But I do agree there's some really interesting key differences. For one, speciation on land is often driven by geological barriers that split populations apart. But these types of barriers are much less common in the ocean where this only really happens to organisms that are restricted to shallow waters (and even then "island-hopping" happens much more commonly)
Depth is a thing and can separate disparate communuties on seamounts like alpine species on mountain tops. The difference is most Maine species have a pelagic larval stage and can disperse widely, so barriers to gene flow are more limited than on land.
Different terrestrial and marine habitats and assemblages come to mind where one may be more complex than another but overall if the degree of niche partitioning at any given trophic level was a wash between land and sea water, I think marine may take the cake on complexity just due to the webs being longer and thus room for more edges between nodes https://pubmed.ncbi.nlm.nih.gov/27322123/
“Ages ago, life was born in the primitive sea. Young life forms constantly evolved in order to survive. Some prospered — some did not. All sorts of life ebbed and flowed like the tide. In the quiet rhythm of the mother sea, life grew, always seeking to survive and flourish.”
https://www.nationalgeographic.org/activity/save-the-plankto...
When I dived in different oceans, I was surprised to see the same fish (most popular ones). It's hard to imagine the same on land. Finding a niche is much easier on land, especially in mountains.
Mountains are like smaller caps - there is a lot more alpha, higher volatility but opportunity size is only a fraction.
Would be cool to make a procedural rendering of the financial markets as a landscape/globe map. "Got a cold front blowing across the tech sector today"
Not true at the extremes I say because pelagic ecosystems have small single cells handling their primary productivity, you have microscopic copepods starting the grazing at the same size as the smallest herbivorous insects, and until recently you had stellars sea cow weighing in at 8-10 t, more than an African elephant.
And some of the algae and the predators even gang up on the zooplankton: https://en.m.wikipedia.org/wiki/Zooxanthellae
There can be an impressive degree of niche partitioning in somd marine habitats though!
You're over simplying it because you think the oceans are more complicated or something.
if you ignore all the non mammal life...
and even considering only mammals, that's only a fraction of the food chain
for example: boars or rats
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.
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)
> 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.
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
After the mother of all extinctions, it would be a field epoch for the scavengers.
The terrestrial food chains information is just incorrect. Fungi are absent in that description. Insects are eaten by countless prey species, apex predators have multiple trophic levels below them. There are countless insect, fungal, and animal carrion feeders.
A post that is so factually inaccurate should not be so upvoted. We shouldn't meta comment, but the rapid decrease in submission and comment quality on Hacker News is really a problem.
And the fact that land animals evolve to marine lifestyles is just expected, oceans are more than 70% of Earth's surface. The lack of marine, pelagic animals is notable in that sense.
Come to think of it, I talk to a lot of five years olds which has definitely impacted how I approach topics.
First, sea life bounced back faster than expected, not faster than other life. Sea life is believed to have been disportionately impacted by the P-Tr extinction phases. Plenty of terrestrial life survived the extinction period. Unless you or anyone else knows better, the worst impacted was on marine life that relied on calcium carbonate. Lots of life survived this extinction event, terrestrial and marine. This paper is not comparing terrestrial and marine recovery rates.
Second, the statement about terrestrial food chains is not simplifying, it is reductive to the point of being incorrect. What does an earthworm eat (or other annelids)? How many trophic layers are present in soil microbiomes? Terrestrial food chains are wonderfully deep and complex, even if marine ones are moreso. You don't have to detract from one emphasize the other. That reduces peoples' understanding.
Third, life originally evolved in marine environment, and migrated to land. Life evolves back and forth between the marine and terrestrial over time. Both are great, and life particularly likes the boundary. Saying "land animals keep going back to the ocean" ignores parts of the story, and also reduces peoples' understanding by giving an incomplete picture.
A good example of "simplify[ing] something and retain[ing] the essence of a valid point" is a wonderful thing, but I have have sincere issues with the degree of simplification and retention here.
2. I replied to the comment to point out that it was a slight exaggeration but directionally is correct. I took it to indicate exactly that, a comparison between length of food chains in either domain. And mentioning complexity among sediments and annelids among them doesn't change that because ocean has very similar and complex communities (and annelids assemblages). I doubt anyone came away from that message thinking that there really are no predators of predators on land but I could be wrong. Really, after intially replying about the shortcoming of the answer, after reading replies I was then left wondering what the commenter did wrong.
I dunno, I'm an ecologist and reasonably familiar with trophic ecology so I suppose it's possible the comment comes across as more misleading than I think to others, (maybe I'm filling in the gaps without realising it)
3. Life does keep coming back to the ocean. Sure there were separate emergences from it, but take tetrapods - I am pretty sure the current understanding is just one event close to 400 million years ago? OTOH dolphins, seals, and manatees all arose from separate ancestors much more recently.
2. My biggest problem was with the level of reduction of terrestrial, not directionality.
3. That is a fair point, and I know you could have listed even more examples than just tetrapods. But the gills to lungs is also a much bigger step, and none of those examples have reacquired gills. So it comes back to the ocean, but with an asterisk.
My thanks for the stimulating discussion.
2. Yeah, since my first take before reading replies to point out it was exaggerated I reckon we don't fundamentally disagree. It has occurred to me since, the reason I probably saw this comment as useful is because while things are really way, way more complex as you've mentioned, when we seek to understand it, we usually do simplify things back down as far as possible while still capturing the essence of whatever aspect of the complexity. For example, simply calculating mean trophic level and simplifying organisms to a single number based on the average trophic level of what they eat [1] which enables modelling key aspects of the system [2]. Then you can do something like.. compare commonalities between a soil ecosystem, which may indeed have a three levels of consumers, to an African savannah. But you are right that it is important to consider a web and not a chain as the fundamental topology, but again if you want to look at one aspect, max lengths of the web, there's a good reason to pull out a single chain. For someone that can drown in complexity, I feel a debt of gratitude for people that have demonstrated when highly simplified models can capture aspects of trophic ecology.
Regarding point three, that's an interesting point. You might be interested in this recent study [3] that suggests that the purpose of gills was originally electrolyte balance, not gas exchange for respiration. If that's the case, terrestrial animals might not have the impetus to 're-evolve' gills. There's no right way to make a living in the ocean though, I reckon as soon as your lifecycle has no obligate terrestrial phases, you've made it.
Until next time, 10 y.o. 'throwaway' account!
[1] https://doi.org/10.1006/jmsc.1997.0280 [2] https://doi.org/10.1093/icesjms/fsr062 [3] https://www.nature.com/articles/s41586-022-05331-7
“ there is roughly 80 times more biomass on land than in the oceans. ”
The majority of animal biomass is in the oceans. the reason for the massive 80x disparity is the study cited by that reference was doing a census based on weight of carbon, and that figure is dominated by largely metabolically inert wood.
By biomass, primary producers in the oceans are indeed much lower, but energetic turnover of phytoplankton is very efficient.. imagine that anywhere the water is greenish it is full of photosynthesizers (and everywhere it is crystal clear as well).
In terms of biomass of non-plants, note that pelagic fish are so hyperabundant that ships with sonar thought they were the seafloor wikipedia.org/wiki/Deep_scattering_layer