title: Joint effects of resources and amphibians on pond ecosystems.
abstract: Primary production can be controlled through bottom-up (e.g., resources) or top-down (e.g., predators) constraints. Two key bottom-up resources in small aquatic systems are light and nutrients, and forest canopy cover heavily influences these factors, whereas amphibian and invertebrate colonizers exert top-down pressure as grazers and predators. We designed our experiment to specifically manipulate two different top-down and bottom-up factors. We manipulated resources by altering light (low/high) and nutrient (low/high) availability; omnivores with the presence/absence of southern leopard frog tadpoles (Lithobates sphenocephalus); and predators with the presence/absence of spotted salamander larvae (Ambystoma maculatum) in a full-factorial experiment conducted over 14 weeks. We observed that both bottom-up and top-down effects were important in predicting lower trophic level biomass. We found a significant top-down effect of salamanders on Daphnia, but tadpoles had the strongest overall effect on the food web, influencing phytoplankton (+), periphyton (-), and chironomids (-). None of our models were good predictors of phytoplankton biomass, but both shading and nutrient availability relatively equally boosted periphyton biomass. We also found large temporal differences in food-web dynamics. Our results underscore the need for more information into how ecosystem functioning could be altered by land use, amphibian extirpation, and climate change.
authors.affiliation: Division of Biological Sciences, University of Missouri, Columbia, MO, 65211, USA. ferowland@mail.missouri.edu.
authors.forename: Freya E
authors.initials: FE
authors.lastname: Rowland
authors.affiliation: Division of Biological Sciences, University of Missouri, Columbia, MO, 65211, USA.
authors.forename: Madelyn B
authors.initials: MB
authors.lastname: Rawlings
authors.affiliation: Division of Biological Sciences, University of Missouri, Columbia, MO, 65211, USA.
authors.forename: Raymond D
authors.initials: RD
authors.lastname: Semlitsch
mesh_terms: D000818:Animals; D057231:Climate Change; D017753:Ecosystem; D020387:Food Chain; D061005:Ponds; D011235:Predatory Behavior
keywords: Anurans; Bottom–up; Food webs; Salamanders; Top–down