Two interesting bits of information here. One is about the numbers of species at risk from extinction, and whether that matters. The other is how many species there are in our gardens.
One is an article about whether it matters that 21% of all mammals species are now at risk of extinction (http://www.iucn.org/about/work/programmes/species/red_list/review/)
It finds that species are not like the passengers in an aeroplane — you can lose a few but the plane flies on. Species are like the rivets that hold on the wings — you can lose a few and the plane flies on (so long as you don’t start trying to loop the loop!). But after a while, you reach a point where the loss of any species can cause the wings to fall off.
The article is here: http://www.newscientist.com/article/mg14319374.100-how-many-species…
The second piece of info is not an article but a website. How many species do you think there are in your back garden? 5? 12? 22?
A chap in East Sussex has been studying one square metre of his back garden since 2003, and has so far identified a staggering (to me) 700 species of plants and animals that live in or have visited that one square metre.
The link for that is here: http://squaremetre1.blogspot.com/