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Write an essay on the many different types of relationships and interactions between organisms.
The behaviours of organisms is important in the role of ecosystems as it helps to maintain the level of stability within it which keeps it diverse in most areas.
A stimulus is a change in the internal or external environment and causes an organism to respond to this via a movement known as Taxes, which is directional. This is when an organism moves its body towards a favourable stimulus (positive taxes) or away from a stimulus ( negative taxes). Kinesis on the other hand, a non-directional stimulus, is when an organism responds to a change in the environment by increasing its speed and the rate of movement, this can be seen in woodlice where they will try to move away from the bright conditions and go towards the dark. In plants, positive phototropism occurs in the shoots and this would be when it bends towards the light in order to maximize photosynthesis, this also helps it to compete against other plants by absorbing most of the light and so less light will pass on to the ones that exist closer to the soil. It is said that those organisms that respond to the stimuli gives it the greater chance of survival and will be able to improve its chances of survival and pass on advantageous alleles to further generations.
Directional selection is a mode of natural selection and it is the cause for some species survival. It is described as the increase in the frequency of an allele over time (typically advantageous) and it increases the chances of an organism's ability to survive and reproduce; can be categorized into many situations such as plants which pass on advantageous alleles i.e. tall plants outcompeting dwarf plants. The main example with directional selection lies within antibiotic resistance, this is when bacteria experience a selection pressure (antibiotics) which affect their survival chances and cause them to die and some will experience mutations. These mutations can be advantageous in the sense that it gives them protection towards antibiotics making them resistant. The mutated allele which offers the bacteria resistance will be seen present in many further generations (division via binary fission) as it improves their survival chances. Furthermore, bacteria divide exponentially which has negative impacts on organisms as it can kill them more easily due to its rapid increase in population which will then produce more toxins given that they are resistant to any antibiotics. This can be detrimental to organisms that are experiencing a genetic bottleneck i.e. pandas because their lack of genetic diversity offers very little chances of resistance to new diseases, possibly leading to the extinction of its species. Therefore, whilst directional selection does indicate that some species were not fit enough to survive, it's still important to maintain the rate at which bacteria mutates as aswell as it having health impacts, it can also have economical impacts on things like farming and tourism. Specifically with bananas as the most popular specie of banana, cavendish, is constantly being genetically modified in order to produce clones - making it vulnerable to diseases due to lack of genetic diversity so its more likely to go moldy which negatively affects countries that are primary product dependent, on bananas, like Ecuador.
Within the Nitrogen cycle, saprobionts like rhizobium help to give nutrients, such as nitrogen, to plant by secreting enzymes and digesting it known as extracellular digestion, which is important for things such as cell growth as nitrogen can be found in nitrogen bases and in the case of the phosphorus cycle, phosphorus can be found in many organic material such as ATP, which is needed for energy. The role of saprobiotic bacteria is therefore very useful and it does this by converting Nitrogen in the air into ammonium, which is then converted into ammonium ions (Nitrogen fixation).The Rhizobium forms a mutualistic relationship with the plant so it provides it with nutrients and receives carbohydrates i.e. glucose in return. Then in nitrification, nitrifying bacteria (Nitrosomonas) will convert ammonium ions into nitrites and thenNitrobacter saprobionts will convert nitrites into nitrates. The nitrates can then either be taken up by plants which is used for growth etc and then its dead matter fed on by animals and when animals dies they return back to ammonia, this process is ammonification. Alternatively, it can be converted back into nitrogen gas by denitrifying bacteria. However, this can reduce the yield of farmer crops because their crops will receive less nutrients so they tend to use artificial fertilizers which supplies their crops with nutrients like nitrate, ammonium ions and phosphorus in order to stimulate growth efficiently. This does have an environmental cost as too much fertilizers can leach into local waterways and this causes an algal bloom preventing sunlight from reaching the bottom of the water where most plants reside, limiting photosynthesis. Moreover, after the plants die the bacteria that feed off them will aerobically respire even more, reducing the dissolved oxygen availability in the water leading to the death of aquatic organisms. The interaction between plants and aquatic organisms is therefore necessary to maintain a stable environment, leading to the introduction of laws which regulate the use of fertilizers.
An ecosystem also has fluctuations in its populations due to the predator-prey cycle. The interaction between organisms relates to it’s trophic levels, an organism's position on the food chain,and the energy available. Trophic levels usually dont go past 5 because there is not enough energy available to support another organism. In an area where there are lots of prey such as snowshoe, it causes its predators (lynx) to feed on them due to the vast availability of food and so this causes interspecific competition. After the population of the prey begin to decrease, the availability of food also decreases so predators will compete against each other (intraspecific competition) for the limited food causing the predator population to decrease.Not only is it food that they compete against each other for but; mates, territory, water and many more. The prey start to increase their population via mating because there are not enough predators to slow their population growth but the predator population increases and consumes the prey, repeating the cycle again. This cycle maintains competition between species and within species.
Lastly, succession is the change in an ecosystem over time; primary succession is when soil is not available i.e. after a volcanic eruption which covered the surface with obsidian and secondary succession occurs when there is already soil available. The pioneer species enter the ecosystem and are able to survive the hostile abiotic conditions as they are well adapted to the environment. They make the abiotic conditions less hostile for new species so they outcompete the pioneer species since they are more well adapted to the new environment. As time goes on, more and more new species are better suited to enter and outcompete existing species which increases the diversity of the ecosystem and this causes the development of the climax community, for example in the UK - Woodlands.