Posts Tagged ‘growth’

  • Explain the concepts of limiting factors and carrying capacity in the context of population growth.
Carrying  capacity is the maximum number of organisms that an area or ecosystem can sustainably support over a long period of time.
There are however limiting factors including temperatures, water and nutrient availability. The main factors are temperature and water availability.
Limiting factors are factors that limit the distribution or numbers of a particular population. Limiting factors are environmental factors which slow down population growth.
Temperature:
There are many ways the temperature can affect species. For example some seeds only grow in extremely high temperatures as it enriches the soil with nutrients and kills competition. However some are damaged if they are too warm or too cold. Some are able to survive low temperature. Animals adapt to the hot/ cold temperature either by burrowing under the ground to avoid heat or having cold blood in the heat.
Water:
All plants/animals need water to survive, for plants have no water could cause the plant to not germinate or seeds to die. No water = Death.
  • Describe and explain S and J populations curves.
S-curve (Sigmoidal) : population growth curve that shows a rapid growth at the beginning then a slow down as the carrying capacity is reached.
J-curve:
A population curve which shows only exponential growth. It starts slow the becomes increasingly fast.
  • Describe the role of density-dependent and density-independent factors, and internal and external factors, in the regulation of populations.
Density-dependent factors:
Factors that lower the birth rate or raise the death rate as a population grows in size. They are negative feedback mechanisms leading to the stability or regulation of the population.
When prey increases so does the predator, but when this occurs the prey decreases and then again the predators decrease too causing the prey to increase again.
Density-independent factors:
Factors that affect a population irrespective of population density notably environmental change. Abiotic factors are density-independent factors, the most important ones are the extremes of weather (droughts, fires and hurricane) and long-term climate change.
These factors have an impact that can increase the death rate and reduce the birth rate, it all depends on how severe the event was.
Factors which regulate population size can be divided into either INTERNAL or EXTERNAL.
Internal:  fertility rates, territory sizes
External: predation, pressure, parasitism
The major cause of population regulation are in the environments, these can be physical or biological.
The physical class of environmental factors are water availability, nutrient availability anf so on.
Biological factors include predators, and competition.
Ways humans can cause population growth:
  • increase available resources
  • reduce competition
  • reduce pressure from predators
  • introduce animals to new areas
Ways to decline population:
  • change environment, cause habitat disruption
  • change the biological environment by introducing new species
  • cause secondary extinctions
  • overkill
  • Describe the principles associated with survivorship curves including, K and r strategists.
Survivorship curves and r and k strategists:
K-strategists are slow growing and produce few, large offspring that mature slowly.
R-strategists, slow and mature quickly and produce many, small offspring.
K= carrying capacity
R= growth rate
K-strategist:
  • low reproductivity
  • large investment in parental care
  • late maturity/longer living
  • slow growth
  • larger size
  • require stable environment
R-straegists:
  • high reproductivity
  • short life
  • low investment in parental care
  • early maturity
  • rapid growth
  • small organisms
  • highly adaptable
  • large number of few species
Survivorship rates:
What influences survivorship rates:
  • competition for resources
  • adverse environmental conditions
  • predator-prey relationships
Example of survivorship curve:
  • curve for species where individuals survive for their potential life span, and die at the same time. Salmons/humans (K-strategists)
  • curve for species where individuals die young but who survives lives very long life turtles/ oysters. (r-strategists)
  • Describe the concept and processes of succession in a named habitat.
Succession: Change in the community structure of a particular area over time.
Primary succession: colonization of newly created land by organisms (rock).
Secondary succession: occurs in places where a previous community has been destroyed. (forest/fire) It is faster than primary succession because of the presence of soil and a seed bank.
Pioneer= earliest community of the succession.
Climax community= the last and final community.
The change from pioneer to climax is called a sere.
Succession is the process of change over time in a community changes in the community of organisms frequently cause changes in the physical environment that allow another community to become established and replace the former through competition. They get more complex at the end.
Zonation:
The arrangement or patterning of plant communities or ecosystems into bands in response to change, over a distance, in some environmental factor.
The main biomes display zonation with altitude on a mountain, or around the edge of a pond in relation to soil moisture.
  • Explain the changes in energy flow, gross and net productivity, diversity and mineral cycling in different stage of succession. 
GP, NP and diversity will change over time as a ecosystem goes through succession. GP is low in early stages then increases as soils become more structured. As food webs become more structured NPP and diversity stabilize as the ecosystem reach climax population.
  • Describe factors affecting the nature of climax communities. 
Climax community:
  • greater biomass
  • higher levels of species diversity
  • more favourable soil condition
  • better soil structure
  • lower pH
  • taller and longer living plant species
  • more k-strategies or fewer r-strategist
  • greater habitat diversity
  • steady state equilibrium
Climate and edaphic factors determine the nature of a climax community. Human factors frequently affect this process through, for example; fire, agricultures, grazing and/or habitat destruction.
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  • Explain the concept of an ecological footprint as a model for assessing the demands that human populations make on their environments.

