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People seem to be misunderstanding niches.
Topic Started: Jan 10 2016, 11:24 PM (3,935 Views)
revin
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A lot of speculation, especially in future evolution, tends to be justified as "this creature is filling this niche because the previous holder has gone extinct." The thing is, niches do not "want to be filled." Most important of all though, some people do not seem to understand the concept of a niche, and in combination with the previous misconception, this leads to excessive convergent evolution. So, I'm going to write up a brief essay which I hope will clear up a few things.

Firstly, there is no such thing as a morphological niche. Just because lizards look like salamanders does not mean they fill a similar niche, nor could one fill the other's niche if the other goes extinct. Lizards are (usually) terrestrial animals that can survive in harsh deserts, while salamanders are semiaquatic or fully aquatic animals which need lots of moisture to survive. That may seem obvious, given that salamanders partially breathe through their skin and undergo metamorphosis, but this sometimes translates to creatures which are physiologically similar as well. Often times, in fact, creatures in a similar niche look and act entirely different.

Here's a good example. Aardvarks and anteaters are an excellent example of convergent evolution. They look so similar, yet they are unrelated and live on opposite sites of the Atlantic. But what unites them in their niche is not their form, but their place in the food web. They both feast on ants and termites and are preyed upon by big cats. While their form is strikingly similar to the point that most people do not know the difference between the two animals, this really is just a side effect of their ecological relations.

Okay, so now say aardvarks go extinct. What can fill their niche? It must be done fast, otherwise there will be too many termites, and… Actually that's not a big deal. There are so many termites in Africa that aardvarks do not significantly reduce their population. There is enough food for termites to survive without aardvarks preying on them. And plus, termites eat dead plants, so there's nothing alive below them in the food web for them to affect.

All evolution should be understood in the context of two things, and two things only: natural selection and mutation. All other sub-theories of evolution, such as the filling of niches, derives from these things. Nothing needs to fill the niche of the now extinct aardvarks. Certain animals could do so if it benefitted their survival, but it's not necessarily to fill niches. But say that mongooses experience a population surge for some reason and some need to become specialised to eat termites in order to get enough food to survive. They don't need to evolve ridiculous snouts, equally strange claws, and a gigantic tongue.

Remember, natural selection is not survival of the fittest, but rather survival of the fit enough. If mongooses can find enough termites to survive by simply evolving slightly longer claws, then that's fine. They don't need to become like aardvarks if they are to "successfully" fill the niche. The point is, now these only slightly changed mongooses are in the same niche as aardvarks.

The main things to take away from this are:
1) Niches reflects food web relations, not morphology;
2) They don't need to be filled; and
3) If a niche is refilled, it is a result of natural selection and not of some strange tendency to fill gaps in the food web because they're open.
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Monster
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I've pointed this out before (several times on forum and in chat), but still see people talking about "{x species} niche" and demanding/insisting that it needs to be filled.

Also an idea that all possible niches will always be filled by something, and quick! This is demonstrably untrue, look at the world today and you'll see a number of potential niches that are either vacant or just don't exist. The vacant ones - why hasn't anything evolved to fill them, or replace whatever last did if this is the result of a recent extinction? If they are set little spaces that create a vacuum when empty then would we not see something immediately taking advantage? But we don't! They remain unexploited. Sometimes things make a move...sometimes nothing does...sometimes it might mean the creation of a different potential niche. Crabs on Christmas Island - apparently those huge crab swarms are possible because the native rodent population has been removed, thus freeing the crabs from their predations. So there's apparently an open 'rodent niche' and what's moved in? Nothing, that's what, nothing is currently trying to be the new Christmas Island rat. Instead we suddenly have a new opportunity for crabs to be crabs en masse. Crabs didn't start behaving like rodents even though they actually probably could have a go at it.

Finally this idea of only being able to have one of each sort of animal existing in the same time and place because of 'competition' comes down to the idea that there's a finite number of niches to be filled. It can't evolve because it will be outcompeted/would be competing with X, people cry. And in the next thread over they'll talk of something being extinct because it was outcompeted - something that they just said could not happen, because apparently evolution avoids competition at all costs and this thing shouldn't have even existed in the first place! First - competition does happen and that's how something can be outcompeted at all (modern African lions compete with spotted hyenas, cheetahs, and wild dogs with really profound and measurable effects on behaviours and population dynamics of all four - they all still fill distinct niches but there's a lot of overlap), second it doesn't always mean it is direct and exclusionary and bound to lead to the extinction of one or the other party. Niche partioning, it is a thing.


I think people hear talk of niches and imagine them as being both set and predetermined, when as you point out they are neither. Same as with species - species are not constant but I suppose people have trouble imagining the world changing in such ways unless it all happens at once (relatively speaking) in some sort of dramatic faunal turnover event.
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LittleLazyLass
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Wasn't there something in tet zoo article once about two different bird species in the same place that had evolved to fill exactly the same niche, prettymuch? At least with smaller fauna, more than one thing can be doing the same thing, nature doesn't have some "taboo" (because it can't have taboos, but that's another can of worms) about that, at least as long as the environment can support them. If the environment can't support both, who knows, maybe they both go extinct!
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Quote:
 
Wasn't there something in tet zoo article once about two different bird species in the same place that had evolved to fill exactly the same niche, prettymuch?


