Hadley cells, Ferrel cells, and polar cells create predictable climate zones.

  • Climate Change and Biome Distribution

    • Projected changes in tree biomass, grass biomass, and total biomass across Africa between the years 2008 and 2100.
    • Alterations in precipitation and temperature.

  • Zonation vs. Succession

    • Zonation is spatial.
    • Succession is temporal.

  • Zonation

    • Refers to changes in community structure along an environmental gradient.

  • Altitudinal Zonation

    • Moving up a mountain, moisture and temperature change, creating distinct vegetation zones.

  • Succession

    • Temporal change: communities evolve and change over time.

  • Primary Succession

    • Starts from bare rock or substrate with no prior soil development.

  • Secondary Succession

    • Occurs after a disturbance to an existing ecosystem, leaving some soil and organic matter behind.

  • Seral Stages

    • We start with a climax community at the top, which may be disrupted by disturbance.
    • Pioneer Species: colonize the area.

  • Ecosystem Properties during Succession

    • Productivity, biomass, stability, and diversity change over time following a disturbance.

  • Habitat Diversity

    • Diverse habitats provide more environmental niches, supporting more specialized species.

  • R-Strategists

    • Thrive in unstable environments with frequent disturbances.
    • Lots of offspring, they mature quickly, and have short lifespans.
      • Example: oysters produce millions of offspring annually.

  • K-Strategists

    • Found in stable environments.
    • Fewer offspring, they grow more slowly, and invest more resources in ensuring survival of each offspring.
      • Example: chimpanzees produce just one offspring every five years

  • Survivorship Curves

    • R-selected species experience high mortality early in life.
    • K-selected species maintain more stable populations.

  • Species Richness

    • Simply the count of different species present.

  • Community Productivity during Succession

    • In early stages, gross productivity starts low but net high.
    • At climax community productivity and respiration ratio come close to or reach one.

  • Ecosystem Stability, Succession, and Biodiversity

    • Intrinsically linked. Progression from bare rock through pioneer stages to climax forest.
    • Increases in biodiversity, biomass, and soil development occur throughout the process.

  • Alternative Stable States

    • No single climax community.
    • Human activity can divert succession to alternative stable states by modifying ecosystem activities like agriculture, grazing, fire management, or deforestation.
      • This is called a plagioclimax community

  • Ecosystem Resilience

    • Depends on diversity and capacity to survive change.
    • Rainforests recover slowly; temperate forests often recover quicker.

  • Human Disturbance

    • Alters Nutrient storage from living plants and soil storage pools.

2.5 Investigating Ecosystems

  • Ecosystem Investigations

    • Allow us to make comparisons between different ecosystems and track changes over time.

  • Quantification

    • Impose measurement systems on it.
    • Converting qualitative to quantitative data allows us to draw conclusions.

  • Proper Identification

    • Ecosystems need precise names and locations.

  • Organism Identification

    • Identify organisms using dichotomous keys.
      • Each step presents two options and clear comparative characteristics rather than subjective terms

  • Sampling Strategies

    • Allow us to study large areas by examining representative parts of that area.

  • Quadrats

    • Our most fundamental tools for environmental monitoring
    • Measure change in space over time.

  • Transects

    • Allow us to study how conditions change across environmental gradients.
    • Record data at specific points along a line.

  • Belt Transects

    • Combine the benefits of quadrats and point transects.
    • Excels at capturing how community composition shifts or changes across boundaries like forest edges, shorelines, or pollution gradients.

  • Sampling Explained

    • Random sampling: prevents bias, but it might miss important patterns.
    • Systematic sampling: ensures even coverage, but could coincide with environmental patterns.
    • Stratified sampling: Targets different habitat types deliberately.

  • Quadrats in Detail

    • Square frame that creates a defined study area.

  • Measurement Techniques

    • Repeating measurement increases reliability by reducing the impact of random errors or anomalies.

  • Biomass

    • Helps us understand energy flow through ecosystems.
    • Requires careful sampling and drying to remove water content.

  • Non-Motile Organisms

    • Several measurement techniques can be applied to non-motile organisms:
    • actual counts: e.g. trees
    • percentage cover: useful for mosses and grasses.
    • percentage frequency: records how often a species appears in sample plots.

  • Estimating Populations of Motile Organisms

    • Counting is labor-intensive and impractical for large areas, so indirect methods must be developed.

  • The Lincoln Index

    • Capture-mark-recapture.
      • Lincoln Index=(Number caught in first sample)⋅(Number caught in second sample)(Number marked in second sample)Lincoln \,Index = \frac{(Number \,caught \,in \,first \,sample) \cdot (Number \,caught \,in \,second \,sample)}{(Number \,marked \,in \,second \,sample)}
    • The proportion of marked animals in the second sample should reflect the proportion of marked animals in the whole population.

  • Species Richness vs. Evenness

    • Species richness is simply the count of different species present - a fundamental biodiversity measure.
      • Community 1 has balance populations, while community 2 is dominated by a single species.
    • Evenness: richness alone doesn't tell the complete story of biodiversity.
    • Species diversity is often determined with the help of the Simpson Diversity Index.

  • Simpson Diversity Index

    • Higher index values indicate greater diversity.
    • Index is most valuable for comparing similar habitats or tracking changes in one location over time
      • D=1−∑n(n−1)N(N−1)D = 1 - \frac{\sum n(n-1)}{N(N-1)}