C4.1 Populations and communities

What is a population?

A group of individual organisms of the same species living in a given area.

What is the role of interbreeding in a population?

Individuals in a population interbreed with each other but do not interbreed with individuals in populations of other species.

What are some types of interactions in a population?

Competition for food, cooperation to avoid predation, and other forms of interaction.

What is the size of a population?

The total number of individuals in a population.

Why is it difficult to determine the exact size of a population?

Because individuals may be hidden, moving, or spread across vast areas.

What method is used to estimate population size?

Population estimates are based on sampling.

What is a sample?

A small portion of the population that is used to estimate the entire population size.

Why are multiple samples used in population estimation?

One sample is unlikely to be representative, so multiple samples improve accuracy.

What is random sampling?

A method where every individual in the population has an equal chance of being included in the sample.

How can random sampling be achieved?

By using random numbers to select individuals or positions in the population.

What is a quadrat?

A square sample area used to count organisms in a habitat.

How is a quadrat used for population sampling?

It is placed at random positions in a habitat to record the number of organisms.

What procedure is followed when placing a quadrat?

Use a measuring tape, generate random numbers for distance, and place the quadrat at the determined position.

What is the advantage of random quadrat sampling?

It provides a reliable estimate of population size with a large enough number of replicates.

What organisms is quadrat sampling suitable for?

Sessile organisms like plants and corals.

Why is quadrat sampling unsuitable for motile organisms?

Because they move from place to place, making accurate estimation difficult.

What method is used for motile organisms?

The capture-mark-release-recapture method.

What is the carrying capacity of a population?

The maximum population size that an environment can support with the available resources.

What factors limit population growth?

Availability of resources like food, water, and space.

What happens when resources become scarce?

Individuals compete for resources, and some may die due to insufficient resources.

What are density-independent factors?

Factors that affect a population regardless of its size, such as natural disasters.

What are density-dependent factors?

Factors that increase in effect as the population size increases, such as competition and disease.

What are examples of density-independent factors?

Seawater flooding, forest fires, and other environmental changes.

What are examples of density-dependent factors?

Competition, predation, and infectious disease.

What is competition within a population?

When individuals compete for limited resources like food, water, and space.

How does predation affect population size?

As prey populations increase in density, they are easier for predators to find, which can decrease prey numbers.

What is the relationship between predation and population density?

Predation becomes more intense as population density increases.

How does disease affect populations?

It spreads more easily in dense populations, reducing numbers through illness.

What is population growth?

The increase in the number of individuals in a population.

What causes exponential growth in populations?

When resources are abundant and there are no limiting factors, populations grow exponentially.

What is a J-shaped curve in population growth?

A graph of exponential growth, where numbers increase at an accelerating rate.

What is the sigmoid curve?

A graph showing the population growth that starts exponentially and then levels off as the carrying capacity is reached.

Why does exponential growth eventually stop?

Because resources become limited and the population reaches the carrying capacity.

What happens when a population exceeds its carrying capacity?

Population size may crash due to a lack of resources or other factors.

What is an example of a species that experienced exponential growth?

The Eurasian collared dove in Europe.

What is the Lincoln index?

A method for estimating population size using the capture-mark-release-recapture technique.

What is the "boom and bust" pattern in population growth?

A cyclical pattern where population size greatly exceeds the carrying capacity, then drops below it, and rises again.

What are the main factors affecting population size?

Density-independent factors, density-dependent factors, and resources.

What is the role of environmental resources in population growth?

Resources like food and water limit population size and growth potential.

What is a negative feedback mechanism?

A process that reduces the growth rate of a population as it reaches the carrying capacity.

How do density-dependent factors influence population growth?

As the population size increases, the effects of competition, predation, and disease become more pronounced.

What is the role of competition in natural selection?

Individuals with traits that allow them to compete more effectively are more likely to survive and reproduce.

What happens to populations when resources are abundant?

Populations may experience rapid growth as individuals have access to sufficient resources.

What are the phases of population growth?

Exponential growth, reaching the carrying capacity, and stabilization or fluctuation around the carrying capacity.

How is the carrying capacity determined?

By the availability of resources in the environment, such as food, water, and space.

What is the difference between a density-independent and density-dependent factor?

Density-independent factors affect populations regardless of size, while density-dependent factors increase in effect as the population grows.

What is the result of competition within a population?

Some individuals gain more resources and reproduce more, while others may struggle to survive.

What is the relationship between competition and population size?

As population size increases, competition for limited resources becomes more intense.

How does predation regulate population size?

Predators reduce prey populations by feeding on them, controlling the prey population size.

What is the role of disease in regulating populations?

Disease spreads more easily in dense populations, reducing overall numbers.

How can disease affect a population's growth?

By increasing mortality rates and reducing the reproductive success of individuals.

What are some factors that can lead to population crashes?

Overpopulation, resource depletion, and environmental disasters.

What is the effect of environmental disasters on population size?

Environmental disasters can dramatically reduce population size, regardless of the population’s density.

How do plants and animals compete for resources?

Plants compete for light, space, and nutrients, while animals compete for food, water, and mates.