The ecological footprint of a population is the area of land, in the same vicinity as the population, that would be required to provide all the population’s resources and assimilate all its wastes. As a model, it is able to provide a quantitative estimate of human carrying capacity. It is, in fact, the inverse of carrying capacity. It refers to the area required to sustainability support given population rather than the population that a given area can sustainably support.

Ecological footprints can be increased by:

  • greater reliance on fossil fuels
  • increased use of technology and energy (but technology can also reduce the footprint)
  • high levels of imported resources (which have high transport costs)
  • large per capita production of carbon waste (high energy use, fossil fuel use)
  • large per capita consumption of food
  • a meat-rich diet

Ecological footprints can be reduced by:

  • reducing use of resources
  • recycling resources
  • reusing resources
  • improving efficiency of resource use
  • reducing amount of pollution produced
  • transporting waste to other countries to deal with
  • improving country to increase carrying capacity
  • importing resources from other countries
  • reducing population to reduce resource use
  • using technology to increase carrying capacity
  • using technology to intensify land

There are many plans and innovations being set to reduce the ecological footprint in the future, this is funded by the MEDCs who have the biggest problems with their ecological footprints.

  • Calculate from appropriate data the ecological footprint of a given population, stating the approximations and assumptions involved.

The ecological footprint calculation is very complex, however approximations can be obtained through the steps outlined in this figure:

The total land requirement (ecological footprint) can then be calculated as the sum of these two per capita requirements, multiplied by the total population.

This calculation clearly ignores the land or water required to provide any aquatic and atmospheric resources, assimilate wastes other than CO2, produce the energy and material subsidies imported to the arable land for increasing yields, replace loss of productive land through urbanzation, and so on.

Factors used in a full ecological footprint calculation would include those in the following list:

  • bioproductive (currently used) land: land used for food and materials such as farmland, gardens, pasture and managed forest
  • bioproductive sea: sea area used for human consumption
  • energy land: an amount of land that is required to support renewable energy instead of non-renewable energy. The amount of energy land depends on the methods of energy generation ad is difficult to estimate for the planet
  • built land: land that is used for development such as roads and buildings
  • biodiversity land: land required to support all of the non-human species
  • non-productive land: land such as deserts is subtracted from the total land available

There are factors ignored when calculating the ecological footprint which influence the amount of land a population needs to support itself:

  • the land or water required to provide and aquatic and atmospheric resources
  • land or water needed to assimilate wastes other than carbon dioxide
  • land used to produce materials imported into the country to subsidize arable land and increase yields
  • replacement of productive land lost through urbanization

If everyone on Earth had the same lifestyle as the ones in the MEDCs, many Earths would be needed to support the global population.

  • Describe and explain the differences between the ecological footprints of two human populations, one from an LEDC and one from a MEDC.

Data for food consumption are often given in grain equivalents, so that a population with a meat-rich diet would tend to consume a higher grain equivalent than a population that feeds directly on grain.

The standards of living between MEDCs and LEDCs  change according to the resource consumption, energy usage and waste production, disparities should be expected between the ecological footprints of LEDCs and MEDCs. LEDCs have small ecological footprints as MEDCs have much greater rates of resource consumption. This is partly because MEDCs have higher incomes and the demands for energy resources is high. MEDCs consume a lot of resources as they are wasteful, they also have more waste and pollution. LEDCs are the opposite with lower consumption as people do not have too much to spend. The economy of the country forces them to recycle many resources, however they are developing and they’re ecological footprint is increasing. MEDCs use twice as much energy in their diet provided by animal products than LEDCs.

  • Discuss how national and international development policies and cultural influences can affect human population dynamics and growth.

Many policy factors influence human population growth. Domestic and international development policies (which target the death rate through agricultural development, improved public health and sanitation, and better service growth by lowering mortality without significantly affecting fertility.

Some analysts believe that birth rates will come down by themselves as economic welfare improves and that the population problem is therefore better solved through policies to stimulate economic growth.

Education and birth control encourages family planning. Parents may be dependent on their children for support when they get older and this may create an incentive for more children.

Urbanization  may also be a factor in reducing crude birth rates.

Policies directed towards the education of women, enabling women to have greater personal and economic independence, may be the most effective method for reducing population pressure.

  • Describe and explain the relationship between population, resource consumption and technological development, and their influence on carrying capacity and material economic growth.

Because technology plays such a large role in human life, many economists argue that human carrying capacity can be expanded continuously through technological innovation. For example, if we learn to use energy and material twice as efficiently, we can double the population or the use of energy without necessarily increasing the impact imposed on the environment. However, to compensate for foreseeable population growth and the economic growth that is deemed necessary, especially in developing countries, it is suggested that efficiency would have to be raised by a factor of 4 to 10 to remain within global carrying capacity.