Tropic Ecology Flashcards
Define a food chain
22:14 Food chain - a linear sequence that reveals which organisms consume which other organisms in an environment
Define a food web
Food web – a more complicated diagrammatic representation of overall pattern of feeding interactions
Define ecology
Ecology - how organisms interact with one another and their environment
All animals are Heterotrophs. All marine consumers feed in one of what five basic ways
- Grazers – herbivores directly consuming plant material. Copepods, gastropod molluscs 2. Predators –carnivores hunting smaller animals. Several levels, herring, tuna, sharks 3. Scavengers – searching for dead organic matter. Common amongst benthic invertebrates 4. Filter feeders (and suspension feeders) – obtain food by removing suspended particles from the water. Barnacles Deposit feeders –extracting food particles contained in the sediment. Worms, starfish
How do bacteria fix carbon?
• Split in bacteria, fixing carbon either aerobically or anaerobically. ○ Aerobic bacteria require oxygen to produce nitrate (NO3-) from ammonia(NH3) Anaerobic bacteria liberate oxygen from sulphate (SO42-) and produce hydrogen sulphide gas (H2S)
Calculating Trophic Levels
• Require / Assume: diet fully characterised and quantified, prey TLs correct, and reflect long term mean. Use data from stomach content analysis • To appreciate what’s going on in a food web is to calculate trophic levels. This can be done by quantifying food webs. ○ The most basic way of doing this would see where its food comes from. Stomach content analysis etc.. ○ Calculate the percentage of each prey species that makes up the diet ○ Take an average of the trophic levels of the prey item and sum them up.
Weaknesses f stomach content analysis
• Assumed diet trophic level (will take a very long time to establish a trophic level of something high up) • Long term mean allowing no variation in space/time - takes a snapshot, but diet will change • Unknown base of production. Can’t run stomach content analysis on each prey species - so we don’t know where the base of production actually starts (algal / bacterial) • Data extremely limited (e.g. vacuity). When fish are pulled up in nets the stress causes vomit and excretion. This would give an incomplete diet. • High sampling effort (e.g. opportunistic feeders). A lot needs to be done to establish the whole picture for a population Net Contamination - can opportunistically feed in net
Strengths of stomach content anaysis
Strengths • High taxonomic resolution - with the stable isotope analysis you never know what the species actually are. • Technologically simple • Tried and Tested - used throughout history Snapshot in time
energy transfer between trophic levels
• Chemical energy is passed upwards through the trophic levels • Results in an increase in biomass of a region • Energy transfer is not efficient, 90% lost per level. • Biomass lower at the top of the chain/web • Energy will be lost through excretion, indigestible material such as the CaCO3 tests of a foram, or silicate tests of a diatom. If we want to estimate potential production at the top of a food chain, i.e. fisheries production, it is necessary to tabulate these energy losses
how can you estimate potental fish populations in an area?
• Rates of production and energy transfer efficiency can then be used to estimate potential fish populations in a region • Useful guides to explain how much production you can expect form a fishery, however, the numbers are not usually accurate as these estimates are far more complicated.
Alternatives to Stomach Contents
Alternatives to Stomach Contents • Scat analysis – useful in large animals e.g. mammals, utilises hard structures e.g. otoliths, cephalopod beaks ○ Can be difficult in the marine environment, disperses quickly ○ Less destructive method • Fatty Acid Profiles - some prey have characteristic FA profiles…used as tracers Look at fractionation of fatty acids within an organism, as these fatty acids are usually taken from other organisms and formed into long chains.
What is isotope fractionation?
• Isotope fractionation = differential partitioning of isotopes between two compounds • Heavy isotopes have a higher bond strength and therefore react slower. The differing in bond strength will give you a rate proportion to the mass difference. The greater the mass difference the greater the difference in the rate of transfer between them.
What is Stable isotope analysis
• Because of processes and mechanisms within an organism fractionation occurs between heavier and lighter isotopes. Lighter or heavier ions can be use preferentially. • Lighter ions are used because ○ They are more common ○ More likely to see the fractionation when there is a comparatively bigger ratio of weight between the ions. • Nitrogen 14 and 15 are used a lot. • This uses =Delta Notation d (‰) ○ `dHX = [(Rsample - Rstandard) / Rstandard] × 1000 ○ Testing the parts per 1000 difference between the standard from the environment and the sample. ○ Carbon Standard = Pee Dee Belemnite (PDB) (expected to know) ○ Nitrogen Standard =Atmospheric N2
Trophic Step Fractionation
• Excretion/Respiration ○ Production of metabolites with light isotopes in deamination/transamination (heavy isotopes become concentrated) • Assimilation Fractionation ○ Preferential use of heavy isotopes during protein biosynthesis • Fractionation between diet and consumer • CONVENTIONALLY ASSUMED ○ Δδ15N = +3.4 ‰ (3.4 part per thousand difference in nitrogen will give you a different trophic levels) Δδ13C = +1.0‰ (1 part per thousand difference in carbon will give you a different food source)
What are the advantages of Trophic Step Fractionation
• independent of gut-contents data (easy to get samples, less destructive and using different body parts means you may be able to calculate trophic levels at different points in its life) • materials largely invisible in gut data can be evaluated, no species id needed • integrate short-term changes into one variable • materials involved are those actually assimilated, doesn’t include accidental swallowing • simple first-order tests of spatial, temporal and ontogenic trends (one easy comparable number)