Energy contents of macrophytes may be estimated by

$A$ plant being eaten by a herbivore,which in turn is eaten by a carnivore,constitutes a:

What is the average price tag for ecosystem services determined by researchers?

In an ecosystem with a simple food web or food chain,if a change occurs at any one trophic level,what characteristic will emerge?

What is formed by the interaction between biotic communities and their environment?

$A$: Agriculture and aquaculture are man-maintained ecosystems.
$R$: All biotic and abiotic factors are managed by humans in these ecosystems.