TOP

Edexcel Categories Archives: Add Topic 5

4.5.17 THE EXTENT TO WHICH ZOOS CAN PLAY A ROLE IN THE CONSERVATION OF ENDANGERED SPECIES

Zoos can play a large role in conserving endangered species by;

1. Conducting research

2. Running captive breeding programmes

3. Reintroducing species into the wild

4. Educating people

Research enables scientists to understand the role of a species in an ecosystem. By understanding the niche, food web, reproductive behaviour, habitat, feeding relationships etc scientists can suggest effective methods of conserving species.

Captive breeding programmes are used to reintroduce species to the wild, build up population numbers and maintain genetic diversity. In a small population many alleles are lost between generations because an individual only passes on 50% of their alleles. E.g.

R = Red, r = white

If the parents only have 2 children and they are both Red (RR) then the r allele has been lost. This is genetic drift and is a big cause of the loss of genetic diversity in an endangered species.

To avoid this studbooks are kept (basically, a family tree for the captive animals) so that only non-related animals are bred with each other. This decreases the change of genetic drift and also decreases the change of genetic disease.

Wild animals are often introduced to captive breeding programmes to avoid these problems

Reintroducing species into the wild has some success, but depends greatly on the species. As a general rule of thumb, the more advanced the species the more difficult reintroduction is. This is because animals need to learn specific behaviours e.g. how to hunt, how to reproduce, how / where to find shelter, group behaviours. Breeding animals in captive environments that mimic the wild has more success because it allows some of these behaviours to be learned in captivity. Feeding the animals in the wild also helps survival rates.

Educating people is essential to conservation. Often just doing something slightly differently will have a big impact on conserving a species e.g. building roads with tunnels under them for badgers.

 

Continue Reading

4.5.16 THE CONCEPT OF SUCCESSION TO A CLIMAX COMMUNITY

Primary succession is the first stage of the ecological succession of plant life from abiotic land with no soil to fully support plant ecosystems (e.g., a forest). In primary succession, pioneer plants like mosses and lichen, start to “normalize” the habitat, creating rudimentary soil from their dead matter. These pioneer plants create conditions for the start of plant growth and so more complex plants like grasses and shrubs begin to colonise the area.

Over time the grass area is colonised by small woody plants, which give way to small trees and finally, after a few hundred years, large trees take over. The large trees represent the climax community because succession stops at this point.

A good example of primary succession takes place after a volcano has erupted. The barren land is first colonised by simple pioneer plants which pave the way for more complex plants, such as hardwood trees by creating soils and other necessities. Unlike secondary succession, which refers to succession after an environmental disaster (such as a forest fire) primary succession occurs on the geologic timescale, over thousands of years.

 

Continue Reading

4.5.13 THE HISTORICAL DEVELOPMENT OF THE THEORY OF EVOLUTION

1798 Malthus publishes paper on population growth. Malthus noticed that the human population was expanding exponentially. He thought that the human population would outgrow its resources and that this would lead to famine and war.

Darwin was influenced by this idea, because he noticed that animal populations grow exponentially and then plateau when they reach the limits the environment can sustain (i.e. the population size is determined by the environment)

1809 Lamarck publishes a mechanism for evolution based on two laws

Law 1: Organs / structures grow if they are used. This means that the environment determines the phenotype of an organism

Law 2: Changes are passed on to the next generation

So a blacksmith, who uses his muscles all day, will grow bigger muscles. This works! But, will the bigger muscles be passed onto his children? No, so Lamarck’s theory is easy to falsify.

1859 Darwin publishes the Origin of species by means of Natural Selection. He publishes with Wallace who wrote to Darwin to discuss his own ideas about evolution. They were very similar to Darwin’s and this prompted Darwin to publish.

 

Continue Reading

4.5.12 HOW NATURAL SELECTION CAN LEAD TO EVOLUTION

Evolution: the idea that one species changes into another over time

Natural Selection: Darwin’s suggestion for the process by which evolution might occur

Evolution by Natural Selection (Darwinian Evolution)

1. There is variation in a species

2. More individuals are born than the environment can sustain, so some individuals must die.

3. The individuals that survive tend to be those that have alleles which give them a selective advantage in their environment (i.e. they are the best adapted to their environment, e.g. camouflaged). These are the “fittest”

4. The fittest survive long enough to reproduce and pass their alleles onto the next generation.

5. Over a few generations the frequency of “fit” alleles increases and the frequency of “unfit” alleles decreases

6. Soon all / most individuals have the “fit” phenotype and the “unfit” phenotype is eradicated

7. This process continues over many generations

8. Over this time new mutations occur, which give new even better alleles

9. Over time the mutations accumulate in the phenotype until the organism is unable to reproduce (i.e. produce fertile offspring) with the original organisms. At this point a new species has been produced (speciation)

This process is speeded up by isolation (see 4.5.14) because this stops the influx of alleles from outside and allows new mutations to accumulate in the genotype more quickly.

Continue Reading

4.5.11 THE EFFICIENCY OF ENERGY TRANSFERS BETWEEN TROPHIC LEVELS

Energy is lost between trophic levels. Energy is lost in the following ways; in respiration (mostly lost through heat), energy still present in egested food, through movement, through digestion, energy still present in excreted materials etc

Of the 100% sunlight energy that reaches plants, ~5% is converted into NPP. Energy is lost in the following ways; reflected light, light of wavelengths not useful to plants, passes through leaves, lost in respiration, lost as heat etc.

Continue Reading

4.5.10 GROSS PRIMARY PRODUCTIVITY, NET PRIMARY PRODUCTIVITY AND PLANT RESPIRATION

NPP = Net Primary Productivity (amount of stored chemical energy the plant has to use for growth. This is directly proportional to biomass)

GPP = Gross Primary Productivity (amount of stored chemical energy the plant earns through photosynthesis)

R = Respiration (amount of energy lost through respiration, i.e. heat, lost as CO2 etc)

Best analogy is a salary. GPP is the amount of stored chemical energy the plant earns through photosynthesis. R is like income tax. The plant has to pay “respiration tax” because it can’t photosynthesis at night & not all parts of the plant are capable of photosynthesis. NPP = disposable income: what the plant has to spend after paying tax.

Continue Reading