ecosystems 🐸

• what is an ecosystem?

  A community of living organisms and their physical environment, interacting as a system.

  Community: has different populations of different species in the same habitat

  Population: same species in the same habitat

  Species: organisms with similar characteristics that produce fertile offspring + same DNA + same ecological niche
• What are some biotic components of an ecosystem?

  PRODUCERS: autotrophic, e.g plants that produce energy during photosynthesis

  CONSUMERS: heterotrophic, break down big compounds into soluble molecules.

  • Primary consumers = herbivores
  • Secondary consumers + tertiary consumers = carnivores

  SAPROBIONTS: bacteria, fungi, break down dead organisms, recycle nutrients.

  DETRIVORES: feed on detritus (Decaying matter) break down into smaller pieces, create larger surface area for decomposition by microbes, recycling of nutrients
• Abiotic factors 


  Physical aspects of ecosystem

  Has elements recycled between abiotic and biotic components

  Energy from: sunlight

  1. LIGHT: Crucial for photosynthesis, impacting plant diversity and consequently consumer variety.
  2. pH: Influences soil type, determining plant species and, in turn, the ecosystem's fauna, effects enzyme denaturing
  3. TEMPERATION: Crucial for enzymic reactions; affects species diversity
  4. OTHER: Oxygen, carbon dioxide, humidity, salinity, pollution, etc.
• Food chains

  • Trophic relationship from producers (photosynthetic organisms) to consumers.

  Levels:

  • First trophic level: Primary producers.
  • Second trophic level: Primary consumers.
  • Third trophic level: Secondary consumers.
  • Fourth trophic level: Tertiary consumers.

  Limitations:

  • Typically limited to fewer than five trophic levels due to energy loss.
• Food webs

  • Food chains form interconnected food webs within ecosystems.
  • Pyramid of numbers:
  • Typically, the number of organisms decreases along the food chain
  • Exception: Large producers, like oak trees, can lead to an inverted pyramid
  • Parasites can also affect pyramid shape, often occurring in large numbers despite their small size
  • Trophic levels:
  • First: Primary producers (plants).
  • Second: Primary consumers (herbivores).
  • Third: Secondary consumers (carnivores).
  • Fourth: Tertiary consumers (top carnivores).
• Energy transfer

  • 5-20% efficient between trophic levels.
  • Explains why most food chains limited to 4 or 5.
  • Reasons for inefficiency:
  • Most energy lost as heat during respiration.
  • Not all parts of organisms consumed or digestible
  • Loss via excretory products.
  • Calculation of energy transfer percentage:
  • Energy transfer (%) = (Energy available after transfer / Energy available before transfer) x 100.
• Primary productivity

  • Primary Productivity (Plants):
  • Photosynthesis: Primary route for energy entering ecosystems.
  • Gross Primary Productivity (GPP): Total light energy converted to chemical energy in photosynthesis.
  • Net Primary Productivity (NPP): Energy available to primary consumers after subtracting respiratory losses.
  • Respiratory Loss (R): Energy lost through respiration.
  • NPP Calculation: NPP = GPP - R.
  • NPP is crucial for ecosystem productivity and agriculture.
• Photosynthesis and Respiration Rates on productivity

  • Graph Interpretation: Potato mass increases where photosynthesis rate exceeds respiration rate.
  • Temperature Impact: Above a certain temperature , respiration rate surpasses photosynthesis due to enzyme denaturation, leading to mass decrease.
  • Glasshouse Temperature Management: Continual temperature increase can exceed photosynthesis rate, reducing yield.
• Consumer Productivity (Animals)

  • Net Production (N): Consumer's net energy production.
  • Calculation: N = I - (F + R).
  • I: Chemical energy in ingested food.
  • F: Energy lost to environment in feces and urine.
  • R: Respiratory losses to environment.
• Interactions between organisms

  • Most interactions involve feeding.
  • Harsh environments like Antarctica have low species diversity, making ecosystems less stable due to limited resources.
  • Greater diversity, like in tropical rainforests, leads to more stability.
  • More resources and links in the food web make ecosystems resilient to species loss.
• Competition as a biotic factor

  • Interspecific Competition:
  • Competition between DIFFERENT SPECIES
  • Plants = resources like light, soil minerals, and water
  • Animals = compete for prey, water, or nesting sites.
  • The competitive exclusion principle = no two species can occupy same niche, don't directly compete for identical resources.
  • Intraspecific Competition:
  • Competition within a species among individuals.
  • More intense than interspecific competition as individuals compete for the same resources like food and mates.
• the nitrogen cycle 


  Nitrogen is made available via nitrogen fixation

  NITROGEN FIXATION:

