Appropriate experimental design to evaluate preferences for microhabitat: an example of preferences by species of microgastropods

Abstract

The intertidal microgastropods Eatoniella atropurpurea, Amphithalamus incidata and Eatonina rubrilabiata are principally found at mid- to low-shore levels in coralline turf and in patches of sediment close to algal turf on rocky shores. All three species are more abundant in coralline turf (i.e. algal beds composed primarily of Corallina officinalis Linnaeus, often containing patches of sediment) than in sediment, although the latter two are also quite abundant in patches of sediment. Eatoniella atropurpurea seem to live on branches of coralline algae, whereas Eatonina rubrilabiata and A. incidata seem to inhabit the sediment. In this study, we investigated whether or not behaviour of these animals accounts for the patterns observed in the field. Particularly, this study deals with choices amongst three microhabitats (coralline algae, coralline algae plus sediment and sediment) by these three species of microgastropods. Laboratory experiments were designed to examine preferences. The designs of such experiments are complex because demonstrating preference necessitates demonstrating different behaviour when confronted with choices from that showed when no choice is available. This study describes an appropriate series of hypotheses about preferences and experimental designs to test them. Preferences were indicated by differences in occupancy of the microhabitats when presented with a mixture and when each type is presented alone. In such experiments, snails did show preferences, except for A. incidata which did not show a pattern. Thus, the behaviour could, at least partially, account for the patterns of distribution in the field. The designs of experiments used here may be of value in other studies of preferences among habitats.

Ecological Studies of Epiphytic Microalgae and Epiphytic Zooplankton on Seaweeds of the Eastern Harbor, Alexandria, Egypt

“…However, the differences in the distribution of abundances of epiphytic zooplankton between the habitats suggest the presence of some mechanisms of host selection. This assumption has to be made with caution; however, further experimental work would be necessary to test hypotheses related to preferences, specificity and choice of habitats (Olabarria et al, 2002). Several studies have reported that low specificity of epifauna to the host plant is quite common in marine systems dominated by macroalgae, presumably because few marine epifaunal organisms live and feed directly on host tissues (Arrontes, 1999;Wikstrom and Kautsky, 2004;Prado and Thibaut, 2008).…”

Distribution, habitat preferences and behaviour of the critically endangered Maltese top-shell Gibbula nivosa (Gastropoda: Trochidae)

“…On the other hand, a lower abundance of snails was recorded from the non-homogeneous cobble/pebble bed, which may be due to differential settlement of larvae, differential mortality rates, or to active migration to other microhabitats (Crowe and Underwood 1998;Olabarria et al 2002). The snails were more abundant in the upper layer of the cobble/ pebble bed, where predation by fish would presumably be higher, suggesting that G. nivosa shows a preference for the upper strata due to factors other than predation.…”

Habitat identity influences species−area relationships in heterogeneous habitats

“…We could not examine this process in this study, although it has been posited that many species of molluscs colonize patches by passive advection through the water column (Beesley et al 1998). Some of these small snails have been shown experimentally to move (by crawling) to their preferred types of habitats (Olabarria et al 2002). Future studies should investigate the mechanisms underlying the observed patterns by quantifying dispersal of individuals within habitats of different composition.…”