| > Yet.. both of those examples are exactly that, omnivores, and both are also sometimes functionally predators. omnivores are not something in between a predator and an herbivore. we are facultative carnivores, we can eat vegetables, but we are not predators. > And it absolutely follows that you can put an omnivore at half trophic step between a primary consumer (i.e. a predator of herbivores) and an herbivore it doesn't follow. Pigs are prey too, but they can eat meat. Above all there is us, humans, but, generally speaking there are the apex predators, which is not "all the predators". A pig or an ape sits above an ant, which is one of the most formidable predator of the animal kingdom. > they absolutely eat herbivores sometimes of course they do. it doesn't change the fact that some of their preys are predators themselves. because they eat them for their meat, not because they are labeled "preys" in the encyclopedia. > That doesn't mean ecosystem complexity is the same everywhere if that's the argument, it doesn't follow that watery ecosystems are the same everywhere too and that they are more complex than any other ecosystem. > Can't say I understand your point was quoting the original comment which goes like this algae-Zooplankton--Predator-Predator-Predator-Predator-Predator-Predator-Predator at the zooplankton level you already have whales eating it. end of the chain. so zooplankton is the equivalent of terrestrial ants that eat plants and then some bird eats the ants and then some small predator eat the bird and then some bigger predator eat the small bird eater then some even bigger predator eat it, until you arrive to an apex predator (a bear, for example). What's the difference? > that marine food chains are longer but not because algae-Zooplankton--Predator-Predator-Predator-Predator-Predator-Predator-Predator but because eukaryotes-bacteria-bacteria-bacteria-bacteria-bacteria-bacteria-Valonia ventricosa |
No, we are omnivores, both behaviorally and physiologically. As I mentioned, predator is a functional class, but we are absolutely are predators - predation is killing something to eat it. Perhaps you mean we aren't obligate predators.
Regarding the trophic position of omnivores and the existence of multiple trophic levels of consumers, which I acknowledged in my first post, it doesn't really matter - you can calculate trophic position by the mean trophic level of the things you eat. Half grass and half cow would be 2.5. Humans are around 2.2 [1], because we are omnivores.
> at the zooplankton level you already have whales eating it.
Well, blue whales are krill specialists and yes have a fairly low trophic level - 3.2 - but it is a cherrypicked example of course. The equivalent is saying an African elephant is a browsing herbivore and generally aren't bothered by predators, which is one less trophic level than the whale example. In reality, both can be preyed upon especially when young or infirm or old [2] and in practice it may be better to not cherrypick.
> What's the difference?
The difference is in the pelagic ecosystem there are often more levels. The difference is due to trophic efficiency, energy gets moved from primary productivity up the chain faster and with less loss.
>but not because algae-Zooplankton--Predator-Predator-Predator-Predator-Predator-Predator-Predator
No, that's exactly why.
Extending Briand and Cohen (1987), we reconsidered which class of ecosystems supports the longest food chains. Among all 113 food webs of Briand and Cohen (Briand and Cohen 1987; Cohen et al. 1990), and also among the 28 webs in three-dimensional habitats, ecosystems with one-celled plant producers have the longest maximum food chains. By “pelagic” ecosystems, we here mean those based on single-celled primary producers (phytoplankton). Among these 113 food webs, the 10 ecosystems with longest maximal chains all had single-celled (phytoplankton) primary producers (fig. 1A). Of the 28 three-dimensional webs, the 16 webs with the longest food chains also had single-celled (phytoplankton) primary producers (fig. 1B). In all, about half (56) of the 113 Briand and Cohen webs and 21 of the 28 three-dimensional webs were supported by single-celled plants. The 10 webs with longest food chains were all aquatic: eight were from pelagic three-dimensional ecosystems (six in oceans and two in lakes) [3]
You may have misinterpreted the study from the abstract but full pdf available from googling the name.
[1] https://www.pnas.org/doi/10.1073/pnas.1305827110 [2] https://onlinelibrary.wiley.com/doi/epdf/10.1111/mms.12906 [3] https://www.journals.uchicago.edu/doi/full/10.1086/686880