24 - Population and sustainability Public

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OCR A Level Biology Module 6 Chapter 24

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Population growth curve most organisms show the same characteristics Phase 1 - period of slow growth birth rate is higher than death rate so the population increases in size Phase 2 - period of rapid growth as the number of breeding individuals increases the total population increases exponentially --> no constraints act to limit the population Phase 3 - stable state population growth is limited by external constraints --> population size fluctuates but its overall size stays stable --> birth and death rates roughly equal Limiting factors exponential growth occurs when there's sufficient nutrients and maximum growth can be achieved but limiting factors prevent further growth and can lead to decline  competition build-up of toxic waste products disease temperature light intensity pH availability of water or oxygen predator or prey numbers Migration immigration --> movement of individuals into an area which increases the population size emigration --> movement of individuals away from an area which decreases the population size Density independent factors factors that affect whole population regardless of its size earthquakes, fires, volcanic eruptions and storms  can remove a whole popualtion of a species from an area
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Interspecific competition competition between different species for the same resource results in the reduction of the resource for all species involved if one is better adapted, it'll win but if they're on equal footing their population sizes will just decrease as numbers drop until the remaining population can survive on what's available Intraspecific competition competition between members of the same species compete for the same resource red squirrels vs grey squirrels for food and territory grey squirrels eat a wider range of food which can be stored as fat so they lived for longer than the red squirrels + it reduced the food available for the red ones so their numbers were reduced the availability of the resource determines the population size and results in fluctuations of the population size over time when a resource is plentiful in a habitat all organisms have enough to survive and reproduce --> increase in population size increased population means more individuals have to share the resources but they're now limited so not all of the individuals survive --> decrease in population size less competition results in smaller populations so less competition therefore more of the individuals survive and reproduce so the population increases again
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Predator-prey relationships sizes of predator and prey populations are interlinked in general, this relationship follows a set pattern: stage one --> increase in prey population means there's more food for predators so more survive and reproduce --> results in increased predator population stage two --> increased predator population means more prey get killed and eaten causing a decline in prey populations --> death rate of prey is higher than birth rate stage three --> reduced prey population can no longer support the predator population so intraspecific competition increases between predators --> predator populations decrease stage four --> reduced predator numbers result in less prey being killed so more prey animals survive to reproduce --> increase in prey population and the cycle begins again fluctuations could also be the result of natural disasters or seasonal changes
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Conservation means the maintenance of biodiversity through human action or management maintenance of genetic diversity, species diversity and management of habitats includes the ecosystems that provide us with natural resources so they don't run out also use reclamation where ecosystems are restored after having been damaged or destroyed --> uses controlled forest burnings which halt succession conservation is dynamic and adapts to constant change Preservation means the protection of an area through restriction of human interference so that ecosystems are kept in their natural state mostly used when preserving ecologically, archaeologically or palaeontologically sensitive resources Importance of conservation Economic --> provide resources for humans to survive and provide an income Social --> many people enjoy areas of natural beauty as well as using them for activities which are beneficial to health and wellbeing Ethical --> all organisms have the right to exist and most play important roles in their ecosystems --> we don't have the right to decide what happens to these organisms
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Sustainable use of resources used to conserve natural resources sustainable resource = a renewable resource that is economically exploited in a way that it will not diminish aims: preserve the environment ensure resources are available for future generations allow humans in all societies to live comfortably enable less economically developed countries to develop through their natural resources create a more even balance for the consumption of these materials existing resources should be used more efficiently --> prevents finite resources being wasted Sustainable timber production allows maintenance of forest's biodiversity while sustaining our supply of wood and meet the demands of consumers small-scale timber production uses technique called coppicing where new shoots form from the cut surface and mature eventually the shoots are cut and more are produced in their place --> used in fencing rotational coppicing takes place so when you've gone all the way round a forest, the first trees are ready to be coppiced again --> maintains biodiversity as the trees never grow to block out light so succession doesn't occur alternative method = pollarding where the trunk is cut higher up so deer and other animals can't get to the shoots large-scale timber production practice selective cutting which involves only felling the largest trees replace trees by replanting rather than waiting for natural regeneration plant trees at optimum distance apart to reduce competition manage pests and pathogens to maximise yields ensure that areas remain for indigenous people DISADV = habitats are destroyed, soil minerals reduced and bare soil is vulnerable to erosion Sustainable fishing overfishing has led to populations of certain species decreasing significantly fish populations may not be able to regenerate which means they disappear as a food source agreed fishing quotas provide limits on the numbers that can be caught in certain areas and of certain species --> maintains the natural population use nets with different mesh sizes commercial and recreational fishing only allowed at certain times of the year --> protects the breeding seasons for some species fish farms have been introduced to maintain the supply of some species while letting the wild ones regenerate themselves
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Conservation and preservation The Terai Arc area of forest and grassland between Nepal and India --> endangered species like Bengal tiger and Asian elephant 7 million people depends on the forest's resources areas of the forest have been destroyed for housing and other developments which bring the humans and animals into more contact and there's conflict elephants eat crops and trample livestock and tigers can kill livestock --> increases the likelihood of animals being shot and killed WWF works with local people to help balance their needs with the conservation of the environment --> solar cookers and biogas generators so they don't need to burn wood + farmers are encouraged to plant mint hedges to keep animals out  The Maasai Mara national reserve in Kenya large area of grassland (savannah) which is home to wildebeest and zebra as well as lions and cheetahs --> named after the Maasai people who live in the area Maasai people traditionally earn money through livestock which can being them into conflict with conservationists as the livestock can overgraze the grassland for wildlife conservation trusts work with the Massai people to make money through ecotourism and conservation rather than farming or to farm in a more sustainable way UK peat bogs peat bogs store water and carbon dioxide and are homes to different plants and animals farmers use them to graze sheep and deer but can lead to conflict with conservationists because overgrazing leads to a loss of moss species, soil compaction and general peat bog erosion government-funded programmes give farmers money to use peat bogs in sustainable ways e.g. lower the numbers of livestock that graze there and remove livestock in winter Human activities affect environmentally-sensitive ecosystems The Galapagos Islands non-native animals introduced by humans eat some native species which causes a decrease in their population sizes non-native plants have been introduced which compete with the native plants causing a decrease in their population sizes eradication programmes have removed wild goats from the smaller islands and wild dogs from the largest island so other species of animals and plants are protects and quinine trees are kept in check with herbicides  when people visit the Islands, they're expected to follow a set of rules which includes not bringing any live plants or animals to the Islands or moving them between the islands Antarctica  visitors cause pollution and shipping accidents have led to oil spills hunting, whaling and fishing have all reduced wildlife populations all waste has to 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 hunting and whaling have been banned for some time The Lake District and Snowdonia National Parks many visitors go walking in the National Parks which leads to erosion of the footpaths and soil loss from the hillsides  soil ends up in the waters and lakes which disturbs the pH of the water in Snowdonia, lots of rain causes erosion of some of the paths and walkers often trample surrounding vegetation authorities attempt to repair and maintain as many of the paths and encourage regrowth of vegetation as often as they can in Snowdonia, volunteers hae dig drains next to the paths to let the water drain off
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