DOI: 10.5061/dryad.95br2
title: Data from: Lottery coexistence on rocky shores: weak niche differentiation or equal competitors engaged in neutral dynamics?

description: Reconciling how niche and neutral processes may be important in species
 coexistence has revealed two important weaknesses in our collective
 understanding of species diversity: few empirical studies have determined
 whether species are truly coexisting, and fewer still have properly
 evaluated whether coexistence is achieved through niche differentiation or
 ecological equivalence. Here, we ask whether two common barnacles, Jehlius
 cirratus and Notochthamalus scabrosus, coexist locally and whether the
 slight but persistent differences in their distribution provide sufficient
 fitness trade-offs to overcome differences in competition. Both species
 recovered after experimental reduction; that is, they coexist, with no
 indication of hierarchical exclusion. No fitness inequalities affected
 species performance or interference effects on vital rates at any shore
 level, indicating no trade-offs in intra-interspecific effects across the
 ecological gradient. Additionally, no relationship was found between per
 capita population growth rates of either species with its own relative
 abundance; that is, neither species has a demographic advantage when rare.
 Instead, a lottery for space during settlement largely determines species’
 distributions, evidenced by the positive correlation across sites and
 tidal elevations between the relative abundances of adults and the
 recruits of the prior season. We conclude that Jehlius and Notochthamalus
 coexist neutrally, or nearly so, but discuss whether small,
 nonsignificant, and probably ephemeral fitness differences, which are
 inconsistent across the tidal gradient, could provide enough niche
 differentiation to promote coexistence.
description: Survey of adult
 barnacles and recruits in experimental plotsData from seasonal photo
 surveys (2008-2010) of the adult barnacles, Jehlius cirratus and
 Notochthamalus scabrosus, and their non-distigunshed recruits in
 experimental plots. Estimates of the percent cover of bare space on the
 rock surface are included. Plots were established and monitored at four
 localities (Temblador, Guanaqueros, ECIM, and Matanzas) separated by 10s
 to 100s of km and at three high intertidal elevations (high, mid, and low
 barnacle zones).dryad barn
 counts.xlsBarnacle recruitment
 monitoring 2009-2010Recruitment onto 10x10
 cm2 plexiglass plates covered with a standard rugosity surface (Safety
 Walk, 3M) that were replaced once monthly over the peak recruitment season
 of 2009-2010 (Nov-Apr). Five plates were deployed and retrieved from the
 high, mid, and low barnacle subzones at four localities then taken to the
 laboratory where newly metamorphosed spat and cyprid larvae were
 identified to species level under a dissecting microscope. The time plates
 were exposed in the field varied somewhat depending on tidal cycles and
 sea conditions.recruitment monitoring
 dryad.xlsBarnacle growth under
 crowding conditionsSize data of adult
 Jehlius (j) and Notochthamalus (n) collected from experimental plots where
 focal individuals were photographed seasonally under under three different
 “crowding conditions”: 1) ‘isolated individuals’ with less than 25% of
 their shells in contact with neighboring barnacles of any species; 2)
 ‘conspecific crowding’ individuals that were in aggregated groups, with a
 minimum of 50% and up to 100% of their shells in contact with other adult
 individuals of the same species, and 3) ‘heterospecific crowding’
 individuals that were in aggregated groups with 50-100% of their shells in
 contact with adults of the other species. The maximum opercular
 carino-rostral length, survival, percent contact with and number of
 neighboring individuals were recorded roughly every 3
 months.