3.2 Human impact on biodiversity

Direct threats remove organisms; indirect threats change the conditions they need to survive.

Overharvesting, poaching and capture for the illegal pet trade remove organisms directly. Habitat loss, pollution, climate change and invasive alien species alter space, resources or interactions indirectly. Both groups can be human-driven.

Poaching kills elephants directly; road building fragments the habitat and indirectly lowers breeding success.

Direct if it kills them; indirect if it first changes habitat or food conditions. State the first effect.

‘Human-caused’ is not the direct/indirect distinction; classify the immediate mechanism.

Multiple pressures can amplify damage when the first one removes the ecosystem’s ability to respond to the second.

Trace pressure → lost function or diversity → weaker resilience → larger later impact. This is more than listing two threats side by side.

Overfishing simplifies a reef food web; later heat stress causes more severe bleaching because fewer functional groups support recovery.

The second impact is larger after the first pressure than it would have been in the intact system.

Two pressures are not automatically synergistic; show the mechanism that changes resilience.

Alien means outside its native range; invasive means the introduced population spreads and causes harm.

Follow arrival → release from controls → increase → impact mechanism → targeted management. Non-native status alone does not prove harm.

Introduced grey squirrels expand, compete with red squirrels and carry squirrelpox; control and habitat refuges target those pathways.

Harmful spread and a demonstrated ecological mechanism are also required.

Do not manage every non-native species identically; identify actual spread, harm and feasible intervention.

The International Union for Conservation of Nature (IUCN) publishes the Red List, which combines population trend, abundance, geographic range, breeding potential and known threats to judge global extinction risk.

Categories run from Least Concern (LC) through increasing levels of threat to Extinct in the Wild (EW) and Extinct (EX). Small or declining populations, narrow or fragmented ranges and low breeding potential raise vulnerability; Data Deficient means evidence is insufficient, not that risk is low.

A widespread species with stable numbers may be lower risk than a rapidly declining species with a small range, even if the latter is locally common.

Uncertainty about risk; prioritize better evidence rather than assuming safety.

A Red List category is a global risk assessment, not a direct prescription for one local action.

A status turns evidence of vulnerability into a shared priority signal, but the best action depends on threat, rights and feasibility.

Governments may fund protection or trade controls; NGOs may restore habitat or monitor; citizens may change consumption or report observations. Match the actor’s lever to the dominant pressure.

If habitat conversion is the main threat, a trade campaign alone is weaker than land-use protection plus local enforcement.

Actors have different powers, constraints, local rights and responsibilities.

Status guides priority; it does not dictate one universal intervention.

A conservation case is complete only when it links the cause of decline, ecological or social impact, intervention and evidence of the outcome. Compare different status pathways rather than treating every threatened species as the same problem.

For each case, keep action separate from success: a law is an intervention, while a measured population or status change is outcome evidence. Also trace consequences through food webs, ecosystem services, livelihoods or culture where the local evidence supports them.

Use the same chain for all three cases: pressure → decline → ecological or social consequence → conservation response → measured outcome.

Conservation effort is not automatically conservation success; status and population evidence must show whether risk actually changed.

A commons fails when each user captures a private short-term benefit while costs spread across the shared resource and community.

Trace private gain → shared cost → resource feedback → governance response. Rules work only if they cover enough users, are monitored and change incentives.

In a fishery, each fisher gains by catching fish before others, but combined harvest can push the stock below recovery. In an ocean gyre, each user gains convenience from disposable plastic while cleanup and ecological damage are spread across the shared ocean.

Users can gain by defecting while others restrain themselves; enforcement or cooperation must alter that payoff.

A commons is not ‘any public place’; the key is shared access plus an incentive that depletes it.