Lecture 4: Habitat Loss (Main Anthropogenic Threats On Biodiveristy) Flashcards
What is habitat loss?
- Conversion of natural habitat into human-dominated habitat.
- e.g. forested area to agriculture.
- Greatest threat to biodiversity.
- Responsible for declines of nearly 50% of mammals, birds and amphibians (IUCN red list data).
- Global problem:
- 50% of land-surface already transformed
- over 2/3 fresh water supplies affected
- 40% oceans affected (e.g. bottom trawling)
How does habitat loss happen?
DeFries et al. (2004) noted that habitat loss occurs in predictable sequence of transition
Stage 1: Pre settlement: Proportion of landscape = 100% Natural ecosystems.
Stage 2: Frontier: Proportion of landscape = mostly Natural ecosystems but some are cleared.
Stage 3: Subsistence: Proportion of landscape = Little Natural ecosystems, but some cleared, some used for small scale agriculture (usually subsistence agriculture (growing food for themselves)), a tiny portion for urban areas. (Urbanisation is starting to happen where people move out of countryside into towns/cities).
Stage 4: Intensifying: Proportion of landscape = very little natural ecosystems, tiny proportion being cleared, some for small scale agriculture, some for intense agriculture, small portion for urban areas and a small portion becomes protected or for recreational use.
Stage 5: Intensive: Proportion of landscape = tiny proportion of natural ecosystems and small scale agriculture, large proportion for intensive agriculture, some for urban areas and protected/ recreational areas.
- Timescale is different in different areas (tho tends to follow above sequence)
Primary Drivers: Agriculture
- between 1700 & 1950 agricultural land increased from 2.65 to 12 million km^2 (a 450% increase over 250 years).
- currently uses 40% of land surface (over 70% in UK) (18.7 million km^2 of cropland, 33.8 million km^2 of pasture (land suitable for grazing animals)).
- ”Green revolution” between 1930s and 1960s a lot of artificial fertiliser, pesticides/herbicides, new crop varieties developed that more productive. Avoided mass starvation but led to intensification and expansion of agriculture. Need to move away from pesticides/herbicides and develop new technologies to help us.
Primary Drivers: Agriculture
Need to feed an expanding population, how? :
- Increase agricultural land (where’s suitable). Predicted we will need additional 10-20% cropland by 2050 - will reduce natural habitat.
- Increase crop yields. By pesticides & fertilisers, may lead to increased pollution. Need to develop methods that increase yields with less habitat destruction & degradation e.g. robot laser weeders.
- Change in diets, avoid waste. Meat & dairy products require more land (animals have to eat) (higher up the trophic pyramid more energy is ‘lost’ from system).
Primary Drivers: Agriculture
Certification schemes can help:
- e.g. Certified Sustainable Palm Oil (haven’t destroyed any land recently to grow the palm oil).
- e.g. Rainforest Alliance focuses on people/incomes, & reserving space for wildlife.
Primary Drivers: Urbanisation
- currently accounts for 3% land use.
- predicted to increase to 9% with 5 billion people by 2030.
- particularly in Asia & Africa, their population is increasing faster.
- 1.2 million km^2 (size of South Africa) predicted to have >75% probability of conversion.
- intense urbanisation leads to 55% loss of biodiversity, reaching close to 80% loss in most extreme cases.
Primary Drivers: Urbanisation
Move towards sustainable & green infrastructure:
- many cities developing green infrastructure plans e.g. more green space, green roofs.
- e.g. in Bangkok. Does provide good habitat for some species but is quite small so not everything will survive.
- e.g. put drainage on the surface rather than underground & put greenery around it, can be a good habitat.
Primary Drivers: Urbanisation
Some city features are more “friendly” to biodiversity than others:
1. E.g. Beninde et al. (2015) showed that biodiversity increases when urban habitats:
- have more green space
- have more habitat types
- have more plant cover
- are less intensively managed
- contain water
Primary Drivers: Extractive industries
- Any industry that removes a resource from the environment/nature.
- e.g. oil, gas, mining, quarrying, fishing, hunting, forestry.
- although not huge amount of area has been destroyed by this, causes other issues e.g. pollution, overexploitation & habitat loss.
- caused estimated 7% deforestation in subtropics.
- in North America, oil drilling led to loss of 30,000 km^2 land between 2000 & 2012.
Primary Drivers: Aquaculture
- Fastest growing area of agriculture (now produces over half seafood).
- Has advantages (e.g. reduces pressure of overfishing, & fish convert energy more efficiently than other groups like mammals) but can destroy habitats (e.g. mangrove forests by shrimp farming, over half of mangroves lost & 40% of endemic vertebrates are threatened).
- Some being replanted.
- (Mangroves provide buffering & reduction of floods so ecosystem services)
Where is habitat loss happening?
- Some biomes been more affected than others.
- Forests (average 50% loss over 5000 years).
- Most temperate forests already lost but are now expanding due to reforestation & rewilding.
Rewilding
- Is the large-scale restoration of nature until it can take care of itself and us again.
- Is challenging.
- Some areas rewild naturally/easily but some don’t.
- Need to take societal concerns on board (e.g. human-wildlife conflict, livelihoods, different stakeholders, public support) (e.g. predators can take livestock).
- UK governmental focus on tree-planting but must be the right trees in the right place (native species).
- Can start small - planted 15 trees & created a meadow area - already home to slow worms, bats, birds, invertebrates and wild plants.
Where is habitat loss happening?
- Deforestation is currently highest in tropics.
- Related to practices established during colonialism (acquiring control of another country & exploiting it economically).
- Some tropical forests (e.g. the Amazon) will likely experience a ‘tipping point’ after which they revert to grasslands. (Trees in rainforests transpire a lot so water evaporating from them, which stimulates cloud cover & rain, so they are self maintaining, so when loose lots of tree cover that cycle stops).
- Just 20-25% loss needed to reach this point (Nobre et al. 2016).
Where is habitat loss happening?
- Grasslands - used to occupy 30-40% of world’s land area.
- Their suitability for agriculture has led to destruction of many natural grasslands.
- e.g. 97% loss of tall prairie in USA.
Where is habitat loss happening?
- Coral reefs - extremely biodiverse.
- Provide food & resources.
- Global economic value of $375 billion a year.
- 25% already damaged beyond repair.
- 75% are at immediate risk.
- 90% are projected to be in danger of being lost by 2030.
- Main risk is coral bleaching due to climate change: overheating leads to loss of symbiotic algae (algae lives inside the coral structure & photosynthesises so producing energy that the coral uses but when gets too hot the algae produces toxic chemicals and the coral eject the algae, can be temporary but can lead to them dying off).
- Overfishing, careless tourism and pollution also contribute to loss.
