AP Biology: Population Ecology - Your Night-Before Review 🚀

Hey there, future AP Bio superstar! Let's get you feeling confident about population ecology. This guide is designed to be your quick, high-impact review for tonight. We'll hit the key points, make connections, and get you ready to ace that exam!

What is a Population?

A population is a group of individuals of the same species living in the same area. Think of it like this:

• 🐝 A hive of bees
• 🌲 A forest of pine trees
• 🧑‍🤝‍🧑 Humans in a city

Populations aren't static; they change in size, density, and distribution due to:

• Resource availability
• Species interactions
• Genetic makeup (affecting adaptation)

Population ecology is all about understanding these dynamics and how they affect the health and growth of species. This knowledge is crucial for conservation and ecosystem management.

Factors Affecting Population Survival

A population's survival depends on a mix of biotic (living) and abiotic (non-living) factors:

Biotic Factors

• Competition: Individuals within or between species fighting for resources (food, water, mates).
• Predation: One species (predator) eats another (prey).
• Disease: Pathogens can decimate populations.

Abiotic Factors

• Resources: Access to food, water, oxygen, shelter.
• Habitat: A suitable place to live and reproduce. 🌱
• Climate: Temperature, precipitation, and extreme weather. 🌧️

Mathematical Equations for Population Growth

Basic Population Change

The simplest equation:

dN / dt = B - D

Where:

• dN/dt = change in population over time
• B = birth rate
• D = death rate

Example: If a population has 42 births and 17 deaths in a year: dN/dt = 42 - 17 = +25 (population increased by 25) 🦎

Exponential Growth

Occurs when a population grows at a constant rate, like compound interest.

Conditions:

• Unlimited resources
• High reproductive rate
• Low mortality rate

Formula:

dN / dt = (r max) (N)

Where:

• dN/dt = change in population size over time
• r max = maximum per capita growth rate
• N = population size

Example: A population of 862 iguanas with rmax = 0.05: dN/dt = (0.05) * 862 = 43.1 New population = 862 + 43 = 905 iguanas 🦎

Important: Exponential growth is unsustainable long-term due to limited resources.

Example: European Rabbits in Australia

Rabbits were introduced to Australia and experienced exponential growth. 🐇

• High reproductive rate
• Led to competition with native species, habitat destruction, and economic impacts.

Logistic Growth

Most populations follow logistic growth, which is an S-shaped curve.

1. Initial Exponential Growth: Rapid increase.
2. Slowing Growth: Due to limiting factors (resource availability, predation, habitat quality).
3. Carrying Capacity (K): The maximum number of individuals an environment can support.

Limiting Factors

These factors limit population growth:

• Density-dependent: Predation, competition, disease (more impact as population increases).
• Density-independent: Natural disasters, climate change (affect all populations regardless of size).

Example: Wolves reintroduced to Yellowstone:

• Wolves (predators) limit elk (prey) population. 🐺
• Elk (prey) limit wolf population (bottom-up control).

Learning Summary ✨

Population ecology studies population dynamics and their interactions with the environment. Key concepts include:

• Population growth and regulation
• Competition, predation, and mutualism
• Use of mathematical models to predict population changes

Understanding population dynamics is vital for conservation and management. Changes in populations are driven by biotic and abiotic factors.

Final Exam Focus 🎯

• High-Priority Topics: Population growth models (exponential vs. logistic), limiting factors, carrying capacity, and the impact of biotic and abiotic factors.
• Common Question Types: Interpreting graphs (growth curves), applying formulas, analyzing scenarios involving species interactions.
• Time Management: Quickly identify key information in questions, practice applying formulas, and don't get bogged down on any single question.
• Common Pitfalls: Confusing exponential and logistic growth, not considering both biotic and abiotic factors, and misinterpreting graphs.

<practice_questions>

Practice Questions

Multiple Choice Questions

1. A population of deer is introduced to an island. Initially, the population grows rapidly, but eventually, the growth rate slows down and the population stabilizes. This is an example of: (A) exponential growth (B) logistic growth (C) density-independent growth (D) random growth

2. Which of the following is a density-dependent factor that can limit population growth? (A) a hurricane (B) a volcanic eruption (C) competition for resources (D) a change in temperature

3. A population of bacteria doubles every hour. This is an example of: (A) logistic growth (B) exponential growth (C) linear growth (D) carrying capacity

Free Response Question

A population of rabbits is introduced to a new habitat. Initially, the population grows rapidly. However, as the population increases, the growth rate slows down and eventually stabilizes.

(a) Draw a graph illustrating the population growth of the rabbits over time. Label the axes and include the carrying capacity (K). (b) Explain the factors that contribute to the initial rapid growth of the rabbit population. (c) Describe the factors that cause the growth rate to slow down and eventually stabilize. (d) If a predator of rabbits is introduced to the habitat, how might this affect the rabbit population? Explain your answer.

Scoring Breakdown

(a) (2 points) - 1 point for a correctly labeled graph (x-axis = time, y-axis = population size) - 1 point for showing a logistic growth curve (S-shape) with a labeled carrying capacity (K).

(b) (2 points) - 1 point for mentioning abundant resources (food, habitat). - 1 point for mentioning low initial competition and predation.

(c) (3 points) - 1 point for mentioning increasing competition for resources. - 1 point for mentioning increased predation or disease. - 1 point for stating that these factors lead to a decrease in birth rate or increase in death rate, causing the growth rate to slow down.

(d) (2 points) - 1 point for stating that the rabbit population would likely decrease. - 1 point for explaining that this is due to increased predation pressure.

FRQ combined with multiple units

A population of fish in a lake exhibits logistic growth. Initially, the population grows rapidly, but over time, the growth rate slows down and stabilizes at the lake's carrying capacity. The fish population is also affected by the presence of a parasitic worm.

(a) Describe the key characteristics of logistic growth. Include a sketch of the population growth curve and label the carrying capacity. (2 points) (b) Explain how density-dependent factors, such as the parasitic worm, can influence the fish population. (2 points) (c) How might changes in the lake's temperature due to climate change affect the carrying capacity of the fish population? (2 points) (d) Describe how the concepts of energy flow and trophic levels apply to this ecosystem. (2 points) (e) If the fish population were to experience a sudden bottleneck event (e.g., a disease outbreak), how might this impact the population's genetic diversity and long-term survival? (2 points)

Scoring Breakdown

(a) (2 points) - 1 point for describing logistic growth as an S-shaped curve with initial exponential growth followed by a plateau. - 1 point for a sketch of a logistic growth curve with labeled axes and carrying capacity.

(b) (2 points) - 1 point for explaining that density-dependent factors like parasites have a greater impact as the population size increases. - 1 point for stating that the parasitic worm can increase mortality or decrease reproductive rates, thus slowing population growth.

(c) (2 points) - 1 point for stating that increased temperature can alter the lake's environment and potentially reduce the carrying capacity. - 1 point for mentioning that changes in temperature can affect oxygen levels, food availability, and suitability of habitat.

(d) (2 points) - 1 point for describing energy flow through trophic levels (e.g., producers to primary consumers to secondary consumers). - 1 point for explaining that fish occupy a specific trophic level and obtain energy from their prey.

(e) (2 points) - 1 point for mentioning that a bottleneck event can drastically reduce genetic diversity. - 1 point for explaining that reduced genetic diversity can make the population more vulnerable to future environmental changes or diseases. </practice_questions>

Good luck, you've got this! 💪