Ecosystems and Species Interactions
B Form and Function: Ecosystems
Ecosystem Structure (Form)
Composed of biotic (living organisms) and abiotic (non-living components) factors.
Biotic community structure: organisms present and their interactions, including feeding, mutualism, and competition.
Abiotic factors: influence ecosystem development (e.g., rainfall levels determining forest, grassland, or desert).
Taiga Example:
Community structure influenced by temperature and rainfall.
High precipitation and cold average annual temperatures.
Nutrient storage in litter is higher compared to tropical rainforests.
Nutrient flow from biomass to litter is relatively faster than in tropical ecosystems.
B4.1 Adaptation to Environment
Adaptations and Habitats:
Species adaptations are correlated to their habitats.
Musk ox: thick coat adapted to low temperatures in northern habitats.
Cactus: water storage tissue in stem related to infrequent rainfall in deserts.
Adaptations: characteristics that suit an individual to its habitat.
Similarities in Terrestrial Biomes:
Wallace Line: division between species in similar environments despite geographical proximity.
Islands west of the line: Asian species.
Islands east of the line: Australasian species.
Convergent Evolution: similar forms of plants and animals evolve independently in similar environments, irrespective of geographic separation.
Mechanism: adaptations needed for survival and thriving in specific environments lead to similar ecosystems.
B4.1.1 Habitat
Habitat Definition:
From Latin "he lives" or "she lives."
The place where an organism lives.
Geographical location.
Physical conditions, ecosystem type, and location within the ecosystem.
Applies to a single organism, population, species, or community.
Example: Ranunculus glacialis (Glacier Crowfoot)
High altitude in the Alps and other European mountains.
Snow-covered sites in winter with little competition.
Short growing season with intense sunlight.
Acidic, moist, well-drained soils.
B4.1.2 Adaptations to the Abiotic Environment
Environment of an Organism:
Everything surrounding an organism.
Biotic factors: living organisms.
Abiotic factors: non-living materials (air, water, rock).
Biotic vs. Abiotic Influence:
Biotic factors dominate in dense communities (e.g., tropical rainforests).
Abiotic factors have more influence in extreme habitats (e.g., deserts, taiga) with low population densities.
All organisms are adapted to their abiotic environment.
Adaptations are evident in plants in extreme habitats such as sand dunes and mangrove swamps.
Adaptations to Specific Environments
Sand Dune Adaptations (Grasses):
Challenges: water conservation, high salt tolerance, sand accumulation.
Adaptations of Lyme Grass (Leymus mollis):
Thick waxy cuticle on leaves to reduce transpiration.
Stomata in furrows to maintain humid air.
Leaves that roll up during droughts to create a humid chamber.
Tough sclerenchyma to prevent wilting.
Rhizomes that grow upwards and deep into the dune to obtain water.
Fructan accumulation in root and leaf cells to increase osmotic potential.
Mangrove Swamp Adaptations (Trees):
Challenges: waterlogged anaerobic soils, high salt concentrations.
Adaptations of Mangrove Trees:
Secretion of excess salt from salt glands in the leaf.
Root epidermis coated in suberin to reduce salt permeability.
Cable roots close to the soil surface for oxygen.
Pneumatophores (vertical root branches) to absorb oxygen from the air.
Stilt roots to buttress the tree in soft mud.
Large buoyant seeds for dispersal.
Accumulation of mineral ions and carbon compounds to increase osmotic potential.
B4.1.3 Abiotic Variables Affecting Species Distribution
Species Distribution:
Where a species lives, shown on a map.
Reflects abiotic factors.
Adaptations suit species to specific physical environments.
Plant Distributions:
Affected by temperature, water availability, light intensity, soil pH, soil salinity, and mineral nutrients.
Range of Tolerance: plant cannot grow outside its range for one or more factors.
Example: Tropical plants cannot survive frosts; northern plants lack adaptations for growth in the tropics.
