Aim The aim of this study is to answer the questions: (1) do small organisms disperse farther than large, or vice versa; and (2) does the observed pattern differ for passive and active dispersers? These questions are central to several themes in biogeography (including microbial biogeography), macroecology, metacommunity ecology and conservation biology.Location The meta-analysis was conducted using published data collected worldwide. MethodsWe collected and analysed 795 data values in the peer-reviewed literature for direct observations of both maximal dispersal distance and mass of the dispersing organisms (e.g. seeds, not trees). Analysed taxa ranged in size from bacteria to whales. We applied macroecology analyses based on null models (using Monte Carlo randomizations) to test patterns relative to specific hypotheses. ResultsCollected dispersal distance and mass data spanned 9 and 21 orders of magnitude, respectively. Active dispersers dispersed significantly farther ( P < 0.001) and were significantly greater in mass ( P < 0.001) than passive dispersers. Overall, size matters: larger active dispersers attained greater maximum observed dispersal distances than smaller active dispersers. In contrast, passive-disperser distances were random with respect to propagule mass, but not uniformly random, in part due to sparse data available for tiny propagules. ConclusionsSize is important to maximal dispersal distance for active dispersers, but not for passive dispersers. Claims that microbes disperse widely cannot be tested by current data based on direct observations of dispersal: indirect approaches will need to be applied. Distance-mass relationships should contribute to a resolution of neutral and niche-based metacommunity theories by helping scale expectations for dispersal limitation. Also, distance-mass relationships should inform analyses of latitudinal species richness and conservation biology topics such as fragmentation, umbrella species and taxonomic homogenization.

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The objective of this study was to assess the impact of parent attention and distraction on symptom complaints by children with and without chronic functional abdominal pain. The water load symptom provocation task was used to induce visceral discomfort in pediatric patients with abdominal pain (N = 104) and well children (N = 119), ages 8-16 years. Parents were randomly assigned and trained to interact with their children according to one of three conditions: Attention, Distraction, or No Instruction. Children's symptom complaints and parents' responses were audiotaped and coded. Children completed a self-report measure of gastrointestinal (GI) symptoms before and after interacting with their parents. Parents' and children's perceptions of their interaction were assessed. Compared to the No Instruction condition, symptom complaints by pain patients and well children nearly doubled in the Attention condition and were reduced by half in the Distraction condition. The effect of attention on symptom complaints was greater for female pain patients than for male patients or well children. Findings for self-report GI symptoms were similar to those for audiotaped symptom complaints. Both pain patients and well children in the Distraction condition rated parents as making them feel better compared to ratings for the Attention condition. Parents of pain patients rated distraction as having greater potential negative impact on their children than attention. Parents' responses to children's symptom complaints can significantly increase or decrease those complaints. Girls with functional abdominal pain are particularly vulnerable to the symptom-reinforcing effects of parental attention. KeywordsFunctional abdominal pain; Attention; Distraction; Social learning; Parent-child interaction While sympathy with joy intensifies the sum of joy in the world, sympathy with pain does not really diminish the amount of pain.-Oscar Wilde, The Soul of Man under Socialism

BAP-PIQ subscales were significantly associated with child functional disability, whereas BSI subscales were unrelated. Protective parent responses partially mediated the relation between parent distress and child functional disability for depression, anxiety, and catastrophizing. However, parent protective behavior fully mediated the relationship between parent helplessness and child functional disability, indicating that feelings of parent helplessness did not uniquely contribute to child functional disability. Discussion Results suggest that when treating youth with chronic pain, parental distress in the context of children's pain needs to be addressed.