Abstract
We report the role of dispersal in the metapopulation dynamics of a protist predator-prey pair, the predaceous ciliate Didinium nasutum Muller feeding on the bacterivorous ciliate Colpidium cf. striatum Stokes. In previous work we showed that this extinction-prone pair persisted as metapopulations in subdivided habitats. An experiment assessed the effects of habitat subdivision on persistence and dynamics. Undivided habitats were 270 or 750 mL in volume, and subdivided habitats (arrays) were sets of nine or 25 linked 30mL bottles (270 or 750mL total volume), each replicated three times. Undivided microcosms allowed maximum dispersal, whereas subdivision reduced dispersal. Within arrays, bottles with more connecting tubes allowed more dispersal. Nine and 25 bottle arrays also differed in the mean number of connections per bottle. The effects of dispersal on predator-prey dynamics were tested by comparing subdivided vs. undivided microcosms, bottles with different numbers of connecting tubes, and nine vs. 25 bottle arrays. We tested the following predictions from metapopulation theory. (i) Predator and prey persistence and predator abundance will be greatest at intermediate dispersal rates. (ii) Prey abundance, local population variability and asynchrony in population fluctuations will be greatest at low dispersal rates. (iii) Predator :prey ratios will be greatest at high dispersal rates. Predictions were confirmed, except for the following. (i) Two measures of synchrony differed in whether they showed the expected pattern. Spatial synchrony (estimated via correlation of densities among patches within sampling dates) showed high variance and did not vary with dispersal rates. However, spatial variability (CV of density across adjacent pairs of linked bottles), showed the predicted decrease with increased dispersal. (ii) Evidence that dispersal increases predator :prey ratios was inconclusive. Predator :prey ratios were lower in undivided 750mL microcosms than in 750mL arrays, possibly because predators over-exploited prey in undivided microcosms, so that both became scarce. Conversely, within arrays, predator :prey ratios were greatest in bottles that allowed the most dispersal, as predicted. This work generally confirms the predicted effects of dispersal on predator-prey metapopulation dynamics. It also demonstrates the need for models to include more realism, e.g. the possibility of over-exploitation with very high dispersal.
Published Version
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