  • bacteria convert atmospheric nitrogen (N2) into ammonia (NH3) or ammonium ions (NH4+), used for amino acid and protein formation + soil fertility
  • bacteria = mostly living free
  • some bacteria = mutualistic associations with leguminous plants
  • nodules on plants have colonies of nitrogen fixing bacteria
  • plant gains fixed nitrogen, bacteria gains carbohydrates and vitamins
• Ammonification 


  Saprobiotic microorganisms decomposers break down organic compounds from dead organisms or waste into ammonia or ammonium ions
• Nitrification 


  Nitrifying bacteria: oxidise ammonium ions (NH4+) into:

  Nitrites: NO2-

  and then

  Nitrates: NO3-

  Plants absorb nitrates by active transport in the roots for protein synthesis
• Denitrification


  Denitrifying bacteria converts nitrates into atmospheric nitrogen, reduce soil fertility

  Bacteria = anaerobic, present in waterlogged soils, shortage of oxygen leads to reduction of aerobic bacteria

  Ploughing helps decrease amount of denitrifying bacteria
• Phosphorous cycle

  • Essential for cell development, ATP, DNA, RNA, and phospholipids.
  • Often insufficient in soil for optimal plant growth; farmers replenish it with fertilizers or effluent.
  • Cycle Stages:
  • Phosphorus locked in rocks and sediments; weathering releases phosphate ions into soil and water.
  • Plants absorb phosphate from soil, which can be consumed by animals; upon death, phosphate returns to soil.
  • Bacteria mineralize organic phosphate in soil, making it available to plants.
  • Phosphorus can end up in waterways and oceans, eventually incorporating into sediments.
• how can a representative sample be produced

  random sampling

  systematic sampling

  repeated enough times to allow a statistical test
• random sampling method

  • To study an area, it's divided into a grid.
  • Random numbers are used to pick coordinates on the grid.
  • A quadrat (a square frame) is placed at each coordinate.
  • Researchers count the number of individuals of each species within each quadrat.
  • This method assumes the quadrat represents the whole area.
  • Using many quadrats reduces the impact of chance from a small sample size.
• systematic sampling method

  • Systematic Sampling:
  • Grid laid over map of study area.
  • Sampling points located at regular intervals.
  • More reliable data than random sampling.
  • Time-consuming process.
  • Point of Saturation:
  • In uniform habitats, after analyzing several quadrats, new species might not be found.
  • Typically, after examining five quadrats without finding new species, further analysis might not yield additional species.
• population estimate for mobile animals

  MARK RELEASE RECAPTURE

  • Stage 1: Capture a sample of animals from the population.
  • Mark them without harm (e.g., tagging fish, putting rings on birds, using dyes or distinctive fur patterns for mammals, painting arthropods).
  • Stage 2: Release marked animals back into the population.
  • Stage 3: Capture a second sample later and count marked individuals.
  • Population Size Estimation:
  • Use the formula: Estimated total population = (Number captured and marked in 1st sample × Total number captured in 2nd sample) / Number of marked individuals recaptured.
• Diversity index 


  Biodiversity: variety of organisms in a habitat

  Species richness: number of different species

  Index of diversity: number of species + number of individuals of each species in area

  CALCULATION:

  $N(N-1)/∑n (n - 1)$

  N= all species

  n= number of animals in each species
• chi squared test


  $∑ (o-e)^2/e$

  Expected = equal division

  Calculated value must be greater or equal to critical value

  degrees of freedom: number of categories - 1

  requires at least two frequency data sets, over 20 total obs, an expected frequency of 5

  CONCLUSION TEMPLATE:

  • Calculated value, ___, is ___ than critical value of ___ so there is/isnt a significant difference between observed and expected values
  • The probability of the difference being due to chance is more/less than ___ so the null hypothesis can be accepted/rejected
  • say smth specific about the actual scenario
• SUCCESSION

  • Constant change in biotic communities due to factors like climate change or organic matter buildup.
  • Development from initial stage (e.g., bare rock or water) to climax community (stable community).
• PROCESS OF SUCCESSION:

  1. Begins with pioneer species (lichens or algae) tolerant of harsh conditions, can photosynthesise and disperse
  2. Pioneer species secrete chemicals to break down rock, creating soil.
  3. Dead pioneer species provide organic matter for decomposers, forming humus, this forms soil, next group can colonise
  4. Mosses colonize, forming a dense mat that traps particles and water. When dead, adds more humus
  5. Successive plant species colonize, leading to increasingly complex communities (grasses, herbs, shrubs, small trees, climax community like woodland).
• Importance of succession:

