For the faculty-led research project I had students study the effect Peucetia viridans (green lynx spider) has on pollination and herbivory* on Hyptis suaveolens, a plant in the mint family.
*Herbivory is the damage on a plant caused by an herbivore (see photo below on right)
Green lynx spiders are cryptically colored, making it difficult for other animals to see them. They sit patiently and wait on the Hyptis suaveolens for unsuspecting prey to come their way. The spiders frequently prey on pollinators (i.e. bees, butterflies, and moths) and herbivores (i.e. grasshoppers and other various vegetation-sucking insects) that visit the plant.
We had two hypotheses for this project:
1. Peucetia viridans may decrease the chance of pollination of Hyptis suaveolens plants they occupy by deterring or preying on pollinators, and
2. Peucetia viridans may decrease the amount of herbivory to Hyptis suaveolens plants they occupy by preying on herbivores.
The students observed pollination visits to the plants and estimated the amount of herbivory on plants with and without spiders for two days.
Overall, the students observed over 300 pollinator visits, including bees, butterflies, and hummingbirds. All visits were timed to determine if the presence of a spider shortened visitation time. We found that spider's presence only reduced bee visitation time; possibly because bees can see the spider or have a greater chance of being predated on.
Students measured herbivory in 92 plants with spiders and 83 plants without spiders and found that herbivory was actually higher in plants with spiders! This was contrary to our hypothesis. I believe that there are two potential explanations for this: 1. when herbivores eat a plant, the plant releases volatile chemicals which can attract predators to the plant, and 2. spiders may move to areas with more prey (i.e. more herbivores).
Thus, the results suggest that spiders may cause a negative impact on pollination through decreased bee visitation time and spiders do not decrease herbivory. If you have any other questions about this study please feel free to leave a comment or contact me!