The land is covered in structures of green coloring. Some look like igloos and some have veins pulsating and moving slowly with membranes which seem to almost be breathing the way lungs do. Some of these structures seem to be not yet completed, growing like a tree grows from a root. They are spreading. All the animals in the land have gone, and the last travelers to find this island by mistake have gone forever too. Some of the structures look like mystical machinery cutting down forests and reshaping the landscape - just machines, but alive.
Millennia, or probably millions of years ago something crashed on earth. It seemed like a ship, but before landing it divided releasing a smaller piece of metal in the air. That piece was falling more slowly and the impact made almost no damage. The rest of the ship crashed in another part of the world. Nothing happened for a long time. The metal was just lying there. If there ever was something alive inside it must have stopped being alive for a reason.
Out of nowhere something triggered the piece of the spaceship and it opened its shell, revealing pieces of technology covered in an overgrown root system. Those roots slowly traveled outwards and colonized the island.
An alien was the sole ship member in a spaceship which crashed on another planet. The alien died suddenly, never showing any symptoms to warn for what was going to happen. The emergency system was activated forcing the Alien into a healing pod but as the entire spaceship was crashing the healing pod had to eject itself to avoid further damage. Nothing could save the alien but something survived inside the healing pod. It was a seed. Almost all of this alien species had those kind of seeds - they were engineered to grow into a small house capable of harvesting water and food in times of extreme dangers. For some reason the seed never stopped growing. It wasn't supposed to turn into anything more impressive than a small shelter yet it overgrew and took over an entire island.
The changed, mutated seed is doing something to the wildlife, which includes the travelers too. But what is happening to the victims? Are they turned into farm animals? Maybe composted or used for raw materials? The goal of the seed is to grow and expand as much as possible and fortify its chances of survival for as long as possible.
How would such an entity use animals for their goal in the most efficient ways possible?
This is not a story based question as regardless of the reason, the plant will still behave the same way. Any answer to this question will not change the story but merely the details in which the seed functions. See it more as an evolutionary behavior question about the efficiency of life. A seed that is not efficient would not thrive but die, therefore whatever the goal of a life-form it must achieve it in the most efficient manner possible otherwise it will not survive for long.
This is more of a mathematical question about biology than an opinion or story based one.
-The seed can do whatever a self sufficient hyper technological computer can do and more; improve itself, sustain itself, protect itself and repair itself.
-Whether the seed is conscious and sentient depends on your definition of consciousness. To some people, consciousness is an illusion created by intelligence; to others it is the result of intelligence and some even believe it comes from the soul, something separated from flesh. I'm not here to answer that question. If you have to believe the seed is more than a calculating machine made of bio matter, something conscious then you are free to do so in your answer.
-The seeds were mass produced and given to all the members of that alien species. They are not supposed to grow in that colonizing manner and such ''mutations'' have never been seen. Truly nothing is impossible but this was the most unlikely of events.