Animal Distributions:
Abiotic factors: water availability and temperature.
Adaptations for Temperature Extremes:
Elephants: large ears for heat dissipation.
Polar bears: small ears to minimize heat loss.
Arid Conditions: desert rats have longer loops of Henle to minimize water loss.
Aquatic Animals: require different adaptations.
Life Cycle Limitations: salmon require fast-flowing freshwater streams for spawning with specific gravel substrates and pH.
Animals have a range of tolerance for each abiotic factor, based on their adaptations.
B4.1.4 Range of Tolerance of a Limiting Factor
Ranges of Tolerance:
Plant and animal species have ranges of tolerance for abiotic variables.
Examples:
Plants: specific soil pH range, sunlight or shade requirements.
Animals: salt concentration tolerance in aquatic habitats, temperature tolerance.
Investigated Through:
Experimental studies.
Correlations between species distribution and abiotic variables.
Example: Mosquito study in Taiwan (Aedes aegypti) requiring a minimum night-time temperature of .
Correlations Investigated By:
Mapping the species range.
Random sampling using quadrats.
Sampling along transect lines.
Transects and Observational Methods
Transects:
Used to investigate species tolerance ranges to abiotic variables.
Should span different levels of the variables of interest.
Example: Slope from woodland to peat bog reveals correlations between plant distribution and temperature, light intensity, and soil pH.
Abiotic variables measured using electronic sensors and portable data loggers.
Transect Sampling Methods:
Line Intercept Sampling: recording organisms that touch a line laid along the ground.
Belt Transects: estimating species abundance in the area between two lines separated by a fixed distance using quadrats.
Observational Transects: recording sightings of target species along a defined route to investigate tolerance ranges and monitor population size changes over time.
Observations: Making observations with sensors
Sensor: Device that records a parameters level.
Data Logging:
Log: Permanent record of measurements taken at regular intervals.
Compact, portable data loggers used to monitor environmental conditions (temperature, light intensity, pH).
Advantages:
Less expensive and easy to operate.
Compact and portable with battery power.
Available for measuring hundreds of different parameters.
Can take repeated measurements rapidly.
Can be left to take measurements automatically over long periods.
Stored data can be easily transferred to a computer.
Applications:
Ecological research.
Medical diagnostics.
Food and drink production monitoring of fermentation.
Flight recorders on aircraft.
Data-Based Questions: Intertidal Zonation
Kite Diagram (Figure 9):
Illustrates the distribution of intertidal species.
Thickness of the shaded region indicates abundance (ACFOR scale).
Analysis:
Methods used to collect data.
Most abundant species in the survey area.
Length of the large shallow rock pool using the scale bar.
Species adapted to shingle, sand, and rock pools.
Reasons for species being absent from the upper parts of the intertidal zone.
Species adapted to the same abiotic environment.
Ways to improve the objectivity of the research.
pH Changes in Rock Pools
pH Monitoring:
Monitored in natural pools or artificial aquatic mesocosms using data loggers.
Ecologists monitor pH in rock pools containing animals and photosynthesizing algae.
pH Cycle:
Rises and falls in a 24-hour cycle due to changes in carbon dioxide concentration.
Lowest values (pH 7) during the night.
Highest values (pH 10) during bright sunlight.
Data-Based Questions: Data-Logging pH in an Aquarium
Experiment Setup:
Aquarium contains pondweeds, newts, and other animals.
Data obtained by data logging using a pH electrode and a light meter.
Artificial illumination with a 24-hour cycle.
Analysis (Figure 11):
Changes in light intensity during the experiment.
Duration of data logging.
pH trend in the light (deduce and explain).
pH trend in darkness (deduce and explain).
B4.1.5 Conditions Required for Coral Reef Formation
Coral Reefs:
Biodiverse marine ecosystems.
Only develop where conditions are suitable for hard corals.
