Human activities, biodiversity loss and global warming
Ecology • Biodiversity and the effect of human interaction on ecosystems
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Key concepts
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Definition and importance of biodiversity
Biodiversity is a measure of how many different species of plants, animals, fungi and microorganisms live in the same geographical area. High biodiversity increases ecosystem stability by reducing dependency of species on single food sources and by providing a wider range of ecological roles and services. Areas such as tropical rainforests and coral reefs show especially high biodiversity and supply many resources that humans use directly and indirectly .
Waste production and pollution: cause and effect
Chemical and biological waste from industry, agriculture and sewage contaminates air, soil and water. Fertiliser runoff increases nutrient loads in lakes and rivers and causes algal blooms; the resulting oxygen depletion kills plants and animals and reduces species richness (eutrophication). Toxic pollutants such as heavy metals bioaccumulate in food chains, reaching high concentrations in top predators and causing population declines. Direct discharge of untreated sewage introduces pathogens and further reduces water quality, limiting the range of species that can survive in affected habitats .
Deforestation and habitat loss: cause and effect
Deforestation removes trees to create farmland, pasture, urban areas or timber resources. Tree removal destroys habitat structure, removes food sources and fragments populations into smaller, isolated groups. Loss of trees reduces carbon sinks and releases stored carbon dioxide when trees burn or decompose, increasing atmospheric greenhouse gases. Reduced transpiration after tree removal alters local climate, soil moisture and increases erosion, further reducing the capacity of the land to support diverse communities and causing some local extinctions .
Land use change, peat extraction and hedgerow removal
Conversion of natural habitats into large-scale agriculture, urban areas and mines removes niches and reduces habitat heterogeneity. Peat bogs and hedgerows act as important biodiversity reservoirs and carbon sinks; extracting peat and removing hedgerows destroys unique species communities and releases stored carbon. Large monocultural fields support far fewer species than mosaics of hedgerows, ponds and woodlands, so intensification of land use lowers local biodiversity and resilience to environmental change .
Greenhouse effect and global warming: mechanism
The greenhouse effect occurs when greenhouse gases in the atmosphere trap more outgoing thermal radiation, raising the Earth's average temperature. Human activities such as burning fossil fuels and deforestation increase atmospheric concentrations of carbon dioxide and other greenhouse gases, altering long-term climate patterns. Ice-core and instrumental records show a large increase in CO2 since pre-industrial times, which links to recent global temperature rise and associated environmental changes .
Biological consequences of global warming
Rising temperatures change the distribution and abundance of species. Many species migrate toward cooler regions (poleward or to higher altitudes) when local temperatures exceed tolerable limits, which disrupts existing ecosystems and species interactions. Arctic ice loss reduces habitat for ice-dependent species and impairs hunting for predators such as polar bears. Sea-level rise threatens coastal habitats and human settlements, while altered rainfall patterns increase the frequency of droughts and floods affecting food production and biodiversity. Range shifts may allow disease vectors and invasive species to expand into new areas, creating further ecological stress and public-health risks .
Key notes
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