Abstract
When predators commonly overexploit local prey populations, dispersal drives the dynamics in local patches, which together form a metapopulation. Two extremes in a continuum of dispersal strategies are distinguished: the “Killer” strategy, where predators only start dispersing when all prey are eliminated, and the “Milker” strategy, in which predator dispersal occurs irrespective of prey availability. Theory shows that the Milker strategy is not evolutionarily stable if local populations are well connected by dispersal. Using strains of the predatory mite Phytoseiulus persimilis, collected from 11 native populations from coastal areas in Turkey and Sicily, we investigated whether these two strategies occur in nature. In small wind tunnels, we measured dispersal rates and population dynamics of all populations in a system consisting of detached rose leaves, spider mites (Tetranychus urticae) as prey, and P. persimilis. We found significant variation in the exploitation and dispersal strategies among predator populations, but none of the collected strains showed the extreme Killer or Milker strategy. The results suggest that there is genetic variation for prey exploitation and dispersal strategies. Thus, different dispersal strategies in the Milker–Killer continuum may be selected for under natural conditions. This may affect the predator–prey dynamics in local populations and is likely to determine persistence of predator–prey systems at the metapopulation level.
Highlights
Dispersal is a key process in population biology, influencing the persistence, distribution, and abundance of populations as well as driving gene flow (Dingle, 1996; Dunley & Croft, 1990; Quinn, Cole, Patrick, & Sheldon, 2011)
| 10385 when local populations are driven to extinction because of overexploitation, whereas persistence is observed at a metapopulation level due to frequent foundations of new local populations by dispersing individuals
Earlier work showed first evidence for the existence of variation in exploitation strategies by the predatory mite P. persimilis, one isofemale line resembling the Killer strategy in which predators started dispersing at prey depletion, the other isofemale line resembling the Milker strategy, in which predators started dispersing before prey elimination, leaving food for their offspring (Pels & Sabelis, 1999)
Summary
Dispersal is a key process in population biology, influencing the persistence, distribution, and abundance of populations as well as driving gene flow (Dingle, 1996; Dunley & Croft, 1990; Quinn, Cole, Patrick, & Sheldon, 2011). The formulation of the Milker–Killer dilemma was inspired by a study of plant-inhabiting mites, the predatory mite Phytoseiulus persimilis Athias-Henriot and its prey, the phytophagous spider mite Tetranychus urticae Koch This spider-mite species occurs in local populations, which can be locally driven to extinction by their predators (Janssen & Sabelis, 1992). Pels and Sabelis (1999) showed that all predator strains exterminated local prey populations, and the timing of dispersal appeared to have a genetic basis: One isofemale line derived from a coastal strain consistently showed dispersal close to or after prey elimination, whereas an isofemale line derived from an inland strain consistently dispersed long before all prey were eliminated These behaviors were in line with Killer-and Milker-like strategies, respectively. We aimed to quantify the extent of variation in dispersal strategies among the sampled populations by estimating dispersal rates in the presence of prey and to test the predicted consequences of dispersal for the population dynamics of predators and prey
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