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The Effect of Forest Composition and Caddisfly Larvae (Limnephilus indivisus ) Presence on Vernal Pond Communities Katie R. Seymore* and Tim J. Maret Forest dynamics in the eastern deciduous forests are changing from oak (Quercus sp.) to red maple (Acer rubrum) dominated forests due to anthropogenic interferences 1 . Understanding how this shift may affect communities in these forests is important, especially for vernal ponds, which receive many of their nutrients from allochthonous sources like senesced leaves 2 . Changes in leaf litter may affect nutrient availability to organisms and influence their ability to survive and metamorphose before temporary waters dry 3,4 . Detrital breakdown in streams has been shown to occur much faster in the presence of shredders, which break down the leaves into fine particulate organic matter 5 . This breakdown makes nutrients available to lower trophic levels like tadpoles and plankton by increasing the surface area for biofilm colonization 6 , and may impact food availability to higher trophic levels (e.g., salamanders) though bottom-up effects 7,8 . Several studies have investigated the effects of changing forest dynamics on vernal pond amphibians; however, these studies ignored the role of invertebrate detritivores (i.e., shredders) 8,9 . Mehring and Maret (2011) demonstrated that leaf litter composition influences caddisfly larvae. Larval feeding, growth, and developmental rates were higher when supplied with maple leaves. This was incongruent with the results of Rubbo and Kiesecker (2004), who raised amphibians on the two different leaf substrates, finding larger sizes and earlier metamorphosis with oak leaves. Rubbo and Kiesecker also used dried leaves, which may have eliminated beneficial microorganisms. The current study is the next step in understanding how different leaf types, in the presence of caddisflies, influence vernal pond communities. Introduction Methods Conclusions References Results Acknowledgements •Funds for this research project were generously provided by the Shippensburg Graduate Research Grant Program •Special thanks to the Wetland Foundation for traveling funds Vernal pond mesocosms were established to investigate the effect of different of leaf substrate (A. rubrum and Q. alba) in the presence or absence the detritivore, L. indivisus, on the community. The treatments included: Q. alba substrate with L. indivisus larvae; OC Q. alba substrate without L. indivisus larvae; O A. rubrum substrate with L. indivisus larvae; MC A. rubrum substrate without L. indivisus larvae; M Organisms were collected from vernal ponds in Tuscarora State Forest, Pennsylvania. Mesocosms included 55 spotted salamander larvae, 125 wood frog tadpoles, 75 caddisflies (if in treatment), 600 g (dry weight) of wet leaves with living microorganisms, and an aliquot of plankton in 1000 liters of well water. Tubs were checked daily for metamorphosing frogs 10 , which were weighed. Twice (May 31 st and June 15 th , the end of the experiment) community parameters were measured, including: zooplankton, chlorophyll a, simplified dial respiration, dissolved oxygen (DO), dissolved organic carbon (DOC), temperature, and pH. The experiment ended when salamanders began to metamorphose, at which time all organisms were collected and the mesocosms were drained. Salamanders were weighted and staged 11 , the percent of caddisflies that Figure 8. Lithobates sylvatica, Limnephilus indivisus, Ambystoma maculatum 1 Abrams, M. D. 1998. The Red Maple Paradox. BioScience 48(5): 355- 364. 2 Webster, J. R. and E. F. Benfield. 1986. Vascular Plant Breakdown in Freshwater Ecosystems. Annual Review of Ecology and Systematics 17: 567-594. 3 Cohen, J. S., S. Ng and N. Blossey. 2012. Quantity Counts: Amount of Litter Determines Tadpole Performance in Experimental Microcosms. Journal of Herpetology 46(1): 85–90. 4 Mehring, A. S. and T J. Maret. 2011. Red Maple Dominance Enhances Fungal and Shredder Growth and Litter Processing in Temporary Ponds. Limnology and Oceanography 56(3): 1106–1114. 5 Short, R. A. and P. E. Maslin. 