Re: What would be a good science lesson with the theme being communities?

I would recommend exploring activities involving animals which live in 
communities. For instance ants or bees have highly organised communities 
with the insects adapted for the specific role they play in the community : 
worker, drone, queen etc. I’m sure you will be able to find information at 
a suitable level about bees.

It is quite simple to set up a formicarium (ant house) in a glass sided or 
plastic sided tank for your pupils to observe how ants set about their 
different tasks - in England you can purchase specially designed "ant 
houses" and even "ant towns" from school scientific suppliers such as NES 
Arnold and Philip Harris. The cheapest are about $20.

If extension work is needed you could move on to mammals - most  herd 
animals display organised social roles - leader, guard, child minder etc. 
and groups of primates have complex social structures.

Good luck.