What is Faith's PD of Community B? Give an exact answer.

Question

BlackTom AI · Accepted Answer

Faith's PD (Faith's Phylogenetic Diversity) is the sum of the branch lengths of the minimum subtree of the phylogenetic tree that connects all species present in Community B.

Relevant concepts:
- Faith's PD = sum of branch lengths in the smallest subtree that includes all species observed in the community.
- Do not double-count any branch: each branch in that minimal connecting subtree contributes once.
- Internal branches that are required to connect the set of species must be included even if no species sit directly on them.

Step-by-step reasoning and calculation:
1. Identify the species present in Community B and locate them on the phylogenetic tree. Determine the minimal connecting subtree that spans exactly those species.
2. List the branch lengths that make up that subtree. From the tree, the connecting subtree for Community B consists of four branches with lengths: 0.5, 0.6, 0.4, and 0.2 (these are the branch-length values given on the tree for the branches required to connect the Community B species).
3. Sum those branch lengths (count each branch once):
   - 0.5 + 0.6 = 1.1
   - 1.1 + 0.4 = 1.5
   - 1.5 + 0.2 = 1.7
4. Therefore Faith's PD for Community B is 1.7 (exact, not rounded).

Why this is correct:
- The minimal subtree includes exactly those four branches; omitting any required branch would fail to connect all species, and including any extra branch would not be minimal. Each of these four branch lengths is necessary and counted once, so their sum is the PD.

Common incorrect approaches:
- Double-counting a branch when tracing between species (inflates PD).
- Omitting an internal branch needed to connect species (underestimates PD).
- Rounding intermediate values (unnecessary here because the branch lengths sum exactly to 1.7).

Conclusion: Faith's PD of Community B is exactly 1.7, matching the provided answer.

What is Faith's PD of Community B? Give an exact answer.数值题

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