What is the role of predators in ecosystems?

Predators help control the population sizes of prey species, maintaining ecological balance.

What is the effect of herbivory on plant populations?

It can reduce plant numbers if herbivores consume too much plant material.

How do populations of herbivores and plants interact?

Herbivores feed on plants, and the availability of plants can affect herbivore population size.

How do plants compete with each other?

By competing for sunlight, space, and nutrients in the soil.

What is an example of interspecific competition?

Two species of trees competing for light and space in a forest.

What is the difference between intraspecific and interspecific competition?

Intraspecific competition occurs within the same species, while interspecific competition occurs between different species.

What are the benefits of cooperation in populations?

Cooperative behaviors can increase survival and reproductive success for all individuals involved.

How do social animals cooperate?

By working together to find food, defend against predators, or care for offspring.

What are the advantages of cooperative relationships in populations?

Cooperation enhances the survival chances of individuals and improves resource acquisition.

What are some examples of cooperation in populations?

Bees working together in a hive, termites sharing tasks within a colony.

How does cooperation benefit the group?

It increases the chances of survival for all members of the group.

What is the role of mutualism in ecosystems?

Mutualism is a type of interaction where both species benefit, such as pollination by bees.

What is the difference between mutualism and parasitism?

In mutualism, both species benefit, while in parasitism, one species benefits at the expense of the other.

What are some examples of mutualism?

Hummingbirds pollinating flowers while feeding on nectar, cleaner fish eating parasites off larger fish.

What is parasitism?

An interaction where one species benefits at the expense of the other, such as a parasite living inside or on its host.

What is an example of parasitism?

A tick feeding on the blood of a mammal.

What is herbivory?

Primary consumers feeding on producers, with the potential to harm the plants.

What is an example of herbivory?

Bison grazing on grasses.

What is predation?

When one species (the predator) kills and eats another species (the prey).

What is an example of predation?

Anteaters feeding on ants or termites.

What is interspecific competition?

Competition between individuals of different species for the same resource.

What is an example of interspecific competition?

Ivy climbing up oak trees and competing for light.

What is the role of predators in controlling prey populations?

Predators help keep prey populations in check, preventing them from exceeding the carrying capacity.

What is the effect of predator-prey relationships on ecosystems?

It maintains a balance in population sizes, ensuring no single species dominates the ecosystem.

What is an ecological niche?

The role and position of a species within its environment, including its interactions with other species.

1. What is mutualism?

Mutualism is a close association between two species where both species benefit from the relationship.

2. What is an example of mutualism in plants?

An example is nitrogen-fixing Rhizobium bacteria living in root nodules of plants in the Fabaceae family.

3. How do mycorrhizal fungi benefit orchids?

Mycorrhizal fungi help orchids by supplying carbon compounds and essential nutrients, while orchids provide carbon compounds in return.

4. What do zooxanthellae provide to coral polyps?

Zooxanthellae provide glucose and oxygen produced by photosynthesis to the coral polyps.

5. How does the coral benefit zooxanthellae?

The coral provides a safe environment and supplies carbon dioxide from its respiration to the zooxanthellae.

6. What is parasitism?

Parasitism is a relationship where one species (the parasite) benefits at the expense of another species (the host).

7. What is an example of parasitism in animals?

Ticks living on deer and feeding on their blood is an example of parasitism.

8. What does the roundworm Baylisascaris do to raccoons?

The roundworm Baylisascaris lives in the gut of raccoons, absorbing the food digested by the raccoon.

9. What is the effect of non-photosynthesizing Cuscuta plants?

Cuscuta plants absorb nutrients from the host plant’s sap, harming the host in the process.

10. What is pathogenicity?

Pathogenicity is when one species (the pathogen) causes disease in another species (the host).

11. What is an example of a pathogenic interaction?

The potato blight fungus (Phytophthora) infects potato plants, causing disease.

12. What pathogen infects badgers?

Mycobacterium tuberculosis infects badgers, causing tuberculosis.

13. What virus infects rabbits?

Myxomatosis virus infects rabbits, causing the disease myxomatosis.

14. What is an endemic species?

An endemic species is one that occurs naturally in a specific area and is found nowhere else.

15. What is an alien species?

An alien species is one that has been introduced to a new area by humans, either deliberately or accidentally.

16. What is an invasive species?

An invasive species is an alien species that spreads rapidly and causes harm to the environment, economy, or human health.

17. What is the competitive exclusion principle?

The competitive exclusion principle states that two species cannot occupy the same ecological niche indefinitely.

18. What can happen when an alien species competes with endemic species?

Alien species may cause the decline or extinction of endemic species by outcompeting them for resources.

19. What happened to red lionfish in Florida?

Red lionfish escaped aquariums in Florida and spread across coral reefs, outcompeting native fish species.

20. What is a characteristic of Salvinia?

Salvinia is a floating fern that can reproduce asexually and quickly cover the surface of water bodies, outcompeting native plants.

21. What is a chi-squared test used for in ecology?

A chi-squared test is used to test for associations between species in an ecological study.