2.1 - Populations

What is a population?

All the organisms of the same species which live in a particular geographical area at the same time.

Why may it be challenging to define the area a population lives?

Because populations may comprise widely dispersed individuals which come together only infrequently, and populations may fluctuate considerably over time.

Why do ecologists study populations?

To understand the factors that influence the size of populations.

What are the three main objectives of managing populations?

Increase population size (e.g., endangered species), decrease population size (e.g., pests), maintain population size (e.g., fisheries management).

Why is it important to study the populations of freshwater mussels?

Due to their endangered status and the lack of ecological assessments.

Why are freshwater mussels considered a keystone species in freshwater ecosystems?

They scrub huge proportions of sediment, algae, and pollutants from waterways and offer a biogeochemical indication of the overall health of a catchment.

How do new species form?

Through reproductive isolation, which can be due to geographical, behavioral, or temporal factors.

Why is estimating population samples important?

To understand the size and characteristics of a population, and to make informed conservation and management decisions.

What sampling technique involves the unbiased selection of organisms with each individual having an equal chance of being chosen?

Random sampling.

What is quadrat sampling used for?

To estimate population size by taking a square of known size and counting the organisms within it.

What is quadrat sampling?

Taking a square of known size and placing it over a section of the population to identify and record the organisms found within an area.

What is the purpose of using quadrats in sampling?

To help identify and record the organisms found within an area.

What are the potential problems with measuring intervals in quadrat sampling?

Too large intervals may result in some species being missed and zonation patterns, while too small intervals may be time-consuming and collect more data than needed.

Why is it important to collect enough quadrats in sampling?

To ensure that the number of species collected levels out and to obtain a representative sample of the population.

When is random sampling used?

When an ecosystem is relatively uniform (homogenous).

What is the technique used in random sampling?

Creating a grid overlaying the ecosystem and using a random number generator to designate which quadrat in the grid is to be sampled.

When is stratified sampling used?

When an ecosystem is not uniform (heterogeneous), such as when the vegetation is clustered into patches.

What is the purpose of stratified sampling?

To obtain a representative sample of the ecosystem, especially when different strata in the ecosystem can be clearly identified.

How can motile animals be randomly sampled?

Through camera traps, mark and re-capture, and GPS tracking.

What is the Lincoln index used for?

To estimate the population size using the capture-mark-release-recapture method.

What formula does the Lincoln index provide to estimate population size?

Population size estimate = M × N/R, where M is the number of individuals caught and marked initially, N is the total number of individuals recaptured and R is the number of marked individuals recaptured.

What is important when estimating population sizes using a specific technique?

To acknowledge the assumptions and limitations associated with the chosen technique.

What assumptions should be considered in the capture-mark-release-recapture method?

1. The marking technique does not influence the behavior or survival of the organism. 2. Marked individuals fully reintegrate into the population. 3. No births, deaths, immigrations, or emigrations during the study period.

What assumptions does the Lincoln index rely on?

1. Marked individuals used are representative of the entire population. 2. The ratio of marked to unmarked individuals accurately reflects the ratio of the population.

How can the accuracy of the Lincoln index be enhanced?

By increasing the sample size and conducting repeated sampling to estimate a mean value.

What is the technique used to estimate the population size of a named species of organism that is able to move?

Capture and count a sample of the population, mark all individuals, release them, allow time to become randomly dispersed, capture a second sample, count the complete sample, count the marked individuals in the second sample, and use the formula M × N/R to estimate the population size.

What is carrying capacity (K)?

The maximum population size that a given environment can sustain over a certain period of time.

What factors influence carrying capacity?

Environmental factors like adequate food, shelter, water, mates, parasitism/predation, and competition.

How does carrying capacity vary over space and time?

It varies depending on the abundance of limiting resources.

What type of competition arises when resources such as food, water, and space are limited?

Interspecific and intraspecific competition.

Why do populations grow in a logarithmic fashion instead of exponential when limiting factors are present?

Due to the influence of limiting factors such as competition for resources.

What is causing declines in native fish populations in the Murray-Darling Basin?

Interspecific competition from alien species like common carp.

How can the carrying capacity of waterways available for use by native fish be increased?

By reducing interspecific competition, for example, by reducing carp biomass (e.g., releasing the carp herpes virus).

What are examples of density dependent limiting factors?

Competition for food, mates, nesting sites, predators, parasites, and pathogens.

How do density dependent factors affect population growth at higher population densities?

