Job of ecologists is to reduce complexity so we can understand and decribe interactions more easily and notice when changes occur.
The interactions between all the species in a community= FOOD WEB
This can be made up of many food chains.
Food webs are highly complex systems e.g. Ythan esturay, Scotland- despite being in the North of Scotlnd- 92 species, 440 feeding links, 5500 food chains.
On the other hand- coral reef just fish: 500-1000 species
Difficult to comprehend and understand.
How do we determine the linkages?
- Observations (visual and photographic) -easier in some habitats e.g African Savannah, may not be so easy in oceanic ecosystems or with nocturnal species. -Getting easier with camera traps and remote cameras- triggered by movement; slow motion cameras etc.
- Stomach content analysis - downside is the animal is killed- useful to use on already deceased individuals e.g. to investigate plastic in stomaches. Some individuals vomit up what they have just eaten when caught. Feeding tube- reach down throat and bring up stomach contents.
- Scat analysis- different species have different ear bones- otoliths- can work out which species is eaten.
- Stable isotope analysis (particularly N) the closer to the bottom of the food chain- the higher the quantity of some N isotopes you will find.
Classify organisms into different levels.