Edge effects reverse facilitation by a widespread foundation species

Abstract

Dense aggregations of foundation species often mitigate environmental stresses for organisms living among them. Considerable work documents such benefits by comparing conditions inside versus outside these biogenic habitats. However, environmental gradients commonly arise across the extent of even single patches of habitat-forming species, including cases where stresses diverge between habitat interiors and edges. We ask here whether such edge effects could alter how habitat-forming species influence residents, potentially changing the strength or direction of interactions (i.e., from stress amelioration to exacerbation). We take as a model system the classic marine foundation species, Mytilus californianus, the California mussel. Results demonstrate that mussel beds both increase and decrease thermal stresses. Over a distance of 6 to 10 cm from the bed interior to its upper surface, peak temperatures climb from as much as 20 °C below to 5 °C above those of adjacent bedrock. This directional shift in temperature modification affects interactions with juvenile mussels, such that thermal stresses and associated mortality risk are higher at the bed surface, but substantially reduced deeper within the adult matrix. These findings provide a case example of how stress gradients generated across biogenic habitats can markedly alter ecological interactions even within a single habitat patch.

Interaction of seed dispersal and environmental filtering affects woody encroachment patterns in coastal grassland

“…Once species successfully establish, they may create a range of stress gradients across a single habitat patch, potentially changing the effect from one of stress reduction to stress induction, with both competition and facilitation operating depending on spatiotemporal scale (Jurgens and Gaylord , Dohn et al. ).…”

The weakest link: sensitivity to climate extremes across life stages of marine invertebrates

“…Nocturnal adults lay eggs on plant leaves, which hatch into larvae, whose body temperatures transition from being governed by leaf temperature to being governed by ambient air temperature as they grow (Woods ). Similarly, intertidal mussels experience distinct thermal micro‐environments as they progress through their life stages (Helmuth and Hofmann , De Nesnera , Jurgens and Gaylord ). Mussel larvae experience oceanic conditions, which might be correlated to their thermal tolerance as intertidal recruits (Sorte et al ).…”

“…Mussel larvae experience oceanic conditions, which might be correlated to their thermal tolerance as intertidal recruits (Sorte et al ). As benthic juveniles, mussels can occupy microhabitats with varying amounts of shelter from solar radiation and heat stress (Helmuth and Hofmann , Jurgens and Gaylord ), which can give rise to differences in tolerance across life stages (Vetter et al , Lewis et al , Cripps et al , Alter et al ). A key next step in determining vulnerability to climate change would be to pair measures of climate sensitivity (as collated here) with observations of climate exposure (body temperatures across habitats) between life stages, including across multiple stressors that occur simultaneously.…”

Persistence and space preemption explain species‐specific founder effects on the organization of marine sessile communities

“…The best known inhibitory effects occur through niche preemption, when early founders monopolize important resources that would otherwise be available to other species (De Meester et al, 2016;Fukami, 2015;Sutherland, 1978), or when first colonizers act as ecosystem engineers, modifying their habitat and preventing the establishment of other organisms (Bonnici, Evans, Borg, & Schembri, 2012;Jones, Lawton, & Shachak, 1994). Depending on intrinsic species traits, however, ecosystem engineering may otherwise play an opposite role and facilitate species arriving later (Fukami, 2015;Jones et al, 1994), for example, by providing tridimensional substrates and therefore increasing settlement grounds (Russ, 1980), or through the mitigation of abiotic stress by supplying more benign microhabitats (Jurgens & Gaylord, 2016;Perea & Gil, 2014;Vogt et al, 2014), ultimately leading to species coexistence and an increase of biodiversity.…”

“…Attraction through chemical cues may constitute an efficient way to promote aggregation in suitable habitats (Pawlik, 1992;Robinson, Larsen, & Kerr, 2011;Silva-Filho, Bailez, & Viana-Bailez, 2012), indirectly increasing the strength of densitydependent regulation mechanisms of founder populations. Positive density-dependent interactions include the mitigation of abiotic stress in crowding intertidal invertebrates (Jurgens & Gaylord, 2016;Minchinton, 1997), caterpillars (Klok & Chown, 1999), and plants (Vogt et al, 2014); enhanced reproduction, such as fruit dispersal in plants (Blendinger, Loiselle, & Blake, 2008) and fertilization in marine invertebrates (Kent, Hawkins, & Doncaster, 2003;Levitan, Sewell, & Chia, 1992) and terrestrial woodlice (Broly, Deneubourg, & Devigne, 2013); and diminishing of predation risk in invertebrates (Denno & Benrey, 1997;Turchin & Kareiva, 1989) and vertebrates (Blumstein & Daniel, 2003;Carrascal, Alonso, & Alonso, 1990). Negative interactions usually lie in some sort of intraspecific competition, which may reach unsustainable levels under conditions of very high-population density (Branch, 1975;Chisholm & Muller-Landau, 2011;Gerla & Mooij, 2014;Hart & Marshall, 2009;Robins & Reid, 1997).…”