  1. Soil becomes deeper and richer in nutrients, supporting more diverse plant species.
  2. climax community with a dominant species that has greatest biomass/biodiversity is formed
  3. stability increases and more complex food webs formed
• DDT

  • DDT:
  • Pesticide poisoning, especially DDT, harmed top carnivores like birds.
  • Peregrine falcon vanished from eastern USA due to DDT poisoning.
  • DDT affects bird's calcium metabolism, leading to thinner eggshells and high egg breakage.
  • DDT Usage:
  • Banned in many developed countries like Britain and the USA.
  • Still used for specific tasks like malaria control due to being cheap to produce.
  • Often a choice between two bad options when deciding on pesticide use.
  • DDT eradicated malaria in many parts of the world
• Herbicides

  • non-selective, killing any plant including crops, used before crop germination or planting, often for clearing areas before cultivation.
  • Others are selective, targeting specific types of plants, applied after crop germination to kill only weeds.
  • Types of Herbicides:
  • Contact Herbicides:
  • Affect only the area they touch on the plant.
  • Kill above-ground parts of the weed they're applied to.
  • Systemic Herbicides:
  • Absorbed by plants, killing all plant tissues.
  • Not affected by light or rain once inside the plant, unlike contact herbicides which can break down or wash off.
• BIOFUELS 


  made from living things or waste product produced

  IMPORTANCE:

  • can reduce gas emissions
  • reduce dependency on fossil fuels
  • are a renewable energy source

  Have a fixed amount of carbon from photosynthesis, don‘t release as much carbon dioxide
• TYPES OF BIOFUELS:

  First generation: biofuels produced from edible crops

  Biodiesel:

  Produced from extracting oil from crops

  Bioethanol:

  Produced from sugar beet/sugar cane/

  corn, fermented to ethanol by yeast
• TYPES OF BIOFUELS

  Second + third: produced from non food crops,

  • produce higher yields
  • dont compete with crops
  • reduce greenhouse gasses

  Lignocellulosic biofuels

  1. breakdown of cellulose in cell walls of plants
  2. microbes used to breakdown non edible plant material via cellulase into sugars
  3. used to ferment ethanol

  Algae

  • photosynthesise to produce biomass, converted to biodiesel
  • don‘t compete for land that could be used for food production
  • sugars produced are fermented into ethanol
• impact of farming 1


  MONOCULTURE: growing the same crop on the same land

  Advantages: cheap, reduced labour cost

  Disadvantages: loss of hedgerows, soil erosion, reduced species diversity (smaller niches/resources), increased crop failure, eutrophication, increased fertiliser, herbicides, pesticides due to diseases + weeds
• impact of farming 2

  Hedgerow removal

  Row of bushes or trees growing together

  Advantages of removal:

  space can be used for growing crop, increased yield

  less need to maintain them

  Easier to manoeuvre large machines

  decreased chances of absorbing light, crops get more light

  remove habitats that might have pests or diseases
• impact of farming 3

  Disadvantages of hedgerow removal:

  soil exposed to erosion

  less flexibility due to fences having to be erected

  less shelter for animals

  less habitat + less resources , decrease species diversity

  predators that reduce pests = reduced, increased pests, more pesticides, even more decreased populations

  reduced aesthetic appearances

  reduced movement and dispersement
• Ways to reduce farming impact

  use organic manure, provide more humus

  delay application of chemical fertilisers

  leave crop stubble, plough later, less soil erosion

  rotate crop growth, reduced crop specific pests

  leave areas of wilderness to develop

  stop destroying hedgerows
• Organic fertilisers

  Farmyard manure/sewage sludge

  Advantages:

  • cheap
  • not lost by leaching
  • improves soil

  Disadvantages:

  • nutrient content low
  • slow release of nutrients
  • might contain disease pathogens
• Inorganic fertilisers

  Pellets containing minerals NPK

  Advantages:

  • Exact composition known, soil balance controlled

  Disadvantages:

  • expensive
  • energy consuming
  • rapid leaching into rivers, more eutrophication
  • Can cause osmotic damage to plants
• Eutrophication 


  Enrichment of aquatic ecosystem by nutrients is called eutrophication

  Issue with fertilisers :

  • can wash away/leach into rivers/sea
  • become over fertile
• why is calculating a species diversity index more useful than counting number of species?


  it considers number of different species and how individuals are distributed
• what is the gradual change into climax communities due to?

  the soil becoming deeper with more humus and rich in nutrients
• how do food webs become more complex in relation to succession?

  The stability and diversity of the ecosystem increases as new

  niches for herbivores, secondary consumers, detritivores and decomposers emerge due to more resources available and food webs become more complex.