1977. Processing of Leaf Litter by a Stream Detritivore: Effect on Nutrient Availability to Collectors. Ecology 58(4): 935-938. 6 Iwai, N., R. G. Pearson, and R.A. Alford. 2009. Shredder-tadpole facilitation of leaf litter decomposition in a tropical stream. Freshwater Biology 54: 2573-2580. 7Chung, N. and K. Suberkropp. 2009. Contribution of Fungal Biomass to the Growth of the Shredder, Pycnopsyche gentilis (Trichoptera: Limnephilidae). Freshwater Biology 54: 2212-2224. 8 Rubbo, M. J. and J. M. Kiesecker. 2004. Leaf Litter Composition and Community Structure: Translating Regional Species Changes into Local Dynamic. Ecology 85(9): 2519–2525. 9 Stoler A. B. and R. A. Relyea. 2011. Living in the Litter: The Influence of Tree Leaf Litter on Wetland Communities. Oikos 120: 862–872. 10 Gosner, K. L. 1960. A simplified table for staging anuran embryos and larvae with notes on identification. Herpetologica 16:183–190. 11 Watson, S., and A. P. Russell. 2000. A posthatching developmentalstaging table for the long-toed salamander, Ambystoma macrodactylum krausei. Amphibia–Reptilia 21: 143–154. Shippensburg University, Shippensburg, Pennsylvania 17257 • A shift in forest composition may not be detrimental for amphibians, potentially decreasing time to metamorphosis and increasing mass. • Trends suggest maple leaves, especially in the presence of the caddisfly larvae, have the greatest bottom-up effect on higher trophic levels. • Presence of shredders influences community dynamics in vernal ponds. Differences between the results of this study and previous studies indicate that shredding by caddisfly larvae mediates the effects of leaf litter on higher trophic levels. • Community interactions on each trophic level may mask individual effects on intermediate trophic levels (e.g., zooplankton). • Salamander mean stage at the end of the experiment showed an interaction between the leaf type and caddisfly presence (F 1,8 =5.03, P=0.055). • Wood frog time to metamorphoses showed the largest response, with the tadpoles in oak without caddisflies metamorphosing later than other treatments. There was an interaction between the leaf type and caddisfly presence (F 1,6 =9.82, P=0.020). Overall, maple leaves promoted faster time to metamorphosis (F 1,6 =17.46, P=0.006), and the presence of shredders also reduce time to metamorphosis (F 1,6 =17.46, P=0.006). • Wood frog mass was highest when raised on maple leaves (F 1,6 =4.382, P=0.081). There was an interaction between the leaf type and caddisfly presence (F 1,6 =3.838, P=0.098). • The presence of caddisflies promoted higher overall survival to metamorphose in the wood frogs (F 1,6 =4.23, P=0.085). • Respiration to photosynthesis ratios had a marginally significant response to leaf type (F 1,11 =0.767, P=0.088). Low R:P ratio in oak treatments suggest a more autotrophic system • Maple leaves had lower C:N ratios than oak leaves (F 1,7 = 11.19, P= 0.012). Figure 2. Wood frog median days to metamorphosis interaction plot Mean±SE (O: 23.7± 0.7, OC: 21.3± 0.3, M:21.3±0.3, MC:21.0±1.0) MANOVAs were used to test for treatment and block effects for overall responses of salamanders and wood frogs, then ANOVAs were run for individual response variables. Caddisfly larvae showed no difference in percent metamorphosing between leaf treatments (t-test; P>0.10). Plankton and water quality showed few significant trends. DOC concentrations were affected by an interaction between leaf type and caddisfly presence on the first sampling date only (F 1,11 =6.45, P=0.035). Copepod nauplii had increased densities in the presence of caddisfly on the first sampling date (F 1,11 =6.113,P=0.039). Figure 3. Mean wood frog mass at time of metamorphosis interaction plot Mean±SE (O:0.361±0.022, OC:0.329±0.010, M:0.363±0.011, MC:0.386±0.011) Figure 4. Percent of wood frogs that survived to metamorphose (±1 SE) Figure 1. Sampling mesocosms for amphibians Figure 5. Mean salamander stage at the end of study interaction plot Mean±SE (O:17.7±0.1, OC:17.4±0.4, M:17.3±0.3, MC:18.0 ±0.1) Figure 7. Mean R:P (±1 SE) sampled mid experiment Figure 6. Mean C:N ratio (±1 SE) of leaf substrate at the of experiment
