Artificial light increases local predator abundance, predation rates, and herbivory

Marshall McMunn, Louie H. Yang, Amy Ansalmo, Keatyn Bucknam, Miles Claret, Cameron Clay, Kyle Cox, Darian Dungey, Asia Jones, Ashley Kim, Robert Kubacki, Rachel Le, Deniss Martinez, Brian Reynolds, John Schroder, and Emily Wood


Human activity is rapidly increasing the radiance and geographic extent of artificial light at night (ALAN). The timing and characteristics of light affect the development, behavior, and physiological state of many organisms. Depending on the ecological context, plants and animals respond to artificial lights in both adaptive and maladaptive ways. Mesocosm experiments have demonstrated both top-down and bottom-up control of populations under ALAN, but there have been few community-scale studies that allow for spatial aggregation through positive phototaxis, a common phenomenon among arthropods. We performed a field study to determine the effects of ALAN on arthropod communities, plant traits, and local herbivory and predation rates. We found strong positive phototaxis in 10 orders of arthropods, with increased (159% higher) overall arthropod abundance under ALAN compared to unlit controls. The arthropod community under ALAN was more diverse and contained a higher proportion of predaceous arthropods (15% vs 8%).  Predation of immobilized flies occurred more 3.6 times faster under ALAN; this effect was not observed during the day. Contrary to expectations, we also observed a 6% increase in herbivory under ALAN. Our results highlight the importance of open experimental field studies for determining the community-level effects of ALAN.

Environmental Entomology

Pulsed seaweed subsidies drive sequential shifts in the effects of lizard predators on island food webs

Jonah Piovia-Scott, Louie H. Yang, Amber N. Wright, David Spiller, Thomas Schoener


Most prominent theories of food-web dynamics imply the simultaneous action of bottom-up and top-down forces. However, transient bottom-up effects resulting from resource pulses can lead to sequential shifts in the strength of top-down predator effects. We used a large-scale field experiment (32 small islands sampled over 5 years) to probe how the frequency and magnitude of pulsed seaweed inputs drives temporal variation in the top-down effects of lizard predators. Short-term weakening of lizard effects on spiders and plants (the latter via a trophic cascade) were associated with lizard diet shifts, and were more pronounced with larger seaweed inputs. Long-term strengthening of lizard effects was associated with lizard numerical responses and plant fertilization. Increased pulse frequency reinforced the strengthening of lizard effects on spiders and plants. These results underscore the temporally variable nature of top-down effects and highlight the role of resource pulses in driving this variation.

Ecology Letters