Which of the following are pioneer species?beaverslichenszebra musselswolves and mountain lionsaspen trees

Pioneer species are the first species to colonize previously disrupted or damaged ecosystems. They are hardy species which are the first to colonize barren environments or previously biodiverse steady-state ecosystems that have been disrupted.

From the list you provided:

1. Beavers: Beavers are not typically considered pioneer species. They are known for their ability to modify environments, but they do not usually colonize disrupted or damaged ecosystems.

2. Lichens: Lichens are a classic example of pioneer species. They are often the first organisms to colonize rocks and can survive in harsh conditions.

3. Zebra Mussels: Zebra mussels are invasive species, not pioneer species. They can dominate new environments, but they do not typically initiate the process of succession.

4. Wolves and Mountain Lions: Wolves and mountain lions are not pioneer species. They are apex predators that come into an ecosystem once it is well established.

5. Aspen Trees: Aspen trees can be considered pioneer species in certain contexts. They are often one of the first trees to grow back after a forest fire, for example.

So, from your list, lichens and potentially aspen trees would be considered pioneer species.