Human impacts

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.

It removes producers and habitat, reducing energy entry into the food web and lowering the number of consumers the system can support.

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.

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

Link the activity to the ecosystem change, then state the effect on biodiversity and/or energy flow in food webs.

Pollution can reduce survival, growth, or reproduction of organisms, so less usable energy is passed to higher trophic levels.

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

By reducing producer biomass and habitat, less energy enters food webs and fewer consumers can be supported.

Human activities often reduce biodiversity and simplify food webs, which lowers resilience and makes ecosystems less able to recover from disturbances.

Removing key species can alter population sizes of other trophic levels and trigger trophic cascades, changing food web structure.

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).

Global trade can introduce invasive species and spread pollutants rapidly, altering species interactions and energy flow in food webs.

Habitat destruction, overexploitation, and pollution.

Toxins can bioaccumulate in organisms and biomagnify up food chains, increasing exposure and health risk for humans as top consumers.

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

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

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

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

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

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

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

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.

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.

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

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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Pollution can be matter pollution (substances) or energy pollution (noise, light, heat).

Wildlife can be injured or entangled and can ingest plastic, reducing feeding and causing starvation.

Some are persistent (do not break down easily), so they remain in ecosystems for long periods and continue to cause harm.

Pollution is the introduction of harmful substances or harmful energy into the environment.

Microplastics are plastic particles smaller than 5 mm in size.

Matter pollution adds substances such as chemicals or plastics; energy pollution adds forms of energy such as noise, light, or heat.

They can enter through air, water, or soil, be taken up by organisms, and then be transferred to predators through feeding.

Many plastics fragment into smaller pieces rather than fully biodegrading, increasing microplastic pollution.

Microplastics are plastic particles smaller than 5 mm.

Toxins can bioaccumulate in organisms and biomagnify up food chains, increasing exposure for humans as top consumers.

Plastics can be transported by rivers and ocean currents and can travel long distances before settling.

Pollution can kill organisms or reduce their growth and reproduction, so less biomass and usable energy are transferred to higher trophic levels.

A persistent pollutant is a substance that resists breakdown and remains in the environment for long periods.

Through food, drinking water, and air.

They persist in ecosystems, continue causing harm, and can build up in organisms and food chains.

Biomagnification increases pollutant concentration at higher trophic levels.

Noise pollution and light pollution (heat can also act as energy pollution).

Pollutants can bioaccumulate in organisms and biomagnify up food chains, leading to highest concentrations in top predators.

Small plastic fragments can be ingested by plankton and invertebrates, transferring to higher trophic levels when predators feed.

Some chemicals act as endocrine disruptors, interfering with hormones, development, and reproduction.

Pollutants can cause toxicity, reduce growth, damage organs, and lower fertility, leading to population decline over time.

Ingested plastic can block digestion, reduce feeding, cause injury, and increase risk of starvation.

Plastic pollution, including macroplastics and microplastics, entering marine ecosystems.

Plastics typically persist and fragment into microplastics rather than decomposing fully through biological processes.

Industry (factory discharge), agriculture (pesticides/fertilisers), fuel combustion, and poorly managed waste.

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.

Invasive species are non-native organisms that spread and cause 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.

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

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

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

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.

It intensifies stress and makes other human impacts more severe.

Climate change is long-term shifts in climate patterns (temperature, rainfall, extremes), mainly caused by increased greenhouse gases.

Species may move toward the poles or up mountains to stay within cooler conditions.

Examples include range shifts, coral bleaching, and more frequent droughts and wildfires.

Loss of sea ice reduces hunting platforms and habitat, lowering survival of ice-dependent predators and changing prey availability.

Many species are adapted to narrow climate conditions. Rapid change can exceed tolerance or shift habitats faster than species can migrate or adapt.

It increases environmental stress and makes other impacts (habitat loss, pollution, overexploitation) more severe.

Climate conditions may change faster than genetic adaptation and faster than migration to suitable habitats.

Sea-level rise can flood and shrink coastal ecosystems such as mangroves and salt marshes, reducing biodiversity.

By reducing primary productivity and changing species distributions, it alters energy capture and feeding interactions.

It usually alters environmental conditions first, which changes productivity and species interactions, rather than removing organisms directly.

More frequent droughts, storms, and fires increase mortality and reduce reproduction, pushing populations below viable levels.

Climate change lowers resilience by increasing disturbance frequency and reducing recovery time for populations.

