The most important reason for biodiversity loss in today’s age is

The correct option is fragmentation and habitat loss.

Biodiversity loss is driven by several human-induced factors, collectively referred to by ecologists as the "Evil Quartet". These four major causes are: habitat loss and fragmentation, over-exploitation, alien species invasions, and co-extinctions. Among these, habitat loss and fragmentation is recognized as the primary and most destructive driver of species extinction in today's age.

1. Habitat Loss:
Direct destruction of habitats is the most significant threat to wild species. The most dramatic examples of habitat loss occur in tropical rainforests. For instance, the Amazon rainforest—often called the "lungs of the planet"—once covered more than 14% of the Earth's land surface, but cover has been reduced to less than 6% due to clearing and burning for agriculture, soya bean cultivation, and cattle ranching.

2. Habitat Fragmentation:
When large, contiguous natural habitats are broken up into smaller, isolated patches due to human activities such as road construction, urbanization, and agricultural expansion, it severely impacts ecological balance. Mammals and birds requiring large territories, as well as animals with migratory habits, are the most severely affected because they cannot survive or breed successfully in confined fragments, leading to rapid population declines.

Comparison with other factors:
While over-exploitation (excessive harvesting of species), alien species invasions (introduction of non-native species disrupting local ecosystems), and co-extinctions (loss of dependent species) are critical threats, they generally affect specific targeted groups or locations. In contrast, habitat loss and fragmentation universally degrade entire ecosystems, making it the single most important cause of biodiversity loss globally.