Ecology

• Ecology: study of living organisms & their envi
• Species is a grp of organisms that can interbreed to produce fertile offspring. If species are not closely related it is ≈ impossible for them to breed. If members of 2 closely related species interbreed & produce offspring, the hybrids may be sterile e.g. mules.
• Popu is a grp of organisms of the same species living in the same area at the same time. If organisms of the same species are separated (geo/temporally) since they are unlikely to breed (even though their ability to remains) they are regarded as diff popu.
• Community is a grp of popu living & interacting tgt in the same area. Ecosystem is made up of a community & its abiotic envi. Habitat is the envi in which a species lives.
• Autotrophs synthesise their own organic molecules & are aka prod. All autotrophs convert inorganic CO2 (from atm/ aq) into organic CHO & other C compounds. The inorganic nutrient compounds are obtained from the abiotic environment. Heterotrophs obtain their organic molecules from other organisms and heterotrophs that ingest other organisms aka cons. Mixotrophs are as the name implies a mix of auto + hetero (eg venus flytrap).
• Other heterotrophs:

  • Detritivores
  • Obtain nutrients by consuming non-living organic sources, like detritus & humus
  • Eg include: dung beetles, earthworms, woodlice & crabs
  • Saprotrophs
  • Live on/ in, non-living organic matter. They secrete digestive enzymes onto the organic matter & absorb the products of digestion. They aka decomposers since they facilitate breakdown of organic materials.
  • Bacteria & fungi
• Nutrient cycling:

  Elements req by an organism for growth & metabolism are regarded as nutrients, e.g. carbon, nitrogen and phosphorus. The supply of nutrients is limited & ∴ ecosystems constantly recycle the nutrients btw organisms. Saprotrophs break down organic nutrients to gain E & in the process release nutrients back into inorganic molecules, e.g. fungi release N as NH3 into the soil. This ensures the continuing availability of nutrients to autotrophs. 
• Most flows of E & nutrients in an ecosystem are btw members of the biotic community. Relatively few flows of E and nutrients enter/ leave from surrounding ecosystems. ∴ ecosystems are to a large extent self-contained & hence self-sustaining. 
• To remain sustainable an ecosystem requires:

  • Continuous E availability, e.g. light from the sun
  • Nutrient cycling - saprotrophs are crucial for continuous provision of nutrients to producers
  • Recycling of waste – certain by products of metabolism, e.g. ammonia from excretion, are toxic. Decomposing bacteria ≈ fulfil this role by deriving E as toxic molecules are broken down to simpler, less toxic molecules.
• Mesocosms are biological systems that contain the abiotic & biotic features of an ecosystem but are restricted in size &/or under controlled conditions.  (+) association = species found in the same habitat (e.g. predator & prey, herbivore & plant, symbiosis). (-) association = Species occur separately in differing habitats (e.g. competitive exclusion, req diff nutrients). No association = species occur as freq apart as tgt. 
• Quadrat sampling can be used in a number of ways including:

  • Estimation of population density/size
  • Measuring the distribution of species
• Quadrats are placed repeatedly in a sample area to provide a reliable estimate. Quadrats can be placed systematically, e.g. in a ‘belt transect’, typically to measure changing distribution/ randomly, e.g. to estimate population density. Depending on the presence/absence, frequency or % coverage of a given species can be recorded. Both systematic & random sampling methods are used to avoid bias in the selection of samples. The major limitation of quadrat sampling is that large & mobile animals cannot be effectively sampled. It is most suitable for plants and small, slow-moving animals.
• All plants & some prokaryotes = photoautotrophs. They use pigments, such as chlorophyll, to trap light E, which is converted into chemical E in C compounds. Very few ecosystems have chemoautotroph producers, e.g. volcanic vents on the ocean floor, which use E from chemical processes. 
• Food chains show E flow through the trophic levels of a feeding rs. Trophic level is the feeding pos of an organism in the food chain. 
• E stored in organic molecules (CHO & lipids) can be transferred by cell respiration to ATP. Inefficiencies in the transfer of E btw & within organisms include: toxic waste organic molecules are excreted, some ingested material is not absorbed and ends up being egested; and some parts of an organism remain uneaten, e.g. woody fibres from plants and the bones of animals.
• No E transfer is 100% efficient: ‘wasted’ heat (thermal) E  is produced too. Unlike light & chemical E organisms cannot convert heat E into forms useful to the organism. Thermal E released from the organism dissipates into the ecosystem & is eventually lost from it. Therefore ecosystems req a continuous supply of E (e.g. sunlight) to persist.
• Chemical E is held in molecular bonds. Therefore as E is lost btw trophic levels it is natural for biomass to be lost too. Biomass therefore is ≈ used to indirectly measure E transfers. As the trophic level ↑, biomass & E available ↓. Higher trophic levels are ≈ less efficient as more E is spent on foraging more mobile prey. Eventually E req to forage > the E gained from foraging, making the trophic level unviable. 
• Pyramids of E always get smaller at higher trophic levels due to the loss of E. Bars should be roughly drawn to scale, e.g. 2nd consumer should be 1/10th of primary consumers. Bottom level will alws start w producers. Subsequent levels show consumers (primary, secondary, etc.)
• Plants require a constant supply of carbon dioxide (CO2) to continually photosynthesise. CO2 from outside moves through stomatal pores in the leaves of land plants & diffuses down conc gradient into the leaf. Photosynthesis uses CO2 to keep conc of CO2 inside leaf low. Organisms carry out respiration to release E in the form of ATP. CO2 is a waste product of cell respiration.
• Peat:


