The Effects of Spatial Subsidies on AmphibiansEPA Grant Number: FP917093
Title: The Effects of Spatial Subsidies on Amphibians
Investigators: Earl, Julia E
Institution: University of Missouri - Columbia
EPA Project Officer: Lee, Sonja
Project Period: August 23, 2010 through August 22, 2013
Project Amount: $111,000
RFA: STAR Graduate Fellowships (2010) RFA Text | Recipients Lists
Research Category: Academic Fellowships , Fellowship - Ecosystem Services: Aquatic Systems Ecology
Spatial subsidies are resources that move from one habitat to another, providing linkages among ecosystems. I plan to determine how spatial subsidies affect the vital rates of species with ontogenetic habitat shifts, which are themselves spatial subsidies. I will assess the impacts of the presence and quality (nutrients and plant secondary compounds) of spatial subsidies (forest leaf litter input to ponds) when compared to within system inputs (aquatic grasses) on amphibian larvae.
Leaf litter, a spatial subsidy, is a resource linking forests and ponds. Leaves provide food for pond organisms but also contain chemicals, like tannins, that can be harmful. I will examine effects of leaf litter on pond amphibians by manipulating leaf input into artificial ponds and examining tadpole survival and diet. I will also measure tannins in pond water varying in tree species and study the effects of tannins on tadpoles, helping us understand how forestry affects pond communities.
This study will examine the effects of the presence and quality of spatial subsidies on the vital rates of species amphibian larvae. To investigate the effects of the presence of spatial subsidies, I will compare tadpole vital rates and diet (using stable isotopes) in pond mesocosms with spatial subsidy input (deciduous leaf litter) to mesocosms containing within system input (aquatic grass) and no input along a light gradient. Because frogs move away from ponds into forest after metamorphosis (another spatial subsidy), this study is a beginning step to understanding spatial subsidy feedback loops between forest and ponds. Although spatial subsidies are essentially nutrient and energy vectors from one ecosystem to another, the subsidy’s effects depend on the degree to which the subsidy’s nutrients are labile, along with the concentrations of other active compounds, such as tannins. To investigate the effects of the quality (primarily tannin concentration) of spatial subsidies on tadpole vital rates, a mesocosm study and a laboratory study have already been performed to compare the community and chemical effects of litter input from different species of trees on tadpoles. To adjust the laboratory study to be more realistic, I plan to conduct an observational study on the tannin concentrations in closed canopy ponds that vary in the species of surrounding trees. Realistic concentrations will then be used in a laboratory experiment.
Theory on spatial subsidies predicts that additional input will support ecosystems with low productivity. Preliminary results show this to be true for leaf litter input and overall macroinvertebrate biomass in ponds, but amphibians appear to have lower survival and growth likely due to high tannin concentrations, lower dissolved oxygen from microbial decomposition, and lower food quality. I hypothesize that tadpoles from clearcut tanks eat and assimilate material from algae, and tadpoles from forest tanks will have isotopic signatures reflecting the detritus available, which has lower food quality than algae. For spatial subsidy quality, I predict leaf litter input with higher tannin concentrations will negatively affect tadpole performance, resulting in differing tadpole performance with litter input from different tree species.
Potential to Further Environmental/Human Health Protection:
Many land use changes, such as forestry practices addressed in this study, may impact the flow and type of spatial subsidy input into ponds. In aquatic systems, spatial subsidies may impact water quality by altering dissolved oxygen levels and transporting secondary plant compounds into water. Information on forestry practices on amphibians and water quality and the indirect and direct causes of those effects will help determine best management practices and help landowners and public managers make educated decisions about their property.