Persistence of an Extinction‐Prone Predator‐Prey Interaction Through Metapopulation Dynamics

Abstract

In theory, predator—prey pairs with extinction—prone local populations can persist through metapopulation dynamics, wherein local populations fluctuate asynchronously, occasionally providing dispersers that prevent permanent extinction in all patches. A few studies have shown that spatial structure can extend predator—prey persistence. However, no studies have unequivocally demonstrated the asynchrony among patches, low dispersal rates, and rescue effects that prove metapopulation dynamics extend persistence. We used a protist predator—prey pair to show that spatial subdivision lengthens persistence through metapopulation dynamics. The pair comprised the predaceous ciliate, Didinium nasutum, feeding on the bacterivorous ciliate, Colpidium cf. striatum. A replicated experiment assessed how habitat subdivision affects persistence. Undivided habitats were of four volumes: 30, 180, 270, and 750 mL. Subdivided microcosms, or arrays, were groups of nine or 25 linked 30—mL bottles (270 or 750 mL total volume). In arrays, predators and prey persisted for 130 d (602 prey and 437 predator generations), at which point the experiment ended. Predators went extinct in undivided microcosms of equivalent volumes within a mean of only 70 d. Predators persisted for a mean of just 19 d in isolated 30—mL bottles (equivalent to isolated patches of arrays). In a separate experiment, prey were driven extinct in four of 15 isolated 30—mL bottles, and persistence times of predators were broadly similar. We documented the following hallmarks of metapopulation dynamics: (1) asynchronous fluctuations in different subpopulations; (2) frequent local prey extinctions and recolonizations; (3) persistence of protists in arrays, despite extinction of isolated local populations; and (4) rescue effects in predator populations. Other experiments measured dispersal rates and the effects on local dynamics of immigrant predators and prey, and initial predator: prey ratios. Only a small fraction of protists dispersed within a generation, consistent with metapopulation dynamics. Immigration of predators increased the frequency of local extinctions of prey, and immigration of prey increased the persistence of both predators and prey. Higher initial predator: prey ratios decreased the persistence of prey in undivided volumes. Although the pair persisted regionally in arrays, data indicated that local extinctions of prey were common. In array patches, predator: prey ratios were higher and predator—prey cycles were shorter than in undivided volumes. Dispersal made local dynamics more prone to extinction, yet promoted regional persistence because the risk of extinction of distant subpopulations became independent.

Immigration of susceptible hosts triggers the evolution of alternative parasite defence strategies

“…It is becoming increasingly clear that migration of hosts and parasites in spatially structured environments has important epidemiological and coevolutionary consequences [1,2], affecting, for example, host-parasite coexistence, local adaptation and coevolutionary dynamics [3][4][5]. Migration may also affect the type of host defence that is favoured by selection [6,7].…”

Increasing frequency of low summer precipitation synchronizes dynamics and compromises metapopulation stability in the Glanville fritillary butterfly

“…If, in contrast, long-range environmental stochasticity is strong, the independence of local dynamics is diminished, the effective number of (independent) local populations is reduced [3] and metapopulation fluctuations increase, which decreases the probability of long-term survival. While rarely quantified for natural systems, theoretical [4] and laboratory [5] studies have highlighted the importance of spatial variation in growth rate in balancing out population fluctuations at the metapopulation level.…”

The effect of metapopulation dynamics on the survival and spread of a novel, conspicuous prey

“…Metapopulation structure and the inter-habitat movement of prey therefore appear to prevent extinction of the aposematic morph by outmigration and establishment in other sub-habitats where predators may be more wary of the novel immigrant. Examples of metapopulation dispersal acting to prevent complete extinction is well supported in the literature (Holyoak and Lawler 1996;Sabelis and Diekmann 1988) describing a 'hide and seek' phenomenon whereby prey migrate to a beneficial habitat with the effect that extinction is prevented. Although these studies describe asynchrony between predator and prey populations as the protecting mechanism preventing extinction, in our model 'havens' are created when a habitats contains a highly wary predator.…”