Answer:
The fact that most eukaryotes reproduce sexually is evidence of its evolutionary success. In many animals, it is actually the only mode of reproduction. The genetic diversity of sexually-produced offspring is thought to give species a better chance of surviving in an unpredictable or changing environment.
In any ecosystem, there are factors to control populations.
In a stream, the predators of a certain organism will help keep populations checked. Moreover, the limited resources, such as space and food, will keep the population from growing out of control.
Answer:
Tropical areas are warm and wet causing for animals to want to hide essentially. Also there is a lot of cover for animals to hide in. Usually in tropical areas there are a lot of predators also, another reason for animals to hide.