19.4 - Predation Flashcards
Predation occurs when…
- one organism is consumed by another.
- When brought in a laboratory, the prey is usually exterminated by the predator
Compare how predation in a lab and in nature is different
- When a population of predator + prey are brought together in a laboratory, the prey is usually exterminated by the predator.
- because the range + variety of the habitat provided is normally limited to the confines of the laboratory.
- In nature = situation is different.
- The area over which the population can travel is far greater and the variety of the environment is much more diverse. In particular, there are many more potential refuges.
- In these circumstances some of the prey can escape predation because the fewer there are the harder they are to find and catch.
- Therefore, although the prey population falls to a low level, it rarely becomes extinct.
Describe evidence collected in labs and in the wild about predator and prey populations
- Evidence collected on predator and prey populations in a laboratory does not necessarily reflect what happens in the wild.
- At the same time, it is difficult to obtain reliable data on natural populations because it is not possible to count all the individuals in a natural population.
- Its size can only be estimated from sampling and surveys.
- These are only as good as the techniques used, none of which guarantee complete accuracy.
- We must therefore treat all data produced in this way with caution.
Describe the effect of predator-prey relationship on population size
- Predators eat their prey, thereby reducing the population of prey.
- With fewer prey available the predators are in greater competition with each other for the prey that are left.
- The predator population is reduced as some individuals are unable to obtain enough prey for their survival or to reproduce,
- With fewer predators left, fewer prey are eaten and so more survive and are able to reproduce.
- The prey population therefore increases.
- With more prey now available as food, the predator population in turn increases.
In natural ecosystems organisms ___ _ ______ __ _____ and therefore the
fluctuations in population size shown in the graph are often less severe.
Eat a range of foods
What are some of the reasons for cyclical fluctuations in populations
- predator-prey relationship
- disease
- climatic factors
Why are these periodic population crashes important
- important in evolution as it creates selectional pressure
- means those who are able to escape predators, or withstand disease or an adverse climate
- are more likely to survive and reproduce
- the population therefore evolves to be better adapted to the prevailing conditions.
The long-term study of the predator—prey relationship of the Canadian lynx and the snowshoe hare was made possible because records exist of the number of furs traded by companies such as the Hudson Bay Company in Canada over 200 years. By analysing these records the relative population size of the Canadian lynx and the snowshoe hare can be determined. The data collected are shown as a graph in Figure 3.
State what assumption is being made if we use the number of each type of fur traded as a measure of the population size of each species.
The assumption is made that the relative numbers of each type of fur traded represents the relative size of each animal’s population at the time.
The long-term study of the predator—prey relationship of the Canadian lynx and the snowshoe hare was made possible because records exist of the number of furs traded by companies such as the Hudson Bay Company in Canada over 200 years. By analysing these records the relative population size of the Canadian lynx and the snowshoe hare can be determined. The data collected are shown as a graph in Figure 3.
Describe the changes that occur in the populations of Canadian lynx and snowshoe hare.
- The population size of the snowshoe hare fluctuated in a series of peaks and troughs.
- Each peak and trough was repeated about every 10 years.
- The population size of the Canadian lynx also fluctuated in a 10-year cycle of peaks and troughs.
- The relative pattern of peaks and troughs is similar for the lynx and the snowshoe hare.
- The rise in the population size of the lynx often (but not always) followed that of the snowshoe hare.
It has long been observed that the population of snowshoe hares fluctuates in cycles. The question is whether these fluctuations are due mostly to predation by the lynx, mostly to changes in the food supply or mostly to
a combination of both. To find out, ecologists fenced off 1 km? areas of coniferous forest in Canada where the hares lived. Separate areas were treated in four different ways:
1) In the first set of areas, the hares were given extra food.
2) In the second set of areas, lynx were excluded.
3) In the third set of areas, the hares were given extra food and lynx were excluded.
4) In the fourth set of areas, conditions were left unaltered as a control.
Below are the results
Calculate by how many times the addition of food increased the population after six years compared with the control.
4 times out of
It has long been observed that the population of snowshoe hares fluctuates in cycles. The question is whether these fluctuations are due mostly to predation by the lynx, mostly to changes in the food supply or mostly to
a combination of both. To find out, ecologists fenced off 1 km? areas of coniferous forest in Canada where the hares lived. Separate areas were treated in four different ways:
1) In the first set of areas, the hares were given extra food.
2) In the second set of areas, lynx were excluded.
3) In the third set of areas, the hares were given extra food and lynx were excluded.
4) In the fourth set of areas, conditions were left unaltered as a control.
Below are the results
Deduce which had the greater influence on the population of hares, the addition of food or the exclusion of the
lynx. Explain your answer.
Addition of food — because the population increased more in every year that data were collected.
It has long been observed that the population of snowshoe hares fluctuates in cycles. The question is whether these fluctuations are due mostly to predation by the lynx, mostly to changes in the food supply or mostly to
a combination of both. To find out, ecologists fenced off 1 km? areas of coniferous forest in Canada where the hares lived. Separate areas were treated in four different ways:
1) In the first set of areas, the hares were given extra food.
2) In the second set of areas, lynx were excluded.
3) In the third set of areas, the hares were given extra food and lynx were excluded.
4) In the fourth set of areas, conditions were left unaltered as a control.
Below are the results
Deduce what conclusions can be drawn from this experiment
- Both food supply and predation influence hare population size.
- Food supply has a greater influence than predation but a combination of both factors has an even greater influence than either of the other two separately.
Explain why a predator population often exterminates its prey population ina laboratory but rarely does so
numbers in population in natural habitats.
- The range and variety of laboratory habitats is much smaller than in natural ones.
- This means that in nature there is a greater range of hiding places and so the prey has more space and places to escape the predator and survive.
Explain how a fall in the population of a predator can lead to a rise in its prey population
- With fewer predators, fewer prey are taken as food.
- The death rate of prey is reduced.
- Assuming the birth rate remains unchanged the population size increases,
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