BiologyTopic 5 – Ecology and evolution

Communities and ecosystems

5.1.1 Define species, habitats, populations, community, ecosystems and ecology. 

Species: a group of organisms that can interbreed and produce fertile offspring.Habitat: the environment in which a species normally lives or the location of a living organism.Population: a group of organisms of the same species who live in the same area at the same time.Community: a group of populations living and interacting with each other in an area.Ecosystem: a community and its abiotic environment.Ecology: the study of relationships between living organisms and between organisms and their environment.

5.1.2 Distinguish between autotroph and heterotroph. 

Autotrophs are organisms that synthesize their organic molecules from simple inorganic substances whereas heterotrophs are organisms that obtain organic molecules from other organisms.

5.1.3 Distinguish between consumers, detritivores and saprotrophs. 

Consumer: an organism that ingests other organic matter that is living or recently killed.Detritivore: an organism that ingests non-living organic matter.Saprotroph: an organism that lives on or in non-living organic matter, secreting digestive enzymes into it and absorbing the products of digestion.

5.1.4 Describe what is meant by a food chain, giving three examples, each with at least three linkages (four organisms). 

A food chain shows the direction of energy flow from one species to another. For example, an arrow from A to B means that A is being eaten by B and therefore indicates the direction of the energy flow.  

Figure 5.1.1 - Example of a food chain

5.1.5 Describe what is meant by a food web.

A food web is a diagram that shows all the feeding relationships in a community with arrows which show the direction of the energy flow. 

5.1.6 Define trophic level.

Trophic level: the trophic level of an organism is its position in the food chain. Producers, primary consumers, secondary consumers and tertiary consumers are examples of trophic levels. 

5.1.7 Deduce the trophic level of organisms in a food chain and a food web.

Plants or any other photosynthetic organisms are the producers. Primary consumers are the species that eat the producers. Secondary consumers are the species that eat the primary consumers and tertiary consumers in turn eat the secondary consumers. 

5.1.8 Construct a food web containing up to 10 organisms, using appropriate information.

Figure 5.1.2 - Food web 

5.1.9 State that light is the initial energy source for almost all communities.

Light is the initial energy source for almost all communities. 

5.1.10 Explain the energy flow in a food chain.

Producers receive their energy from light energy (the sun) by means of photosynthesis. After this, the energy in organic matter flows from producers to primary consumers to secondary consumers to tertiary consumers. This is because producers will be eaten by primary consumers which in turn will be eaten by secondary consumers and so on. However, between these trophic levels, energy is always lost. All of the trophic levels lose energy as heat through cell respiration. Also, as the organic matter passes from one trophic level to the next, not all of it is digested and so we have loss of energy in organic matter through feces. This energy then passes on to the detritivores and saprotrophs. Another energy loss occurs through tissue loss and death which can happen at any trophic level. Once again, this energy would be passed on to detritivores and saprotrophs as they digest these. Detritivores and saprotrophs in turn lose energy as heat through cell respiration.  

Summary:  

1. Energy flows from producers to primary consumers, to secondary consumers, to tertiary consumers...

2. Energy is lost between trophic levels in the form of heat through cell respiration, faeces, tissue loss and death.

3. Some of this lost energy is used by detritivores and saprotrophs. These in turn also lose energy in the form of heat through cell respiration. 

5.1.11 State that energy transformations are never 100% efficient.

Energy transformations are never 100% efficient. 

5.1.12 Explain that energy enters and leaves ecosystems, but nutrients must be recycled.

Energy is not recycled. It is constantly being supplied to ecosystems through light energy and then flows through the trophic levels. As it flows through the trophic levels energy is lost in feces, tissue loss and death. This energy from these losses is passed on to detritivores and saprotrophs. However the energy is then lost from the ecosystem as the remaining energy in the trophic levels and the energy in the saprotrophs and detritivores is lost through cell respiration in the form of heat. As a result, energy needs to be constantly supplied to the ecosystems. Nutrients on the other hand are different as they constantly have to be recycled. Carbon, nitrogen and phosphorus are all examples

of nutrients. There is only a limited supply of these as they are not resupplied to the ecosystems like energy. Therefor they have to be recycled over and over. They are absorbed from the environment, used by living organisms and then returned to the environment.

Summary: 

1. Energy is not recycled. Constantly being supplied to the ecosystem through light energy.2. Energy is lost from the ecosystem in the form of heat through cell respiration. 3. Nutrients must be recycled as there is only a limited supply of them. 4. They are absorbed by the environment, used by organisms and then returned to the

environment. 

5.1.12 State that saprotrophic bacteria and fungi (decomposers) recycle nutrients.

Saprotrophic bacteria and fungi (decomposers) recycle nutrients. 

The greenhouse effect

 

5.2.1 Draw and label a diagram of the carbon cycle to show the processes involved.

The carbon cycle (click to expand)

5.2.2 Analyse the changes in concentration of atmospheric carbon dioxide using historical records.

See video (coming soon)

5.2.3 Explain the relationship between rises in concentrations of atmospheric carbon dioxide, methane and oxides of nitrogen and the enhanced greenhouse effect.

