Uploaded by Diptesh Sarkar


Assignment 4 Solution
Diptesh Sarkar
1) Redundant species hypothesis
The Redundancy Hypothesis assumes that more than one species plays a given role within an
ecosystem (Walker, 1992). Environmental conditions in ecosystems are dynamic, and a
community of diverse species may be more likely to contain a particular species that is
tolerant of stress conditions (for example, during drought, high or low temperatures, soil
disturbed by tillage) and maintain overall stability in the function of the ecosystem.
According to the redundancy hypothesis, species that play the same roles in the ecosystem
(sometimes referred to as a guild) can compensate for each other if some are lost under
particular conditions. In this way, species redundancy enhances the ability of an ecosystem to
recover from a disturbance (resilience).
Plant productivity depends on species biodiversity.
3) S is the species richness, A is the area of the region, and z is a constant defining slope.
Then the species area relation is
Any power on this type of equation can be made linear by using taking log
compare this with straight line equation y=m*x+c we get
y=logs, slope(m)= z, x=logA, intersection on y axis is logC
4) Nitrogen fixing bacteria depends on leguminous plants as their primary source. N fixation
will be reduced, Losing N from soil and immobilization of nitrogen by microorganisms can
also take place. This will all result in lack of nitrogen in soil, and low uptake by the
organisms consuming those plants will also suffer from low nitrogen and will have difficulty
in producing required amino acids.
5) a)The intermediate disturbance hypothesis suggests that local species diversity is
maximized when ecological disturbance is neither too rare nor too frequent.
b) At high levels of disturbance, due to frequent forest fires or human impacts like
deforestation, all species are at risk of going extinct.
c) At intermediate levels of disturbance, diversity is thus maximized because species that
thrive at both early and late succession stages can coexist.
6) Ecological efficiency describes the efficiency with which energy is transferred from one
trophic level to the next. It is determined by a combination of efficiencies relating to
organism resource acquisition and assimilation in an ecosystem. It’s the percentage of energy
transferred from lower trophic to higher trophics, in one direction only. Three categories of
transfer efficiency are required to predict energy flow from primary production to secondary
Consumption efficiency: net percentage of productivity of a trophic level consumed by
immediate higher level described by energy absorbed/energy produced.
Assimilation efficiency: percentage of ingested food assimilated described by energy
assimilated/energy absorbed
Production efficiency: percentage of assimilated energy converted to new biomass described
by net production/energy assimilated.
The ten percent law for the transfer of energy from one trophic level to the next trophic level.
During the transfer of energy from organic food from one trophic level to the next, only about ten
percent of the energy from organic matter is stored as flesh. The remaining is lost during transfer,
broken down in respiration, or lost to incomplete digestion by higher trophic levels.Energy is also
lost due to decay, respiration, wound, old age etc.
7) The gases in the atmosphere that absorb radiation are known as "greenhouse gases"
(sometimes abbreviated as GHG) because they are largely responsible for the greenhouse
effect. The greenhouse effect, in turn, is one of the leading causes of global warming. The
most significant greenhouse gases are water vapor (H2O), carbon dioxide (CO2), methane
(CH4) and nitrous oxide (N2O). The most important reasons is the burning of fossil fuels.
Fossil fuels contain carbon, and when they are burnt this carbon combines with oxygen in the
atmosphere to form carbon dioxide.
Solution: We have to go through filtration process at chimney which purify CO2,CO before
releasing it in air. You can help to reduce the demand for fossil fuels, which in turn reduces
global warming, by using energy more wisely. Buying products with minimal packaging will
help to reduce waste. Better sewage system of wastage so that that does not compose
methane, reducing use of fertilizers, less use of AC, refrigerators and awareness of people can
help to not more increase in global temperature.
Polar bearsScientific name-Ursus maritimus
Life pattern: Polar bears can live up to 25 or 30 years in the wild. The top Arctic predators,
polar bears primarily eat ringed seals but also hunt bearded seals, walrus, and beluga whales,
and will scavenge on beached carrion such as whale, walrus, and seal carcasses found along
the coast. These bears often eat only seals' skin and blubber, leaving the carcass for other
animals to scavenge and thus playing a critical role in the Arctic food chain.
Habitat: Polar bears live throughout the ice-covered waters of the circumpolar Arctic, with
distribution dependent on food availability and sea-ice conditions; they are most often found
at the convergence of sea ice and open water, and where seals congregate. It can be find in
arctic basin, Baffin bay, East Greenland etc area.
Population Size: The US Geological Survey estimated the global population of polar bears at
24,500 in 2005. In 2015, the International Union for the Conservation of Nature (IUCN)
Polar Bear Specialist Group (PBSG) estimated the population at 26,000 (range 22,000–
31,000) but additional surveys published since then bring the total to near 28,500 with a
relatively wide margin of error.
Metapopulation Dynamics: It is find 1)Arctic Basin 2)Baffin Bay 3)Barents Sea 4)Chukchi
Sea 5)Davis Strait 6)East Greenland 7)Foxe Basin 8)Gulf of Boothia 9)Kane Basin 10)Kara
Sea 11)Laptev Sea 12)Lancaster Sound 13)McClintock Channel 14)Northern Beaufort
15)Norwegian Bay 16)Southern Beaufort 17)Southern Hudson Bay 18Viscount Melville
19)Western Hudson Bay.
If we consider these each area as one patch where all these patches have an equal chance of
receiving colonies and equal chance of extinction at a time then by Levin’s model of
metapopulation we can write
where p=fraction of currently occupied patches,
c=probability per empty patch of colonization
e=probability per patch of extinction
Behaviour: Unlike brown bears, polar bears are not territorial. Although stereotyped as being
voraciously aggressive, they are normally cautious in confrontations, and often choose to
escape rather than fight. Satiated polar bears rarely attack humans unless severely provoked.
However, due to their lack of prior human interaction, hungry polar bears are extremely
unpredictable, fearless towards people and are known to kill and sometimes eat humans.
Conservation Status: Polar bear population sizes and trends are difficult to estimate
accurately because they occupy remote home ranges and exist at low population densities.
Polar bear fieldwork can also be hazardous to researchers. As of 2015, the International
Union for Conservation of Nature (IUCN) reports that the global population of polar bears is
22,000 to 31,000, and the current population trend is unknown. Nevertheless, polar bears are
listed as "Vulnerable" under criterion A3c, which indicates an expected population decrease
of ≥30% over the next three generations (~34.5 years) due to "decline in area of occupancy,
extent of occurrence and/or quality of habitat". Risks to the polar bear include climate
change, pollution in the form of toxic contaminants, conflicts with shipping, oil and gas
exploration and development, and human-bear interactions including harvesting and possible
stresses from recreational polar-bear watching.
Establishment of community awareness and conservation programs and designation of a
protected area that is locally appropriate (such as a conservation or community resereve) may
also be urgently required to safe guard the future of this threatened species. More forestation,
and source of food can also help toward this. Concerns over the future survival of the species
led to the development of national regulations on polar bear hunting, beginning in the mid1950s. The Soviet Union banned all hunting in 1956. Canada began imposing hunting quotas
in 1968. Norway passed a series of increasingly strict regulations from 1965 to 1973, and has
completely banned hunting since then.