[kuhewa]

Mammal species can be herbivores or predators though? If you are referencing the existence of omnivores, that's fair, but they'd just kinda sit at a half step between herbivore and predator. Really you'd want to consider not just one type of predator but secondary consumers that eat herbivores, tertiary consumers that eat them, like a snake, and quartenary consumers that eat them, like a hawk.

There's a little exaggeration in that comment but directionally it holds true, marine food chains are longer, in part because primary production in pelagic ecosystems is single cell phytoplankton instead of plants, and the small size of things a lot of room for higher trophic levels in terms of energetics.

https://pubmed.ncbi.nlm.nih.gov/27322123

[peoplefromibiza]

> that's fair, but they'd just kinda sit at a half step between herbivore and predator

no it doesn't.

We are not predators and are not herbivores.

swines are not herbivore but not predators.

But in fairness it's not very common, the real point is that if we look at the data, mammals are mostly carnivores, 63% of them is, but that doesn't imply being a predator.

The other point is that the cycle is not predator eats herbivore which eats plants.

That is a mammal-centric view that completely removes from the equation the majority of lifeforms on Earth, 'cause mammals are a minority of the species in nature.

Many predators also feed from other lesser predators, example: snakes. Snakes don't eat herbivores, they eat small rodents that usually eat other smaller animals.

Truth is the cycle is a lot more about bacteria that eats a substance (that probably comes from the putrefaction of some dead animal) that creates some other substance that other bacteria live on and they too produce something that simple life forms use to produce energy and after many of these steps, maybe there's some plant or fungi that consumes those nutrients in the soil and then "do you have time to talk about our lords and saviors the insects, the 900 thousands species of them?"

Oceans are not absolutely more complex than terrestrial life and why should they be? Life on Earth evolved over hundreds of millions of years, it makes sense that it adapted to every ecosystem the Earth has to offer.

> marine food chains are longer

a bit longer doesn't mean what the original comments was about.

The study also says that the chain is longer in the lowest segment of the chain where the size is microscopic.

So when you arrive at the zooplankton level, you are already at very large animal eats helpless food (plants or soup of proteins) and then get eaten by a predator or it's too big to be annoyed by anybody (elephants and whales, for example)

[kuhewa]

Most of that reply was taking issue with using predator instead of carnivore or more broadly 'consumer', which is fair. Actually I'm not sure if that was what you were getting at, because this was in response to me pointing out omnivores are a half trophic step between herbivore and predator (consumer):

> We are not predators and are not herbivores.

> swines are not herbivore but not predators.

Yet.. both of those examples are exactly that, omnivores, and both are also sometimes functionally 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. The way trophic levels are described are in fractional numbers of the mean trophic level of what you eat. Predator is a functional group rather than a descriptor trophic level, but when it comes down to it very few animals are pure functional specialists and very rarely does one sit perfectly at a given trophic level - to use your snakes example, they absolutely eat herbivores sometimes even if they are usually eating things that eat animals. Cows consume the occasional insect, I've seen algae-specialist green sea turtles opportunistically eat dead fish, and some shark species eat a non-negligible amount of grass. But I'm going to continue calling sea turtles grazing herbivores and sharks consumers and predators, because that is true to a first approximation.

Regarding ecosystem complexity, I don't believe I mentioned it other than length of trophic chains. However I'll point out that this

> Oceans are not absolutely more complex than terrestrial life and why should they be? Life on Earth evolved over hundreds of millions of years, it makes sense that it adapted to every ecosystem the Earth has to offer.

Doesn't follow. Sure, life evolved everywhere, speciation occured and niches have been pretty well filled. That doesn't mean ecosystem complexity is the same everywhere, there are a number of identified drivers of species richness and functional diversity (e.g. latitude) and decades of theory to try to explain why, because a rainforest is more complex than a sweetgrass prarie, and a coral reef is too. A rainforest probably beats a lot of marine ecosystems, say a soft sediment continental shelf in terms of complexity due to greater species richness, simply more connections between species at many levels and lots of niche partitioning.

Can't say I understand your point about food chains being longer due to microscopic primary producers. That is still the energetic pathway that feeds into the rest of the ecosystem.

> a bit longer doesn't mean what the original comments was about.

My reading of that comment was exactly that, that marine food chains are longer. That commenter exaggerated a bit the degree to which that is true. That study I linked provides some plausible mechanisms of why that may be.

[peoplefromibiza]

> 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

[kuhewa]

> we are facultative carnivores, we can eat vegetables, but we are not predators.

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 “pe￾lagic” ecosystems, we here mean those based on single-celled primary producers (phytoplankton). Among these 113 food webs, the 10 ecosystems with lon￾gest 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