From what I've seen--which is limited--the answer from Gause's law is that "close enough" isn't good enough, it has to be exactly the same. So if one bird species forages for food in the tops of bushes, and the other forages in the lower layers of bushes, they're different niches.

Quote:
 
At least with smaller fauna, more than one thing can be doing the same thing, nature doesn't have some "taboo" (because it can't have taboos, but that's another can of worms) about that, at least as long as the environment can support them.


My understanding of ecology is that populations grow until they reach a constraint that keeps them from growing any higher. So there can't really be enough to support them indefinitely. This could be mistaken, though.

The thing to remember when talking about speculative evolution, though, is that we're working on an evolutionary time scale. So while eventually two species that exploit the environment in the exact same way might have one have to either partition or go extinct, in the "snapshot" of a project that isn't so.
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flashman63
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It basically falls under the assumption that nature wants something, and that evolution is a concious force. Evolution isn't hard and fast, it's what just so happens to happen.
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It's kind of like the "rule" among fantasy mapmakers that rivers never bifurcate. Of course they do, but it's rare and you've got to understand the conditions that lead to it and how it's likely to evolve in the long term (in bifurcating rivers one side usually dries up eventually). The same goes for competing species in a niche.
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Monster
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So if one bird species forages for food in the tops of bushes, and the other forages in the lower layers of bushes, they're different niches.


Yeah, another thing people tend to do is underestimate how narrowly defined a niche can be. Again, though, it isn't unrealistic for two things to try for the same niche. I wouldn't say it was the norm because in most environments there are so many things that could be done, but it can happen.

Quote:
 
So while eventually two species that exploit the environment in the exact same way might have one have to either partition or go extinct, in the "snapshot" of a project that isn't so.


Yes, exactly. While creating a whole world with numerous creatures (because it's always 'creatures' here, not plants, hah) all doing pretty much the same thing is both dull and lacking plausibilty, having scenarios which show strong competition between species is not necessarily so. If the creator can describe the effects well, it isn't necessarily bad. Preferable to a world in which everything is somehow all harmonious and balanced and competition is limited to predator-prey or intraspecies stuff.
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That said, ultimately different species can occupy exceptionally similar if no entirely the same niche (see for example his answer to my question on how multiple Early Cretaceous dolphin analogues worked together), so as long as there are enough resources there can be a high number of functionally similar animals.
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Okay, so now say aardvarks go extinct. What can fill their niche? It must be done fast, otherwise there will be too many termites, and… Actually that's not a big deal. There are so many termites in Africa that aardvarks do not significantly reduce their population. There is enough food for termites to survive without aardvarks preying on them. And plus, termites eat dead plants, so there's nothing alive below them in the food web for them to affect.

An example that has recently evolved would also be the aardwolfs, is a species of hyaenid, completely adapted to an insectivorous diet, but this is not occupying or filling niche, but taking advantage of the food source. There is no competition with Aardvark either, although aardvarks are a little older and have established there more that aardwolfs.

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I think this might help out here

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Something that really annoys me is when people seem to think that in the future a single group will hold a single niche. For example, say somebody decided that in their project seals will become the new filter-feeders in the future. Now look at the present day. Marine filter-feeders include:
Various fish
Various sharks
Crabeater seals
Balleen whales
Manta rays
Maybe even a few others that I've forgotten
It is very rare for a single animal group to hold a single niche. Multiple animals can inhabit the same niche, just in a different location or with a very slight variation.

Sorry, rant-mode deactivated. I just wanted to be clear with those who tend to make the erroneous assumptions I mentioned above.
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LittleLazyLass
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Quote:
 
So if one bird species forages for food in the tops of bushes, and the other forages in the lower layers of bushes, they're different niches.
I don't know, that seems like one of those behaviours that over-generalizes. Like, on an individual level, is one species really specifically feeding at the top of bushes? Bird gotta eat man. He don't care about no rules.

This almost seems like another case of man trying to put things into boxes when nature is so fluid.
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Depends. Gouldian finches and other timid birds will only forage on ground when in a large group even with different species, mostly because there will be a couple "Sentry" birds on the look out while the other feeds. (I don't believe this has much to do with niches, I'll say something about niches after this)

Most birds just generalize in areas they feed in, but they do have "favorite spots" to feed or sleep, etc... (But it has to have the food they are looking for. Imagine penguins going into african grasslands looking for fish! I don't think this has to do with niches, does it?)

You can have many different animals in that niche or take advantage of said niche in the same area, but as most/all of you know, there is a huge difference between taking advantage of a source and "filling in" a niche. But if there is too much competition for such niche, ONLY ONE WILL TAKE THE THORNE! HAHHAHAHAHA :evilsmile: I'm being too silly for this topic... :glare:
Edited by Steampunk FireFinch, Jan 13 2016, 08:18 AM.
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It's true. There aren't many animals out there that wouldn't raid a bird's nest if they could get away with it.
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