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Situation: A terrestrial environment on a megaworld (artificial construct). I'm thinking of how invasive species tend to dominate the ecosystems they move into--how about the ultimate invasive species?

The westbird really likes to go west. It has no territory, it is a parasitic egglayer so it doesn't need to nest. It is a soaring hunter by preference but it can live on vegetation if it has to. It keeps moving west so it's always moving into new territory whose local life isn't adapted to competing with that variety of westbird.

Given the size of the world pretty substantial evolution will occur before a given westbird's descendants complete a trip around the planet so they never actually return to an environment. Of course there are more westbirds but westbirds at a location at different times have no more genetic access than populations in different places normally do--thus they will be somewhat different, providing an ever-changing enemy for the local flora and fauna.

The weakness of the westbird is that it must be viable in all substantial environments because it will pass through them in it's eternal migration. Harsh environments will no doubt kill most of the westbirds that cross but the survivors reproduce rapidly when they reach a more hospitable place.

The big concerns I have are massive deserts (think what happens to a westbird that encounters a mega-Sahara) and large oceans (although I think this can be covered by making the birds not age so they don't die out when they hit water they can't cross in a lifetime.)

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  • $\begingroup$ f they are moving west that slowly then the local organisms will have plenty of time to adapt to them. basically you can''t have it both ways either they make a circuit so fast that everything will adapt or so slowly that the locals wll adapt, the real issue is how do they synchronize? otherwise they will be spread out everywhere as the travel at different rates. $\endgroup$ – John Jun 3 '17 at 3:41
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    $\begingroup$ @John Remember--they're on a construct, far bigger than any real planet could be. It could be a million years to get around it. And they don't really need to synchronize, there will be intermixing. It's to the bird's advantage to move promptly, though, so it gets the first crack at the new environment. Being slow is a disadvantage that will get bred out. $\endgroup$ – Loren Pechtel Jun 3 '17 at 4:05
  • $\begingroup$ I would say that those so–called invasive species do not tend to dominate ecosystems here on Earth. Rather, they tend to either displace aboriginal life, or fail with gaining a foothold. $\endgroup$ – can-ned_food Jun 3 '17 at 4:33
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    $\begingroup$ I agree with @can-ned_food - You are suffering from survivor bias. Imported species which don't out-compete the locals never get going. So it is only the successful species which get characterized as invaders. $\endgroup$ – WhatRoughBeast Jun 3 '17 at 16:25
  • $\begingroup$ if they aren't synchronized then they are all over a huge part of the planet, with some much further ahead than others, more than enough distribution for a selective pressure. As parasitic egg layers their offspring will also lag behind plus birds often evolve ways of dealing with parasitic egg layers like smashing their eggs, cuckoo get away with it becasue they stick around and threaten the host egg of the birds in question if the host does not take care of cuckoo eggs . $\endgroup$ – John Jun 4 '17 at 14:28
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My concern with the concept, if I've properly understood it, isn't the success of the bird itself, but more that no part of the planet would remain unaccustomed to them for long no matter what. Sure, a mega planet would take far longer to circumnavigate than Earth, especially for a small animal doing so via muscle power. Even so, it's still a round object, where moving west indefinitely will mean you come from the eastern horizon once more eventually. So no part of the planet, at least along the latitudes where this bird lives, would remain untouched by this bird for long.

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  • $\begingroup$ I realize no place will remain untouched. The thing is this is a rapidly evolving species, the next time it comes around it's going to be different. $\endgroup$ – Loren Pechtel Jun 3 '17 at 17:14
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    $\begingroup$ That's possible, but not a guarantee. A million years isn't that long on that scale. But your original question was COULD such a bird exist, which I didn't even answer, I'm sorry. Sure it could exist. Just its impact may be different from what might initially seem obvious is all. $\endgroup$ – Cereza Jun 3 '17 at 18:12
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If it keeps moving then it will impact perhaps harshly on local species but not for long. Local species will adapt unless your bird has some special abilities. It can't kill off the natives it needs them to look after it's eggs. It's continually moving into places it's not used to so locals will have an advantage. It doesn't take over nesting sites or physically endanger other birds, so it's impact won't be too bad.