The earths mean average temperature is regulated by a steady equilibrium which exists between the energy reaching the earth from the sun and the energy reflected by the earth back into space. The incoming radiation is short wave ultraviolet and visible radiation. Some of the radiation will be absorbed by the atmosphere and some of it will be reflected back from the earths surface into space. The radiation that is reflected back into space is infrared radiation which has a longer wavelength. Green house gases such as carbon dioxide, methane, and oxides of nitrogen tend to absorb some of the reflected infrared radiation and re-reflect it back towards the earth. This is what causes the

greenhouse effect and it results in an increase in average mean temperature on earth. It is a natural phenomenon. However, since there has been an increase in the green house gases in the past century, this has resulted in an increase of the green house effect leading to higher than normal average temperatures which could lead to disastrous consequences in the future. 

Summary: 

1. The incoming radiation from the sun is short wave ultraviolet and visible radiation.2. Some of this radiation is absorbed by the earths atmosphere.3. Some of the radiation is reflected back into space by the earths surface. 4. The radiation which is reflected back into space is infrared radiation and has a longer

wavelength. 5. The greenhouse gases in the atmosphere absorbe some of this infrared radiation and re-

reflect it back towards the earth.6. This causes the green house effect and results in an increase in average mean

temperatures on earth. 7. A rise in greenhouse gases results in an increase of the green house effect which can be

disastrous for the planet. 

5.2.4 Outline the precautionary principle.

The precautionary principle holds that, if the effects of a human-induced change would be very large, perhaps catastrophic, those responsible for the change must prove that it will not do harm before proceeding. This is the reverse of the normal situation, where those who are concerned about the change would have to prove that it will do harm in order to prevent such changes going ahead.

5.2.5 Evaluate the precautionary principle as a justification for strong action in response to the threats posed by the enhanced greenhouse effect.

There is strong evidence that shows that green house gases are causing global warming. This is very worrying as global warming has so many consequences on ecosystems. If nothing is done, and the green house gases are in fact causing the enhanced green house effect, by the time we realize it, it will probably be too late and result in catastrophic consequences. So even though there is no proof for global warming, the strong evidence suggesting that it is linked with an increase in green house gases is something we can not ignore. Global warming is a global problem. It affects everyone. For these reasons, the precautionary principle should be followed. Anyone supporting the notion that we can continue to emit same amounts or more of the green house gases should have to provide evidence that it will not cause a damaging increase in the green house effect. 

5.2.6  Outline the consequences of a global temperature rise on arctic ecosystems.

Global warming could have a number of disastrous consequences largely affecting the arctic ecosystems: 

The arctic ice cap may disappear as glaciers start to melt and break up into icebergs. 

Permafrost will melt during the summer season which will increase the rate of decomposition of trapped organic matter, including peat and detritus. This in turn will increase the release of carbon dioxide which will increase the green house effect even further.  

Species adapted to temperature conditions will migrate north which will alter food chains and have consequences on the animals in the higher trophic levels. 

Marine species in the arctic water may become extinct as these are very sensitive to temperature changes within the sea water.

Polar bears may face extinction as they loose their ice habitat and therefore can no longer feed or breed as they normally would.

Pests and diseases may become quite common with rises in temperature.  As the ice melts, sea levels will rise and flood low lying areas of land. Extreme weather events such as storms might become common and have disastrous

effects on certain species. 

Populations

5.3.1 Outline how population size is affected by natality, immigration, mortality and emigration.

Natality: increases population size as offspring are added to the population.Immigration: increases population size as individuals have moved into the area from somewhere else and so this adds to the population. Mortality: decreases the population as some individuals get eaten, die of old age or get sick.Emigration: decreases the population as individuals have moved out of the area to go live somewhere else.

5.3.2 Draw and label a graph showing a sigmoid (S-shaped) population growth curve. 

5.3.3 Explain the reasons for the exponential growth phase, the plateau phase and the transitional phase between these two phases. 

The sigmoid graph showing the population growth of a species has three phases which are; the exponential phase, the transitional phase and the plateau phase. At the start of the sigmoid curve we can see the exponential phase. This is where there is a rapid increase in population growth as natality rate exceeds mortality rate. The reason for this is because there are abundant resources

available such as food for all members of the population and diseases as well as predators are rare. As time passes, the population reaches the transitional phase. This is where the natality rate starts to fall and/or the mortality rate starts to rise. It is the result of a decrease in the abundance of resources, and an increase in the number of predators and diseases. However, even though population growth has decreased compared to the exponential phase, it is still increasing as natality rate still exceeds mortality rate. Finally, the population reaches the plateau phase. Here, the population size is constant so no more growth is occurring. This is the result of natality rate being equal to mortality rate and is caused by resources becoming scarce as well as an increase in predators, diseases and parasites. These are the limiting factors to the population growth. If natality rate starts to drop then mortality rate will drop too as more resources become available. As natality rate starts to increase again so does mortality rate as resources become scarce. This keeps the population number relatively stable. If a population is limited by a shortage of resources then we say that it has reached the carrying capacity of the environment. 

