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Explaining habitat choice?

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Old Friday 21st June 2019, 00:33   #1
melisande
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Explaining habitat choice?

Why is it that species which seem very similar choose different habitats? The species I am currently wondering about are the White Ibis and the Glossy Ibis. Here, in Florida, the Glossy Ibis is almost never found away from wetlands whereas the White Ibis is found almost anywhere -- in wetlands, but also in parking lots and everywhere in between. Their body plan (including the bill) seems almost identical and I imagine they either do or could take very similar prey. Then why this big difference in habitat choice? Or rather why is one species so restricted and the other not?
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Old Friday 21st June 2019, 23:41   #2
jurek
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There are two species precisely because they have different habitat choice. Usually, the ecology says, when there are two species with identical habitat choice, one outcompetes another to extinction. The situation can be stable when two specialize in different habitats. I guess originally Glossy Ibis had the upper hand, being super-adapted to wetlands which offer the biggest density of food.

After Man started creating new habitats, the situation became a bit weird: there suddenly appeared new habitats to which no bird was adapted. So in man-made habitats you can see generalists, usually coming from savanna-like habitat which humans replicate. Here White Ibis suddenly found itself better adapted.

Sorry, I don't know details of ibis anatomy what makes Glossy Ibis less able to feed on dry places than White Ibis.

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Old Wednesday 26th June 2019, 17:01   #3
nartreb
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>There are two species precisely because they have different habitat choice.

Not in this case - the two species have different geographic origins.

And in the general case, it's not necessary to occupy a distinct habitat in order to avoid competition. Wildebeest and zebra occupy the same prairies but don't compete much (in fact they help to preserve each other's niche) because they have different feeding habits.

Furthermore, if competition for food is the only source of rivalry, displacement of one species by another can be extremely slow, especially in slow breeders like ibis. Currently both species are increasing in US population at about 4% per year, so there's apparently no food shortage (nor nest site shortage).

However, I have no information about any differences in habit or anatomy of these ibis. Having spent much time in Florida, I can't say I've ever noticed one habitually in drier habitat than the other. ("Dry" is of course a relative term in most of Florida...) I did find a source mentioning that some white ibis populations have become very habituated to people - so maybe that's what you've noticed. Why glossy ibis may not have become as easily habituated to humans is unclear, but it's conceivable that its Old World origins exposed it to heavy human predation in the evolutionarily recent past.
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