How can a sudden change in an ecosystem affect it? include some natural events and human impacts. how can negative impacts be minimized?

It depends on the type of change, if it is environmental, let's say that a new predator was introduced into an ecosystem, the ecosystem would certainly see some figures of animals decrease.

Deforestation is an example of a human cause of disruption to an ecosystem. Deforestation can destroy habitats which, of course, decreases amount of specific animals as sometimes we even burn trees from the rain forest.

Another human cause includes human waste. Our waste can make ecosystems unbalanced.

For negative impacts to be minimised, we must stop things like deforestation and care more for the ecosystems and the environment.

I hope this helps.

the correct answer is: b. pantala flavescens, because these organisms would have a high level of genetic variation due to sexual reproduction.  

because involves two organisms (parents) whose genetic material combines, sexual reproduction leads to genetic variation in new generations of offspring. the offspring is an unique organism, with new genome, more protected with the higher ability to adapted. this process is fundamental to evolution.