Relationship among settling, demography and habitat selection: an approach and a case study

Natal experience and conspecifics influence the settling behaviour of the juvenile terrestrial isopod Armadillidium vulgare

Cues used by dispersing juveniles to assess habitat quality can be based on public information available to all individuals or on private information obtained from experience in the natal habitat. The presence of conspecifics (public information) and natal habitat quality (private information) have been shown to influence habitat preferences in many species, but the relative importance of these two cue types is seldom investigated. We examined whether habitat quality relative to the natal habitat had a stronger influence on the settling decisions of the juvenile terrestrial isopod Armadillidium vulgare (Latreille, 1804), than sign of conspecifics. We raised juvenile A. vulgare in either high- or low-quality habitats and then observed how the presence of conspecific sign influenced their preference for each of these habitats. When conspecific sign was absent, juveniles preferred high-quality habitat, regardless of their natal habitat. When the low-quality habitat was treated with conspecific sign, juveniles born on low-quality habitat continued to prefer the high-quality habitat, but juveniles raised on high-quality habitat displayed no preference. This suggests juvenile isopods respond to these cues hierarchically: they first search for habitats higher in quality than their natal habitat and then cue into conspecific sign when the preferred habitat is unavailable.

Habitat selection, facilitation, and biotic settlement cues affect distribution and performance of coral recruits in French Polynesia

Habitat selection can determine the distribution and performance of individuals if the precision with which sites are chosen corresponds with exposure to risks or resources. Contrastingly, facilitation can allow persistence of individuals arriving by chance and potentially maladapted to local abiotic conditions. For marine organisms, selection of a permanent attachment site at the end of their larval stage or the presence of a facilitator can be a critical determinant of recruitment success. In coral reef ecosystems, it is well known that settling planula larvae of reef-building corals use coarse environmental cues (i.e., light) for habitat selection. Although laboratory studies suggest that larvae can also use precise biotic cues produced by crustose coralline algae (CCA) to select attachment sites, the ecological consequences of biotic cues for corals are poorly understood in situ. In a field experiment exploring the relative importance of biotic cues and variability in habitat quality to recruitment of hard corals, pocilloporid and acroporid corals recruited more frequently to one species of CCA, Titanoderma prototypum, and significantly less so to other species of CCA; these results are consistent with laboratory assays from other studies. The provision of the biotic cue accurately predicted coral recruitment rates across habitats of varying quality. At the scale of CCA, corals attached to the “preferred” CCA experienced increased survivorship while recruits attached elsewhere had lower colony growth and survivorship. For reef-building corals, the behavioral selection of habitat using chemical cues both reduces the risk of incidental mortality and indicates the presence of a facilitator.