Abstract
Bioindicator species are extensively used for rapid assessment of ecological changes. Their use commonly focuses on changes in population abundance and individual sizes in response to environmental change. These numerical and demographic shifts likely have behavioral and physiological mechanistic drivers that, if understood, could provide additional insights into the use of these species as bioindicators of habitat health.The Atlantic ghost crab, Ocypode quadrata, is a global bioindicator species of human disturbance on sandy shores. Individual size and population abundance of O. quadrata decline dramatically at sites with human disturbance, and the causes of this phenomenon remain unclear.Here, we test the hypothesis that individual and population‐level changes at disturbed sites reflect changes in burrowing behavior and energetics. Specifically, we examine whether or not the burrowing behavior (e.g., burrow fidelity and longevity) of O. quadrata changes because of human disturbance. We also examine energy required for burrowing by O. quadrata across different levels of human disturbance.We show that O. quadrata have the highest burrow fidelity and longevity at sites with low level of human impact, and weakest burrow fidelity and longevity at pristine sites. O. quadrata reduce the burrowing energy allocation by manipulating the burrow dimension and increasing the burrow longevity even under low levels of human disturbance.Overall, this study shows that human disturbances not only change the behavior of organisms, but also shift energetic balance. Our results support the use of a bioenergetic approach to better understand how human disturbances influence natural populations, and the specific use of this approach with this bioindicator species.
Highlights
Bioindicator species are widely used to identify and measure human-related ecological changes (McGeoch, 1998; Carignan & Villard, 2002; Siddig, Ellison, Ochs, Villar-Leeman, & Lau, 2016; Spellerberg, 2005) in many different ecosystems from forests (Pearce & Venier, 2006; Rainio & Niemelä, 2003; Maleque, Maeto, & Ishii, 2009) to coral reefs (Erdmann & Caldwell, 1997; Hallock, Lidz, CockeyBurkhard, & Donnelly, 2003)
Despite the fact that studies on the energetic results of human disturbance in bioindicator species are limited to a few examples (Adams & Ham, 2011; Toro, Navarro, & Palma-Fleming, 2003), there are several examples to show that alterations in the physiological/energetic conditions of nonbioindicator organisms are due to direct (Williams, Lusseau, & Hammond, 2006; Symons, Pirotta, & Lusseau, 2014; Villegas-Amtmann, Schwarz, Sumich, & Costa, 2015) and indirect human impacts (Griffen, 2018; Leo, Dahlke, Storch, Pörtner, & Mark, 2018; Thomas et al, 2016)
We have shown that O. quadrata alter their burrowing behavior under the influence of various levels of human disturbances
Summary
Bioindicator species are widely used to identify and measure human-related ecological changes (McGeoch, 1998; Carignan & Villard, 2002; Siddig, Ellison, Ochs, Villar-Leeman, & Lau, 2016; Spellerberg, 2005) in many different ecosystems from forests (Pearce & Venier, 2006; Rainio & Niemelä, 2003; Maleque, Maeto, & Ishii, 2009) to coral reefs (Erdmann & Caldwell, 1997; Hallock, Lidz, CockeyBurkhard, & Donnelly, 2003). The most widespread responses of ghost crabs to human disturbances on sandy shores are decreases in population abundance and individual body sizes (Schlacher et al, 2016 and citations therein; Gül & Griffen, 2018a, 2018). These changes are often measured using burrow counts, a nondestructive and efficient technique for assessing both the abundance and size distribution of ghost crabs (Schlacher et al, 2016). The precise mechanistic reason for observed demographic changes remains unclear Besides these demographic changes, ghost crabs alter their burrow architecture under human influence (Gül & Griffen, 2018a; Lucrezi & Schlacher, 2010; Schlacher & Lucrezi, 2010), implying that there may be an energetic component to the response of ghost crabs to disturbance. We further predicted that burrowing would represent an energetically expensive behavior and that this energetic cost should be influenced by changes in the frequency of burrows and the size of burrows across beaches with different levels of human disturbance
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