The presence of a mutualist spider in a certain area improves the survival of an herbaceous shrub by reducing the impact of herbivorous insects. These spiders are preyed on by lizards, and lizards are eaten by birds. An increase in the density of lizards would most likely have a direct effect on spiders and a effect on the plant.

An increase in the density of lizards would most likely have a negative direct effect on spiders and a negative indirect effect on the plant.

Explanation:

Many animals modify their environments, apparently to reduce predation risk .Scincid lizards are included or excluded from 21 replicated plots, and spiders therein are classified as exposed or sheltered, depending on whether they are uncovered in their web or hidden in cocoons, leaves/debris, or burrows. Exposed spiders are greatly affected by the presence of predatory scincid lizards, whereas sheltered spiders are not. More specifically, lizards, which forage close to the ground, reduce the abundance of exposed spiders by two-thirds but have no effect on the abundance of sheltered spiders. Sheltered spiders are able to avoid predation and share space with lizards, suggesting that shelter construction is a mechanism for reducing predation risk and has important population consequences.