Summary:

Exponential phase:

1. Rapid increase in population growth.2. Natality rate exceeds mortality rate.3. Abundant resources available. (food, water, shelter)4. Diseases and predators are rare.

Traditional phase:

1. Natality rate starts to fall and/or mortality rate starts to rise.2. There is a decrease in the number of resources.3. An increase in the number of predators and diseases.4. Population still increasing but at a slower rate.

Plateau phase:

1. No more population growth, population size is constant. 2. Natality rate is equal to mortality rate.3. The population has reached the carrying capacity of the environment. 4. The limited resources and the common predators and diseases keep the population

numbers constant. 

5.3.4 List three factors that set limits to population increase. 

1. Shortage of resources (e.g. food)2. Increase in predators3. Increase in diseases and parasites

 

Evolution

5.4.1 Define evolution

Evolution is the cumulative change in the heritable characteristics of a population. 

5.4.2 Outline the evidence for evolution provided by the fossil record, selective breeding of domesticated animals and homologous structures. 

Fossils, selective breeding and homologous structures have provided scientists with evidence that support the theory of evolution. As they started to study fossils they realised that these were not identical but had similarities with existing organisms. This suggested that organisms changed over time. Selective breeding of domesticated animals also provides this evidence as the domestic breeds have similar characteristics to the wild ones and can still breed with them. As selected wild individuals with desirable characteristics were bred, over time this resulted in a more desirable species from a human point of view. An example of this is the taming of wild wolves and their selective breeding in order to produce the domestic dogs we know today. This suggests that not only have these animals evolved but also that they can evolve rapidly. Finally scientists have found a number of homologous structures within different species. Many bones in the limbs are common to a number of species and therefore suggests that these have evolved from one common ancestor. 

5.4.3 State that populations tend to produce more offspring than the environment can support. 

Populations tend to produce more offspring than the environment can support. 

5.4.4 Explain that the consequence of the potential over production of offspring is a struggle for survival.

If the mortality rate remains lower than the natality rate then a population will keep growing. As more offspring are produced, there will be less resources available to other members of the population. If there is an over production of offspring this will result in a struggle for survival within the species as the resources become scarce and individuals in the population will start to compete for these. This results in an increase in mortality rate as the weaker individuals in the population will lose out on these vital resources that are essential for their survival. 

5.4.5 State that members of a species show variation. 

Members of a species show variation.

5.4.6 Explain how sexual reproduction promotes variation in a species.

Sexual reproduction is important for promoting variation as even though mutations form new genes or alleles, sexual reproduction forms a new combination of alleles. There are two stages in sexual reproduction that promote variation in a species. The first one is during meiosis during

which a large variety of genetically different gametes are produced by each individual. The second stage is fertilisation. Here, alleles from two different individuals are brought together to form one new individual. 

5.4.7 Explain how natural selection leads to evolution.

Individuals in a population differ from each other. Some individuals will have characteristics that make them well adapted to their environment whereas others will have characteristics that make them less adapted to their environment. The better adapted individuals are the ones that are more likely to survive and produce offspring while the less adapted ones are more likely to die. This is called natural selection. Natural selection results in the better adapted individuals to pass on their characteristics to more offspring as the lesser adapted ones are more likely to die before they reproduce. Over time, this result accumulates and a new generation is created with the favourable characteristics that makes this species better adapted to its environment. Natural selection has lead to the species evolving. 

5.4.8 Explain two examples of evolution in response to environmental change; one must be antibiotic resistance in bacteria.

Antibiotic resistance in bacteria is a common problem. It results from the transfer of a gene that gives resistance to a specific antibiotic usually by means of a plasmid to a bacterium. Some bacteria will then have this gene and become resistant to the specific antibiotic while others will lack the gene and so will die if exposed to the antibiotic. Over time, the non-resistant ones will all die off as doctors vaccinate patients, but the resistant ones will survive. Eventually, the resistant ones will be the only ones left as a result of natural selection and so a new antibiotic must be created. However, this has to be done on a regular basis as the bacteria keep evolving and become resistant to multiple antibiotics. 

The Peppered Moth is another example of evolution in response to environmental change. There are two types of these moths, one species has a light colour while the other one is darker. When Britain begun industrialising, the soot from the factories would land on trees and so the darker moths then had an advantage over the light ones as they could easily hide from predators. Before the soot, both types of moths were eaten by predators however now that the darker ones were able to hide the lighter ones got eaten more often.The population of the darker moths rapidly increased while that of the lighter ones rapidly decreased until only the dark moths were left. All the lighter moths were less adapted to the environmental change and so they could no longer survive in that new environment.