  Partially decomposed organic matter can be compressed to form brown soil-like peat. Peat is a highly effective carbon sink. Once dried, peat burns easily & can be used as a fuel. Coal is formed when deposits of peat are buried under other sediments. The peat is compressed & heated over millions years eventually becoming coal. The cycle of sea-level Δ that happened during the Carboniferous period caused coastal swamps to be buried promoting the formation of coal.
• Formation of oil and gas from ancient oceans:

  Some CO2 will directly dissolve in water, but most will combine w water to become carbonic acid (H2CO3). Both dissolved CO2 & HCO3- are absorbed by aquatic plants & other autotrophs that live in water. H+ ions explains how CO2 ↓ pH of water.
• CO2 + H2O → H2CO3 → H+ + HCO3–
• Some animals secrete calcium carbonate (CaCO3) structures to protect themselves:

  • Shells of molluscs
  • Hard corals exoskeletons
• When animals die soft body parts decompose, but CaCO3 remains to form deposits on ocean floor which are then buried & compressed to eventually form limestone rock. Imprints of hard body parts remain in the rock as fossils. Limestone rock is a huge carbon sink.
• Methanogens are archaea microorganisms that produce methane as a metabolic byproduct in anaerobic conditions. ≈ during ATP prod methane is produced from CO2. Methanogens are found in a variety of anaerobic environments: wetlands, digestive tracts of animals, marine & freshwater sediments and landfill sites (w organic matter buried). Methane released into atm can be removed through oxidation by hydroxyl radicals.

  Methane + hydroxyl radical → carbon dioxide + water
• Evidence for ↑ CO2:

  • Keeling curve 
  • Keeling curve video
  • Ice Cores
  • Analyse CO2 conc of air bubbles trapped in ice & estimate the year based of the depth of the ice core
• Greenhouse effect:

  1. Approx 25% of solar radiation is absorbed by the atm
  2. Approx 75% of solar radiation penetrates the atm & reaches Earth’s surface
  3. Earth’s surface absorbs shortwave solar E & re-emits at longer wavelengths (as heat). 
  4. Up to 85%* re-emitted heat is captured by greenhouse gases in the atm.
  5. Heat passes back to the surface of the Earth, causing warming
• The greenhouse gases that have the largest warming effect on the Earth are:

  • carbon dioxide 
  • water vapour (e.g. clouds)
• NOx are released naturally by bacteria in some habitats & also by agriculture and vehicle exhausts. Greenhouse gases make up < 1% of the atmosphere. For IB js assume clouds mostly have cooling efx by slowing down greenhouse effect. 
• Evi for correlation btw atm CO2 & avg global ℃:

  • Global ℃ show large variations & despite this there is strong support for correlation btw atm CO2 & global ℃
  • Most ↑ & ↓ in CO2 have correlated with ℃ ↑ & ↓. The same trend has been found in other ice cores.
• Ice core:

  The core shows annual layers, which can be used to date the air bubbles trapped in the ice. Analysis of the gas content of the bubbles gives both the conc of CO2 in the atm and the air ℃ (from oxygen isotopes) at the time ice was formed. 
• Link btw human emissions & atm levels of CO2:

  Anthropogenic = human-caused. As atm CO2 levels have ↑, the amt of CO2 absorbed by carbon sinks has ↑. 
• ↑ greenhouse gas conc will likely cause:

  • ↑ global avg ℃
  • More frequent & intense heat waves
  • Some areas becoming more prone to droughts
  • Some areas more prone to intense periods of rainfall & flooding
  • More frequent & powerful tropical storms 
  • Δ to ocean currents, e.g. weakening of the Gulf Stream would mean colder ℃ in north-west Europe
• Ocean acidification:

  When CO2 dissolves in water it forms a variety of molecules: dissolved free CO2, H2CO3, HCO3-, CO32-. It is not just the creation of carbonic acid that affects pH; formation of bicarbonate and carbonate ions also releases H+ ions thus further ↓ pH of seawater. 
• Carbonate ions are not very soluble, therefore conc in seawater is low. Dissolving CO2 ↓ carbonate conc further, carbonate ions are an important building block for structures such as sea shells & coral skeletons and therefore cons of carbonate ion impedes calcification.
• Ocean absorbs abt 25% of CO2 emitted into atm ∴ as atm CO2 ↑ so does conc in ocean. Since 1800, pH of seawater* has ↓ by 0.1 pH units this is approx 30% ↑ in acidity. Estimates of future CO2 levels indicate that by 2100 seawater could be 150% more acidic (further ↓ of 0.5 pH). Also, by 2100, coral reefs may erode faster than they can be rebuilt, thus affecting the approx 1 milly species that depend on coral reef habitat. 
•  At risk:

  • Marine calcifying species, including oysters, clams, sea urchins, shallow water corals, deep sea corals, and calcareous plankton.
  • Need to absorb carbonate ions from seawater to make the calcium carbonate in their skeletons.

  Benefit:

  • Photosynthetic algae and sea grasses
  • Low CO2 is a limiting factor for photosynthesis