Conditions:
Depth: Less than 50 m for light penetration.
pH: Above 7.8 for calcium carbonate deposition.
Salinity: Between 32 and 42 parts per thousand to avoid osmotic problems.
Clarity: Water must be clear for light penetration.
Temperature: for coral and zooxanthellae health.
Coral reefs typically develop between north and south of the Equator.
B4.1.6 Abiotic Factors Determining Terrestrial Biome Distribution
Biome Development:
Specific ecosystem type develops with any combination of abiotic factors.
Species composition varies geographically, but adaptations are similar.
All ecosystems of a specific type are a biome.
Principal Determinants:
Temperature and rainfall.
Relationship: ecosystem determined by combination of mean annual precipitation and mean annual temperature (Figure 14).
B4.1.7 Biomes and Convergent Evolution
Biome Definition:
Groups of ecosystems that resemble each other due to similar abiotic conditions.
Convergent Evolution:
Plants and animals evolve similar adaptations in response to similar conditions.
Distantly related species facing the same problems find the same solutions.
Example: Cacti in America and euphorbias in Africa have similar adaptations for water conservation and storage.
Major Biomes and Climatic Conditions
Characteristics of Major Biomes (Table 1):
Tropical Forest: high temperature, high precipitation, minimal seasonal variation, high light intensity.
Temperate Forest: medium temperature, high/medium precipitation, warm summers, colder winters, medium light intensity.
Taiga (Boreal Forest): low temperature, high/medium precipitation, short summers, long/cold winters, medium/low light intensity.
Hot Desert: high temperature, very low precipitation, minimal seasonal variation, high light intensity.
Grassland: high/medium temperature, medium precipitation, dry season or variation, medium/low light intensity.
Tundra: low temperature, very low precipitation, very short summer, very cold winter, low light intensity.
B4.1.8 Adaptations to Hot Deserts and Tropical Rainforests
Hot Deserts:
High daytime temperatures, cold nights, very low rainfall, limited soil development.
Examples: saguaro cactus and fennec fox.
Saguaro Cactus Adaptations:
Wide-spreading root system.
Deep tap roots.
Fat stems with storage tissue.
Pleated stems.
Vertical stem orientation.
Thick waxy cuticle.
Leaves reduced to spines.
CAM metabolism.
Fennec Fox Adaptations:
Nocturnal behavior.
Underground den.
Long thick hair.
Hairs covering foot pads.
Pale-colored coat.
Large ears.
Variable ventilation rate (panting).
Tropical Rainforests:
High temperatures, high precipitation, high light intensity.
Examples: yellow meranti tree and spider monkey.
Yellow Meranti Tree Adaptations:
Tall growth (over 100 m).
Hard dense wood.
Buttressed trunk.
Smooth trunk.
Broad oval leaves with pointed tips.
Evergreen leaves.
Photosynthesis enzymes adapted to high temperatures.
Massive seed production.
Spider Monkey Adaptations:
Long arms and legs.
Flexible shoulders.
Hook-like hands without thumbs.
Feet that act as extra hands.
Long prehensile tail.
Highly developed larynx.
Diurnal activity.
Breeding at any time of year.
C Interaction and Interdependence: Ecosystems
System Interactions:
Ecosystems function through interactions, interdependence, and integration of components.
Coherent entity with emergent properties from component interactions.
Boreal forest example: living things interact via competition, predation, mutualism, and commensalism.
Interactions with the non-living environment: nutrient recycling through food chains.
Photosynthesis:
* Driven by sunlight.
* Provides endless supply of energy supporting feeding relationships.
Organism Effects:
* Organisms modify their environment, impacting other organisms.
C4.1 Populations and Communities
Interactions Regulating Population Size:
Organisms interact with their own and other species, regulating population size.
Types of Interactions:
Increase/maintain population size.
Limit population size.
Example: European pine sawfly larvae feeding on Scots pine branch.
