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Populations and Sustainability

Populations and Sustainability

 

  • The factors that determine a population size are Abiotic Factors and Biotic Factors

    • Population size is total number of organisms of one species in a habitat

    • A given ecosystem of habitat will have a carrying capacity which is the maximum population size that can be maintained over a long period of time in the given habitat

    • A population growth curve will have 3 key features 

      • A lag phase: few individuals, still acclimatising so overall population growth rate is low and slow 

      • A log phase: Resources are plentiful so conditions for reproduction are good and the rate of the population increases rapidly as the rate of reproduction drastically outweighs the rate of mortality 

      • A stationary phase: This is when the population nears the carrying capacity and the rates of reproduction and mortality are approximately equal and the habitat cannot support a larger population the population will fluctuate very slightly around the carrying capacity (graph oscillates above and below)

    • A habitat that reaches carrying capacity does so because limiting factors affect the growth of a given population. Some of these limiting factors are density dependent which act just as strongly irrespective of the size of the population others are density dependent and as the population increases the factor will influence the size of the population more strongly. An example of density independent may be temperature being low while a density dependent factor may be the availability of Food 

    • 2 Strategists for the population growth of an organism 

      • K-strategists (THINK - HUMANS K (anishka)

        • For these populations limiting factors exert a more significant effect as the population size gets closer to the carrying capacity 

        • They are usually birds or larger mammals 

        • They will typically have a low reproductive rate and slow development as well as an old reproductive age an a longer lifespan 

      • R-strategists (THINK R - RAPID)

        • The population size increases so rapidly that it exceeds the carrying capacity before limiting factors have an effect. Once the carrying capacity is exceeded there are not enough resources to enable survival 

        • This leans a death phase is entered and the population size decreases 

        • Known as a boom and bust 

        • Often species such as mice, insects, spiders and weeds 

        • Exhibit a high reproductive rate, quick development, young reproductive age and s short life spac with small body mass (THINK INVERSE OF K) 

    • Interaction between Predators and Prey

      • As the predator population increases more prey are eaten and the prey population decreases which leaves less food for the predator which in turn leads to predator population decreasing and thus with fewer predators the prey population can again increase and then there is once again more food for the predators which leads to an increase in predator population and this cyclical interaction continues 

      • Graphically represented: Prey population will oscillate to a greater extent in larger numbers than predator population. The predator population will also oscillate with the peaks in its population being just prior to lows in prey population 

      • MAKE SURE: to not show predator population to ever be higher than prey as this would not occur 

    • Interaction in Competition: 

      • Competition occurs when resources are not present in adequate amounts 

      • 2 types: interspecific and intraspecific 

        • Intraspecific is competition between individuals of the same species. This occurs as factors such as food availability etc. This acts to keep the population relatively stable. To a degree is what enables natural selection  

        • Interspecific competition is competition between individuals of different species and affects population size and distribution of a species. As there is more overlap between two species niches there is more competition as if the niche is the same only one will survive or at the very least one population will be far smaller (tested by Gause with 2 bacteria) Also affected by the other factors that may be more suitable for one species 

  • Conservation & Preservation:

    • Conservation: maintaining biodiversity as well as the diversity between species and the maintenance of a variety of habitats and ecosystems in an active management process with human intervention 

    • Preservention: keeping species and habitats as they are now by eliminating elimination any human impact on the ecosystem 

  • Strategies and Reasons for Conservation: 

    • We threaten biodiversity through over-exploitation of wild populations for leisure or trade purposes as we harvest species at a faster rate than they can replenish themselves

    • Strategies: 

      • Protected areas such as national parks or sites of special scientific interest 

      • In situ and ex situ conservation, in situ being at the site itself and ex situ being in a different environment 

      • Raising capacity by adding food 

      • Adding individuals to enlarge a population

      • Control predators and poachers

      • Vaccinate individuals 

      • Prevent pollution or disruption and intervene to restrict the progress of succession (coppicing, mowing or grazing) 

    • Why?

