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I came across a law in Ecology, that states that the mass and energy of an ecosystem are conserved.

Source: Law-4 of pg-35

Ecosystem is an open system, the conservation of mass and energy shouldn't apply to it. Isn't it?

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  • $\begingroup$ Yes in a way, it's conserved, I would send you to watch this youtube.com/watch?v=HxTnqKuNygE $\endgroup$ – Ismasou Jan 24 '17 at 18:33
  • $\begingroup$ In their defense, we never really see a perfectly closed system in real life. Some things are just close enough to model as closed systems (i.e. energy interaction with the environment is minimal). I'm not sure the extent to which that is true in this case, but I imagine it is at least somewhat true. Most of the energy and mass in the system are conserved or balanced. Mass especially, energy is a bit iffier with energy sources and sinks that would definitely be "outside" the ecosystem having a big effect. $\endgroup$ – JMac Jan 24 '17 at 18:36
  • $\begingroup$ @JMac Almost all ecosystems on Earth take in huge quantities of energy from the sun (directly or indirectly). They also radiate huge quantities to the universe at large so that the net is modest compared to either the input or the output. Now, I wouldn't treat that as something you could model as a closed system from a physics POV, but it may be good enough for the ecologists. At least on time scales short compared to big ecological shifts. $\endgroup$ – dmckee Jan 24 '17 at 19:17
  • $\begingroup$ @dmckee Yeah that's what I was trying to get at as well. They are probably pretty close to balanced; but the behavior (especially for energy) isn't really like a closed system. I was thinking the same reasoning as you for why they would say that though. I'm sure for the scales (and uncertainty) that ecologists operate at they are modeled as closed or with limited outside interaction. $\endgroup$ – JMac Jan 24 '17 at 19:25
  • $\begingroup$ If you look at the whole of Page 35, the first "law" contradicts the fourth "law" that the OP mentioned. Reading page 34 might suggest that the book is more about "philosophical wind and woffle" than "hard science". I don't see what the discussion about Special Relativity and the impossibility of faster-than-light mass transfer on p.34 has to do with anything in practical ecology! $\endgroup$ – alephzero Jan 24 '17 at 20:29
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It's a different field of subject, so borrowed statements like 'mass and energy is conserved' should be taken with a pinch of poetic salt. You are correct in that ecosystems (as found on Earth) are open systems and conservation of mass and energy doesn't apply.

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