AP Biology: Community Ecology - The Night Before 🌃

Hey! Let's get you totally prepped for the AP Bio exam with a super-focused review of community ecology. We'll break down everything you need to know, keep it chill, and make sure you're feeling confident. Let's do this! 💪

Introduction to Communities and Species Diversity

Community: A group of different populations living in the same area. Think of it like a neighborhood, but with all sorts of species. 🏘️
- Can be large or small, found in various environments (land, water, air).
- Species interact through competition, predation, and mutualism.
Why Study Communities?
- Understanding community dynamics helps us understand how ecosystems function.
- Important for managing and conserving ecosystems.
Species Diversity: The variety of species in a community. It's not just about the number of species, but also how evenly they're distributed.
- High diversity = many species with balanced populations. 💡
Simpson's Diversity Index: A way to measure diversity.
- Formula: Diversity Index = 1 - Σ (n / N)^2
  - n = number of organisms of a particular species
  - N = total number of organisms of all species

Exam Tip

Remember, a higher Simpson's Diversity Index indicates a more diverse and stable community. Practice calculating this index with different data sets.

Community Interactions

Predator and Prey (+/-)

One organism (predator) eats another (prey). It's a classic food chain dynamic. 🐍
- Predator-prey relationships are key for energy transfer in ecosystems.
- Predators can control prey populations, creating trophic cascades (effects on other levels of the ecosystem).
Image: A classic predator-prey relationship.

Competition (-/-)

Interspecies Competition: When two species compete for the same limited resources (food, habitat, water). 🤼
- Can lead to a decrease in one population or stabilization of both.
- Niche Partitioning: Species divide resources to avoid competition.
Image: Two species competing for the same resource.

Memory Aid

Think of competition as a fight for resources. The more overlap in needs, the more intense the competition.

Mutualism (+/+)

Both species benefit from the relationship. It's a win-win! 🤝
- Example: Acacia tree and acacia ants. Ants get food and shelter; tree gets protection. 🐜
Image: Acacia ants protect the tree and get food in return.

Commensalism (+/0)

One species benefits, the other is neither helped nor harmed. 🤷
- Example: Barnacles on a whale. Barnacles get a ride and access to food; whale is unaffected. 🐋
Image: Barnacles benefit from their attachment to the whale.

Parasitism (+/-)

One species (parasite) benefits at the expense of the other (host). 🤕
- Parasites are usually smaller than their hosts and feed off part of them.
- Example: Ticks on a dog. Ticks get food; dog loses nutrients and can get diseases. 🐕
Image: Ticks are parasites that feed on the blood of their hosts.

Key Concept

Remember the +/- symbols! It's a quick way to classify these relationships. Also, pay attention to the size difference in parasitism vs predation.

Memory Aid

Use the acronym "PCMP" to remember the types of community interactions: Predation, Competition, Mutualism, Parasitism. Then, remember that commensalism is the odd one out where one species is unaffected.

Final Exam Focus

High-Priority Topics:
- Species diversity and Simpson's Index
- Types of community interactions (predation, competition, mutualism, commensalism, parasitism)
- Trophic cascades and the role of keystone species
- How community interactions influence energy and nutrient transfer
Common Question Types:
- Multiple choice questions on identifying types of interactions.
- Free-response questions analyzing community data and calculating diversity indices.
- Scenarios that require you to predict the effects of changes in community structure.
Last-Minute Tips:
- Time Management: Don't get bogged down on one question. Move on and come back if you have time.
- Common Pitfalls: Misidentifying interactions, not paying attention to the +/- symbols, and forgetting the Simpson's Index formula.
- Strategies: Read questions carefully, underline key terms, and use diagrams to visualize interactions.

Exam Tip

Practice explaining each type of interaction using specific examples. This will help you on both MCQs and FRQs. Also, make sure you can calculate Simpson's Index quickly and accurately.

Practice Questions

Practice Question

Multiple Choice Questions

In a forest ecosystem, a population of deer is preyed upon by wolves. Which of the following best describes the relationship between the deer and the wolves? (A) Mutualism (B) Commensalism (C) Parasitism (D) Predation
A species of clownfish lives within the tentacles of a sea anemone. The clownfish is protected from predators by the anemone's stinging tentacles, and the clownfish helps the anemone by eating parasites. This relationship is an example of: (A) Competition (B) Commensalism (C) Mutualism (D) Parasitism
A researcher is studying a community of plants and finds that several species of plants compete for the same limited resource, sunlight. What is the most likely outcome of this competition? (A) An increase in the population of all plant species. (B) Niche partitioning among the plant species. (C) A decrease in the population of all plant species. (D) The extinction of all plant species.

Free Response Question

A group of researchers is studying a forest ecosystem. They collect data on the number of individuals of four different tree species in two different areas of the forest. The data is shown in the table below:

Tree Species	Area 1	Area 2
Species A	100	20
Species B	50	80
Species C	20	40
Species D	30	60

(a) Calculate the Simpson's Diversity Index for both Area 1 and Area 2. Show your work. (b) Based on your calculations, which area has a higher species diversity? Explain your answer. (c) Describe the possible ecological factors that could lead to differences in species diversity between the two areas.

Scoring Breakdown for FRQ

(a) (4 points total) * Area 1: (100/200)^2 + (50/200)^2 + (20/200)^2 + (30/200)^2 = 0.25 + 0.0625 + 0.01 + 0.0225 = 0.345 * Diversity Index = 1 - 0.345 = 0.655 (2 points) * Area 2: (20/200)^2 + (80/200)^2 + (40/200)^2 + (60/200)^2 = 0.01 + 0.16 + 0.04 + 0.09 = 0.3 * Diversity Index = 1 - 0.3 = 0.7 (2 points)

(b) (2 points total) * Area 2 has a higher species diversity (1 point). * Explanation: Area 2 has a higher diversity index (0.7) than Area 1 (0.655), indicating a more diverse community (1 point).

(c) (2 points total) * Possible factors include: different levels of sunlight, water availability, soil nutrients, disturbances (e.g., fire, logging), presence of invasive species, or different predator-prey relationships (2 points). Students should get points for any 2 relevant factors.

You've got this! Go ace that exam! 🚀

Community Ecology

Chloe Sanchez