      • Ethics: Every species can be seen to have value and we have an ethical duty to protect them for their sakes and for future generations etc.

      • Economic: Direct economic value in that when they are harvested they can be sold for profit such as plants, beneficial organisms for use in medication etc. and even natural predators to act as pest control 

      • Social: Tourism (links to economic) people find them aesthetically pleasing to view and some are attractions thus generate profit by enabling people to come and view them 

      • Aesthetic value: good to look at so should be kept 

  • Sustainable Management 

    • Timber Production

      • On a small scale: Coppicing whereby the stem of a tree is cut close to the ground so that new shoots can grow from the cut base and mature into new stems which can then be used 

      • On a small scale: Pollarding the stem is cut higher up to avoid deer eating emerging shoots 

      • To provide timber consistently, woodland managers divide woodland areas into sections and cut one section each year in a process known as rotational coppicing. Using this process by the time the first sections need to be cut again the new stems have matured and are ready to be cut 

      • This is good for biodiversity as it assures light reaches the shrub layer and thus increasing biodiversity, it also assures there are alway habitats for organisms

      • On a large scale: Often clear felling was used and would destroy the soil pH and mineral level, cause surface runoff and leave soil susceptible to soil erosion. Now this is rarely practices and each area of woodland is left for 50-100 years to mature btu this timescale is not cost effective. As a result numerous techniques are used 

        • Any harvested tree is replaced by another 

        • Local people should benefit 

        • The forest or woodland must be able to maintain its ecological function 

      • There is also practice of selective felling whereby only the largest and most valuable trees are harvested which leaves the habitat and ecosystem largely unaffected 

      • Sustainable management is used to enable each tree to supply more wood through the control of pests and pathogens and only planting species which are known to grow well as well as employing optimal tree spacing 

    • Fish Stock: 

      • Fisheries: Marine stewardship council proposed three principles 

        • Fishing must take place at a level which allows it to continue indefinitely and overfishing must thus be avoided, the optimum is to maintain fish at the carrying capacity 

        • Fishing must be managed to maintain the structure, productivity and function as well as the diversity of the ecosystem 

        • Fisheries must adapt to comply with local, national and international regulations 

      • Aquaculture:

        • Breeding fish in an aquatic environment 

        • Provides sustainable fish stock 

        • Expanding rapidly and expected to feed more people than traditional fisheries 

      • Also the sizes of the mesh on nets can be controlled to reduce the number of ‘unwanted’ and discarded fish are caught and to also assure that younger fish can get through the net 

      • Fishing Quotas could be used: limiting the amount of certain fish species that fishermen are allowed to catch such that only a safe amount are captured 

        • Can cause more fish to be thrown back but these may often die so not wholly effective 

Case Studies: 

 

Balancing Human Needs and Preservation

  • The Terai Region (Nepal) 

    • Variety of endangered species found in the region and many people live in the region

    • Forest destroyed to make way for housing and other development which brings humans and animals closer in contact and increases conflict (tigers killing livestock) 

    • Conservation charities such as WWF work with local people to meet their needs without damaging the environment such as providing solar cookers and biogas generators to prevent the harvesting of wood from the forest. Mint hedges are advised to be planted around crops to keep animals away 

    • Waterholes have also been built and measures against poaching have been put in place, they have also acted to educate the local individuals on the 

  • Maasai Mara

    • Large savannah grassland home to large populations of wildebeest, lions etc. as well as many individuals in the area who earn a living through livestock but overgrazing destroys the grassland 

    • Conservationists helping individuals make money from the land through conservation and ecotourism as opposed to farming and teaching sustainable farming so economic needs are met with little damage to the ecosystem, additionally the land has been placed in trusts and made into wildlife reserves or national parks for conservation

  • Peat Bogs

    • Areas of upland UL have peat bogs which store water and carbon dioxide and are an environment for many plants and animals

    • Farmers use the bogs to graze sheep and deer which leads to conflict with conservationists as this causes a loss of moss species and soil compaction reducing biodiversity 

