Threats to Biodiversity Flashcards
How many species are there in the world?
A conservative estimate = 7million
Most are terrestrial animals
2/3 in tropics
What proportion of tropical rainforests have been cleared by humans?
- 50% tropical rainforest has been cleared by humans
- Many countries have no primary forest left
How many species have been described and named?
Only between 1.4million and 1.8million
Mostly smaller organisms that haven’t been found e.g. insects, fungi, bacteria
What is extinction and is it a natural process?
Extinction : when a species ceases to exist after the last individual in that species dies
It is a natural process // eventually all species become extinct
Most mammals have a species lifespan of 1 million years
What does biologist E.O Wilson think about the current extinction rate?
E.O Wilson thinks that:
- current rate of extinction is 1000x background rate
- 30-50% of species could be extinct within 100 years
Why do biodiversity hotspots have greater rates of extinction?
- 50% of flora + fauna are in one of the 30 hotspots which together make up only 2% of the land area on Earth
- These areas are very vulnerable to habitat loss + many species within them are endemic
With a more complex food web, is an ecosystem more or less resilient?
> The more complex a food web, the more resilient it is to the loss of one species or reduction in its population size
If one type of prey // food source // predator is lost, others will fill the gap left
Why are communities in young ecosystems that are undergoing succession more vulnerable ?
- When flora+fauna colonise bare land, there are few species at first
- Species diversity increases w time until a climax community is reached when species composition is stable
- So communities in young ecosystems undergoing succession may be more vulnerable than those in more resilient + stable older ones
How can the presence of limiting factors accelerate the process of extinction?
- Difficult for organisms to get enough raw materials for growth e.g. water is limiting in a desert
- Any change that makes it even harder may result in species disappearing
- If abiotic factors required for life are in abundance (water, light, nutrients) the system is more likely to manage if one is reduced
What is inertia of an ecosystem?
Inertia is the property of an ecosystem to resist change when subjected to a disruptive force.
It is key to helping planners know which site will resist change // recover most quickly
What are natural hazards?
Naturally occurring events that may have a negative impact on environments (+humans)
What are environmental disasters?
- caused by human activity
- e.g. loss of tropical rainforest on massive scale
- e.g. oils spills
What is the major cause of loss of biodiversity and give 3 examples?
Loss of Habitat
- In Philippines, Vietnam, Sri Lanka, Bangladesh (high human pops.) most wildlife habitat + primary forest lost
- Mediterranean // only 10% original forest cover remains
- In Madagascar by 2020, predicted only protected moist forest area left // home to lemurs + other endemic species which could become extinct
What is fragmentation of habitat?
- A large area is divided up into a patchwork of fragments
- Separated from each other by roads, towns, fences, fields etc…
- Fragments are isolated in a degraded landscape + act as islands
- Higher edge to area ratios as fragments get smaller
- Greater fluctuations of light, temp + humidity at edge than middle
- Invasion of habitat by pests // humans increases + spread of disease increases
What is pollution?
Pollution caused by human activities can degrade or destroy habitats + make the unsuitable to support the range of species that a pristine ecosystem can support
Name two examples of local pollution
Spraying of pesticides may drift into wild areas
Oil spills may kill many sea birds and others
What can environmental pollution lead to?
Environmental pollution by emissions from factories and transport can lead to acid deposition or photochemical smog
2 examples of when introducing non-native species has worked
- potatoes from the Americas to Europe
- rubber trees from the Amazon to SE Asia
3 examples of when introducing non-native species has been a disaster
- Dutch Elm disease came from imported American logs to Europe + decimated elm populations
- Sudden oak death also imported same way
- Flora+fauna in Australia well adapted to environment but has been unable to compete with aggressive invasive species e.g rabbits, red foxes, camels, blackberry
Name a population that was wiped out in the wild by the spread of disease
The last population of black-footed ferrets in the wild was wipe out by canine distemper in 1987
How do modern agricultural practices reduce biodiversity?
- monocultures
- genetic engineering
- pesticides
Fewer species + varieties of species are grown commercially and more + more pest species removed
What is the importance of tropical rainforests?
- contain over 50% of all species of plants + animals on Earth in just 6% of the land area
- produce 40% of oxygen that animals use
- high species diversity
- high habitat diversity
How much of the land area on Earth did tropical rainforests cover in 1950?
14% of the Earth’s land surface
How much of the Earth’s timber is in tropical rainforests?
50% of the Earth’s timber is in tropical rainforests
Timber is the next biggest resource after oil in the world today
How many people live in the wet tropics?
At least 2 billion people live in the wet tropics + many of these rely on rainforests for subsistence agriculture
Why is a low density human population sustainable in the tropical rainforest?
- A low density of human population is sustainable as they clear a small area of forest, grow crops for two or three years then move on to the next as the soil is exhausted
- This is called shifting cultivation
- Works as long as there is enough time for forest to regenerate before the same area is cleared again (up to 100 years)
What happens if the forest does not fully regrow before it is cleared again?
There is a gradual degradation of nutrients + biodiversity
Once plants are cleared or burned, why does fertility reduce rapidly?