Community Interdependence:
Seed of red dead-nettle (Lamium purpureum) has elaiosome, a nutritious structure attractive to ants.
Ant carries seed to nest, feeds elaiosome to larvae, then deposits seed in nutrient-rich waste area.
C4.1.1 Populations
Definition:
Group of individual organisms of the same species living in a given area.
Characteristics:
Members interbreed with each other but not with other species.
Interactions include competition for food or cooperation to avoid predation.
Size and Distribution:
Ranges from few to billions.
May be one or many populations of a species.
Populations often separated by geographical barriers (e.g., islands).
Emergent Properties:
Develop as a result of interactions between individuals.
Example: Wildebeest herd minimizing predation risk by moving within the herd.
C4.1.2 Estimation of Population Size
Challenges:
Impossible to count every individual.
Animals use camouflage or move.
Populations spread over vast areas.
Estimation:
Based on sampling.
Multiple samples are better.
Every individual has equal chance of inclusion in a sample through random sampling.
Random Sample:
Every member of a population has an equal chance of being selected.
Avoid unconscious bias using random numbers.
Measurement: Sampling Error
Inferential Statistics:
Uses sample data to make inferences about an entire population.
Assumes sample represents the entire population.
Example: Mean leaf length in a sample estimates the mean length of all leaves on the tree.
Sampling Error:
* Definition: the difference between a sample statistic and the equivalent value for the whole population.
* Example: difference between estimated and true population size.
* Random sampling ensures equal chance of selection, reducing sampling error.
C4.1.3 Random Quadrat Sampling
Quadrats:
Square sample areas marked out using a quadrat frame.
Procedure:
Repeatedly place quadrat frame at random positions in a habitat.
Record numbers of organisms present each time.
Random Positioning:
Baseline marked along the edge of habitat using a measuring tape.
Random numbers generated to determine distances along and across the habitat.
Quadrat placed at the distances determined by the random numbers.
Suitability:
Suitable for sessile organisms (fixed position, do not move).
Unsuitable for most animals.
Mathematics: Standard Deviation
Definition:
Measure of the variability of data.
Calculation:
Easy to find the mean and standard deviation using a calculator or computer.
Observations must be quantitative (counts or measurements).
Interpretation:
Low standard deviation: little variation between values in the sample.
Evenly spread population, similar number of individuals in each quadrat.
High standard deviation: a lot of variation between values.
Uneven population, many more individuals in some parts of the habitat.
Confidence:
Lower the standard deviation, the more confidence in estimates based on the data.
C4.1.4 Capture-Mark-Release-Recapture
Organisms:
Sessile: conifer trees or corals remain in one position.
Motile: organisms including basking sharks and bees move from place to place.
Methods:
Quadrat sampling: suitable for sessile organisms.
Capture-mark-release-recapture method and the Lincoln index: used for motile organisms.
Lincoln Index Assumptions
The following assumptions are made about the period of time between capture and recapture:
There is no migration into or out of the population.
There are no deaths or births.
Marked individuals mix back into the population and have the same chance of being captured on the second occasion as unmarked individuals.
The marks remain visible.
The marks do not increase the chance of predation or other threats to survival.
C4.1.5 Carrying Capacity and Competition
Resource Dependence:
Populations take materials (water, oxygen, food) from their environment.
Larger populations need more resources.
All resources are limited in amount or rate of production.
Competition:
If a resource becomes scarce, population members compete for it.
If a population grows too large, some individuals do not obtain enough resources.
These individuals are likely to die, reducing the population size.
Carrying Capacity:
Maximum size of a population that an environment can support.
One or small number of resources likely to limit population size.
C4.1.6 Negative Feedback Control
Population Dynamics:
Size can rise or fall over time.
Long-term increase if successful.
Long-term decreases due to ecological changes.
Populations commonly fluctuate but remain relatively stable due to negative feedback control.
Types of Factors:
Density-independent factors: effect is the same regardless of population size.
