Density dependence, spatial scale and patterning in sessile biota

Abstract

Sessile biota can compete with or facilitate each other, and the interaction of facilitation and competition at different spatial scales is key to developing spatial patchiness and patterning. We examined density and scale dependence in a patterned, soft sediment mussel bed. We followed mussel growth and density at two spatial scales separated by four orders of magnitude. In summer, competition was important at both scales. In winter, there was net facilitation at the small scale with no evidence of density dependence at the large scale. The mechanism for facilitation is probably density dependent protection from wave dislodgement. Intraspecific interactions in soft sediment mussel beds thus vary both temporally and spatially. Our data support the idea that pattern formation in ecological systems arises from competition at large scales and facilitation at smaller scales, so far only shown in vegetation systems. The data, and a simple, heuristic model, also suggest that facilitative interactions in sessile biota are mediated by physical stress, and that interactions change in strength and sign along a spatial or temporal gradient of physical stress.

Delay driven spatiotemporal chaos in single species population dynamics models

“…Self-organised patterns are noted in beds of blue mussel populations, Mytilus edulis, on intertidal ats with signi cant variability in mussel density observed on larger scales of meters, but with no apparent within-cluster di erence. It is suggested that the interaction between individual mussels is the only underlying mechanism of such pattern formation (Gascoigne et al 2005, van de Koppel et al 2008). In the quest of revealing irregular spatial distributions, the most intuitive starting point would be amongst cyclic populations, as they tend to be regulated by highly nonlinear interactions (Bjørnstad et al 2002).…”

The role of shore crabs and mussel density in mussel losses at a commercial intertidal mussel plot after seeding

“…Losses on culture plots associated with or following seeding are clearly density dependent (Gascoigne et al 2005;Capelle et al 2014Capelle et al , 2016. Seeding practice in bottom culture leads to a highly heterogeneous distribution of mussels on culture plots, with high mussel densities within the space occupied by mussels (Capelle et al 2014).…”

Production efficiency of mussel bottom culture

“…However, Newell (2007) strongly recommends a more homogeneous spreading of the seed, contrary to current culture practices (see also Figure 1.2). Seed fished from natural beds relayed in different densities and followed at different scales showed that density effects may be dependent on the spatial scale and the season (Gascoigne et al 2005).…”

“…Losses on culture plots associated with or following seeding are clearly density dependent (Gascoigne et al 2005, Capelle et al 2016). …”

“…On culture plots, other loss factors may be more dominant than sea star predation, such as loss associated with relaying or density dependent losses (Gascoigne et al 2005, Capelle et al 2016. The loss rate of mussels surviving the initial seeding is uncorrelated with length or salinity, and is notably less…”