RESOURCE SUBSIDIES ACROSS THE AQUATIC-TERRESTRIAL BOUNDARIES OF TEMPORARY PONDS

Author

Kelley Ann Fritz, Southern Illinois University CarbondaleFollow

Date of Award

12-1-2017

Degree Name

Doctor of Philosophy

Department

Zoology

First Advisor

Whiles, Matt

Abstract

Aquatic habitats are closely linked to surrounding terrestrial environments via reciprocal subsidies. Much of the research on these subsidies has been focused on streams, while subsidies across aquatic-terrestrial boundaries of other aquatic systems, like temporary ponds, have received little attention. Temporary ponds are seasonally inundated aquatic habitats and patterns of energy transport across transient aquatic-terrestrial boundaries are not well understood. To address the lack of information regarding these cross-habitat subsidies, I quantified: 1) leaf litter inputs, 2) amphibian egg inputs, 3) terrestrial insect inputs, 4) amphibian metamorph emergence, and 5) aquatic insect emergence for eight temporary ponds. Terrestrial insect inputs to ponds represented substantial high-quality subsidies to ponds that are generally unaccounted for in similar studies. While larger ponds produced greater total fluxes to terrestrial habitats, smaller ponds were often more productive per unit area. Therefore, a mosaic of small ponds may produce greater or equivalent subsidies and may be of greater value to terrestrial food webs than a single large pond. Resource subsidies of energy and nutrients can be transported via physical forces or biotic processes, such as animal migration or emigration. I quantified net nutrient fluxes associated with amphibian migrations across aquatic-terrestrial boundaries of eight temporary ponds in Illinois. I measured carbon (C), nitrogen (N), and phosphorus (P) subsidies from forests to ponds, in the form of eggs, and the reciprocal subsidies from ponds to forests via juvenile emigration. Juvenile emergence biomass did not resemble egg biomass, as not all species bred successfully in each pond, resulting in variability in the magnitude of nutrient fluxes both across ponds and species. The forest was not always the recipient system of net nutrient fluxes. Hydroperiod, trophic interactions, and species composition explained some dynamics of N and P subsidies. Most studies have focused on the magnitude of cross-boundary fluxes, but the impact of a subsidy is mediated by the size of the flux as well as the quality and relative abundance of similar resources in the recipient habitat. Long-chain polyunsaturated fatty acids (LC-PUFAs) are necessary for proper physiological function, are unevenly distributed across the landscape, and animals differ greatly in their ability to synthesize them de novo. This creates the potential for limitation and increases their possible importance as a subsidy. I examined LC-PUFA tissue concentration and export in eight species of emerging amphibian metamorphs across eight temporary ponds in a wetland complex. I found that tissue concentrations and export of LC-PUFAs varied across species, but were generally within the ranges of several freshwater fish and aquatic insects. Anurans exported higher amounts of LC-PUFAs than salamanders, largely due to the higher emergence biomass of anurans. Further, I explored fatty acid profiles and immune function of wolf spiders in wetland and upland habitats. Wetland spiders had higher tissue levels of aquatic-derived LC-PUFAs and elevated immune function compared to upland spiders. These patterns suggest aquatically derived nutrients, such as LC-PUFAs, may benefit organisms exploiting freshwater habitats.