Example: Seawater flooding, forest fires.
Density-dependent factors: increasing effect as the population becomes larger.
Basis for negative feedback mechanisms.
Reduce larger populations, allow smaller populations to increase.
Groups of Density-Dependent Factors:
Competition for limited resources (water, food, light).
Predation: more intense if prey population is denser.
Infectious disease, parasitism, prey infestation: increase with population density.
C4.1.7 Population Growth Curves
Reproduction:
Leads to exponential growth in populations.
Positive feedback because breeding increases individual numbers, and a larger number of individuals can breed more.
Limiting Factors:
Density-dependent factors lead to negative feedback effects that prevent exponential growth.
Without these factors, populations tend to go through exponential growth.
Exponential Growth Cases:
Occurs when a species spreads into a new area and finds a new ecological niche.
Resources are abundant so they do not limit population growth.
Few or no predators, pathogens, parasites, or pests target the population.
Example: Spread of Eurasian collared dove across Europe.
Characteristics and Phases : Population Growth
Collared Dove Population:
Population growth has now stopped in areas of Europe where there was exponential growth.
Numbers are stable or falling.
Limited Resources:
Exponential growth cannot continue indefinitely because environmental resources are limited, so the carrying capacity will eventually be reached.
Curve Change:
Shape on a graph changes from a J-shape to an S-shape.
S-shaped graphs are called sigmoid curves.
Population Cycles:
Not all populations reach a plateau phase after exponential growth.
Many show a cyclical pattern of "booms" and "busts."
Population Crash:
May occur after reaching its maximum.
May happen if produces toxins which accumulate and cause harm.
C4.1.8 Modelling of the Sigmoid Population Growth Curve
Idealized Model:
Often simplifies complex systems.
Experimental Modelling:
Can be done using duckweed or yeast.
A small number of organisms should be introduced with abundant resources for growth and no other organisms that limit population.
Numbers should be monitored by datalogging or regular counts.
Duckweed Experiment:
Stemless photosynthetic water plant that inhabits ponds and lakes.
New fronds are produced asexually that separate from the parent, increasing the size of the population.
Various experiments are possible, for example:
What is the carrying capacity of a given container?
What conditions of light, nutrients or container surface area are ideal for population growth?
Yeast Experiment:
A saprotrophic fungus used to make bread and produce alcohol by fermentation.
It can reproduce asexually by budding (producing small extra cells by mitosis).
C4.1.9 Community Definition
Interdependence Importance:
All species depend on relationships with other species for their long-term survival.
Community:
A group of populations living together in an area and interacting with each other.
Typically consists of hundreds or even thousands of species living together in an ecosystem.
Ecological Research:
Important part of ecology is research into interactions between organisms in communities.
Relationships are complex and varied, and may:
Benefit one species and harm the other (e.g., parasite and host).
Benefit both species (e.g., hummingbird and flower).
C4.1.10 Competition vs. Cooperation
Intraspecific Relationship:
Exists between individuals of the same species, usually within the same population.
Categories:
Competition.
Cooperation.
Competition:
Individuals share an ecological niche and require the same resources.
Competition occurs unless a resource is abundant.
Natural selection favors traits that allow individuals to compete more effectively.
Cooperation:
Individuals cooperate in various ways.
Commonly has advantages, as all individuals benefit, whereas in competitive relationships all individuals tend to be harmed to some degree.
C4.1.11 Interspecific Relationships
Classified Inter-species relationships : relationship is classified by type of interaction.
Categories:
Herbivory: Primary consumers feeding on producers.
Predation: One consumer species (the predator) killing and eating another consumer species (the prey).
Interspecific competition: Two or more species using the same resource.
Mutualism: Two species living in a close association, with both species benefiting from the association.
Parasitism: One species (the parasite) obtaining food from the (harmed) host.
Pathogenicity: One species (the pathogen) causing a disease in the (harmed) host.
