How exactly does drought lead to a decline in biodiversity across ecosystems?

Drought leads to a decline in biodiversity across ecosystems through several interconnected mechanisms:

• Water scarcity reduces habitat quality: Many plants and animals depend on consistent water supplies for survival. When drought lowers water levels in rivers, ponds, wetlands, or soil, aquatic and semi-aquatic species lose habitat, leading to local population declines or even extinctions.

• Plant stress and mortality: Lack of moisture weakens or kills plants, especially those not adapted to dry conditions. This loss reduces food and shelter available for herbivores and species further up the food chain, creating a ripple effect throughout the ecosystem.

• Increase in competition and predation: As water sources dry up, animals are forced into smaller areas, increasing competition for remaining resources like water, food, and shelter. Predators may have an easier time catching weakened or concentrated prey, which can further reduce populations.

• Altered species composition: Drought-tolerant species gain an advantage, while less-adapted species decline or disappear. Over time, this shifts the makeup of the community, often lowering overall species diversity and simplifying the ecosystem.

• Disruption of ecological processes: Essential cycles, like nutrient cycling and decomposition, slow down when soil moisture drops and microbial activity declines. This affects plant growth and regeneration, impacting ecosystem stability and resilience.

• Fragmentation and isolation: When drought makes certain habitats unlivable, populations can become isolated in small pockets, making them more vulnerable to disease, inbreeding, and local extinction.

• Failure of reproduction and recruitment: Many amphibians, insects, and plants rely on wet conditions to reproduce. Drought can cause breeding failures, lower seed germination, and reduce the survival rates of offspring, compounding population declines.

These stresses rarely occur in isolation and often act together, leading to sharp reductions in the number (abundance) and types (diversity) of organisms in affected ecosystems. Some systems and species can recover after occasional droughts, but repeated or prolonged droughts can lead to permanently reduced biodiversity.