Publication Date:
2014-12-09
Description:
Predator community composition can alter habitat quality for prey by changing the strength and direction of consumptive effects. Whether predator community composition also alters prey density via nonconsumptive effects during habitat selection is not well known, but is important for understanding how changes to predator communities will alter prey populations. We tested the hypothesis that predator community composition (presence of caged trout, caged dragonflies, or caged trout + dragonflies) alters colonization of aquatic mesocosms by ovipositing aquatic insects. In a previous experiment in this system, we found a spatial contagion effect, in which insects avoided pools with predators, but only when predator-free pools were isolated (~5 m away from predator pools). Here, we removed the isolated predator-free pools, allowing us to test whether insects would make fine-scale (~1 m) oviposition decisions in the absence of preferred isolated pools. We also estimated consumptive effects by allowing predators to feed on colonists for 5 days following colonization. All insects collected after 21 days were dipterans, dominated by Chironomidae. Total colonization, measured as the number of developing larvae after 21 days, was not affected by either predator presence or composition. Consumption was significant in the trout only treatment, reducing larval insect density by 46 ± 37% (mean ± SE). No other predator treatment significantly reduced prey density, although the proportion of chironomid larvae in protective cases increased in response to direct predation from dragonflies, indicating an antipredatory behavioral response. Taken together, these results reveal that predator community composition altered larval survival and behavior, but colonizing females either did not or could not assess these risks across small scales during oviposition. We found no evidence that predatory trout or dragonflies altered colonization of adjacent mesocosms by aquatic dipterans (i.e., larvae of the adult Chironomid pictured above). However, both trout and dragonflies (but not trout + dragonflies) had consumptive effects on the colonized larval community. We interpret our results in light of previous studies as a function of (1) a failure of colonizing insects to differentiate predator risk at small scales; and (2) possible spatial contagion effects that override colonization decisions at small scales.
Electronic ISSN:
2045-7758
Topics:
Biology
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