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Harvard Forest REU Symposium Abstract 2009

  • Title: The Presence of Spiders Reduces Ant Activity in Bogs
  • Author: Samantha K Hilerio (Worcester Polytechnical Institute)
  • Abstract:

    Little is known about how top predators in bogs interact. Our experiment investigated the effect of spiders and pitcher plants, two top predators in New England bogs, on the activity level and capture rate of ants, a common prey item. We hypothesized that the presence of either predator would decrease the activity level of ants, and further, that web-weaving spiders and hunting spiders would affect the ants differently. We created experimental bog settings in 10-gallon (51cm x 20 cm) terrariums each holding sphagnum moss, a medium-sized pitcher plant (Sarracenia purpurea), and an ant nest (Tapinoma sessile) extracted from a local bog. Tanks were assigned one of four spider addition treatments: one hunting spider, one web-weaving spider, one hunting spider plus one web-weaving spider, or three hunting spiders. Half the tanks were also assigned a pitcher plant manipulation: a mesh plug that prevented the plants from catching prey. Two pitfall traps measured ant activity in each tank. We extracted prey from the pitfall traps and all unplugged pitcher plants every 24 hours during six 4-day observation periods. Results showed that the presence of spiders decreased ant capture by pitfall traps (p=0.02). In single spider additions, the type of spider added (hunting versus web-weaving) did not affect ant abundance. However, in both pitfall traps and pitcher plants, the abundance of spiders added (1 versus 3) influenced the mean number of ants caught (p<0.05). The feeding status of pitcher plants (plugged versus unplugged) did not affect pitfall trap capture of ants. The strong influence of spiders and the comparatively low influence of pitcher plants on ants in this system raises the need for further investigation of spiders as a keystone predator in bogs.

  • Research Category: Physiological Ecology, Population Dynamics, and Species Interactions