6. if predators reduce prey abundance to very low levels, how might variable predator environments affect the evolution of flexible mating strategies? 7.if a plant can improve its ability to obtain water by growing more roots, why shouldn't the plant always grow more roots? 8. how could you experimentally determine whether migrating birds use day length or temperature as an environmental cue for migration? 9. what is the relationship between correlation and causation? 10. wh the energy obtained from each prey item, the abundance of each prey item, and the handling time of each prey item? en determining whether to feed on small, medium, or large prey, why should predators evaluate both