IB Biology HL 1-2: Populations and Communities

Questions and Answers

What type of factors increase their impact as the population size increases?

Density dependent factors (correct)

Resource availability

Carrying capacity limits

Environmental conditions

Which phase of population growth is characterized by rapid increase without significant limiting factors?

Deceleration phase

Sigmoid phase

Exponential phase (correct)

Plateau phase

Which of the following best describes the relationship between breeding and deaths in a population approaching carrying capacity?

Decreased breeding and decreased deaths

Increased breeding and decreased deaths

Decreased breeding and increased deaths (correct)

Increased breeding and deaths remain constant

What can be inferred about the results of using models like mesocosms in studying population dynamics?

They help investigate carrying capacity and growth factors Signup and view all the answers

Which of the following describes a scenario that leads to exponential population growth?

Movement into a new niche with abundant resources Signup and view all the answers

What is the definition of a population in an ecological context?

A group of individual organisms of the same species living and interacting in an area Signup and view all the answers

Which method is best suited for estimating the population size of sessile organisms?

Random quadrat sampling Signup and view all the answers

Which statement about carrying capacity is correct?

It varies for each population within different habitats. Signup and view all the answers

In the context of estimating population size using capture-mark-release-recapture, what does 'R' represent?

Number of marked organisms recaptured Signup and view all the answers

What is a primary characteristic of density-dependent factors affecting population size?

Their impact increases as population density increases. Signup and view all the answers

Which method utilizes random sampling to estimate the size of a population?

Quadrat sampling Signup and view all the answers

Which of the following assumptions must be made during the capture-mark-release-recapture technique?

The population remains closed to migration and reproduction during the study. Signup and view all the answers

What does 'sampling error' refer to in the estimation of population size?

The difference between the true population size and the estimated value Signup and view all the answers

Study Notes

Populations and Communities Overview

A population consists of individuals of the same species that interact and live in a defined area.
A species is characterized by its ability to interbreed and produce fertile offspring.

Estimation of Population Size

Population size is estimated rather than directly counted, particularly useful for large populations.
Sampling involves selecting a random sample, where each member has an equal chance of being chosen.
Quadrat sampling involves a fixed-size frame for estimating the size of sessile organisms.
Sampling error represents the discrepancy between actual and estimated values.

Quadrant Sampling for Sessile Organisms

Quadrat method is effective for counting non-moving organisms.
Random sampling is achieved through marking boundaries and using random numbers for selection.
Standard deviation can be used to measure variability in the data collected.

Capture-Mark-Release-Recapture Method

Used for estimating population size of motile organisms.
Process includes capturing, marking, releasing, and later recapturing individuals.
The Lincoln index formula calculates population size: ( \text{Population size} = \frac{M \times N}{R} ), where:
- M = initially marked individuals
- N = total individuals captured in the second round
- R = number of recaptured marked individuals
Assumptions include no migration, no births or deaths during the study, and marks being visible without affecting survival.

Carrying Capacity and Competition

Carrying capacity refers to the maximum population size that an ecosystem can sustain.
Each habitat has unique carrying capacities based on available resources.
Competition arises from limited resources such as water, food, light, and territory.

Density-Dependent and Density-Independent Factors

Negative feedback controls population size, leading to periodic population fluctuations that stabilize over time.
Density-independent factors affect populations regardless of their density, e.g., natural disasters like fires.
Density-dependent factors only impact larger populations significantly:
- Increased competition, predation, and spread of diseases or parasites can lead to greater mortality and reduced reproduction.

Population Growth Curves

Sigmoid curves illustrate population growth dynamics with distinct phases:
- Exponential growth occurs in the absence of effective density-dependent factors or in resource-rich environments.
- Carrying capacity showcases the plateau phase when resources become limited.

Modeling Sigmoid Population Growth Curves

Models can be created using small environments (mesocosms) with plentiful resources to observe growth.
Experiments may utilize organisms like duckweed or yeast, focusing on how initial population numbers and resources influence carrying capacity.
Examination of model strengths and limitations is essential to understand real-world applications.

Description

Explore the key concepts related to populations and communities in IB Biology HL. This quiz covers definitions, interactions among species, and methods of estimating population size through random sampling. Test your knowledge and understanding of how populations function within ecosystems.