M4

Question 1

The effect of predation on a population

Answer 1

In a simple relationship in which a predator feeds on only one type of prey, an increase in the prey population means that more food is available, and the predator population therefore also increases. This causes the prey population to derease, in turn resulting in a decrease in the predator population. If members of the remaining prey population cannot escape, they may all be eaten, and so die off. This will also result in the demise of the predator species. In situations where at least some prey can escape, however, equilibrium between the two species is reached. In cases where a predator population feeds on more than one type of prey, the predator may consume a larger proportion of a certain species if numbers of the other prey species have decreased.

Question 2

example of effect of predation on prey

Answer 2

In Canada, the snowshoe hare is preyed upon by lynxes. Both of these species show sudden changes in their population densities every 10 years, as shown in the graph below.
This is because the lynxes, being predators, increase in number only after an increase in the hare population; their population curve therefore seems to `lag’ behind the hare curve. In large communities, the populations of predator and prey fluctuate over time. Predator numbers copy those of the prey and will increase or decrease after a change in prey numbers. For either population to survive, there will always be more prey than predators.

Question 3

Factors that may affect the abundance of predator and prey distribution

Answer 3

Number of predators competing for the same prey
Availability of prey’s food
Reproduction rate
Death rate (factors other than predation)
Ratio males to females
Size of ecosystem
Movement between ecosystems
Number of shelter sites available

Question 4

effects of interspecific competition on the population

Answer 4

When the competition is interspcific, (between two or more species) one species is usually better suited and will always have a higher population than the other, even when that resource and the populations fluctuate. (see 4.1 for population graph)

Question 5

effects intraspecific competition on a population

Answer 5

intraspecific competition takes place between two organisms of the same species. For example, two oak trees growing too close together fighting for sunlight and nutrients or two male deer competing for mates.

Question 6

allelopathy

Answer 6

Competition between plants involves allelopathy, where a plant releases specific biochemicals (allelochemicals) that influence, either detrimentally or beneficially, the growth of other individual plants around it. Often, alleopathy involves plants releasing chemicals into the soil to prevent other plants from growing in the same space.

Acacia trees, which are the main diet of giraffes, let off allelochemicals when they are eaten to warn nearby acacias that there is a grazing giraffe around, in which case they cut off their water flow to the leaves and become bitter, unpleasant and even poisonous.

Question 7

The effect of symbiosis (general) on a population

Answer 7

Symbiosis allows for an increase in biodiversity and therefore a more resilient ecosystem. For example, coral reefs are only possible because the coral (animals) has a symbiotic relationship with photosynthetic algae. The reefs provide a unique environment for fish and marine invertebrates.

mutualism –> bees and flowers

commensalism –> shark and teef cleaning fish

parasitism –> mosquitoes and people, fleas and animals