ENVISCI LONG QUIZ 2

Population

is a group of organisms of the same species that live in the same area.

Population Dynamics

is the study of how and why populations change in size, distribution, and structure over time.

Population Size and Density

The total number of individuals in a population and the number of individuals per unit area or volume.

Population density

is a better indicator of pressure on local infrastructure and resources. A city with a high density will experience more strain on its housing, transportation, water supply, and sanitation systems than a city with the same total population spread over a much larger area. It directly informs land-use planning, zoning regulations, and the need for public services.

Population Distribution

The spatial arrangement of individuals within an area, which can be clumped, uniform, or random.

Clumped distribution

the most common type, suggests resources are patchy (like waterholes) or that the species is social (like a herd of deer).

uniform distribution

often indicates strong competition or territoriality, like penguins nesting a set distance apart.

random distribution

which is rare, implies that resources are evenly spread and social interactions are neutral.

Population Growth

The change in population size is determined by four primary factors: births, deaths, immigration (individuals entering a population), and emigration (individuals leaving a population).

positive growth

rate means a population is increasing.

negative growth

rate means it is decreasing.

theoretical models of population

exponential growth model
logistic growth model

exponential growth model

which describes a population's growth in an idealized, unlimited environment

logistic growth model

which incorporates environmental limits and carrying capacity (K)—the maximum population size that an environment can sustain.

Carrying capacity

is determined by the amount of available resources (food, habitat, water)

Exponential Growth

Imagine a scenario with a few bacteria in a petri dish full of nutrients. They have everything they need: unlimited food, endless space, and no predators. Their population will not just grow; it will accelerate. This is the essence of exponential growth. It describes how a population multiplies at a rate that is proportional to its current size. The larger the population gets, the faster it grows, because there are more individuals present to

Assumptions of exponential growth

✓ Unlimited Resources: There is no shortage of food, water, space, or other necessities.

✓ No Predation or Disease: Individuals don't get eaten or suffer from diseases that would limit the population.

✓ Constant Growth Rate: The per-individual rate of birth and death remains constant, regardless of how large the population becomes.

Logistic Growth

Now, let's consider what actually happens in that petri dish. As the bacteria multiply, they start to run out of nutrients and space. Their waste products may accumulate, making the environment toxic. The growth rate slows down and eventually stops. This is logistic growth. It's a much more realistic model because it acknowledges that every environment has a carrying capacity (K).

Assumptions of Logistic Growth

✓ Limited Resources: Resources are finite, leading to competition as the population grows.

✓ Density-Dependence: The growth rate depends on the population density. As the population approaches the carrying capacity, the birth rate tends to decrease, and the death rate tends to increase.

r-Strategist

(Quantity over Quality): A mosquito lays hundreds of eggs in water. The vast majority will not survive to adulthood due to predation or environmental changes. There is zero parental care. This strategy works well in unpredictable environments.

K-Strategist

(Quality over Quantity): The Philippine Eagle lays only one egg every two years. Both parents invest enormous time and energy into raising the chick, protecting it until it can survive on its own. This strategy is successful in stable environments where competition is high.

survivorship curve

is a graph showing the proportion of individuals surviving to each age. It visually represents a species' life history strategy.

Type I (Late Loss)

High survival through early and middle ages, with a sharp increase in death rates in old age. Example: Humans, elephants (K-strategists).

Type II (Constant Loss)

A constant death rate over the organism's life span. Chance of dying is independent of age. Example: Birds, small mammals, lizards.

Type III (Early Loss)

Extremely high death rates for the very young, then a leveling off for those that survive. Example: Oysters, mosquitos, fish (r-strategists).

Population Ecology

is the study of populations in relation to environment, including environmental influences on density and distribution, age structure and population size. A great local example of population ecology is the study of the invasive Golden Apple Snail (Pomacea canaliculata), or , in Philippine rice paddies.

Density

Researchers measure how many snails are found per square meter of a rice field. This helps determine the economic damage to rice crops.

Distribution

They map out which regions, provinces, and farms have kuhol infestations and track how they spread through irrigation canals and waterways.

Age Structure

Scientists analyze the ratio of eggs (the familiar pink clusters), young snails, and adult snails. A population with many young snails indicates it will likely continue to grow rapidly.

Population Size

This involves estimating the total number of snails in an area over time. Ecologists track whether the population is increasing, decreasing, or stable from one planting season to the next.

Age Structure

Scientists analyze the ratio of eggs (the familiar pink clusters), young snails, and adult snails. A population with many young snails indicates it will likely continue to grow rapidly.

Environmental Influences

This is the core of the study. Ecologists examine how the environment affects the snail population.