Factors Affecting Population Size Quiz

Which of the following is an example of competition among species?

• A lion hunting a zebra.

• Two bird species competing for nesting sites.

• A flood destroying a forest.

• A human building a dam.

Answer explanation

The correct choice is 'Two bird species competing for nesting sites' because it directly illustrates competition for resources between species, unlike the other options which involve predation or environmental changes.

What is the primary effect of predation on the predator population?

• It decreases the predator population.

• It increases the predator population.

• It stabilizes the predator population.

• It has no effect on the predator population.

Answer explanation

Predation primarily decreases the predator population as it leads to competition for food and resources. When prey is scarce, predators may struggle to survive, resulting in a decline in their numbers.

Which human activity is most likely to cause a density-independent effect on a population?

• Overfishing in a lake.

• Building a city in a forested area.

• Introducing a new predator species.

• Planting trees in a deforested area.

Answer explanation

Introducing a new predator species can drastically affect prey populations regardless of their density, making it a density-independent effect. In contrast, overfishing, urban development, and tree planting are density-dependent or habitat-related.

How does predation affect the population size of prey species in an ecosystem?

• It increases the population size of prey species.

• It decreases the population size of prey species.

• It has no effect on the population size of prey species.

• It stabilizes the population size of prey species.

Answer explanation

Predation typically decreases the population size of prey species, as predators consume them. This dynamic is crucial in regulating prey populations and maintaining ecosystem balance.

Which scenario best illustrates competition among species?

• A wildfire spreading through a grassland.

• Two plant species competing for sunlight.

• A predator-prey relationship between wolves and deer.

• A volcanic eruption affecting an island.

Answer explanation

The scenario of two plant species competing for sunlight best illustrates competition among species, as it involves direct rivalry for a limited resource, which is a key aspect of interspecific competition.

What is the likely outcome when two species compete for the same limited resource?

• Both species will thrive equally.

• One species will outcompete the other.

• Both species will become extinct.

• The resource will become unlimited.

Answer explanation

When two species compete for the same limited resource, typically one species will be better adapted to exploit that resource, leading to its dominance and the decline of the other species.

Which of the following is a real-life example of a density-independent factor?

• A drought affecting a region.

• A wolf pack hunting deer.

• A bacterial infection spreading in a population.

• A tree species outcompeting another for sunlight.

Answer explanation

A drought affecting a region is a density-independent factor because it impacts populations regardless of their density, unlike the other options which involve interactions between species or depend on population size.

How do human activities such as pollution affect ecosystems?

• They increase biodiversity.

• They decrease biodiversity.

• They have no effect on biodiversity.

• They stabilize biodiversity.

Answer explanation

Human activities like pollution lead to habitat destruction and species decline, which ultimately decrease biodiversity. This loss affects ecosystem stability and resilience.

How can human activities influence ecosystems and affect population sizes?

• By introducing new predators.

• By altering habitats through deforestation.

• By increasing natural disasters.

• By reducing competition among species.

Answer explanation

Human activities like deforestation alter habitats, leading to changes in species populations. Additionally, increased natural disasters can disrupt ecosystems, further affecting population sizes and biodiversity.

Which of the following is a density-independent factor affecting population size?

• Disease outbreak.

• Predation.

• Hurricane.

• Competition for food.

Answer explanation

A hurricane is a density-independent factor because it affects population size regardless of the population's density. In contrast, disease outbreaks, predation, and competition for food are density-dependent factors.