can't succeed first challenge

How did you set up your ecosystem? From memory, the point of that challenge was to try and satisfy the hunting requirements of the 2 blue cat creatures you start with. So you need enough tier 2 creatures so that their reproduction rate matches the cat's hunting rate, enough tier 1 creatures to feed the tier 2 creatures you added, and enough plants to feed the tier 1 creatures. I think I ended up creating 4 tier 2 creatures and 8 tier 1s. You can work backwards to see exactly what you need.