The Impact of Human Activities on Ecosystems
Human activities can alter ecosystems by changing which species are present and how energy and nutrients move through the environment.
Human pressures can reduce biodiversity, weaken ecological interactions and interfere with essential processes such as nutrient cycling, productivity and population regulation.
Understanding their impacts helps explain why ecosystems become less stable and less resilient when exposed to significant human disturbance.
Overexploitation
Overexploitation means harvesting species or resources from the wild at rates faster than natural populations can recover. This includes overhunting and overfishing.
Impact on community structure
Overexploitation removes individuals from a population so rapidly that it collapses or becomes functionally extinct. Predators lose prey, competitors shift in abundance and food webs become unbalanced. Species that depended on the exploited organism either decline or change their behaviour.
This often triggers trophic cascades, where changes at one trophic level ripple through the whole community. The loss of one species can open niches for invasive or opportunistic species, further altering the composition of the community.
Impact on ecosystem functioning
Ecosystem processes slow down or break down. If a heavily exploited species was a grazer, pollinator or top predator, essential functions such as controlling herbivores, maintaining vegetation or regulating nutrient turnover are weakened. Productivity decreases, resilience drops and recovery from disturbances becomes harder.
Habitat Destruction
Habitat destruction occurs when natural habitats are no longer able to support the species present, resulting in the displacement or destruction of its biodiversity.
Examples include harvesting fossil fuels, deforestation, dredging rivers, bottom trawling, urbanization, filling in wetlands and mowing fields.
Impact on community structure
As habitat is removed or broken into small patches, species lose feeding grounds, shelter and breeding sites. Many decline or disappear, reducing richness. Fragmentation isolates populations, making gene flow difficult and increasing vulnerability to inbreeding.
Mutualistic relationships, such as pollination and seed dispersal, break down. Predators may find it harder to hunt, while some generalist species expand, skewing the community towards fewer, more adaptable organisms.
Impact on ecosystem functioning
Reduced vegetation cover lowers primary productivity and alters water cycles. Soil erosion increases and nutrient cycling becomes slower, decreasing soil fertility. Fragmented ecosystems cannot regulate climate or water as effectively. This decreases the overall stability and resilience of the ecosystem.
Monocultures
Monoculture is the agricultural practice of producing or growing a single crop, plant, or livestock species, variety, or breed in a field or farming system at a time.
Planting the same crop in the same place each year removes nutrients from the earth and leaves soil weak and unable to support healthy plant growth, in addition to decreasing biodiversity.
Impact on community structure
Monocultures strip away species diversity. Complex food webs are replaced by simplified systems with fewer niches and fewer interactions. Natural enemies of pests decline because the habitat no longer supports them, which allows pest populations to increase dramatically. Pollinators, soil organisms and decomposers also decline due to limited food or habitat.
Impact on ecosystem functioning
Low diversity weakens ecosystem stability and resistance to disturbances. Nutrient cycling becomes less efficient because fewer species contribute to decomposition and soil turnover. Pest outbreaks become more common, forcing reliance on pesticides. Heavy use of fertilisers and irrigation can degrade soil structure and reduce long-term productivity.
Growing the same crop over a large area year after year is known as monoculture. Explain why an outbreak of pests is more of a problem in monoculture than where a mixture of crops is grown.
Pollution
All forms of pollution pose a serious threat to biodiversity, with issues affecting biodiversity in Australia generally being categorised as relatively local in nature (e.g. specific waste from poorly managed activities) or relating to broad landscape processes (e.g. nutrient enrichment in the Great Barrier Reef from farming or inappropriate pesticide use).
Impact on community structure
Pollution affects species differently. Sensitive organisms decline first, which shifts the balance towards tolerant or invasive species. Toxic substances can impair reproduction, growth and survival, reducing population sizes. Bioaccumulation and biomagnification move pollutants up the food chain, harming predators and disrupting predator–prey relationships. Algal blooms driven by nutrient pollution reduce light, kill plants and drastically reshape aquatic communities.
Impact on ecosystem functioning
Pollution interferes with photosynthesis, respiration and decomposition. Nutrient pollution can cause eutrophication, lowering oxygen levels and forming dead zones where few species can survive. Chemical pollutants reduce productivity and alter nutrient cycling. Plastics change sediment structure and reduce the ability of ecosystems to filter water.
Explain how large-scale deforestation for agriculture would lead to a decrease in the diversity of organisms in the area.
Under natural and suitable conditions, bare soil would eventually become covered by a woodland community. Explain how farming practices prevent this from happening.