Populations in ecosystems

Question 1

Define ecology.

Answer 1

The study of inter-relationships between organisms and their environment including abiotic and biotic.

Question 2

Define populations.

Answer 2

A group of individuals of one species that occupy the same habitat at the same time.

Question 3

What factors affect the size of a population?

Answer 3

• the effect of abiotic factors
• interactions between organisms of different species form a community

Question 4

Define a community.

Answer 4

Populations of different species living and interacting in a particular place at a specific time.

Question 5

Define a species.

Answer 5

A group of organisms that can interbreed to produce fertile offspring.

Question 6

What is an ecological niche?

Answer 6

Describes how organisms fit into an environment, governed by its abiotic and biotic adaptations.

Question 7

Define population size.

Answer 7

The number of individuals in a population.

Question 8

Describe abiotic factors influencing population size.

Answer 8

• Temperature: temperature falls below optimum meaning enzymes work slower and denature.
• Light: ultimate energy source for most ecosystems.
• pH: affects enzyme activities.
• Water and humidity: affect transpiration rates, where water is scarce and populations are small.

Question 9

Define immigration.

Answer 9

Where individuals join a population from outside.

Question 10

Define emigration.

Answer 10

Where individuals leave a population.

Question 11

Define competition.

Answer 11

Where 2 or more individuals share any resource that’s insufficient to satisfy all their requirements fully, competition results.

Question 12

Describe intraspecific competition.

Answer 12

• Competition between members of the same species for resources.
• Greater availability of resources allows for a greater population, and vice versa.

Question 13

Describe interspecific competition.

Answer 13

• Individuals of a different species compete for resources.
• When 2 species compete, one usually has a competitive advantage, one population gradually increases and the other diminishes.
• When one species fully dies, it is known as the competitive exclusion principle.

Question 14

Define the competitive exclusion principle.

Answer 14

When two species compete, the one that uses the resources most effectively eliminates the other. No two species can occupy the same niche.

Question 15

Define predation.

Answer 15

Occurs when an organism is consumed by another.

Question 16

Describe the effect of predator-prey relationships on population size.

Answer 16

• Predators eat their prey, reducing prey population.
• Fewer prey means competition between predators increases.
• Predator populations reduce as some are no longer able to survive and reproduce.
• Fewer predators means prey can reproduce so their populations increase.
• Which in turn, increases predator population.

Question 17

Define abundance.

Answer 17

The number of individuals of a species in a given space.

Question 18

Name two sampling techniques to study habitats.

Answer 18

• random sampling (frame quadrats)
• systematic sampling (transect belt)

Question 19

Describe point quadrats and frame quadrats.

Answer 19

• Point quadrats (horizontal bar supported by two legs) - consists of ten holes; throughout each a pin is dropped. Every species that touches the pin is recorded.
• Frame quadrats (square frame divided by string of wire into equally sized subdivisions) - quadrat placed in different locations within the area. The abundance of quadrat is recorded.

Question 20

Describe sampling at random.

Answer 20

1. Lay out two long tape measures at right angles, along two sides of the study area.
2. Obtain a series of coordinates by using random number taken from a table or generate by a computer.
3. Place a quadrat at the intersection of each pair of coordinates and record the species within it.

Question 21

Describe variations due to genetic factors.

Answer 21

• Mutation: chromosomes may or may not be changed and passed onto the next generation.
• Meiosis: special form of nuclear division that produces new combinations of alleles before they are passed into the gametes, all of which are therefore different.