Group dynamics and relocation decisions of a trap-building predator are differentially affected by biotic and abiotic factors

Current Zoology, 2017, 63(6), 647–655 doi: 10.1093/cz/zow120 Advance Access Publication Date: 16 January 2017 Article Article Group dynamics and relocation decisions of a trap-building predator are differentially affected by biotic and abiotic factors Noa KATZa, Roni SHAVITa, Jonathan N. PRUITTb, and Inon SCHARFa,* a Department of Zoology, Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel and bDepartment of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, CA 93106-9610, USA *Address correspondence to Inon Scharf. E-mail: . Received on 4 October 2016; accepted on 22 December 2016 Abstract Most habitats in nature are heterogeneous, incorporating favorable and unfavorable microhabitats for different animals, based on their ecological niche. Unsuitable microhabitats have negative consequences for individual growth and survival. Animals, therefore, should fine-tune their location within the habitat by dispersing away from such microhabitats. We studied the suitability of different constant microhabitat conditions for wormlion larvae, a trap-building predator, tested in groups under laboratory conditions. Wormlions construct pit-traps in loose soil and capture small arthropod prey. As wormlions occur in high densities in nature, testing in groups is thus more indicative of their natural behavior than testing individuals. Wormlions responded strongly to biotic conditions—high conspecific density, starvation, and large body mass of conspecifics—by either increasing pit-relocation events or moving away from the microhabitat center to the periphery of the arena, probably opting for a way out. In other instances, individuals increased their distance to the nearest neighbor, thereby changing the spatial pattern toward a more regular pattern, potentially indicating interference competition. The only abiotic condition apparently perceived by wormlions as unsuitable was shallow sand, which led to frequent relocations. The two other abiotic factors—illumination and sand particle size—had no observable effect on behavior, although wormlions in nature always occur under shade in fine sand, and prefer both shade and fine sand particle size under laboratory conditions when given a choice. Under the fine spatial scale of the present experiment, biotic factors appear to be more influential than abiotic ones. Key words: antlions, dispersal, relocation, spatial pattern, wormlions. Dispersal and habitat selection are important processes for population and meta-population dynamics (Clobert et al. 2009). A species’ ability to disperse or to distinguish between different habitats will impact its capacity to respond to environmental changes, colonize new habitats, and increase genetic diversity. Therefore, these processes have a great influence on individual survival and reproduction (Harrison 1989; Clobert et al. 2009; Price 2010). Habitat evaluation and choice is influenced by many biotic and abiotic factors, to name but a few: intra-specific density and competition, predation and parasitism risk, inbreeding avoidance, energetic/searching costs, and optimal temperature (Belovsky 1981; Martin 2001; Bowler and C The Author (2017). Published by Oxford University Press. V Benton 2005; Ronce 2007; Benard and McCauley 2008). Ideally, animals should choose the habitat providing the best chance of survival and reproduction. The relative importance and interaction between biotic and abiotic factors in their effect on habitat choice is complex, and often species-specific (Rosenberg 1987). For instance, warbler habitat choice in Arizona is strongly affected by precipitation and also by interactions between co-occurring, ecologically similar species (Martin 2001). Juvenile corals select where to settle based on abiotic cues, such as light, but are also attracted to certain cues produced by algae, indicating that the site is suitable for settlement (Price 2010). 647 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact Downloaded https://academic.oup.com/cz/article-abstract/63/6/647/2908138 by guest on 15 July 2018 648 However, even within the same species, the relative importance of various factors may fluctuate. The relative importance of biotic and abiotic factors also often depends on the spatial scale considered, with smaller-local scales being more sensitive to biotic factors and larger scales to abiotic factors (Jackson et al. 2001; Price 2010). Once a habitat has been chosen, individuals need either to coexist with conspecifics or to further disperse. The spatial pattern reflects whether individuals are clumped together in space or scattered around. In other words, it is a spectrum bounded in its two edges by individuals much closer to each other than expected and individuals maximizing as much as possible the distances among them. The spatial pattern reflects both biotic and abiotic factors. For example, a regular spatial pattern could result from competition over limited resources or other negative interactions among individuals. A clumped spatial pattern could stem from aggregation in prey-rich small areas, or other benefits, such as dilution the risk of predation (Henschel and Lubin 1997; Perfecto and Vandermeer 2008; Scharf et al. 2008a; Hirsch 2011; Santini et al. 2011). Clumping together is also a product of abiotic conditions that enable lower expenditure on maintenance, fast growth or better reproduction and survival (e.g., available water or suitable temperature: Watson et al. 2007; Scharf et al. 2011; Halliday and Blouin-Demers 2014). The dispersion of conspecifics is influenced by betweenindividual interactions, such as attraction or repulsion, and by dispersal tendency and ability (Svendsen 1974; Fangliang et al. 1997). Attraction and repulsion are related to various factors, such as sociability level of the species and individuals (Febrer et al. 2006), or the best way to defend against predation [either grouping or spacing out; Scharf et al. (2012) and references therein]. Abiotic factors are not only important for initial habitat choice but also crucial for dispersal decisions. Individuals tend to disperse away when preferred local abiotic conditions deteriorate, as typical in ephemeral habitats (Ronce 2007). The spatial pattern type of individuals in a certain habitat (i.e., regular, random, or clumped patterns) can fluctuate through time with changing conditions, such as density and food availability (Cushman et al. 1988; Matsura and Takano 1989; Orians and Wittenberger 1991; Juell et al. 1994). Individual position in the habitat center or periphery is also important, because it often results from the trade-off between hunger and safety (outer po (...truncated)