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Pattern in trait-space use | Hypothesis | Attacked trait spaces marginal? 1 | Attacked trait spaces restricted?1 | Attacked trait spaces distant? |
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Monophagous, attacked trait space marginal and adjacent to alternative host (Figure 2(a)) | Adjacency favours host shifting (adjacent errors hypothesis) | Ancestral host: marginal Novel host: marginal but rare2 | — | Attacked spaces close2 |
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Oligophagous, attacked trait spaces marginal and adjacent (Figure 2(b)) | Adjacency persists after host shifting (adjacent oligophagy hypothesis) | Ancestral host: marginal Novel host: marginal | — | Attacked spaces close |
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Nascent host races, attacked trait spaces marginal and distant (Figure 2(c)) | Distance permits, and is also symptomatic of, genetic isolation (trait distance-divergence hypothesis) | Ancestral host: marginal Novel host: marginal | — | Attacked spaces distant |
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Pair of monophagous species, attacked trait spaces central on each host (Figure 2(d)) | Other isolating mechanisms reduce importance of trait-space distance (distance relaxation hypothesis) | Ancestral host: not marginal Novel host: not marginal | Ancestral host: restricted (central) or nonselective Novel host: restricted (central) or nonselective | Attacked spaces neither close nor distant |
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