Estimating population size & sampling
Practice Flashcards
Flip to reveal answersWhy do ecologists estimate population size instead of counting every organism?
Track your progress — Sign up free to save your progress and get smart review reminders based on spaced repetition.
All 14 Flashcards — Estimating population size & sampling
Sign up free to track progress and get spaced-repetition review schedules.
Question
Why do ecologists estimate population size instead of counting every organism?
Answer
Counting everything is **impractical** — there are too many, many **hide**, and many **move** — so a random **sample** is counted and scaled up.
Question
Why must sampling be random?
Answer
To avoid **bias**, so the sample is **representative** of the whole habitat.
Question
Which method is used for non-moving organisms like plants?
Answer
**Quadrat sampling** — count organisms in random quadrats, find the mean, and scale up.
Question
Which method is used for animals that move?
Answer
**Capture–mark–release–recapture** — moving animals can't be counted in a fixed area.
Question
How does quadrat sampling estimate a population?
Answer
Count organisms in several **random quadrats**, find the **mean per quadrat**, then **scale up** to the whole habitat area.
Question
What are the steps of capture–mark–release–recapture?
Answer
**Capture** and **mark** a first sample, **release** them, let them mix, **recapture** a second sample, and count how many are marked.
Question
State the Lincoln index equation.
Answer
**N = (M × n) ÷ m**.
Question
In the Lincoln index, what is M?
Answer
The **number marked** (and released) in the **first** sample.
Question
In the Lincoln index, what is n?
Answer
The **total size of the second** sample (the recapture).
Question
In the Lincoln index, what is m?
Answer
The number in the second sample that were **already marked** (recaptured marks).
Question
What is N in the Lincoln index?
Answer
The **estimated total population size**.
Question
Name two assumptions of capture–mark–release–recapture.
Answer
Marked animals **mix back evenly**; **no births, deaths or migration** between samples; marks are **not lost or harmful**; marking doesn't change the chance of recapture.
Question
If 60 are marked, a second sample of 80 contains 20 marks, what is the estimated population?
Answer
N = (60 × 80) ÷ 20 = **240**.
Question
A memory hook for choosing the method?
Answer
**Sit still → quadrat; runs away → recapture.**
Read the notes
Full study notes for Estimating population size & sampling
Topic 3.8 hub
Populations and communities
More from Topic 3.8
All flashcards in this topic
Biology exam skills
Paper structures & tips
Track your progress with spaced repetition
Sign up free — Aimnova tells you exactly which cards to review and when, so you remember everything before your IB exam.
Start Free