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6.6 Populations and sustainability (6.6.5 Balancing the conflict between…
6.6 Populations and sustainability
6.6.5 Balancing the conflict between conservation and human needs
Terai Arc
An area of forest and grasslands on the border between Nepal and India. A variety of plants and animals are found, including endangered species like the Bengal Tiger and Asian elephant
Nearly 7 million people also live in this area and many of them depend on the forest's resources to survive
Areas of the forest are also being destroyed to make way for more housing and other development
e.g Elephants can eat and trample crop fields and tiger can kill livestock. This increases the likelihood of these animals being shot and killed
Conservation charity WWF has worked with local people to help balance their needs with conserving the forest and its wildlife
E.g The charity has provided people with solar cookers and biogas generators so they don't need to use wood from the forest as fuel
The Maasai Mara
A national reserve in Kenya. A large of grassland which is home to huge populations of wildebeest and zebra, as well as lions and cheetahs
The Maasai people traditionally earn a living by raising livestock such as cattle. This may bring them into conflicts with conservationists
E.g Overgrazing by livestock can destroy grassland for wildlife
Conservation trusts work with the Maasai people to help them make money from their land through conservation and ecotourism projects rather than farming
Uk Peat Bogs
Lots of upland parts of the UK are home to peat bogs - areas of wet peat. These peat bogs store water and carbon dioxide so lots of different plants and animals live there
Farmers use the peat bogs to graze sheep and deer but this leads to conflict with conservationists. Overgrazing causes loss of moss species, soil compaction (which increases water runoff down sheep paths) and general peat bog erosion
Government-funded programmes such as Environmental Stewardship Scheme, gives money to farmers to use the peat bogs in a sustainable way e.g remove livestock over winter
The Galapagos Islands
Non native plants
have also been introduced to the islands. These compete with native plant species causing a decrease in their populations
Non native animals
introduced to the islands by humans eat some native species. This has caused a decrease in the populations of native species. E.g non-native dogs, cats and black rats eat young giant tortoises and Galapagos land iguanas
Eradication programmes
have removed wild goats from some of the smaller islands and wild dogs from the largest island. Quinine trees are kept in check using chemical herbicides and by uprooting young trees.
When visiting, there are a list of rules which include not bringing any live plants or animals onto the islands, visitors are only allowed to visit in the company of a licensed guide
Antartica
Visitors to Antarctica have caused pollution in the past by dumping sewage into the sea and leaving rubbish. Shipping accidents have lead to oil spills, which severely affect wildlife
Hunting, whaling and fishing have all reduced wildlife populations in the area
All waste apart from food waste and sewage must be taken away by ship for disposal in other countries
Ships that use thick oil as fuel are banned from Antarctic waters
There are tourist restrictions e.g tourists are only allowed on land at certain locations for a few hours
6.6.1 What determines population size?
Carrying capacity: The maximum population size that can be maintained over a period in a particular habitat
Limiting factor: The factor whose magnitude slows down the rate of a natural process
Population size and carrying capacity
A (Lag Phase) - there may only be a few individuals, which are still acclimatising to their habitat. At this point, the rate of reproduction is low, and the growth in population size is slow
B (Log phase) - resources are plentiful, and conditions are good. Reproduction can happen quickly, with the rate of reproduction and mortality are equal. The population size therefore stays stable, or fluctuates very slightly up and down in response to small variations in environmental conditions each year
C (Stationary phase) - the population size has levelled out at the carrying capacity as the habitat cannot support a larger population. IN this phase, the rates of reproduction and mortality are equal. The population size therefore stays stable or very slightly fluctuates up and down in response to small variation in environmental conditions each year
Limiting factors
Limiting factors can be abiotic e.g the amount of shelter in an ecosystem limits the population size of a species because there's only enough shelter for a certain number of individuals
Limiting factors can also be biotic, e.g interspecific competition limits the population of a species because the amount of resources available to a species is reduced
Limiting factors determine the carrying capacity of an ecosystem
Factors
Abiotic factors
The population size is the total number of organisms of one species in a habitat
The population size of any species varies because of abiotic factors, e.g the amount of light, water or space available, the temperature of their surroundings or the chemical composition of their surroundings
When abiotic conditions are ideal for a species, organisms can grow fast and reproduce successfully
e.g When the temperature of a mammal's surroundings is the ideal temperature for metabolic reactions to take place, they don't have to use up as much energy maintaining their body temperature. This means more energy can be used for growth and reproduction, so their population size will increase
When abiotic conditions aren't ideal for a species, organisms can't grow as fast or reproduce as successfully.
E.g when the temperature of a mammal's surroundings is significantly lower or higher than their optimum body temperature, they have to use a lot of energy to maintain the right body temperature. This means less energy will be available for growth and reproduction, so their population will decrease
Biotic factors
Interspecific competition
Interspecific competition is when organisms of different species compete with each other for the same resources
e.g red and grey squirrels compete for the same food sources and habitats in the UK
Interspecific competition between two species can mean that the resources available to both populations are reduced
e.g if they share the same source of food, there will be less available to both of them. This means both populations will be limited by a lower amount of food. They'll have less energy for growth and reproduction, so the population sizes will be lower for both species
I
nterspecific competition can also affect the distribution of species. If two species are competing but one is better adapted to its surroundings than the other, the less well adapted species is likely to be out-competed - it won't be able to exist alongside the better adapted species.
e.g Since the introduction of the grey squirrel to the UK, the native red squirrel has disappeared from large areas. The grey squirrel has a better chance of survival because it's larger and can store more fat over winter
Intraspecific competition
The population of a species increases when resources are plentiful. As the population increases, there'll be more organisms competing for the same amount of space and food
Eventually, resources such as food and space become limiting - there isn't enough for all the organisms. The population then begins to decline
A smaller population then means that there's less competition for space and food, which is better for growth and reproduction - so the population starts to grow again
The maximum stable population size of a species that an ecosystem can support is called the carrying capacity
Predation
Predation is where an organism kills and eats another organism. The population sizes of predators and prey are controlled by negative feedback
As the prey population increases, there's more food for predators, so the predator population grows.
E.g in the graph on the right the lynx population grows after the snowshoe hare population has increased because there's more food available
As the predator population increases, more prey is eaten - so the prey population then begins to fall.
E.g greater numbers of lynx eat lots of snowshoe hares, so their population falls. This is an example of negative feedback - the prey population is restored to a more stable size
This means there's less food for the predators, so their population decreases (more negative feedback) and so on.
E.g reduced snowshoe hare numbers means there's less food for the lynx, so their population falls
Interactions between populations