Ecosystems are too biodiverse to respond to human-caused threats.

Natural selection cannot keep up with the constant human-caused threats.

Evolution tends to occur more rapidly while under stress.

Newly introduced species almost never thrive in unfamiliar ecosystems.

All of these answer choices are correct.

Evolution tends to occur more rapidly while under stress.

Explanation:

When a condition decreases the fitness in the population directly or indirectly, it is called as a stressful condition. Due to the stress the population faces some kind of threat and usually the number of organisms in population also starts to decrease. Such threats favor evolution because organisms try to adapt to the new condition and survive. In absence of any stress there would be no need to change and hence evolution would also be slow.

For example, after antibiotics discovery posed a serious threat to bacteria, many bacterial species evolved to be antibiotic resistant. In the stressful conditions of desert, many plant species have evolved to have fleshier stems and leaves reduced as spines to prevent excess water loss.