Heat stress, drought, altered rainfall, and extreme events can reduce photosynthesis and lower primary productivity.

Climate change acts as a multiplier that increases stress and reduces ecosystem resilience.

Deforestation or urbanisation removes producers (plants) from ecosystems.

Pollutants can damage leaves or block stomata, reducing CO2 uptake and lowering photosynthesis.

Air pollutants damage plant tissues and climate change alters rainfall/temperature, reducing photosynthesis and productivity.

Ecosystems depend on energy input (photosynthesis) and recycling of matter (nutrients). Human actions can reduce productivity, remove biomass, and disrupt cycles.

With fewer producers, less energy is captured by photosynthesis and less biomass is created at the base of the food web.

Primary productivity is the rate at which producers create biomass using photosynthesis.

Heat stress and altered rainfall increase drought and reduce plant growth, so less biomass is produced.

Trees store carbon. When forests are removed (often burned or decomposed), stored carbon is released as CO2 and less is absorbed.

Fewer trees means less transpiration and often less local rainfall, increasing drying and erosion risk.

Biomass is removed, so nutrients leave the ecosystem instead of being returned to soil by decomposition.

Built surfaces replace producers and fragment habitats, so less photosynthesis occurs and food webs weaken.

Removing producers reduces photosynthesis, so less energy becomes biomass at the base of the food web.

Monocultures simplify food webs and reduce biodiversity, so the system is less able to recover from disturbance.

Human activities can alter nutrient cycles (nitrogen/phosphorus), the carbon cycle, and the water cycle.

Harvest removes biomass from the ecosystem, so energy and nutrients leave instead of being recycled by decomposition.

Harvest removes biomass, so fewer nutrients return to soil through decomposition, increasing reliance on fertilisers.

Humans reduce energy flow (lower productivity) and disrupt matter storage/transfer (alter cycles).

Harvest removes biomass → fewer nutrients return via decomposition → soil fertility declines unless fertiliser is added.

Deforestation reduces energy input (fewer producers) and reduces matter storage (less carbon in biomass/soil).

When producers are removed, less energy enters food webs, biomass decreases, and ecosystem stability often falls.

A tipping point is a threshold beyond which an ecosystem undergoes rapid and often irreversible change.

By adding pollutants and changing habitats, humans alter survival, reproduction, and energy transfer across trophic levels.

Toxin builds up within one organism over time.

Planetary boundaries are limits within which humanity can operate safely without destabilising Earth systems.

Bioaccumulation is the buildup of toxins in a single organism over its lifetime because uptake is faster than removal.

Pollution is the introduction of harmful substances or harmful energy into the environment.

Gradual pressure builds → threshold crossed → sudden ecosystem flip → new stable state forms.

Crossing boundaries increases the risk of large-scale ecosystem change and loss of resilience.

Biomagnification is the increasing concentration of toxins at higher trophic levels as predators consume contaminated prey.

Toxin concentration increases at higher trophic levels.

They persist, build up in organisms, and can move through food chains for long periods.

Examples include climate change, biodiversity loss, nitrogen/phosphorus cycles, and ocean acidification.

Bioaccumulation happens within one organism over time. Biomagnification happens between trophic levels and increases up the food chain.

Plastics persist and fragment into microplastics (<5 mm) that can be ingested at low trophic levels and passed upward.

Low resilience means an ecosystem cannot absorb disturbance, so it reaches a threshold and flips more easily.

Pollutants can reduce growth, survival, or reproduction, so less biomass is passed to higher trophic levels.

Coral reefs can flip from coral-dominated to algae-dominated after repeated warming and pollution, and recovery can be very slow.

Excess nitrogen/phosphorus can cause eutrophication, leading to oxygen depletion and loss of consumers in aquatic food webs.

Pollutants reduce survival and reproduction, causing population declines and local extinctions.

They eat many contaminated prey, so toxins stored in tissues reach the highest concentrations in top predators.

Mercury can move from plankton → small fish → larger fish → tuna, leading to highest concentrations in top consumers (including humans).

Define biomagnification, describe a simple food chain, and state why top predators (and humans) get the highest concentration.

Feedback loops can lock the system into a new stable state and restoring original conditions may be costly or impossible.

Planetary boundaries show that exceeding environmental limits can reduce resilience and trigger major ecosystem shifts.

Industry, agriculture, transport, and waste disposal can all introduce pollutants.