- Fast rate of respiration + decomposition means forests are v fertile w high levels of biomass in trees + plants
- Most nutrients held in plants, not the soil
- Once plants cleared // burned, fertility reduces rapidly because heavy rainfall washes the nutrients + soil away
- Vegetation is not there to lock up the nutrients nor to protect the soil
- So more forest is cleared to get the short-term fertility for crop growth
How does a narrow geographical range increase the risk of extinction?
If a species only lives in 1 place + that place is damaged or destroyed, the habitat is gone
e.g. the Golden Lion Tamarin
How does a low genetic diversity (small pop. numbers) increase the risk of extinction?
- A small pop. has a smaller genetic diversity + is less resilient to change
- As individual numbers fall, there is more interbreeding until pops. are so small they are the ‘living dead’ or become extinct
e.g. Snow leopard, tiger, Lonesome George
How do low population densities + large territories increase the risk of extinction?
- If an individual of a species requires a large range over which to hunt + only meets others for breeding, then habitat fragmentation can restrict it territory
- If there’s not a large enough area left, or they’re unable to find each other (due to city/road/farm splitting up territory) they are less likely to survive
e.g. giant panda
How do large bodies increase the risk of extinction?
- the 10% rule means that large top predators are rare
- they tend to have large ranges, low pop. densities + need a lot of food
- they also compete w humans for food, may be a danger to humans + are hunted for sport
How does a low reproductive potential increase the risk of extinction?
Reproducing slowly + infrequently means the population takes a long time to recover
e.g. whales
How does migrating seasonally increase the risk of extinction?
- Migrating animals need the habitats at both ends of the migration route. If one is destroyed, they get there to find no food or habitat
- Barriers on their journey can precent them from completing it e.g. salmon trying to swim upriver to spawn
How does having niche requirements increase the risk of extinction?
e.g. the giant panda (only 2000 left) mostly eats bamboo shoots in forests in central China
How does being edible to humans and herding together increase the risk of extinction?
Overhunting or over harvesting can eradicate a species quickly, esp. if species lives in large groups e.g. shoals of fish
Also under threat from humans are tigers // whilst not eaten, their body parts are used in traditional Chinese medicine so demand for them is v high
How doe being an island organism increase the risk of extinction?
Dependent of the size of the island:
- populations tend to be small
- islands have high degree of endemic species
- genetic diversity tends to be low
- vulnerable to introduction of non-native species to which they have no defence mechanism
e.g. the dodo
What is the minimum viable population size for large carnivores?
Thought to be 500 individuals
- There may be 400 Sumatran tigers left
What is the ICUN?
- World Conservation Union
- Aim is to encourage + assist societies to conserve the diversity of nature
- To ensure use of natural resources is ecologically sustainable
What is the ICUN Red List?
Determines conservation status of a species based on several criteria including:
- population size
- degree of fragmentation
- trophic level
- probability of extinction
How many species on the ICUN Red List are listed as threatened?
40%
Recovered species - Golden lion tamarin // description
- Small monkey
- Endemic to Atlantic coastal rainforests of Brazil
- Amongst rarest animals in world
- 1000 in wild and 500 in captivity
Recovered species - Golden lion tamarin // ecological role
- omnivores
- prey to large cats, birds of prey
- live in family groups in tropical rainforest in the canopy
Recovered species - Golden lion tamarin // pressures
- only 2% of native habitat is left
- poaching can get US$20,000 per skin
- predation is great in the wild + their food source is not dependable
Recovered species - Golden lion tamarin // methods of restoring populations
- Captive breeding programme for last 40yrs
- Over 150 institutions involved + exchange individuals to increase genetic diversity
- Some reintroduced into wild but only 30% success rate as habitat is threatened + many predators (inc. humans)
Extinct species - Dodo // description
Large flightless bird endemic to island of Mauritius
Extinct species - Dodo // ecological role
- No major predators on Mauritius so dodo had no need of flight
- Dodo was a ground-nesting bird
Extinct species - Dodo // pressures
- In 1505 Portuguese sailors discovered Mauritius + ate dodo as source of fresh meat
- Later, island used as penal colony + rats and monkeys introduced
- These at dodo eggs + humans killed them for sport and food
- Conversion of forest to plantations destroyed their habitat
- Known to be extinct by 1681
Extinct species - Dodo // Consequence of disappearance
- island fauna impoverished by loss of dodo
- became an icon due to its apparent stupidity (it had no fear of humans, never having had need to fear predators)
Mountain gorilla, Rwanda (critically endangered, umbrella species) // why endangered?
- For years has been victim of deforestation, poaching + accidental victim of civil wars + unrest
- Destruction of its habitat has left it without a home or food source
- Population been reduced to 800 members
Mountain gorilla, Rwanda (critically endangered, umbrella species) // why is it critically important they should be conserved
- Ecocentrics argue gorillas have intrinsic value + human impact on environment should be reduced
- Conservation of gorillas requires preservation of forest, land + food sources
- Not only conserve gorilla but also retain ecosystem they’re part of + species within it
- Anthropocentrics argue gorillas have aesthetic value (ecotourism)
- Many people visit countries like Rwanda with sole intention of seeing gorillas + this has given struggling economy boost + positive international attention