    • As a result government funded programs such as Environmental Stewardship Scheme awards farmers money to use the bogs in a sustainable way such as carrying out measures of surface runoff or lower the livestock that use the bogs and remove livestock at times 

 

Human Activity in Environmentally sensitive Ecosystems 

  • Galapagos Islands: 

    • Small group of islands in the Pacific Ocean with numerous rare species of plants and animals recently inhabitants and tourists has increased a lot 

    • HABITAT DISTURBANCE: Population increase has placed large demands on the resources such as water, energy, sanitation and increased pollution etc. (there was an oil spill 2001) 

    • OVER-EXPLOITATION: Overexploitation of resources has increased with numerous animals being killed for economic value as well sale with sea cucumber and tortoise numbers dropping hughley having a large impact on the ecosystem (some foundations such as the Charles Darwin research institute are acting to conserve and bring numbers back up of)

    • INTRODUCED SPECIES: Species introduced by inhabitants and tourists can outcompete some of the native species. Goats for example have overrun some islands and lead to soil erosion and some other introduced animals can hunt and kill smaller native organisms 

    • Management: 2 key strategies by the Darwin institute 1. Prevent introduction and reduce impact so far: Search arriving boats for foreign species and introduce natural predators to reduce damage to the environment caused thus far and culling (against goats THINK: video 360 no scopes). 2. Education and Introduction of No-Go zones 

  • Antarctic: 

    • Most southern continent and has attracted many scientists and tourists alike and more interest recently from Fishermen 

    • Overexploitation through Overfishing, whaling and hunting as seen in the example of Krill has caused damage to the food chain and ecosystem as a whole 

      • This is managed through the introduction of trigger levels which when reached mean fishing has to be conducted equally in all areas only to a catch limit to prevent a negative impact on the ecosystem 

    • Threats through pollution, hunting and poaching such as those posed to albatrosses and petrels (pollution through oil spills etc. as well) the birds will often swallow the hooks of boats attempting to catch fish in attempting to catch the fish themselves

      • This can be avoided by using bird scaring lines and weighted lines which sink out of the area a bird can reach as well as fish outside of feeding times

    • General pollution such as sewage into the ocean region and leaving rubbish from tourists or oil spills industrially

      • All waste must be taken away by boat and sewage should be treated before emptying 

      • Tourist restrictions in place 

      • Hunting and whaling have been banned 

  • Lake District: 

    • Invasive species have escaped from gardens and spread into the woodland and now outcompete many native species, some can form a canopy preventing light from reaching the woodland bed

      • Must be physically removed by conservationists

    • Limestone pavement has eroded and is being damaged but is an excellent environment for butterflies and rare ferns 

      • They are legally protected through the limestone pavement orders 

    • Footpath erosion and loss of soil as a result which then ends up in waterways and lakes and disturbs pH causing other issues in the wildlife which inhabits the ecosystem, many tourists may also walk on soil damaging plant species 

      • Regular repair and maintenance on the paths and educate walkers on the importance of sticking to the path. Regrowth is also being encouraged

    • Mires are often nutrient deficient and under threat from burning and grazing. 

      • Mires are now managed being rewetted to prevent them from becoming dry. In areas with rare birds or species the area is being carefully managed and grazing limited 

    • Hay meadows: support a rich diversity and are under threat from artificial fertiliser a d loss of species diversity 

      • Thus farmers are paid to maintain it 

  • Snowdonia: 

    • Farmers dig ditches to dry the land but this causes poor water quality in rivers and rain flows faster increasing flood risk 

      • Drainage ditches are benign blocked by hay bales 

    • Conifers are often planted as crops but this dries out the moorland as the trees absorb the water 

      • When the trees are cut some of the branches are used to block the ditches to slow water flow and keep the land moist 

    • Moorland was burnt to provide a varied habitat but this was stopped for grazing but the old heather burns easily so this increases risk of accidental fires. 

      • Controlled fires are lit to prevent heather becoming too old or dry 

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