Anywhere but here: local conditions motivate dispersal inDaphnia

Abstract

Dispersal is fundamental to population dynamics. However, it is increasingly apparent that, despite most models treating dispersal as a constant, many organisms make dispersal decisions based upon information gathered from the environment. Ideally, organisms would make fully informed decisions, with knowledge of both intra-patch conditions (conditions in their current location) and extra-patch conditions (conditions in alternative locations). Acquiring information is energetically costly, however, and extra-patch information will typically be costlier to obtain than intra-patch information. As a consequence, theory suggests that organisms will often make partially informed dispersal decisions, utilising intra-patch information only. We test this proposition in an experimental two-patch system using populations of the aquatic crustacean, Daphnia carinata. We manipulated conditions (food availability) in the population’s home patch, and in its alternative patch. We found that D. carinata made use of intra-patch information (resource availability in the home patch induced a 10-fold increase in dispersal probability) but either ignored or were incapable of using of extra-patch information (resource availability in the alternative patch did not affect dispersal probability). We also observed a small apparent increase in dispersal in replicates with higher population densities, but this effect was smaller than the effect of resource constraint, and not found to be significant. Our work highlights the considerable influence that information can have on dispersal probability, but also that dispersal decisions will often be made in only a partially informed manner. The magnitude of the response we observed also adds to the growing chorus that condition-dependence may be a significant driver of variation in dispersal.

Can pathogens optimize both transmission and dispersal by exploiting sexual dimorphism in their hosts?

“…(a) Experiment 1: The probability of dispersal from a crowded habitat Two-patch microcosms were built by interconnecting two 950-ml containers with PVC-piping (15 mm diameter) and a closing valve between patches. We have previously shown that highdensity conditions in a local patch directly induce Daphnia dispersal [26] and that info-chemicals contained in 'crowded' water influence Daphnia life-history [27]. To stimulate dispersal, we simulated a high-density environment in the first patch using crowded-conditioned water (electronic supplementary material) and introduced 20 infected individuals (by pathogen C1 only) and 20 unexposed controls (i.e.…”