They exert a greater effect on population growth, individuals compete more for resources, are more easily located by predators and parasites, and are more vulnerable to infection and disease.

What are some examples of physical (abiotic) factors that can affect population growth?

Temperature, precipitation, humidity, acidity, salinity, etc.

What are some examples of catastrophic events that can affect population growth?

Floods, tsunamis, fire, drought.

What is the difference between density-dependent and density-independent limiting factors?

Density-dependent factors are affected by population density, while density-independent factors are not dependent on population density.

Why is modelling the population growth of freshwater fish invasions important?

To predict population expansion trends and optimize management actions.

Why are carp ranked among the world's most invasive fish taxa?

Due to their wide range of tolerance and being a generalist species.

How have common carp been introduced into Australia?

Both deliberately to imitate the European environment, and accidentally through the escape of ornamental or aquaculture fish.

What type of population growth curve did carp likely undergo when colonising the Murray-Darling Basin for the first time?

Rapid exponential (logarithmic) increase to produce a J-shaped growth curve.

What is the common pattern observed in natural populations, including carp, for population growth?

Sigmoid (S-shaped) / logistic population growth curve.

What happens as a population size increases in the logistic growth curve?

Density-dependent factors come into play, limiting the rate of population growth.

Is the global human population experiencing exponential growth or logistic growth? Why?

Exponential growth, as historical growth appears to be exponential rather than logistic.

How did the yeast population develop over the time of the experiment?

Population size oscillated around the carrying capacity (K).

Explain the population growth observed in the yeast experiment.

It exhibited logistic growth, oscillating around the carrying capacity.

In the yeast experiment, how might the population growth have differed if the sugar in the original solution was increased?

It might have initially increased the growth rate, but eventually, the population would reach a new carrying capacity.

In the yeast experiment, how might the population have differed if the sugar in the solution was replenished every day of the experiment?

The population might have continued to grow without reaching a stable carrying capacity.

How can increased frequency and duration of drought affect the growth of Macquarie turtles?

It can delay growth due to increased intraspecific competition for food, leading to decreased reproduction.

What is intraspecific competition?

Competition among members of the same species for limited resources such as food, water, and space.

What are the outcomes of intraspecific competition?

Adaptation of individuals to different niches, displacement of less-competitive individuals, and regulation of population size.

What is an example of intraspecific cooperation?

The social amoeba Dictyostelium discoideum forming a multicellular structure consisting of spores on top of a stalk when faced with starvation.

What is mutualism?

A symbiotic interaction between two or more species where both parties obtain benefits from the relationship.

What is an example of seed dispersal mutualism?

Australian freshwater turtles dispersing wetland-associated plants and dugongs and green turtles dispersing viable seagrass seeds in the Great Barrier Reef.

What is predation?

An ecological interaction where a predator captures and consumes its prey.

How do predator-prey relationships regulate animal populations?

Through density-dependent factors and negative feedback.

How can introduced predators, like the red fox in Australia, disrupt population dynamics?

Introduced predators can be more efficient than native predators, leading to disruptions in population dynamics and potential extinction of native animals.

What is a community in ecology?

Communities consist of a diverse array of populations within a specific area, ranging from plants and animals to fungi and bacteria.

What are the components of communities?

Communities consist of plants, animals, fungi, and bacteria.

How do populations interact in a community?

Populations interact and coexist, forming complex ecological relationships and contributing to the overall functioning of the ecosystem.

What are the two mechanisms that can influence population dynamics in communities?

Top-down control and bottom-up control.

What is top-down control in population dynamics?

When the abundance or behavior of lower trophic levels in a food chain is regulated by the presence and activities of organisms at higher trophic levels.

What is an example of an organism exerting top-down control?

Grey wolves (C. lupus) exert top-down control in Yellowstone National Park.

What is bottom-up control in population dynamics?

When the availability of resources at lower trophic levels influences the abundance and distribution of organisms at higher trophic levels.

What factors can exert bottom-up control?

Factors such as nutrient availability, climatic conditions, and primary productivity.

How can nutrients have a positive bottom-up effect on seagrass?

The positive bottom-up effect is due to the availability of nutrients and nutrients increase abundance/plant growth rates.

How can nutrients have a negative bottom-up effect on seagrass?

The negative bottom-up effect occurs as excess nutrients cause a bloom in algae growth/eutrophication/competition and limited nutrients have a negative effect on seagrass growth.