Affiliate Marketing Secrets

Im a bit confused about these questions and would very much appreciate it if you could help me out a little bit please?
Thanks!
1. Succession
In 1908, a meteoroid or cometary body exploded above boreal forest of Tunguska in central Siberia, resulting in the largest impact event over land in Earth’s recent history. How might succession have differed after this event compared to a forest fire in terms of succession type and the timescale of reaching a climax community?
2. Niche
A realized niche describes the niche occupied by an organism in the presence of other competing species.
True/False
3. Genetic variability & evolution
(a) Why does evolution require the presence of genetic variability?
(b) Why is genetic variability not sufficient for evolution (i.e. what else is needed for evolution to occur)?
4. Convergent evolution
Convergent evolution can be found when two separate and distinct species evolve similar traits as a result of adaptation to selective pressures from similar environment. Find an example (not mentioned during class) of two species that followed convergent evolution. Justify your answer giving the name of both ancestor species and why you consider they are a good example of convergent evolution.
5. threats to biodiversity
(AM) What are the 4 of the most important threats to biodiversity? List them in descending order of importance.