Contrasting Population and Life History Responses of a Young Morph-Pair of European Whitefish to the Invasion of a Specialised Coregonid Competitor, Vendace

Abstract

Invasions of non-native species represent a global problem of great scientific interest. Here we study in detail the response in population and life history characteristics of closely related native species, with divergent habitat preferences, that are impacted by an invading species over a sufficient time period to allow a new stable state to become established. A time series of 20 years starting at the first occurrence of the invader (vendace Coregonus albula (L.)) allows exploration of the long term population and life history response of two ecologically, morphologically, and genetically different native sympatric morphs (DR- and SR-) of congeneric whitefish C. lavaretus (L.). The whitefish morphs are taxonomically equally related to the invading vendace, but only the planktivorous DR-whitefish share its pelagic niche. We would expect that the ecological differences between the whitefish morphs may be used as a predictor of competitive effects. Vendace exhibited an initial boom-and-bust development, and has continued to fluctuate in density. The responses of the pelagic DR-whitefish were: i) an immediate habitat shift, ii) a subsequent population decline caused by increased annual mortality, and iii) a new stable state at a lower density and apparently relaxed competition. The ecologically more distant benthivorous SR-whitefish also showed significant, but a much more limited response during this process, indicating damped indirect interactions through the food-web. This long-term case-study found that in two native eco-species equally related to the invader, only one of the eco-species was highly affected. Direct competition for resources is obviously important for species interactions, whereas the taxonomic relatedness per se seems to offer little predictive power for invasion effects.

Food‐web structure and mercury dynamics in a large subarctic lake following multiple species introductions

“…The current fish assemblage was also well established in comparison to typical investigations of the impacts of non‐native species in fresh waters; vendace have been present since the 1960s, with lake trout stocked from early 1970s onwards (Salonen & Mutenia, ; Præbel et al ., ). Sufficient time should therefore have passed for the ecosystem to reach a relative stable state (Sandlund et al ., ), potentially being less prone to population fluxes and boom‐and‐bust cycles, which are often pronounced in small, zooplanktivorous fish species following initial introductions (Bøhn et al ., ; Salonen et al ., ; Eagles‐Smith et al ., ). The approaches used also ensured that these findings should be robust, given the general agreement between multiple lines of mutually supportive evidence (i.e.…”

Recruitment of sympatric vendace (Coregonus albula) and whitefish (C. lavaretus) is affected by different environmental factors

“…Fish were sampled by means of 6-m-deep pelagic and 1.5-m-deep benthic gillnets from 1976 to 2013. The pelagic gill nets were set at 2-8 and 12-18 m depth, sometimes also at 22-28 m in 1987, 1993, 2009and 2013. From 198718.5, 22, 24, 28, 34, 39 and 46 mm) were used at each depth, whereas in 2013, one gang of single pelagic nets (6 9 25 m; 10, 12.5, 16, 19.5, 22.5, 26, 29, 35, 39, 45 and 52 mm) was used at each depth.…”

“…Both species largely prey on zooplankton, with vendace as the most specialised and efficient zooplanktivore (Bøhn & Amundsen ), being able to suppress whitefish in the pelagic habitat (Sandlund et al. ). In hydropower reservoirs, water‐level variation affects fish through reduced production of various groups of prey in the littoral zone, and by possible dewatering of spawning grounds during egg incubation.…”

“…Both species commonly exhibit variable year-class strength, and vendace also often show cyclic fluctuations, likely driven by intraspecific factors and exploitation, with cycles as short as 2 years (Aass 1972;Hamrin & Persson 1986;Sandlund et al 1991;Auvinen 1995;Bøhn & Amundsen 1998). Both species largely prey on zooplankton, with vendace as the most specialised and efficient zooplanktivore (Bøhn & Amundsen 1998), being able to suppress whitefish in the pelagic habitat (Sandlund et al 2013). In hydropower reservoirs, water-level variation affects fish through reduced production of various groups of prey in the littoral zone, and by possible dewatering of spawning grounds during egg incubation.…”

Long‐term ecological studies in northern lakes—challenges, experiences, and accomplishments

“…; Salonen et al ; Sandlund et al ). These fluctuations are apparently related to intraspecific competitive interactions (Bøhn et al ; Amundsen et al ; Sandlund et al ). Despite these fluctuations, the overall strong population buildup of vendace has strongly influenced the trophic network in Pasvik lakes (Bøhn et al ).…”