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Species interactions can strongly influence the size and dynamics of epidemics in populations of focal hosts. The "dilution effect" provides a particularly interesting type of interaction from a biological standpoint. Diluters - other host species which resist infection but remove environmentally-distributed propagules of parasites (spores) - should reduce disease prevalence in focal hosts. However, diluters and focal hosts may compete for shared resources. This combination of positive (dilution) and negative (competition) effects could greatly complicate, even undermine, the benefits of dilution and diluter species from the perspective of the focal host. Motivated by an example from the plankton (i.e., zooplankton hosts, a fungal parasite, and algal resources), we study a model of dilution and competition. Our model reveals a suite of five results: • A diluter that is a superior competitor wipes out the host, regardless of parasitism. Although expected, this outcome is an ever-present danger in strategies that might use diluters to control disease. • If the diluter is an inferior competitor, it can reduce disease prevalence, despite the competition, as parameterized in our model. However, competition may also reduce density of susceptible hosts to levels below that seen in focal host-parasite systems alone. • As they decrease disease prevalence, diluters destabilize dynamics of the focal host and their resources. Thus, diluters undermine the stabilizing effects of disease. • The four species combination can generate very complex dynamics, including period-doubling bifurcations and torus (Neimark-Sacker) bifurcations. • At lower resource carrying capacity, the diluter’s dilution of spores is 'helpful' to the focal host, i.e., dilution can elevate host density by reducing disease. But, as the resource carrying capacity increases further, the equilibrium density of the diluter increases while the density of the focal host decreases, despite competition. Namely, the negative effects of competition start to outweigh the positive effects of dilution from the perspective of equilibrium density of the focal host., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Background: In Chile, there has been an increase in suicide rates from 1.1 to 2.6 per 100,000 among adolescents aged 10 to 14 years and from 4.4 to 8.9 per 100,000 among those aged 15 to 19 years, Aim: To identify protective factors for suicidal ideation according to parenting styles, as described by Barber et al., Material and Methods: The relation between suicidal ideation and parenting styles was assessed in a random sample of 2,346 Chilean school attending adolescents aged 13 to 20 years old (59% women) from three cities: Antofagasta (Northern Chile, II Region), Santiago (Central, Metropolitan Region) and Concepción (Southern, VIII Region). Participants were tested with the Chilean adaptation of the Cross National Adolescents Program (CNAP) Plus questionnaire developed by Barber et al. The relation between suicidal ideation and parenting styles was assessed using regression analyses., Results: Correlations between suicidal ideation and parenting styles were mostly significant, yet weak. High odds ratios were observed among parents who had a strong psychological control, inconsistent control, lack of expression of affection and covered marital hostility., Conclusions: High adolescent self-esteem, a good relationship with parents, psychological parental autonomy, expression of physical affection, social support and paternal monitoring were protective factors against suicidal ideation.

Theoretical models suggest that overlapping generations, in combination with a temporally fluctuating environment, may allow the persistence of competitors that otherwise would not coexist. Despite extensive theoretical development, this "storage effect" hypothesis has received little empirical attention. Herein I present the first explicit mathematical analysis of the contribution of the storage effect to the dynamics of competing natural populations. In Oneida Lake, NY, data collected over the past 30 years show a striking negative correlation between the water-column densities of two species of suspension-feeding zooplankton, Daphnia galeata mendotae and Daphnia pulicaria. I have demonstrated competition between these two species and have shown that both possess long-lived eggs that establish overlapping generations. Moreover, recruitment to this long-lived stage varies annually, so that both daphnids have years in which they are favored (for recruitment) relative to their competitor. When the long-term population growth rates are calculated both with and without the effects of a variable environment, I show that D. galeata mendotae clearly cannot persist without the environmental variation and prolonged dormancy (i.e., storage effect) whereas D. pulicaria persists through consistently high per capita recruitment to the long-lived stage.