Invasive species take quite a few generations to make an impact, normally they're in smallish numbers and take a few generations even on small islands. The reason they have an impact is THEY DON'T GO AWAY. They eat resources and take nesting sites.

But if you must then have the birds originate in a harsh arid landscape, because then they will evolve into very tolerant of environment birds with a high birth/survival rate in good times who will eat anything other birds will. They then have a good chance of surviving as a successful species, but I don't think they'll have the impact you are thinking of.

Some butterlies like the ones in this link migrate for generations before returning to their place of origin, they don't really make an impact that much except briefly.

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    $\begingroup$ I'm not thinking of it having a substantial impact on the local life because it doesn't stick around. $\endgroup$ – Loren Pechtel Jun 3 '17 at 17:21
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Yes, it is possible.

You state your world is an artificial construct. A little background first: For reference, Jupiter has an equatorial circumference of about 273,000 miles; migratory birds will typically fly 160 miles a day; which means they would take about 1706 days to circumvent Jupiter; about 5 Earth years. A 2 million year circumvention would require a circumference of 116,800,000,000 (117 billion) miles; implying a radius of 37,178,594,706 (37 billion) miles. So 10 times the distance of Pluto. About 55 light hours.

Just to be clear from an engineering perspective, you are talking about a large object; even in just a Dyson ring form likely requiring more mass than we have in our solar system, and so far from its parent sun I question its utility. Either that, or your westbirds cannot manage more than a few miles a day; which makes them implausible, even a migrating Monarch butterfly can cover 25 miles in a day, without wind assistance.

Given your figures I infer an advanced level of technology, and given that, absolutely no reason for your construct to have deserts, oceans, volcanoes or anything else your westbirds cannot cross.

Even if this construct has been abandoned by the original engineers for millions of years (to allow for evolution), migratory patterns are themselves subject to evolutionary pressures, which can include avoiding flying over landscape that can kill the migrants: Landscape without food or fresh water, or landscape with no place to rest.

But birds can stay aloft for six months; it is certainly plausible for your westbirds to double something we actually know exists IRL.

Another adaptation you could implement is live birth, instead of eggs. I don't think that makes it a non-bird; it is still a flying creatures with wings, beak, etc. Live birth would allow the westbird to skip egg incubation; just land and give birth. On Earth, many animals are on their feet within minutes of being born. Westbirds, instead of being born featherless and naked, could be retained longer by the mother and born ready to fly within a day; just dry out the feathers, experiment a little and off they go. Like some animals, you can have the Westbirds able to delay birth by a week or two, in order to find a suitably safe place to do it.

I think live birth would make them more independent and self-sufficient, a big problem when they are constantly entering new territory with new challenges, landscape, food, defending species and predators.

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  • $\begingroup$ Yeah, I'm talking a Dyson Sphere sized world. I don't think it's going to be able to go anything like 160 miles/day on an ongoing basis as it has to spend a decent amount of time looking for food. I definitely like the live birth idea, I was stuck on the bird notion and didn't think of different reproduction. And I'm thinking of a construct that has been around for ages with the creators long gone. $\endgroup$ – Loren Pechtel Jun 3 '17 at 17:17
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This scheme of the moving wave would work well initially for the westward. A successful invasive predator which is not super mobile tends to wipe out all local prey and then itself suffer a population crash (e.g. cats, mongooses). The continual movement of the westbird would hit the locals hard but then the westward moves on, allowing the survivors to repopulate. Oceanic predators do this - like tuna or dolphins. The idea of a wave of predators with a huge front is a good one too: the local prey cannot escape by moving laterally because the wave is so broad.

I think that the original westbird nest parasite scheme makes it a little trickier because you would wind up with multiple waves. Having mobile young who travel with the wave and are supported by parents/siblings is more workable.

Consider if the westbird were not just predators but omnivores. They eat everything. It could be like a perpetual world-circumnavigating plague of omnivorous locusts.

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