That's very vague. Collapse how? According to other comments we have already remove 60% of species, why wasn't that enough to cause a collapse. Other species take up the slack left by those removed.
https://en.wikipedia.org/wiki/Ecological_collapse
Let's look at it from a different perspective though. If thousands of scientists are wrong and we improve the environment but there was never any danger of human extinction then we still end up with a more enjoyable planet. If thousands of scientists are right and we don't improve the environment then we all die.
Seems like a pretty easy decision to me.
No pollination means many fallow meadows and dead plants.
This means either weeds spreading or top soil depletion.
This also means many crops we depend on will not survive because various helper species aren’t available.
Earthworms dying mean no areation of soil, or the impact of other insects to improve the eco system.
So no those other species aren’t taking up the slack as you put it. Wasps aren’t interchangeable with moths for example.
But I too want to understand better how far this collapse impacts human beings.
- Commercial bee populations aren't declining. (There has been an increase in Colony Collapse Disorder, but lost colonies are replaced and total bee population hasn't declined.)
- The vast majority of the world's food supply does not depend on pollination from insects. To quote from https://en.wikipedia.org/wiki/List_of_crop_plants_pollinated...:
> The most essential staple food crops on the planet, like corn, wheat, rice, soybeans and sorghum, need no insect help at all; they are wind-pollinated or self-pollinating. Other staple food crops, like bananas and plantains, are sterile and propagated from cuttings, requiring no pollination of any form, ever.
- None of the crops that require pollination from insects are essential to human survival. It's hard to see how their loss could lead to our extinction.
- Crops can be pollinated by hand or machine.
- Crops can be propagated without seeds.
- Crops can be grown in all kinds of unbelievable conditions. Crops can be grown without soil. They can be grown in space stations, completely isolated from Earth's ecosystems.
- Extinction is a very strong claim. To support it, it wouldn't be enough, for example, to show that 90% of the population would die off, leaving 750 million people. They need to propose a mechanism by which all humans would die.
Fertile soil is not just dirt. Talk to a soil expert and you'll find out very quickly how difficult it is to keep soil healthy, especially if you punish it every day with pesticides and herbicides. See you long you can maintain production if you don't have a support system of insects, arachnids, worms, fungi and so on. You'll end up with just dirt. Nothing grows in just dirt. You can try to keep up production by downing it in fertilizer, but in the end you'll just prolong the inevitable; loss of crop and collaps of production.
See how many humans you can feed by growing crops in space stations. See how long you can maintain a closed ecosystem in space.
To your last point; if you lose more than 30% to 30% of the productive workforce, you can kiss human civilization goodbye; our manufacturing is highly de-centralized, but heavily interdependent and without safety buffer.. Our infrastructure is wide-spread and needs tons of maintenance. Lose enough people and it all comes crashing down, leaving the survivors with broken machinery for which they don't have energy, don't have the knowledge to operate let alone repair if (not when) they stop working. They will also have to deal with all the poison and radioactive fallout from all the fission reactors that experience core-meltdown because nobody's around anymore to power them down over the period of ten years.
Don't kid yourself; saving what's left of this earth's ecosystem is the only shot we have. There's not techo-utopia down the road to carry us to eternity and the heat-death of the universe. Its you and me and the rest of us puny humans that will have to do the saving.
Say plankton dies off, say animals eating plankton die, say humans eating those animals now have less food. Say all the fish die and we are reduced to land-based food. Now we have more space competing for farm land, we have to clear forest. Clearing adds to CO2 emissions, construction, more emissions, less CO2 being taken out. It's clear how this is all one giant feedback loop. Less biodiversity, more overabundance of something else, which leads to less consumption of something else which leads to collapse of ecosystems which leads to use trying to patch things up and doing even more harm.
Just zoom out and think about things that consume things and how that loops back directly to humans, environment, overproduction, overuse and eventually unsustainable usage of resources until there are none left.
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.