TITLE PAGE - acumen - The University of Alabama
TITLE PAGE - acumen - The University of Alabama TITLE PAGE - acumen - The University of Alabama
Studies that have examined community structure in cave and groundwater ecosystems following organic pollution events commonly cite competitive exclusion (e.g., due to differential life histories and physiologies; see above discussion) by facultative species as a possible mechanism behind the extirpation of obligate-cave species (e.g., Sinton 1984, Notenboom et al. 1994, Sket 1999, Sket 2005; Culver and Pipan 2009). Both the continued presence of obligatecave species within the manipulation reach following the litter addition (e.g., short-term population response) and the positive correlations between energy availability and obligate-cave species productivity reported in other cave studies (e.g., long-term population response; Huntsman et al. 2011b and Chapter 5), indicate that increased energy-availability, at least within the bounds of this and previous studies (Fig. 4), does not necessarily cause the extirpation of obligate cave species through competitive interactions with facultative species. Thus, the changes in cave community structure following pollution episodes are more likely due to changes in water quality (e.g., toxic chemicals, heavy metals, anoxic conditions) rather than changes to interspecific competitive interactions due to modifications in cave ecosystem energy dynamics (e.g., increase in highly labile organic matter). Carbon flow through cave food webs In surface streams, microorganisms (e.g. bacteria and fungi) serve as important intermediates in the transfer of carbon from particulate and dissolved organic matter to consumers at higher trophic levels (Suberkropp & Klug 1976, Bärlocher & Kendrick 1981; Hall & Meyer 1998). Carbon flow through cave stream food webs flows through similar pathways. Simon et al. (2003) found that dissolved organic carbon was available to primary consumers and predators following immobilization through epilithic biofilms. Additionally, Simon & Benfield (2001) reported fungal colonization patterns of CPOM and wood were similar in cave and 55
surface streams. Thus, it is likely that uptake of leached dissolved organic carbon microbial biofilms was instrumental in the transfer of corn-litter carbon to the macroinvertebrate, crayfish, and salamanders in the manipulation reach. Throughout the litter amendment experiment conducted in this study, samples were collected to analyze microbial δ 13 C composition via compound-specific stable isotope analysis of phospholipid fatty acids. These analyses will be complete in the near future and will help elucidate the role of microbes in the flow of carbon through the food web in Bluff River Cave. Cave streams vs. surface streams Facultative species, as opposed to obligate-cave species, dominated macroinvertebrate biomass both before and after the litter amendment and were also the component of the cave community responsible for the large increase in total macroinvertebrate biomass following the litter amendment. Previous litter-breakdown studies in cave streams have also reported that facultative species accounted for the majority of macroinvertebrate biomass in litter-bags (Brussock et al., 1988; Galas et al., 1996; Venarsky et al. 2012). Given the dominance of facultative species in this and other cave studies, it appears that some cave streams have much more in common with surface streams than previously appreciated. In addition to community structure, several of the characteristics that define the environment of cave ecosystems, such as the lack of light and dependence on allochthonous sources of energy, are also similar to some surface stream ecosystems. For example, forested headwater surface streams can have dense canopies throughout the year, which cause both continuously low rates of primary production and a consequently heavy reliance on allochthonous inputs of organic matter from the surrounding watershed to support in situ productivity (see Webster et al. 1983, Lowe et al. 1986, Mulholland et al. 1997; Wallace et al. 1999). 56
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surface streams. Thus, it is likely that uptake <strong>of</strong> leached dissolved organic carbon microbial<br />
bi<strong>of</strong>ilms was instrumental in the transfer <strong>of</strong> corn-litter carbon to the macroinvertebrate, crayfish,<br />
and salamanders in the manipulation reach. Throughout the litter amendment experiment<br />
conducted in this study, samples were collected to analyze microbial δ 13 C composition via<br />
compound-specific stable isotope analysis <strong>of</strong> phospholipid fatty acids. <strong>The</strong>se analyses will be<br />
complete in the near future and will help elucidate the role <strong>of</strong> microbes in the flow <strong>of</strong> carbon<br />
through the food web in Bluff River Cave.<br />
Cave streams vs. surface streams<br />
Facultative species, as opposed to obligate-cave species, dominated macroinvertebrate<br />
biomass both before and after the litter amendment and were also the component <strong>of</strong> the cave<br />
community responsible for the large increase in total macroinvertebrate biomass following the<br />
litter amendment. Previous litter-breakdown studies in cave streams have also reported that<br />
facultative species accounted for the majority <strong>of</strong> macroinvertebrate biomass in litter-bags<br />
(Brussock et al., 1988; Galas et al., 1996; Venarsky et al. 2012). Given the dominance <strong>of</strong><br />
facultative species in this and other cave studies, it appears that some cave streams have much<br />
more in common with surface streams than previously appreciated. In addition to community<br />
structure, several <strong>of</strong> the characteristics that define the environment <strong>of</strong> cave ecosystems, such as<br />
the lack <strong>of</strong> light and dependence on allochthonous sources <strong>of</strong> energy, are also similar to some<br />
surface stream ecosystems. For example, forested headwater surface streams can have dense<br />
canopies throughout the year, which cause both continuously low rates <strong>of</strong> primary production<br />
and a consequently heavy reliance on allochthonous inputs <strong>of</strong> organic matter from the<br />
surrounding watershed to support in situ productivity (see Webster et al. 1983, Lowe et al. 1986,<br />
Mulholland et al. 1997; Wallace et al. 1999).<br />
56
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