Predator nonconsumptive effects on prey recruitment weaken with recruit density, supplementary material@en

We investigated the nonconsumptive effects (NCEs) of predatory dogwhelks (Nucella lapillus) on intertidal barnacle (Semibalanus balanoides) recruitment through field experiments on the Gulf of St. Lawrence coast and the Atlantic coast of Nova Scotia, Canada. We studied the recruitment seasons (May-June) of 2011 and 2013. In 2011, the Gulf coast had five times more nearshore phytoplankton (food for barnacle larvae and recruits) during the recruitment season and yielded a 58% higher barnacle recruit density than the Atlantic coast at the end of the recruitment season. In 2013, phytoplankton levels and barnacle recruit density were similar on both coasts and also lower than for the Gulf coast in 2011. Using the comparative-experimental method, the manipulation of dogwhelk presence (without allowing physical contact with prey) revealed that dogwhelk cues limited barnacle recruitment under moderate recruit densities (Atlantic 2011/2013 and Gulf 2013) but had no effect under a high recruit density (Gulf 2011). Barnacle recruits attract settling larvae through chemical cues. Thus, the highest recruit density appears to have neutralized dogwhelk effects. This study suggests that the predation risk perceived by settling larvae may decrease with increasing recruit density and that prey food supply may indirectly influence predator NCEs on prey recruitment.本研究依托加拿大圣劳伦斯湾沿岸与新斯科舍省大西洋沿岸的野外实验，探究了掠食性狗岩螺（Nucella lapillus）对潮间带藤壶（Semibalanus balanoides）补充群体的非消耗性效应（nonconsumptive effects, NCEs）。研究覆盖2011年与2013年的藤壶补充季（5-6月）。2011年，圣劳伦斯湾沿岸在藤壶补充季的近岸浮游植物（藤壶幼体与补充群体的食物来源）丰度是新斯科舍大西洋沿岸的5倍，补充季结束时的藤壶补充密度较后者高出58%。2013年，两地的浮游植物丰度与藤壶补充密度均较为相近，且均低于2011年圣劳伦斯湾沿岸的水平。采用比较实验法，通过操控狗岩螺的存在（不允许其与猎物发生物理接触）的实验发现，在中等补充密度条件下（2011和2013年的大西洋沿岸、2013年的圣劳伦斯湾沿岸），狗岩螺的化学信号会抑制藤壶的补充；但在高补充密度条件下（2011年的圣劳伦斯湾沿岸），该效应并不显著。藤壶补充群体可通过化学信号吸引沉降幼体附着，因此极高的补充密度似乎抵消了狗岩螺的抑制效应。本研究表明，附着幼体所感知的捕食风险可能随补充密度的升高而降低，且猎物的食物供给可间接影响捕食者对猎物补充群体的非消耗性效应。