Kelly, an avid birdwatcher, wants to construct a dichotomous key to help identify the different species of birds she observes.Which would NOT be a useful character to include in this key?

Question

BlackTom AI · Accepted Answer

A dichotomous key depends on characters that differ between the taxa to split groups repeatedly into two alternatives, so only traits that vary among the species and are reliably observable are useful.

1) Relevant knowledge points and concepts
- A dichotomous key requires contrasting, variable, and observable characters to separate species (not traits that are constant across the whole group).
- Useful characters are diagnostic (show consistent differences between species) and practical to observe in the field or lab.
- A character that is shared by all members of the group cannot be used to divide the group further.

2) Step-by-step reasoning
- Evaluate each option for: variability among bird species, observability, and diagnostic value.
  a) Beak shape: Varies strongly (e.g., hooked, cone-shaped, long probing bills) and correlates with feeding niche — good for splitting species.
  b) Body markings: Patterns like stripes, spots, wing bars differ among species and are easy to observe — useful.
  c) Eye colour: Can differ among species (dark vs. pale irises) and sometimes is diagnostic; though sometimes harder to see, it is variable and usable.
  d) Presence of feathers: All birds possess feathers; this trait is uniform across the group being keyed (no variation to split species) — not useful.
  e) Colour of feathers: Plumage colour often differs between species and sexes and is one of the primary field characters — very useful.

3) Calculations or intermediate steps
- No numeric calculations are needed. The intermediate “step” is the binary decision: does this trait vary among the target species? If yes → useful; if no → not useful. Presence of feathers = no variation → not useful.

4) Why the correct answer is correct
- “Presence of feathers” cannot separate any bird species because it is a shared, invariant trait of the entire class Aves; a dichotomous key needs traits that divide the set into different groups.

5) Why the other options are incorrect (i.e., why they are useful)
- a, b, c, e are variable and observable characters that commonly distinguish bird species (beak shape, body markings, eye colour, feather colour).

6) Conclusion
- Therefore the character that would NOT be useful is d. Presence of feathers. This matches the provided correct answer.

Kelly, an avid birdwatcher, wants to construct a dichotomous key to help identify the different species of birds she observes.Which would NOT be a useful character to include in this key?单项选择题

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