Grade 12 Environmental Studies - Part 2 Predator-prey relationships

Question 1

Define predation

Answer 1

• The biological interaction where one species, the predator, kills and eats another species, the prey.
• Predator and prey evolve together and are part of the same environment.

Question 2

How do predators maintain greater diversity within an ecosystem?

Answer 2

1. Regulating the abundance and distribution of prey species - as creditors increase the prey decreases
2. Increasing biodiversity = preventing a single species from becoming dominant
3. Keeping prey population genetically fit by removing sick, injured and weak individuals
4. providing vital food sources for scavengers

Question 3

Explain how the preditor-prey relationship works:

Answer 3

1. Prey population decreases - due to predator killing
2. food availalbe for predators also decrease
3. predator numbers subsequently decline
4. reduced predator pressure increase prey numbers again
5. cycle repeats again and again
6. result is cyclical rising and falling of numbers of prey population - with a SLIGHTLY LATER cyclical pattern of the predator

Question 4

Discuss the aphid-ladybird relationship:

Answer 4

• Aphids are insects that suck the sap out of many different plants, including crops = they are Parasitic pests
• Several ladybird species feed on aphids = predators
• Aphid = prey, ladybird = predator
• Female ladybird lay batches of bright yellow eggs amongst the aphid colonies
• Adults feed on the aphids and larvae that hatch from the eggs will also feed on the aphids, reducing aphid population.
• THis reduces food supply for ladybirds
• Ladybird population begins to decrease
• Aphid population can begin to recover
• TWO POPULATIONS FLUCTUATE UP AND DOWN

Note: Careful with insecticides that can kill ladybirds

Question 5

Discuss the lion-zebra relationship:

Answer 5

• Lion = predator, zebra = prey
• Both evolve adaptations to outwit the other
• adaptation = speed of movement
• Fastest lions are able to cath and eat their prey more easily than slower lions, so they survive and reproduce.
• Gradually faster lions make up more of the population.
• The fastest zebras are able to escape lions, thus faster zebras survive and reproduce.
• Both organisms become faster to adapt to their environments, their relationship stays the same = they are both getting faster.
• Predator-prey relationship thus beneficial for the fitness of BOTH species.
• Co-evolution of species (they both change)
• Lions have a larger range of prey, not only zebra.
• If lion were to become extinct, all these species will increase, but if zebra were to become extinct, lion would still survive on other species e.g. rooibok.

Question 6

Discuss the shark-fish relationship:

Answer 6

• Sharks are top predators in nearly every part of every oceans
• thus they keep populations of other fish and other marine organisms healthy and in balance in the ecosystem
• Sharks eat efficiently going after sick or slower fish in a population
• By removing the sick and weak they prevent the spread of disease and strenthen the gene pool of the prey species.
• Largest, strongest and healthiest fish generally reproduce in great numbers, the outcome is larger numbers of healthier fish.

NB: Look at activity on page 10 - 11 and complete.

Question 6

Mention 3 requirements that a group of organisms must satisfy before it can be called a population.

Answer 6

#

Question 7

How do food webs impact on population?

Answer 7

Multiple food webs are made up of:
1. carnivores,
1. herbivores,
1. producers,
1. scavengers and
1. decomposers.

They all help to keep the ecosystem healthy and balanced.
**
The removal on one species from a food web may have a large impact on the population of many other species. **
The web is made up of several food chains joined together.
E.g. grass -insect-vole-hawk
E.g.grass-iinsect-frog-jackal
E.g. grass - insect-vole-jackal
Slugs, rabits and insects ALL eat grass, so if population of slugs is decreased, there would be more grass for rabbits and insects, so their populations would increase. Thrushes would have to eat more insects to maintain their population so possible that their population decrease. This may reduce the population of voles and frogs.

This disruption is even worse in the TOP PREDATORS - Lions and Sharks removed from food web, then prey populations would rapidly increase. E.g. loss of lions, leopards, wild dogs and hyenas in some parts of Africa, have allowed babboons to increase - creating other problems.

Question 8

What is a food web?

Answer 8

An interconnected set of all the food chains in an ecosystem.

Question 9

**Multiple food webs are made up of:

Answer 9

1. carnivores,
2. herbivores,
3. producers,
4. scavengers and
5. decomposers.

Question 10

What factors are largely to blame for the reduction of top predators?

Answer 10

Human activities like over-fishing, pollution, habitat destruction, hunting etc.