Spatial Subsidies, Trophic State, and Community Structure: Examining the Effects of Leaf Litter Input on Ponds
In aquatic systems, light and subsidy input often co-vary along a canopy cover gradient. This creates systems where subsidies are more prevalent in areas with low primary productivity and less prevalent in areas with high primary productivity. We expect ecosystem processes and community structure to respond to these changes in resources. We examined the effects of light and subsidy input (leaf litter) on ponds by placing pond mesocosms along a canopy gradient and manipulating litter input. We then sampled mesocosms for ecosystem and community parameters for 2 years during April (pre-leaf out), July (full canopy), and November (start of leaf fall). Neither canopy cover nor litter input tended to dominate effects overall, highlighting the importance of the light-subsidy gradient combination that is frequently encountered in temperate aquatic systems. Ponds shifted from an autotrophy/heterotrophy balance to net heterotrophy with increasing canopy cover in concordance with our predictions. Although litter input affected dissolved oxygen, we did not detect an effect of litter on trophic state, primary production, or community respiration. We additionally found effects of both canopy cover and litter input on community composition, but very differently than that found in streams. In general, the grazer and shredder macroinvertebrate functional feeding groups were rare in the pond mesocosms, and thus did not respond to treatments. The collector proportion of the community, mainly chironomids, increased with canopy cover and was higher in mesocosms with litter input than those without. Contrary to predictions, there were few differences between subsidy input type (leaves or grass) despite differences in litter quality. This study, along with many others, highlights the importance of canopy gradients in determining ecosystem function and community composition.
Keywordsleaf litter canopy cover primary production community respiration nutrients macroinvertebrates zooplankton
We would like to thank M. Osbourn, K. Cohagen, K. Malone, D. Leach, N. Woodburn, and E. McDonald for help in the field, P. Castello, D. Drake, J. Fairchild, S. Olson, and L. Johnson for help in the laboratory, and C. Galen, C. Rabeni and two anonymous reviewers for comments on previous versions of this manuscript. Financial support was provided by the National Science Foundation (DEB-0239943). JEE was supported by a Life Sciences Fellowship, TWA Scholarship, and Conservation Biology Fellowship through the University of Missouri and an Environmental Protection Agency STAR Fellowship.
- Clesceri LS, Greenberg AE, Trussell RR, Eds. 1989. Standard methods for the examination of water and wastewater. Washington, DC: American Public Health Association.Google Scholar
- Earl JE. 2012. Effects of spatial subsidies and canopy cover on pond communities and multiple life stages in amphibians. Dissertation, University of MissouriGoogle Scholar
- Edwards FK, Lauridsen RB, Armand L, Vincent HM, Jones JI. 2009. The relationship between length, mass and preservation time for three species of freshwater leeches (Hirundinea). Fundam Appl Limnol 173:321–7.Google Scholar
- McCauley E. 1984. The estimation of the abundance and biomass of zooplankton in samples. In: Downing JA, Rigler FH, Eds. Secondary productivity in fresh waters. Blackwood (NJ): Blackwell. p 228–65.Google Scholar
- Merritt RW, Cummins KW, Eds. 1996. An introduction to the aquatic insects of north america. Dubuque (IA): Kendall/Hunt Publishing Company.Google Scholar
- Myer E. 1989. The relationship between body length parameters and dry mass in running water invertebrates. Archiv für Hydrobiologie 117:443–51.Google Scholar
- Nakano S, Miyasaka H, Kuhara N. 1999. Terrestrial-aquatic linkages: Riparian arthropod inputs alter trophic cascades in a stream food web. Ecology 80:2435–41.Google Scholar
- SAS. 2004. SAS/STAT user’s guide. Cary, NC: SAS Institute.Google Scholar
- Semlitsch RD, Todd BD, Blomquist SM, Calhoun AJK, Gibbons JW, Gibbs JP, Graeter GJ, Harper EB, Hocking DJ, Hunter ML Jr, Patrick DA, Rittenhouse TAG, Rothermel BB. 2009. Effects of timber harvest on amphibian populations: understanding mechanisms from forest experiments. Bioscience 59:853–62.CrossRefGoogle Scholar
- Thorp JH, Covich AP, Eds. 2009. Ecology and classification of North American freshwater invertebrates. San Diego, CA: Academic Press.Google Scholar
- USDA, NRCS. 2010. The PLANTS database. Baton Rouge (LA): National Plant Data Center. http://plants.usda.gov.
- Wetzel RG, Likens GE. 2000. Limnological analysis. New York: Springer.Google Scholar