What would be the consequences of a world that has only one dominant species of non-oceanic animal life?

Question

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?

Answer 1

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.

Answer 2

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).

Answer 3

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.