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6 – Human impact on the environment
deforestation / agriculture / overfishing / pollution / forestry / mining / urban expansion
a. Endangered: at risk of extinction – few breeding pair left
Natural selection – determined by environmental factors: predators / shortage of food / disease
random mutation = advantageous allele to survive + reproduce – passed to offspring
threatened: habitats changing faster (due to human activity) than new mutations allow species to adapt
Habitat destruction
deforestation of tropical rainforests
hedgerow removal to accommodate agricultural machinery: lose wildlife corridor supporting variety of animals
Pollution:
o PCBs – banned: still found in environment close to manufacturing sites
o Oil: transport accidents – oil spill in ocean = endanger animals
Over-hunting & collecting – food / exotic pet / fashion / medicine / souvenir / ornament
Competition from non-indigenous / domestic species – introduced to area they didn’t evolve
population increases: less natural predators/pathogens + less intraspecific competition for food/habitat
out-compete native species + introduce disease = numbers decline = reduce biodiversity + impact food chain
Extinct: death of last individual of species capable of reproduction
Change in climate: reduce vegetation & atmospheric O2 levels
change to environment at rate natural selection can’t keep up with
Human activity – habitat destruction
b. Conservation: sensible management of biosphere to maintain habitats & enhance biodiversity while allowing
human activity
ensures conservation of existing gene pools
- maintains variation: alleles potentially have selective advantage for species’ survival with environmental changes
- potential sources of food / chemicals / medicine
- ethical: we have responsibility to preserve & not damage environment
- many crop plants have wild relatives – may have useful genes: breed back into crops to increase productivity
Habitat protection: nature reserves & national parks & SSSI (sites of special scientific interest)
protect entire ecosystem (prevent man building)
International cooperation: restrict trade in endangered species
CITES (Convention on International Trade in Endangered Species)
- strict customs controls: fines & jail sentences – not all countries involved & hard to catch smugglers
Ecotourism: education & money to employ locals – species more valuable alive = more incentive to conserve
Education: WWF – non-profit global organisation
Legislation: prevent overfishing
Captive breeding programmes by zoos / botanic gardens
- sperm banks – use in captive breeding to ensure genetic variation in populations
- seed stores: rare seeds in controlled environment – protect against extinction
- reintroduction programmes – red kite
, c. agricultural exploitation: increase in efficiency/intensity of food production to meet growing human demands
- human population & food demand increase = conflict between farming & conservation
- farmers encouraged to manage farms for biodiversity with subsidies (paid)
Hedgerow removal – accommodate machinery: lose wildlife corridor supporting variety of animals = reduce biodiversity
Pesticides: harm beneficial species & pests
Monoculture: grow single variety of crop over large area of land
Increased fertiliser: same nutrients removed from soil & not replaced from harvesting = eutrophication
Increased pesticide: ideal environment for pests – non-selective = harm beneficial species & pests
Reduced species diversity: 1 habitat
Deforestation: mass removal of trees to clear land for other use (cattle / farming crops)
reasons
- land for agriculture – subsistence farming & cash crops / grazing cattle
- timber extraction: building materials, fuel, paper & packaging
consequences
- habitat destruction = biodiversity loss
- soil erosion: tree roots no longer bind soil – rainfall removes top soil = less succession
- desertification – seedlings can’t grow
- increased flood risk – increased sedimentation (top soil removed & deposited downstream on rivers)
- CO2 = climate change – trees store lots of CO 2
o reduced uptake (less photosynthesis)
o released during decay
o burnt
o burning fossil fuels to power machinery to transport/process trees
- less rainfall – less transpiration (less water returns to atmosphere)
- lose valuable source of plant chemicals – potential benefits for humans
managing forests – important to preserve natural woodland: enhance biodiversity
- Coppicing: cut trees close to ground + allow stumps to regenerate/grow
o Tree not killed: many new shoots grow from stump
o Repetition: reliable source of timber
o Coppiced woodland: range of ages of coppiced trees = variety of habitats = biodiversity increase
- Selective cutting: oldest/largest trees removed – leaves majority intact = reduces impact of soil erosion
- Plantations: fast-growing species planted – new trees planted when cut down = long-term sustainable timber supply
- Protected areas – preserve species
Overfishing – harvesting rate > birth rate = population numbers decline / not maintained
- Restrict (bigger) net mesh size: enable smaller fish to escape – to reproduce
- Exclusion zones: prevent fishing in overfished areas
- Fishing seasons: prevent fishing during breeding season
- Fishing quotas: based on scientific estimates of fish stock size
- smaller fishing fleets
- fish farming – fish intensively reared
+ convert food to body protein more efficiently than other animals – larger size
+ lower carbon footprint – don’t need to heat environment
+ less wild fish harvested – allow fish stocks to replenish
- densely stocked = disease spreads easily
- antibiotics – resistance
- pesticides – harm marine invertebrates
- waste (ammonia & faeces) – increase nitrate concentration = eutrophication
- invasive species = outcompete wild fish for food/habitat + spread disease – reduce wild fish no.s & biodiversity
- breed with wild fish & reduce genetic diversity (dilute gene pool)
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