My go to example is if we lose insects which pollinate plants we would have a very very hard time growing certain foods. There is a certain unforeseeable complexity to these things.
Just a speculatory example, losing migratory birds could weaken the soil microbiome and seed biodiversity in the places they migrate to, from, and over. There could be a crop-critical organism in their path that relies on the regular influx of new bacteria or seeds from a certain place.
On what we have already removed: a building likely still stands if you remove 60% of the contents of the building, the last 40% is what is really holding it up.
Just a speculatory example, losing migratory birds could weaken the soil microbiome and seed biodiversity in the places they migrate to, from, and over. There could be a crop-critical organism in their path that relies on the regular influx of new bacteria or seeds from a certain place.
On what we have already removed: a building likely still stands if you remove 60% of the contents of the building, the last 40% is what is really holding it up.