Ecosystems and Energy transfer
Ecosystems: Key Terms
Habitat
Species are adapted to life in specific habitats.
Definition: A habitat is the place where an organism lives.
Habitats can vary in size:
Large: e.g., a desert.
Small: e.g., an individual tree.
Small habitats are known as microhabitats.
Habitat Specialists: Species that can only survive in specific habitats.
Generalists: Species that can survive in a range of habitats; more likely to invade new habitats.
Invasive Species: Non-native species that can disrupt ecosystem interactions and cause problems.
Population
A population is defined as all individuals of one species living in a habitat.
Size of a population represents the abundance of a species.
Distribution: The exact location of a population within its habitat.
Community
Species interact with one another, forming communities.
Definition: A community consists of multiple populations living and interacting in the same area.
Example: A garden pond community includes fish, frogs, newts, pond snails, and various aquatic plants.
Ecosystem
An ecosystem is a community and its interactions with the non-living parts of its habitat.
Characterized by energy flow and nutrient recycling.
Components: Biotic (living) and abiotic (non-living).
Vary in size (e.g., small pond vs. ocean) and complexity (desert vs. tropical rainforest).
No ecosystem is self-contained; organisms can migrate between ecosystems.
Biotic & Abiotic Factors
Biotic Factors
Abundance and distribution are influenced by living factors such as:
Predation: Interaction where one organism consumes another.
Food Availability: Determines survival and reproductive success.
Intraspecific Competition: Competition among individuals of the same species for resources.
Interspecific Competition: Competition among different species.
Cooperation: Mutual assistance between organisms.
Parasitism: One organism benefits at the expense of another.
Disease: Pathogens affecting population sizes.
Impact of Biotic Factors on a Community
Availability of Food: High food supply increases survival chances; e.g., rainforest vs. desert.
New Predators: Introduction of predators can imbalance ecosystems; e.g., red foxes in Australia.
Pathogens: New diseases can decimate populations; e.g., coronavirus pandemic.
Competition: Resource competition can lead to decreased populations; e.g., grey squirrels outcompeting red squirrels in the UK.
Abiotic Factors
Non-living factors affecting populations include:
Light Intensity and Wavelength: Essential for photosynthesis.
Temperature: Influences metabolic rates and growth.
Turbidity: Cloudiness of water could impact aquatic life.
Humidity: Affects plant turgor and transpiration.
Soil or Water pH: Different species have specific tolerance ranges.
Salinity: Affects osmoregulation in aquatic life.
Oxygen/Carbon Dioxide Concentration: Vital for respiration and photosynthesis.
Impact of Abiotic Factors on a Community
Light: More light increases plant growth via enhanced photosynthesis.
Temperature: Affects photosynthetic rates.
Moisture Levels: Essential for survival of all organisms.
Soil pH and Mineral Content: Affects available nutrients for plant growth.
Wind Intensity and Direction: Influences transpiration rates in plants.
Carbon Dioxide Levels: Essential for photosynthesis; affects plant growth.
Oxygen Levels: Critical for aquatic animals; species survival is contingent on oxygen availability.
Niches: Distribution & Abundance
Niche Definition
A niche is defined as the role of a species in its habitat, including:
What it eats.
Which other species depend on it for food.
Time of activity (e.g., diurnal or nocturnal).
Specific living locations within the habitat.
Competitive Exclusion Principle: No two species can occupy the same niche simultaneously; one will outcompete the other.
Abundance: The number of individuals of a species living in a habitat can be influenced by niche occupancy; competitors may decrease abundance.
Distribution: Where a species lives is often determined by its adaptation to habitat factors.
Practical: Determining Distribution & Abundance
Counting Organisms
Assessing abundance requires counting organisms:
Small areas: feasible to count all individuals.
Larger areas: sampling methods are used to estimate total numbers.
Sampling Methods
Random Sampling: Randomly selected positions avoid bias.
Systematic Sampling: Sampling points at fixed intervals, useful to study environmental features.
Transects: Lines extending over specific gradients to measure changes systematically.
Methods of Sampling
Quadrats: Square frames used to estimate species abundance and distribution.
Size varies according to the species studied.
Types: Frame quadrats for sessile organisms, point quadrats for denser areas.
Frame Quadrats: Used for various sizes of organisms; can provide data on presence, frequency, abundance, and percentage cover.
Point Quadrats: Vertical frames with pins for measuring contact with species.
Transects
Can measure changes across a habitat:
Continuous vs. Interrupted transects, each recording different species contact along a defined line.
Measuring Abiotic Factors
Relevant abiotic factors must be measured in relation to species distribution and abundance.
Equipment and techniques should be chosen based on specific studies, as not all factors apply to every habitat.
Representing Results
Kite Diagrams: Visual representation of species distribution and abundance; can also incorporate abiotic factor changes across transects.
Stages of Succession
Ecosystem Dynamics
Ecosystems are dynamic and undergo changes over time, a process known as succession.
Primary Succession: Occurs on newly formed/exposed land, beginning with pioneer species like mosses and lichens that lead to soil formation.
Stages include:
colonization by pioneer species.
soil development leading to larger plants and trees.
establishment of a climax community, which represents a stable ecosystem.
Secondary Succession: Occurs on previously occupied land where soil exists; follows similar steps as primary succession but starts at a later stage.
Human Impact on Succession
Human interference can prevent natural succession and stabilize communities e.g., through grazing, mowing, or other activities that maintain certain ecosystem states.
Net Primary Productivity
Definition and Calculation
Net Primary Productivity (NPP): Rate at which energy is stored as biomass by producers minus losses due to respiration (R).
Equation: NPP = GPP - R
Units: Can be expressed as energy per area over time, e.g., J m^{-2} yr^{-1}.
Importance of NPP
Represents energy available to primary consumers and decomposers.
Worked Example NPP Calculation
For grass in a meadow:
GPP = 17,500 kJ m^{-2} yr^{-1}
R = 14,000 kJ m^{-2} yr^{-1}
NPP = 17,500 - 14,000 = 3,500 kJ m^{-2} yr^{-1}.
Calculating Efficiency of Biomass & Energy Transfers
Energy Transfer in Food Chains
Energy transfer occurs when producers are eaten by primary consumers, continuing up the food chain.
Trophic Levels: Stages in a food chain indicating the flow of energy.
Energy Losses in Food Chains
Energy transfer efficiency is less than 100%, with energy lost at every level:
Approx. 90% of energy lost through respiration, waste, or non-consumed parts.
Leftover energy is available for growth, termed net productivity.
Calculating Efficiency of Energy Transfer
Equation: ext{Energy Efficiency} = rac{ ext{Net Productivity}}{ ext{Energy Received}} imes 100
Worked Example: Toad energy received = 10,000 kJ m^{-2} yr^{-1}, losses = 9,000 kJ m^{-2} yr^{-1} leads to 1,000 kJ m^{-2} yr^{-1} productivity.
ext{Efficiency} = rac{1,000}{10,000} imes 100 = 10\
$.
Calculating Efficiency of Biomass Transfer
Dry Biomass: Measured for accurate estimates of energy stored.
Equation: ext{Efficiency of Biomass Transfer} = rac{ ext{Biomass Transferred}}{ ext{Biomass Intake}} imes 100.
Example: If aphids collectively have a dry mass of 4.1 kg feeding on a bush with 35 kg dry mass, efficiency is calculated as follows:
E = rac{4.1}{35} imes 100 o E = 11.7\%$$.
Examiner Tips and Tricks
Be prepared to calculate GPP or R from NPP.
Describe investigations considering changing independent variables and how to ensure results are valid.
Understand principles of all ecological terms and processes discussed.