Does removal of an alien predator from small islands in the Baltic Sea induce a trophic cascade?

Abstract

Changes in carnivore abundance can alter the distribution and abundance of plants on a community wide basis, an effect known as a trophic cascade. Because alien predators can have a disproportionate impact, compared to native predators, on herbivore populations, they may induce stronger trophic cascades in plant communities than native predators. We studied the indirect effects of the removal of an alien predator, the American mink Mustela vison on plant communities on small islands in the Baltic Sea, SW Finland. Mink had been removed from a group of islands for 12 yr, while another group of islands with mink presence served as a control area. Field voles Microtus agrestis and bank voles Myodes glareolus exert strong grazing pressure on the island vegetation and are an important part of mink diet. On nine islands of the mink removal area and five islands of the control area we studied the vegetation in ten randomly chosen plots; five in herbaceous and five in woody (i.e. dwarf shrub) vegetation. We studied the cascading impacts of mink predation on grassy and woody vegetation using the Shannon diversity and equitability indices and comparing abundances of different species between mink removal and control islands. Diversity and equitability of plant communities were higher on mink removal islands. In grassy patches, abundances of several species differed between mink removal and control islands. Our results demonstrate, for the first time, that alien predator removal may induce a trophic cascade on small islands.

Top predators as biodiversity regulators: the dingo Canis lupus dingo as a case study

“…Trophic cascades occur when a predator alters the abundance of species across more than one link in a food web and indirectly influences plant biomass (Polis, 1999). An increasing body of evidence suggests that large mammalian predators can induce trophic cascades and influence plant communities in terrestrial ecosystems either directly by suppressing herbivore populations through predation or indirectly by affecting herbivore foraging behaviour (McLaren & Peterson, 1995; Fortin et al , 2005; Frank, 2008; Fey et al , 2009).…”

Predator manipulation experiments: impacts on populations of terrestrial vertebrate prey

“…According to this hypothesis, top-down regulation launches a trophic cascade (Paine 1980) in which predators limit the abundance of herbivores, which in turn releases plants from grazing pressure. While the existence of trophic cascades is well established in many aquatic and terrestrial systems (e.g., Schmitz et al 2000, Shurin et al 2002, Borer et al 2005, examples of the indirect effects of vertebrate predators on plants via impacts on mammalian herbivores are still scarce (Sinclair et al 2000, Hamba¨ck et al 2004, Aunapuu et al 2008, Fey et al 2009). Sinclair (1989) defined population limitation as the processes that set the equilibrium density of a population, whereas population regulation refers to processes by which the population returns to its equilibrium density.…”

Habitat-mediated impact of alien mink predation on common frog densities in the outer archipelago of the Baltic Sea

“…First, mink are known to prey on snakes occasionally (Niemimaa and Pokki 1990;Kiseleva 2009), and while the impact of this predation is unknown, the release from mink predation might increase snake abundances and thus snake impact on frogs in the removal area. Second, mink removal may also have a positive impact especially on adders via increasing the densities of voles (Banks et al 2004;Fey et al 2009). Snakes may then shift to frogs as alternative prey when vole densities on islands are low.…”