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CHAPTER 3 TESTING ENERGY LIMITATION OF A CAVE STREAM ECOSYSTEM USING A WHOLE-REACH DETRITUS AMENDMENT Abstract Energy limitation has long been considered the primary factor influencing in situ evolutionary and ecosystem processes in cave ecosystems. Few studies, however, have provided adequate data to test this hypothesis, either because they have focused on specific ecosystem processes or trophic levels, or because they involved factors (e.g., heterogeneous organic pollution) that confound data interpretation. In this study, the energy-limitation hypothesis in cave ecosystems was tested explicitly using a detrital manipulation experiment. From February 2010 to February 2011, a 100-m reach of a carbon-poor cave stream was amended with cornlitter and the response in consumer biomass was followed relative to that of an upstream reference reach. During one year of pre-manipulation (February 2009 to January 2010), mean standing crop organic matter was 19 to 34 g ash-free dry mass [AFDM] m -2 . The corn litter amendment significantly increased mean standing crop organic matter in the manipulation reach to 423 g AFDM m -2 . Total macroinvertebrate biomass increased by more than 5 times following the litter amendment. Stable isotope analyses indicated that corn-derived carbon represented 16- 73% of macroinvertebrate biomass depending on taxon, indicating that increases in consumer biomass were driven by assimilation of corn-derived carbon. However, biomass of facultative surface species significantly increased following the amendment, while the biomass of obligate cave species remained unchanged. Facultative species are adapted to energy-rich surface 39
streams, while the obligate-cave species are adapted to survive in the energy-poor cave environment. These differences in evolutionary history likely contributed to the differential response to the corn litter amendment. While cave communities per se have the ability to exploit short-term increases in energy availability, species-specific responses are dictated by differing selective pressures and resulting life-history traits. Introduction Community ecologists have identified several mechanisms that influence the structure and function of ecosystems, including predator-prey interactions, disturbance regime, and resource quantity and quality (Morin 2011). Likewise, evolutionary biologists have identified many of the same mechanisms as important drivers in both morphological and life history evolution (see Stearns 2000, Reznick et al. 2001). Thus, an understanding of evolutionary history can provide insight into the factors that influence species abundance, diversity, or composition within communities. This study illustrates how cave ecosystems are an ideal setting to examine the interplay between evolutionary history and contemporary community structure. In cave ecosystems, there is no photosynthetic primary production and chemolithoautotrophy appears to be limited to relatively few systems (Sarbu et al. 1996; Engel et al. 2004), making most communities entirely reliant on allochthonous sources of organic matter (100% donor-control; Polis and Strong 1996). Limited surface connectivity reduces the quantity of detrital inputs, while their quality is diminished by prior biologic processing in soil horizons and transport flow paths. Thus, limitation mediated by the availability of organic carbon, as opposed to via nitrogen (N) or phosphorus (P) supply, has historically been considered the primary factor influencing both ecological and evolutionary processes in cave ecosystems (Culver et al. 1995; Graening and Brown 2003; but see Schneider et al, 2010). 40
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THE INFLUENCE OF ENERGY AVAILABILIT
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ABSTRACT Detritus from surface envi
Page 5 and 6: LIST OF ABBREVIATIONS AND SYMBOLS m
Page 7 and 8: NC IL ON U.K. VIAT VIE Fig. North C
Page 9 and 10: AIC K-S Akaike information criterio
Page 11 and 12: laboratory work and was an excellen
Page 13 and 14: LIST OF TABLES TABLE 2.1 TABLE 2.2
Page 15 and 16: LIST OF FIGURES FIGURE 2.1 (a) Box
Page 17 and 18: FIGURE 4.3 Growth models for Orcone
Page 19 and 20: chemolithoautotrophy-based systems;
Page 21 and 22: ecology, 51, 31-53. Gibert J. & Cul
Page 23 and 24: CHAPTER 2 EFFECTS OF ORGANIC MATTER
Page 25 and 26: community structure in cave “pits
Page 27 and 28: communities and how variation in co
Page 29 and 30: the different source locations was
Page 31 and 32: of natural-log transformed data (%
Page 33 and 34: peak in organic matter in Big Mouth
Page 35 and 36: Figs. 5a, b). The breakdown rate of
Page 37 and 38: per litter bag. Similarly, Huntsman
Page 39 and 40: ags was the greater retention of li
Page 41 and 42: Historically, limited resource inpu
Page 43 and 44: Culver, D.C. & Pipan, T. (2009) The
Page 45 and 46: Merritt, R.W., Cummins, K.W. & Berg
Page 47 and 48: Table 1. Mean (1 S.D.) macroinverte
Page 49 and 50: Table 2. Mean (±1 S.D.) daily temp
Page 51 and 52: Figure 1. (a) Box and whisker plot
Page 53 and 54: Figure 3. Non-metric multidimension
Page 55: Figure 5. Box and whisker plot of l
Page 59 and 60: More recent observational and exper
Page 61 and 62: of netting (mesh size 2.5×1.5-cm)
Page 63 and 64: the two end-members. This conservat
Page 65 and 66: crop organic matter significantly i
Page 67 and 68: macroinvertebrate biomass to levels
Page 69 and 70: and surface streams (20-35,000 g m
Page 71 and 72: these factors, the stable isotope a
Page 73 and 74: surface streams. Thus, it is likely
Page 75 and 76: subsides to ecosystem dynamics have
Page 77 and 78: populations. Journal of Applied Eco
Page 79 and 80: Poulson T.L. & Lavoie K.H. (2001) T
Page 81 and 82: Wood P., Gunn J. & Perkins J. (2002
Page 83 and 84: Table 2. Mean (±1 standard deviati
Page 85 and 86: Table 2. Continued Chironomini Para
Page 87 and 88: Figure 1. Mean (bars are standard e
Page 89 and 90: Figure 3. Non-metric multidimension
Page 91 and 92: CHAPTER 4 REXAMINING EXTREME LONGEI
Page 93 and 94: individuals, he predicted that it w
Page 95 and 96: A phylogeographic study by Buhay &
Page 97 and 98: differences in size structure among
Page 99 and 100: and females in Tony Sinks Cave were
Page 101 and 102: Estimates of life span for O. austr
Page 103 and 104: available size-classes were well re
Page 105 and 106: References Anonymous (1999) Cave Sc
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Huryn A.D. & Wallace J.B. (1987) Pr
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Whitmore N. & Huryn A.D. (1999) Lif
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Table 2. Estimated life span (years
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Figure 1. Annual growth increment (
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Figure 3. Growth models for Orconec
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CHAPTER 5 CONSUMER-RESOURCE DYNAMIC
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following incidental inputs of orga
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Temperature data were not available
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minimum (Venarsky et al., 2012b). A
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100% organic matter (i.e., maximum
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Macroinvertebrate biomass varied si
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Discussion The energy-limitation hy
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crayfish captured in most months we
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systems is likely high, especially
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function of microbial films in grou
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Crustacean Biology, 4, 35-54. Momot
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Whitmore N. & Huryn A. (1999) Life
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Table 2. Assimilation efficiencies
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Table 3. Continued Tanypodinae 0.03
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Table 5. Estimates of mean wood and
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Figure 1. (A) Box and whisker plot
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CHAPTER 6 OVERALL CONCLUSIONS Due t
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characteristics (e.g., higher growt
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characteristics, highly efficient p
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