Ecological speciation in a generalist consumer expands the trophic niche of a dominant predator

Abstract

Ecological speciation - whereby an ancestral founder species diversifies to fill vacant niches - is a phenomenon characteristic of newly formed ecosystems. Despite such ubiquity, ecosystem-level effects of such divergence remain poorly understood. Here, we compared the trophic niche of European whitefish (Coregonus lavaretus) and their predators in a series of contrasting subarctic lakes where this species had either diversified into four ecomorphologically distinct morphs or instead formed monomorphic populations. We found that the trophic niche of whitefish was almost three times larger in the polymorphic than in the monomorphic lakes, due to an increase in intraspecific specialisation. This trophic niche expansion was mirrored in brown trout (Salmo trutta), a major predator of whitefish. This represents amongst the first evidence for ecological speciation directly altering the trophic niche of a predator. We suggest such mechanisms may be a common and important - though presently overlooked - factor regulating trophic interactions in diverse ecosystems globally.

Figure 1

The total (convex hull) and core (SIBER ellipse) isotopic niche of monomorphic (top row) and polymorphic (bottom row) whitefish populations. Large sparsely-rakered (LSR) = black open circles; small sparsely-rakered (SSR) = open turquoise circles; large densely-rakered (LDR) = closed orange circles; densely-rakered (DR) = open blue circles.

Figure 2

Mean proportion of littoral, pelagic and profundal diet items in stomach contents in focal species in lakes with monomorphic (K = Kilpis; R = Raha; V = Vuontis) and polymorphic (I = Inari; M = Muddus; P = Paadar) whitefish populations. See Fig. 1 legend for whitefish morph abbreviations.

Figure 3

The total (convex hull) and core (SIBER ellipse) isotopic niche of brown trout in subarctic lakes with monomorphic (top row) and polymorphic (bottom row) whitefish populations.

Figure 4

Isotopic niches of all fish species present within each lake. SIBER ellipses represent the core niche of each species, whilst convex hulls represent the total trophic diversity of the whole community. AB = alpine bullhead (Cottus poecilopus); AC = Arctic charr (Salvelinus alpinus); BT = brown trout (Salmo trutta); B = burbot (Lota lota); G = grayling (Thymallus thymallus); LT = lake trout (Salvelinus namaycush); P = pike (Esox lucius); PE = perch (Perca fluviatilis); SB = nine-spined stickleback (Pungitius pungitius); M = minnow (Phoxinus phoxinus); V = vendace (Coregonus albula). See Fig. 1 legend for whitefish morph abbreviations.