Based on communities A, B, and C depicted below, beta diversity will be higher for which pair of communities?

Question

BlackTom AI · Accepted Answer

Beta diversity quantifies species turnover (how different two communities are in species composition). A common way to measure it is Jaccard dissimilarity = 1 − (number of shared species / number of species in the union). Higher dissimilarity = higher beta diversity.

Step 1 — identify species counts and overlap from the diagrams:
- Community A: 5 species (black tree, small black shrub, green tree, red flower, orange bush; also a yellow vine appears but the label says A = 5 species).
- Community B: 5 species (green tree, yellow vine, blue tree, gray herb, gray conifer; B = 5 species).
- Community C: 3 species (black tree, green tree, orange bush; C = 3 species).

Step 2 — determine shared species:
- A and B share the green tree and the yellow vine (2 shared species).
- A and C share the black tree, the green tree, and the orange bush (3 shared species — C is essentially a subset of A).

Step 3 — compute Jaccard dissimilarity for each pair:
- A vs B: |A| = 5, |B| = 5, shared = 2 → union = 5 + 5 − 2 = 8.
  Jaccard dissimilarity = 1 − (shared / union) = 1 − (2/8) = 1 − 0.25 = 0.75.
- A vs C: |A| = 5, |C| = 3, shared = 3 → union = 5 + 3 − 3 = 5.
  Jaccard dissimilarity = 1 − (3/5) = 1 − 0.6 = 0.4.

Step 4 — interpret results:
0.75 (A vs B) > 0.4 (A vs C), so beta diversity is higher between A and B because they share fewer species and have a larger proportion of unique species.

Why the other choice is incorrect:
- Communities A and C have lower beta diversity because C’s species are almost entirely contained within A (high overlap), producing a low dissimilarity (0.4).

Conclusion: Beta diversity is higher for Communities A and B, which matches the provided correct answer (Communities A and B).

Based on communities A, B, and C depicted below, beta diversity will be higher for which pair of communities?单项选择题

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