How would you demonstrate the effects of abiotic factors on an organism?
You could demonstrate them directly through experiments or indirectly through observing natural ecosystems.
You could demonstrate them 1) directly through experiments or 2) indirectly through observing natural ecosystems.
You could run experiments where you limit a certain abiotic factor or purposefully decrease its quality while keeping other factors constant. For example, you could lower the oxygen content of a closed system where fruit flies live and compare their lifespan, their reproduction rates, their body size, their foraging efficiency, in the lower oxygen environment compared to fruit flies living in an identical environment with normal oxygen content.
It would be much harder to run these types of experiments on larger animals because their habitats are often very complex and there are ethical guidelines all scientists must adhere to. Experiment such as this one though provide direct evidence of the affects of abiotic factors on an organism.
You could also observe natural systems, although it would be much harder to prove the direct relationship of an abiotic factor on an organism. For example, if you were studying the same riverine system for an extended period of time (decades) and all of a sudden the river was degraded significantly by pollution or some other human activity, you could look at how the populations change before and after. Again, you could see if their lifespan changed, if reproduction rates changed, etc.
It would be difficult to prove, without a doubt, that any changes observed were due to decreased water quality. However, with a long-term study, you might be able to determine some trends and make reasonable deductions.
If you're really interested, you may want to skim or read the following studies:
Biotic and abiotic factors investigated in two Drosophila species – evidence of both negative and positive effects of interactions on performance
Thermal plasticity in Drosophila melanogaster: A comparison of geographic populations