C4.1.12 Mutualism Examples
Nitrogen-Fixing Bacteria in Plants:
Rhizobium bacteria living in root nodules of plants in the Fabaceae family and exchanging materials with the plant.
Mycorrhizal Fungi and Orchids:
Mycorrhizal fungi growing into the roots of plants in the Orchidaceae family and exchanging nutrients with the orchid.
Photosynthesizing Algae and Corals:
* Photosynthesizing zooxanthellae living in the cells of hard corals and exchanging materials with the coral.
C4.1.13 Resource Competition: Endemic vs. Invasive Species
Species Definitions:
Endemic species: occur naturally in an area.
Alien species: introduced by humans.
Invasive species: alien species that increase and spread rapidly.
Competitive Exclusion Principle:
Two species cannot occupy the same ecological niche indefinitely.
Alien species compete with endemic species for resources.
Impacts of Invasive Species:
Small realized niche: declines in population.
Extinction: loss of niche and eventual regional extinction.
Human Impact:
* Humans transport high numbers of species to new areas, resulting in numerous alien and invasive species.
C4.1.14 Tests for Interspecific Competition
Associations Between Species:
Recorded in quadrats during sampling of a habitat.
Competitive exclusion might discourage two species from growing together.
Alternative Hypotheses:
Ho: two species are distributed independently (the null hypothesis).
H₁: two species are associated.
Chi-Squared Test:
Used to test hypotheses.
Valid if all expected frequencies are 5 or larger and the sample was taken at random.
Evidence:
* Stronger evidence for competition can be obtained by carrying out an experiment in a habitat.
Field Manipulation:
Remove of one of two species could be removed from quadrats in grassland.
If the remaining species increases in number, interspecific competition is evident.
Laboratory Experiments:
Species could be grown together and apart to investigate whether they compete for resources.
C4.1.15 Chi-Squared Test
Types of Use:
Testing for independence or association.
Testing goodness of fit.
Contingency Table:
Used to compare observed and expected results.
Expected numbers calculated assuming independence.
C4.1.16 Predator-Prey Relationships
Population Dynamics:
If predator kills prey the prey population is one smaller.
Dynamic Equilibrium:
Birth and death rates of predator are approximately equal.
Populations of prey and predators do not show this dynamic equilibrium.
Cyclical Oscillations:
Populations of prey and predators have the following four basic interactions:
* A increase in prey numbers increases food availability for predators, so predator numbers rise.
* A rise in predator numbers increases predation of prey, so prey numbers fall.
* A fall in prey numbers decreases food availability for predators, so predator numbers fall.
* A fall in predator numbers decreases predation of prey, so prey numbers rise.
C4.1.17 Top-Down & Bottom-Up Control
Population Interactions:
Many communities populations are controlled by interactions between trophic levels in a food chain.
Trophic Level Control Top-Down:
Acts from a higher trophic level to a lower one.
Example: increase in predator numbers reduces numbers of prey in lower trophic levels.
Trophic Level Control Bottom-Up:
Acts from a lower trophic level to a higher one.
Populations of producers also may be limited by the availability of mineral nutrients in the soil or in water.
Comunities Varitions:
Communities depend on whether more populations are controlled by top-down or bottom-up interactions.
C4.1.18 Allelopathy and Antibiotics
Primary Metabolites:
Substances that are intermediates or end products.
Secondary Metabolites:
Substances produced by pathways in some taxonomic groups that: are not essential for cell growth and have a wide range of functions, are antibiotics and allelopathic agents, and are released into the environment, where they are toxic to other organisms and deter potential competitors.
Antibiotics:
Secreted by microorganisms to kill or prevent the growth of other microorganisms.
Allelopathic Agents:
Secreted into the soil by plants to kill or deter the growth of neighbouring plants.
Allelopathy in Ailanthus altissima:
Releases an allelopathic chemical ailanthone.