Population Ecology Quiz

Direct Methods of Estimating Population Size

• A census is a direct method where every individual in a population is counted.
• This method works best when organisms are large enough to be seen and the area being counted is not too large.
• Suitable organisms for direct methods include slow-moving or stationary ones, such as snails, tortoises, plants, barnacles, or mussels.
• If the area is too large to count every individual at once, indirect methods like aerial photographs (e.g., penguins, seals, large trees), helicopters (e.g., elephants), or census forms (e.g., household counts) can be used.

Indirect Methods of Estimating Population Size

• Indirect methods estimate population size by counting a sample of the population and using calculations.
• Two common methods are quadrat and mark-recapture.

Quadrat Method

• This method counts individuals in small measured areas (quadrats).
• The formula to estimate the total population size is: N = (number in sample x size of whole habitat) / size of quadrat
• Random sampling is crucial as the distribution of organisms may vary across the area.

Mark-Recapture Method

• This is for mobile organisms like butterflies, birds, or fish.
• Individuals are captured, marked, released, then recaptured at a later time.
• The formula to estimate the total population size is P = (M x C) / R where:
• P = estimated population size
• M = total number of marked animals
• C = total number of animals caught in the second sample
• R = total number of marked animals recaptured in the second sample

Ensuring Reliable Results (for Indirect Methods)

• The population must be closed, meaning no immigration or emigration.
• Marking should not harm the individual or affect its movement.
• There should be sufficient time for the marked individuals to mix with unmarked ones, but not enough time for major births or deaths.
• Sampling should be repeated several times to calculate an average population estimate.

Population Growth Forms

• There are two main types of population growth: exponential and logistic.
• Exponential growth occurs in ideal, unlimited environments, represented by a J-curve.
• Logistic growth reflects restricted environments (resources are limited). It follows an S-curve and approaches a carrying capacity.

Limiting Factors

• Limiting factors are environmental factors that restrict population growth.
• They can be categorized as density-dependent (e.g., predators, resources, disease) or density-independent (e.g., natural disasters, weather).
• Density-dependent factors are affected by the population size.
• Density-independent factors occur regardless of population size.

Competition

• Competition occurs when individuals strive for limited resources (food, water, space).
• Ecological niches are the roles individuals play in a community, including the resources they use and how they interact.
• Intraspecific competition is between individuals of the same species.
• Interspecific competition is between individuals of different species.
• Competition can lead to specialization or competitive exclusion.

Ecological Niches

• An ecological niche is an organism's role in its community, encompassing its interactions and resources.
• A habitat is the physical address of an organism; a niche is the organism's occupation within the community.

Symbiotic Relationships

• Symbiotic relationships involve close interactions between different species, benefiting one or both species.
• Mutualism: both species benefit.
• Commensalism: one species benefits while the other is neither harmed nor helped.
• Parasitism: one species benefits at the expense of the other (host).

Predation

• Predation occurs when one organism (predator) consumes another (prey).
• Predators play a role in regulating prey populations and maintaining biodiversity.
• Predators influence the prey population size.

Predator-Prey Relationship

• Predator and prey populations influence each other.
• Changes in one population frequently correlate with changes in the other population.

Social Organization

• Many animals live in social groups, dividing tasks amongst individuals for better survival.
• Social organization improves survival chances and allows for more efficient resource use and protection.

Types of Social Organization

• Individuals may cooperate in many different ways, including predator avoidance.
• Collective hunting allows for better success in capturing prey.

Labour Tasks (in social insects):

• Social insects like bees have specialized roles in the hive (e.g., worker, drone, queen) to perform tasks for colony welfare.

Age and Gender Distribution

• Population pyramids show the age and sex distribution of a population.
• These pyramids can indicate growth patterns (rapid, stable, declining).
• Factors like birth and death rates influence these patterns.

Ecological Succession

• Ecological succession is the gradual change in an ecosystem over time.
• Disturbances like fires or floods can initiate succession.
• Primary succession starts on bare land (e.g., volcanic rock).
• Secondary succession occurs in areas that were previously inhabited.
• Stages include pioneer species (first colonizers), intermediate species, and a climax community.

Human Population

• Human populations have increased exponentially through time, due to several factors.
• A variety of factors influence human population growth, including disease, mortality rates, and availability of resources.
• Comparing more-developed and less-developed countries reveals significant differences in population growth rates and living standards, highlighting population dynamics impacted by environmental, social, and economic factors.