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I have a world that has unexpected lifeforms detected. There are to-be-revealed reasons for it, but the way the ecosystem is set up is:

  • Microbial life is abundant everywhere
  • There is a single species of plant form that has colonized the land
  • There is a single avian species that feeds on those plants

The rest of the life exists in the oceans, in which significant biodiversity exists. I am willing to change things slightly so that, for example, near the shorelines there is more land-based biodiversity if the planet itself seems completely unrealistic.

What would the consequences be of such an ecosystem? At the very least it would be extremely susceptible to microbial disease, since it's basically a planet-wide monoculture. What rules would have to exist on that life to work? I can imagine that the life should only exist at a certain latitude range, but is there anything else?

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  • $\begingroup$ No intermediate-size life like arthropods? $\endgroup$ – PatJ Nov 8 '16 at 16:18
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    $\begingroup$ The idea behind the story is that there is a race of aliens that "preserve" things. Their motives aren't exactly known (that's just me saying that I honestly have no idea why at the moment, and they're about a dozen chapters away from being revealed :-) ). I was hoping for something like "this is highly unstable" in the answer below, because it would give the aliens something to preserve, namely the unstable ecosystem. $\endgroup$ – Michael Stachowsky Nov 8 '16 at 16:21
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    $\begingroup$ It's generally discouraged to accept an answer within 30 minutes of posting a question. Doing so may discourage other, possibly better answers. $\endgroup$ – Frostfyre Nov 8 '16 at 16:23
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    $\begingroup$ When you say, "One species," how diverse can that species be? Generally speaking, of one animal can breed with another animal and produce fertile offspring, they're considered the same species. So, while there are many dogs in all manner of shapes and sizes, they're all "dogs". Exactly how diverse are your birds and plants? $\endgroup$ – Azuaron Nov 8 '16 at 17:09
  • $\begingroup$ That's an interesting question. I believe that the way I want it to work is as follows: if a specimen is taken from one side of the planet and another specimen is taken from another, it is not possible to determine where they each came from. $\endgroup$ – Michael Stachowsky Nov 8 '16 at 17:16
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This would be highly unstable.

You already mentioned susceptibility to disease but there are many other things such as drought, flooding, etc where variety leads to survival.

The main thing though is that your two single species would immediately start to specialize. Some plants would be in wetter or dryer or warmer or colder areas, they would adapt to those environments. Some birds would become heavier and take to the ground, others would fly further. Some birds would become predators, others prey.

It would take time, thousands, even millions of years, but the process would begin immediately as the original forms exploded out to fill every available niche in the biosphere.

For the short time it did match then yes, you are right. The plants would be limited to a certain terrain and conditions. Salinity, Ph level, sunlight, temperature. Can they survive frost? The birds would then only live where they could feed on the plants.

The birds would either need to store food/hibernate/migrate over winter or the plants would need to be active year-round.

With the lack of predators the bird population would tend to explode until they ate all the plants. The plant population would then collapse, the birds would starve to death, and the plants would regrow. This population boom-bust cycle would repeat every few generations.

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  • $\begingroup$ Also remember Obligate Herbivores are an extreme rarity in nature. Generally herbivores limit themselves to a plant diet not because of an inbuilt preference but because they lack the ability to reliably and safely take down and kill the much more energy dense food source of meat. Most herbivorous species such as cows or deer will happily consume meat when available to them (such as cattle eating chicks who wander too close or deer feasting on carrion they come across in the wild) In a predator free environment such as your world some of the avians will be more capable of killing their fellows $\endgroup$ – Neberu Nov 8 '16 at 18:50
  • $\begingroup$ Those members who are able to and adapt to cannibalizing will see a huge advantage in survivability due to a more energy dense food source and will trend to larger size and increased aggression, essentially becoming, over time, more predatory. This activity might actually mitigate the collapse of the S curve described in Tim B's answer but only if it happened quickly and across a wide enough spectrum of the species. The adoption of behavior such as this would be dependent on many factors such as the natural behavior and timidity of the original examples introduced. $\endgroup$ – Neberu Nov 8 '16 at 18:57
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Spoilers ahead for the Ender's Game series of books

One good model for the kind of non-diverse ecosystem that you are looking for is the planet Lusitania from Orson Scott Card's "Speaker for the Dead" (and further detailed in the subsequent novels).

On this planet there is an intelligent virus called the Descolada whose primary goal was to create a suitable ecological habitat for an alien race that meant to colonize it. The mechanism it utilized basically destroyed the DNA of most organisms, guiding the evolution of all life on the planet. This took a healthy, diverse ecosystem and over thousands of years whittled it down to a handful of planet-wide species. The ecology of the planet was thus forcefully placed into a rigid symbiotic lifecycle. Species spent their lives in stages. One such started out as bipedal mammals that spent their lives among trees. Once they were deemed mature, they were "planted" and became trees themselves. Those trees gave genetic rise to new mammals. Or bison-like creatures that have the grass they graze on in their life-cylce. The stability of the system was enforced by killing outside infuences (the planet was deadly for humans).

Without going any more into details, the main point I'm trying to make is that if you want a very low-diversity ecosystem, you may need to come up with some outside force shaping the genetic outcomes of the planet (solar radiation? I dunno).

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  • $\begingroup$ Turning mammals into trees? What kind of stuff are those aliens smoking? $\endgroup$ – Mast Nov 8 '16 at 19:49
  • $\begingroup$ enderverse.wikia.com/wiki/Pequeninos are really interesting. $\endgroup$ – rwfeather Nov 8 '16 at 20:06
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Earth has only one dominant species of animal life, including the oceans. You can have a look at the various environmental disasters and just scale them down a bit if your world's life doesn't also rule the oceans.

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