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are potentially capable of supporting relatively large populations of obligate cave species.
Additionally, the energetic budgets provide the first quantitative explanation of why K-selected
life-history characteristics and highly efficient physiologies are an evolutionary advantage to
obligate cave species.
Introduction
The movement of resources among ecosystems, commonly referred to as resource
subsidies (sensu Polis & Strong, 1996), is an ever-present feature within the ecological
landscape. The roles that such subsidies play in structuring recipient ecosystems can vary widely
as a function of resource quantity, quality (e.g., C:N:P ratios), and type (e.g., nutrient vs. organic
matter vs. prey; see Cebrian, 1999; Moore et al., 2004; Marczak et al., 2007). Cave ecosystems,
however, appear to represent an extreme endpoint along the resource subsidy spectrum because
the lack of light prevents primary production, which causes nearly all caves (except those
systems based on chemolithoautotrophy; see Engel et al., 2004) to be reliant on inputs of organic
matter from surface environments to support biological productivity (Poulson & Lavoie, 2001;
Simon et al. 2007). However, reduced surface connectivity typically limits allochthonous inputs,
which has caused caves to be characterized as energy-limited ecosystems (Hüppop, 2001 &
2005).
One line of evidence that indicates cave ecosystems are energy-limited environments is
the remarkable set of traits that are shared among many obligate cave species, such as lower
metabolic rates, increased starvation resistance, and more K-selected life-history characteristics
(e.g. long life span, slow growth rate, and reduced fecundity; see Hüppop, 2001 & 2005;
Venarsky et al., 2012b). Energy limitation also appears to be an important factor structuring
entire cave communities, as several studies have reported community shifts or increased biomass
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