Trying to fit in: are patterns of orientation of a keystone grazer set by behavioural responses to ecosystem engineers or wave action?

Abstract

The distribution of animals varies at different temporal and spatial scales. At the smallest scale, distribution may be orientated in regard to particular environmental variables or habitat features. For animals on the rocky intertidal, the processes which set and maintain patterns of distribution and abundance in wave-exposed areas are well studied, with explanatory models focused on wave action and, more recently, the role of biogenic habitats. In contrast, patterns of orientation by intertidal animals have received less attention, although having ecological and fitness consequences. Here, we report tests of competing models to explain the observation that limpets on steeply sloped surfaces orientate downwards. A greater proportion of downwards-facing limpets was found in sheltered sites and areas without barnacles and this pattern was consistent across many shores and sampling occasions. Additionally, the frequency at which limpets were dislodged after a storm was independent of orientation. To test whether orientation is a behavioural response to habitat-forming barnacles, barnacles were removed and/or killed from patches of substrata and the change in proportion of downwards-facing limpets measured. The proportion increased with barnacle removal and this behaviour was a response to the structure of the barnacles, not a biotic effect associated with the living organism. Our study suggests that biogenic habitat not wave action sets patterns of limpet orientation and barnacle shells, regardless of whether the barnacle is alive or not, limit the ability of limpets to adopt a downward orientation.

Benthic assemblages associated with native and non-native oysters are similar

“…Experimental treatments were allocated randomly to plates. Orientation of substratum can affect epibiotic assemblages, which may be further altered by the presence of biogenic structure (Fraser et al, 2014;Glasby and Connell, 2001). Therefore intertidal plates were bolted directly on to boulders, randomly chosen in the mid to low intertidal zone, in a horizontal or vertical orientation, and all were at least 1 m apart.…”

Self-ordering in the distribution of limpets: The role of previous occupants

“…This lack of understanding is scale-dependent. For example, we know that certain habitat properties (relative humidity; Cook, 1981;temperature;Pincebourde et al, 2007;topography;Fraser et al, 2014) may modify the spatial arrangement of some animals; in contrast though, we also know that desiccation risk per se is not changed by limpets having different small-scale distributions (Coleman, 2010). There is, however, much less knowledge on how a given habitat property may influence an individual to use a given resting site within that habitat.…”

“…In common with many other limpet species, it exerts an extremely strong habitat structuring effect, controlling habitat state and variability (Branch, 1985;Coleman et al, 2006;Southward, 1964). One of the notable features of limpets on rocky shores is a strong pattern of non-random distributions (Coleman et al, 1999;Coleman et al, 2004b;Fraser et al, 2014). In common with other invertebrates, such non-random distributions are often explained in the context of reduction of risk from predators (Coleman et al, 2004a) and/or abiotic stressors (see Coleman, 2010 for review).…”

Inter-individual variation partially explains patterns of orientation on steeply sloped substrata in a keystone grazer, the limpet Cellana tramoserica

“…the sun, north/south, upwards/downwards). In marine systems, patterns of orientation have, with a few exceptions (Crisp and Barnes 1954;Fraser et al 2014), only been examined as a response to environmental properties (e.g. wind or wave direction, or sun position (e.g.…”

“…For example, snowy owls display different patterns of orientation depending on their plumage colouration, with a greater number of less spotted and white individuals orientating into the sun compared with heavily spotted individuals (Bortolotti et al 2011). The orientation of intertidal limpets during low tide is also highly variable (Fraser et al 2010), but relatively little is known of the processes that contribute to these patterns of behaviour at a population level (see Fraser et al 2014Fraser et al , 2015. Before investigating the causal basis for variations in orientation within and between populations of a single species, it must first be established whether observed differences are a result of intrinsic differences between individuals or as a consequence of variations in the environment or habitat (Chapman 2000).…”