Small changes have major impacts to an ecosystem.
A report revealed that noise can impact both plants and animals, changing the entire ecosystem they inhabit as a consequence. My town of Colchester can no longer afford the electricity for street lights, so they turn most of them off at night, which is a boon for wildlife, because artificial lighting impacts their natural cycles; the local rare glowworm population in Colchester will benefit.
Introduce a new cat into a garden and there will be an impact upon the local rodent and bird population, and a knock-on impact upon plants and animals related to the rodent and bird activities. Even the local cats change due to the new felid addition, changing the behavior as a result, which impacts everything else they interact with.
When much of the agricultural land in the UK is a desolate wasteland thanks to European rules many animals and plants suffer, bees starve. Ironically the love of the British for their gardens offer a refuge for bees and birds who might otherwise starve in the countryside. Grave yards, railway and motorway embankments undisturbed by humanity become the new homes of every refugee plant and animal.
I hope that one day my definition for sustainability: “action in harmony with nature,” is universally adopted and then implemented in all decision-making.