Biology: Populations and Sustainability

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(a)i

explain the significance of limiting factors in determining the final size of a population

A habitat cannot support a population large than its carry capacity because of limiting factors which place a limit on population size.

The limiting factors may include:

Resources:

Food

Water

Light

Oxygen

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(a)ii

Nesting sites

Shelter

Effects of other species:

Predators

Parasites

Intensity of competition for resources

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(b)

explain the meaning of the term carrying capacity

The maximum population time that can be maintained over a period of time in a particular habitat

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(c)

describe predator–prey relationships and their possible effects on the population sizes of both the predator and the prey

When the predator population gets bigger, more prey are eaten

The prey population then gets smaller, leaving less food for the predators

With less food, fewer predators can survive, and their population size decreases

With fewer predators, fewer prey are eaten, and their population size increases

With more prey, the predatory population gets bigger, and the cycle continues

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(d)i

explain, with examples, the terms interspecific and intraspecific competition

Interspecific competition

Competition between individual of different species can affect both the population size and the distribution of a species in an ecosystem as no two species can occupy the same niche

Red v Grey squirrel

The red squirrel outcompetes the grey in conifer forests, but the grey squirrel outcompetes the red in forests with less than 75% conifers

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(d)ii

Intraspecific competition

Competition between individuals of the same species

If food supply becomes a limiting factor, the individuals best adapted to obtaining food will survive and reproduce, whereas those less well adapted will die out and fail to pass on their genes.

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(e)

distinguish between the terms conservation and preservation

Conservation is the maintenance of biodiversity, but the area can still be sustainably exploited

Preservation protects species by leaving their habitat untouched

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(f)i

explain how the management of an ecosystem can provide resources in a sustainable way, with reference to timber production in a temperate country

Selective felling

  • Some mature trees, diseased trees and unwanted species are harvested, leaving other trees to develop and distribute seeds to fill the gaps

Str*p felling

  • Small patches, or strips, of forest are cleared completely, leaving other patches untouched.
  • Large areas are not felled at the same time, so loss of species and soil erosion are avoided
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(f)ii

Coppicing

  • Trees are cut down, leaving stumps from which new shoot develop. These have a well developed root system and so grow fast. After a few years the shoots are cut and yield poles. Can be repeated indefinitely. Small strips or patches are cut in different years, providing a variety of habitats so producing high biodiversity
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(g)

explain that conservation is a dynamic process involving management and reclamation

Maintaining biodiversity in dynamic ecosystems requires careful management to maintain a stable community or even reclaim an ecosystem by reversing the effects of human activity

Some management strategies may include:

  • Raising the carrying capacity by providing extra food
  • Moving individuals to enlarge populations, or encouraging natural dispersion of individuals between fragmented habitats by developing dispersal corridors of appropriate habitat
  • Restricting dispersal of individuals by fencing
  • Controlling predators and poachers
  • Vaccinating individuals against disease
  • Preserving habitats by preventing pollution or disruption, or intervening to restrict the progress of succession
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(h)i

discuss the economic, social and ethical reasons for conservation of biological resources

Economic

  • Many species provide a valuable food source
  • Genetic diversity in wild strains of domesticated species may be needed in future for certain characteristics
  • Natural environments are valuable sources of potentially beneficial resources e.g. medicines
  • Natural predators of pests can act as biological control agents
  • Wild insect species pollinate crop plants
  • Other organisms maintain water quality, protect soil and break down waste products.
  • There is also evidence that reduced biodiversity may cause reduced climatic stability
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(h)ii

Social

  • Ecotourism relies on biodiversity, as does recreation

Ethical

  • Every species has a value in its own right
  • Every living thing has the right to survive
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(i)i

outline, with examples, the effects of human activities on the animal and plant populations in the Galapagos Islands

In 1980 the population of the Galapagos Islands was 5000, and about 4000 tourists visited every year. In 2005, the population was 28,000, and 100,000 tourists visited every year.

  • Dramatic increase in population size has placed huge demand on water, energy and sanitation services
  • More waste and pollution have been produce
  • The demand for oil has increased
  • 2001 oil spill had an adverse effect on marine and costal ecosystems
  • Increased pollution, building and conversion of land for agriculture has caused destruction and fragmentation of habitats
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(i)ii

  • Species have been harvested faster than they could replenish themselves.
    • Giant tortoises were taken to be eaten on long voyages
    • Fishing for exotic species of fish has decimated the population
    • Depletion of sea cucumbers has had a drastic effect on under-water ecology 
    • International market for Shark-fin has led to the deaths of around 150,000 sharkseach year
    • Humans have introduced many non-indigenous species
      • The red quinine tree spread rapidly and outcompetes the native species. Its presence has changed the landscape from mostly low scrub and grassland to a closed canopy forest. Many native animals have lost their nesting sites.
      • Goats
        • eat species unique to the islands,
        • outcompete giant tortoises for grazing,
        • tramples on tortoise nesting sites
        • transforms forests into grassland, causing soil erosion
      • Cats hunt a number of indigenous species
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