Human impact on biodiversity

Habitat destruction is the removal or severe damage of a habitat so it can no longer support its original species.

It occurs when individuals overuse a shared resource for short-term gain, leading to long-term depletion and collective loss.

Habitat fragmentation is when one large habitat is broken into smaller, isolated patches. The habitat still exists, but populations become separated.

Habitat loss, overexploitation, pollution, climate change, and invasive species are major threats.

Destruction removes the habitat completely or makes it unusable. Fragmentation splits habitat into smaller, isolated patches.

Direct threats target species directly (e.g., poaching), whereas indirect threats damage ecosystems as a side effect (e.g., habitat loss, climate change).

Overfishing can cause stock collapse and alter food webs, e.g. Atlantic cod declined dramatically due to heavy fishing.

Overexploitation means unsustainable use: take more than can be replaced.

An invasive species is a non-native organism introduced by humans that spreads rapidly and harms native ecosystems.

Human activity is the main driver, including habitat destruction, overexploitation, pollution, and climate change.

Overexploitation is using a natural resource faster than it can be replaced by reproduction or regrowth.

Habitat loss reduces available food, shelter, and breeding space, causing population decline and increased extinction risk.

Because individuals act in their own short-term interest while the costs of overuse are shared by everyone.

They disrupt ecosystem balance by outcompeting native species and altering food webs.

Edges are often hotter and windier (and can be drier), and may have more predators or invasive species.

Examples include deforestation for agriculture, draining wetlands for development, and clearing grassland for crops.

Poaching often removes breeding adults, so birth rates fall and populations decline quickly.

Fragmentation creates smaller, isolated populations, increasing extinction risk and making it harder to find mates.

If removal exceeds reproduction, population size declines. Once numbers drop too low, recovery becomes difficult.

Overharvesting and poaching are direct threats because they remove individuals from populations.

Removing organisms faster than they can be replaced breaks feeding links, reduces prey availability, and can trigger trophic cascades.

Overfishing, poaching, and logging of old-growth forests are common examples.

They may lack natural predators, compete strongly for resources, or reproduce quickly in the new ecosystem.

Removing top predators or key species can cause trophic cascades and change community structure.

They outcompete, prey on, or bring diseases to native species, causing population declines or extinctions.

Habitat loss and climate change are indirect threats because they alter ecosystems and affect many species at once.

Biodiversity is the variety of life, including diversity of species, habitats, and genetic diversity within species.

Smaller, isolated populations have fewer mates, lower gene flow, and are more vulnerable to random events.

Isolation reduces gene flow. Smaller populations are more likely to inbreed, lowering genetic diversity and adaptability.

It removes producers and habitat, so less energy enters the food web and fewer consumers can be supported, reducing stability.

Fewer individuals and species remain, so the ecosystem has less functional diversity and recovers less well after disturbance.

Overfishing in open oceans where no single country controls the resource can lead to stock collapse.

Small populations have lower genetic diversity, are more affected by random events, and may struggle to reproduce successfully.

Because without regulation, individuals maximise personal benefit, leading to overuse and depletion.

Removing organisms breaks feeding links, reduces energy transfer, and can trigger trophic cascades.

Without natural enemies, invasive predators can rapidly reduce prey populations and disrupt entire food webs.

By introducing regulations, quotas, enforcement, or shared agreements that limit overuse and promote sustainability.

Declining population size or catch per unit effort (more effort needed to get the same catch).

Because they change habitat conditions or ecosystem processes that multiple species depend on.

Use quotas or regulated harvesting so removal stays below replacement rate.

Poaching or overharvesting directly reduces population size and can push species toward extinction.

Old-growth forests may be cut faster than they regrow, reducing habitat and biodiversity for decades.

Direct impacts remove organisms or energy entry (e.g., habitat loss, overharvesting, pollution); indirect impacts change conditions or interactions (e.g., invasive species, climate change).

It reduces species richness and can cause local extinctions as populations lose space, food, and shelter.

Multiple interacting threats reduce resilience and make ecosystems less able to recover.

Edge effects are changes at habitat boundaries, such as higher temperature and wind, lower humidity, and more predators or invasive species.

Use buffer zones or increase reserve size to reduce the proportion of habitat near edges.

Overexploitation removes organisms faster than they reproduce, reducing population size and disrupting energy transfer in food webs.

Fragmentation isolates populations, limits gene flow, increases edge effects, and reduces overall ecosystem stability.

Name the threat, describe how it affects species or habitats, and explain the consequences for population size or ecosystem stability.

They directly harm native species but also indirectly alter ecosystem structure and processes.

When several pressures act at once (e.g., habitat loss plus climate change), recovery is harder and tipping points are more likely.

Because preventing decline is easier and cheaper than restoring ecosystems after severe damage or species extinction.

Amazon rainforest cleared for cattle ranching removes habitat for many species and reduces ecosystem resilience.

Wildlife corridors connect isolated patches, allowing movement, gene flow, and breeding between populations.

Fragmentation reduces gene flow and increases edge effects, which lowers population viability and biodiversity.

Sustainable management such as quotas, seasonal bans, protected areas, or selective gear reduces removal rates.

Overexploitation reduces population sizes, which can reduce species richness and lower ecosystem resilience.

Human activities often change ecosystems rapidly and commonly reduce biodiversity.

Human population growth and high resource consumption, combined with technology and global trade, allow rapid and large-scale environmental change.

Humans can change environments over years using machinery and infrastructure, act across regions via global supply chains, and cause damage that takes decades or centuries to recover.

Invasive species are non-native organisms that spread and cause harm to ecosystems, biodiversity, or humans.

Introduced for pest control → toxic to predators → predators die → toads spread rapidly.

An invasive species is a non-native species that spreads and causes harm to ecosystems, biodiversity, or humans.

They are poisonous, so native predators that eat them die, reducing predation pressure and allowing rapid population growth.

They often have few or no predators or diseases in the new ecosystem and can reproduce rapidly.

Common pathways include global trade (ship ballast water), travel, the pet trade, and intentional introductions for farming or pest control.

They often escape their natural predators, parasites, and diseases, so survival and reproduction increase.

Examples include ship ballast water, global trade, or the pet trade.

Ballast water introduction → rapid reproduction → clog pipes → filter plankton → disrupt food webs.

They remove plankton from the water. With less plankton, less energy is available to native filter feeders and higher trophic levels.

They can outcompete native species, reduce biodiversity, and disrupt food webs by redirecting energy flows.

They can outcompete native species for food/space and can prey on native species or introduce disease.

Define the term, name a pathway, then apply a case study (cause → spread → ecological impact on biodiversity/food webs).

Introduced for hunting → few predators + plenty of food → population explosion → overgrazing → habitat damage.

Humans introduce them, but the damage happens through altered species interactions (competition, predation, disease) that disrupt food webs.

Conservation status describes how close a species is to extinction and how urgently it needs protection.

The International Union for Conservation of Nature (IUCN) publishes the IUCN Red List categories.

Population size, population trend (increasing/decreasing), geographic range, and known threats are key factors.

Near Threatened (NT) → Vulnerable (VU) → Endangered (EN) → Critically Endangered (CR).

It helps prioritise action and funding by showing which species are most at risk and need urgent protection.