Ask Mao Zedong – he knows best.
During his crazy reign in the ‘60s & ‘70s, he had some brilliant ideas.
In addition to erasing Chinese culture & to sacrificing big chunks of the population, he wiped out the sparrows of China. During the Four Pests Campaign of 1958–1962, the population was ordered to kill following pests: mosquitoes, rodents, flies and sparrows.
The first three of them are somewhat reasonable, as they are carriers for really nasty diseases – e.g., malaria and ‘the Black Death’. The sparrows were hated, because they picked the seeds after the peasants had sown the fields.
Logically, killing all the sparrows equals higher yields, right?
Let’s do it.
Mao: 1 – Sparrows: 0
The people actually hunted the birds by all means. Peasants made a constant noise around trees, to prevent the small birds from landing. The exhausted sparrows just fell down to the ground after a while, as they couldn’t find safe places to rest. It is estimated that 2 Billion of them were killed in a short time.
Mao: 2.000.000.000 – Sparrows: 0
With the sudden extermination of the species, a never-seen problem arose.
Indeed, the sparrows were eating a part of the seeds. But, what they actually ate the most were insects – e.g., grasshoppers. After the peasants rid the sparrow overnight – a natural predator –, the number of grasshoppers exploded. Billions of them swarmed over the fields & destroyed whole harvests with their immense appetite.
A biblical punishment for dumb decisions.
The crops were bitterly needed during the Great Leap Forward. People were already starving, due to man-made famines. An estimated 20–40 million persons died. The Grasshoppers made things even worse. It took years to control this special (gu)pest.
Even today, the sparrow population hasn’t completely recovered.
As you have seen, the disappearance of a single species causes years of famine.
Just hope that your scenario never ever happens and be nice to sparrows
Sparrows: WIN – Mao: T.K.O.
Mao. That escalated quickly.