ESS ecology
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.
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.
Respiration: Organisms break down glucose with oxygen to release energy, producing carbon dioxide and water.
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.
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 , herbivore productivity . 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.
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).
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 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.
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.
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