1. Populations contain no animals that are consistently less discriminating than others in their choice of substrates.
2. Previous experience in atypical substrates does not alter preferences for typical substrates.
3. Animals live slightly longer in very fine-grained substrates than in coarser ones.
4. Their growth rates do not differ over a range of particle sizes.
5. Animals select the smaller grains in a substrate to build their tubes with.
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