Invasive plant architecture alters trophic interactions by changing predator abundance and behavior

Area of Science:

• Ecology
• Invasive Species Biology
• Community Ecology

Background:

• Plants, as primary producers, initiate food chains but can also directly influence predators by altering habitat architecture.
• Invasive plants can fundamentally change native vegetation structure, leading to underappreciated trophic ramifications.
• Spotted knapweed (Centaurea maculosa) invasion has altered western North American grassland architecture.

Purpose of the Study:

• To investigate how changes in vegetation architecture due to spotted knapweed invasion affect native web spider populations and predation rates.
• To quantify the impact of invasive plants on predator abundance, community structure, and foraging success.
• To understand the indirect effects of invasive plants on food webs via plant-predator-consumer interactions.

Main Methods:

• Long-term monitoring of invaded and uninvaded grasslands.
• Observational studies on spider behavior and web construction.
• Field experiments to assess predation rates and reproductive success.

Main Results:

• Native web spider abundance was 38 times higher in C. maculosa-invaded grasslands.
• Dictyna spider densities increased 46-74 times, persisting over 6 years.
• Dictyna webs on C. maculosa were larger, captured more prey (especially large prey), and increased Dictyna reproduction rates.
• Overall Dictyna predation on invertebrates increased 89-fold.

Conclusions:

• Invasive plants that alter vegetation architecture can significantly impact native food webs.
• Plant-mediated effects on predators represent a crucial, yet often overlooked, pathway for invasive species impacts.
• Changes in habitat structure by invasive plants create novel plant-predator-consumer linkages with substantial ecological consequences.