Communal roosting sites are potential ecological traps: experimental evidence in a Neotropical harvestman

Abstract

Situations in which animals preferentially settle in low-quality habitat are referred to as ecological traps, and species that aggregate in response to conspecific cues, such as scent marks, that persist after the animals leave the area may be especially vulnerable. We tested this hypothesis on harvestmen (Prionostemma sp.) that roost communally in the rainforest understory. Based on evidence that these animals preferentially settle in sites marked with conspecific scent, we predicted that established aggregation sites would continue to attract new recruits even if the animals roosting there perished. To test this prediction, we simulated intense predation by repeatedly removing all individuals from 10 established roosts, and indeed, these sites continued to attract new harvestmen. A more likely reason for an established roost to become unsuitable is a loss of overstory canopy cover caused by treefalls. To investigate this scenario, without felling trees, we established 16 new communal roosts by translocating harvestmen into previously unused sites. Half the release sites were located in intact forest, and half were located in treefall gaps, but canopy cover had no significant effect on the recruitment rate. These results support the inference that communal roost sites are potential ecological traps for species that aggregate in response to conspecific scent.

Species differences and geographic variation in the communal roosting behavior ofPrionostemmaharvestmen in Central American rainforests

“…2 has been studied between the months of January and May, which includes the dry season (FebruaryApril) and parts of the wet season. Spiny palms are used as roosting sites throughout this period, and the observation that the locations of the communal roosts are stable from one year to the next (Teng et al 2012;Grether et al 2014), combined with what is known about the mechanism of roost formation , indicates that spiny palms are used as aggregation sites year-round at this site. That is, if the communal roosts were abandoned for part of the year, they would presumably form in different spiny palms in different years, because individuals are not roost-site faithful and suitable spiny palms are not limiting Teng et al 2012).…”

“…The communal roosts of harvestmen can be dense aggregations, in which most individuals are clinging to other individuals, or loose aggregations in which most individuals are in contact with the substrate (reviewed in Machado & Macias-Ordonez 2007). Some species roost in caves or other dark places (Holmberg et al 1984;Willemart & Gnaspini 2004;Chelini et al 2011), while other species roost on the exterior surfaces of rocks or vegetation exposed to sunlight (Coddington et al 1990;Grether et al 2014). The most frequently proposed functions of Neotropical harvestman roosting aggregations are safety from predators, through dilution and/or chemical defenses, and protection from desiccation (Coddington et al 1990; Machado et al 2000; Willemart & Gnaspini 2004;Machado & Macias-Ordonez 2007;Wade et al 2011;Chelini et al 2011).…”

“…2 at Refugio Bartola has been the subject of several short studies focused on clarifying the mechanisms of roost formation. Mark-recapture studies established that individual harvestmen are not roost-site faithful Teng et al 2012), and yet aggregations have formed in the same locations for over 10 years (Teng et al 2012;Grether et al 2014). The long-term use of specific sites does not appear to be a product of habitat limitation.…”

“…2 Teng et al 2012), so we did not duplicate this work. Instead, we carried out a removal experiment at spiny palm aggregation sites (see Grether et al 2014). In the context of the species comparison, the primary relevance of the removal experiment is that it yielded data on Prionostemma sp.…”

Understanding sensory mechanisms to develop effective conservation and management tools

“…Built sound-damping walls around compressor stations [59] Communal roosting site act as an ecological trap by attracting conspecific to their scent regardless of the colony's fate Olfactory None suggested [60] Higher temperatures due to global warming reduced the efficacy of sexual scent signals in rock lizards Olfactory None suggested [61] over which acoustic signals can be perceived by animals [16]) and this has been demonstrated to interfere with signaling behavior and communication (e.g. [17,18]), and reduce foraging efficiency (e.g.…”