Research ArticleECOLOGY

Landscape variation influences trophic cascades in dengue vector food webs

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Science Advances  21 Feb 2018:
Vol. 4, no. 2, eaap9534
DOI: 10.1126/sciadv.aap9534
  • Fig. 1 Path diagrams for the terrestrial and aquatic SEMs.

    The terrestrial model (n = 70) used a robust maximum likelihood estimator (A). In the aquatic model (n = 156), turbidity (clear/murky), aquatic plants (presence/absence), and Aedes spp. larvae (presence/absence, due to zero inflation) were modeled as binomial variables, using a weighted least squares estimation with robust standard errors (B). R2 values represent variance explained. Model fit was assessed using χ2 statistics, comparative fit index (CFI), root mean square errors of approximation (RMSEA), and standardized root mean square residual (SMRS). Solid arrows display paths from independent to dependent variables, dotted arrows display covariances, circles are latent variables, and rectangles are measured variables. Blue arrows, positive effects; red arrows, negative effects; gray arrows, nonsignificant effects. Effects represent correlations based on the best fitting covariance structure for each model and might be causative, but are not so by definition. Path coefficients (standardized effect sizes) are near each arrow. ***P < 0.001, **P < 0.01, *P < 0.05, and P < 0.1. “Agri. habitat,” “Water habitat,” and “Forest habitat” are total area of agricultural, surface water, and forested areas in the landscape, which was a 250-m-radius area centered on the focal building. “Precipitation” represents the total monthly precipitation, and “Temperature” represents the monthly (aquatic model) and two-monthly (terrestrial model) mean temperature before sampling. “Cont. habitats” represents the number of container-like habitats in the landscape. EC is electrical conductivity, and pH is the acidity of container habitat water. L. predators, large predators; Mic.-Hetero, micro-Heteroptera.

  • Fig. 2 A simplified food web that includes Aedes and its predators in the aquatic and terrestrial environment.

    Blue and white arrows show the direction of energy flow from prey to predator. In the center of the figure, the life cycle (dark brown arrows) of Aedes shows that adult female mosquitoes lay eggs, which develop into larvae that will pupate, after which adult mosquitoes will emerge. In these different life cycle stages, Aedes spp. are exposed to different predators in the terrestrial (upper gray area) and aquatic (lower blue area) environments.

  • Fig. 3 Mean abundance ± SE and % presence of terrestrial and aquatic taxa in or near buildings in three landscape classes.

    Green bars display forest landscapes, which were those areas in which forest (canopy cover > 30%) constituted 30% or more of the study area. Red bars are urban landscapes (urban areas constitute 25% or more of the landscape), and all other areas are considered agricultural landscapes (blue bars). The sample size (n) for the terrestrial species (A) in agriculture, forest, and urban landscapes was 32, 21, and 17, respectively; for aquatic species (B), this was 63, 57, and 34. Mean abundance of Aedes, house geckos, and spiders was compared using linear models (significant P values are given in the figure) and Tukey’s post hoc test (groups are noted with letters). For other taxa, we used zero-inflated negative binomial models. When AIC values were more than two points higher than the null model, the habitat effect was considered significant and Tukey’s post hoc test was then used on the count and zero-inflated models. Aedes spp. abundance is given as trapped mosquitoes per 24 hours, for spiders, geckos, and tokays; this is the number of individuals per 100-m2 wall, and for cats, this is the number per household. Abundance of aquatic taxa is given as individuals per water-filled container-like habitats.

  • Fig. 4 Predator taxon diversity and richness for the three main predator groups in different landscape types.

    In the boxplots, the horizontal bar gives the median, the box gives the interquartile ranges, the whiskers give the largest and lowest values with a maximum extent of 1.5 times the interquartile range, and the values on the x axis show the sample size (n). Diversity is given as Hill numbers (the exponential of Shannon’s entropy index). Predator richness is given as rarefied curves, which show the increase in recorded taxa with increasing number of observed individuals. Confidence intervals were calculated following Chao’s bootstrap method (30). Curves that are leveling off indicate that predator richness was estimated well by the sampling. When curves do not level off, it is expected that more taxa would have been detected with greater sample sizes. (A) Gecko species diversity on buildings in agricultural (yellow), forest (green), and urban (red) landscapes. (B) Rarefied gecko species richness curves, (C) spider family diversity, (D) rarefied spider family richness curves, (E) aquatic predator diversity (including invertebrate families, Anura, and fish), and (F) rarefied aquatic predator richness curves.

  • Fig. 5 Predicted values based on structural equation models.

    In (A), the change in species abundance as an effect of changes in tokay density is given (individuals per 100 m2). Aedes spp. abundance (trapped individuals per 24 hours) is shown in yellow with a small dashed line, spider density (individuals per 100 m2) is shown in blue with a large dashed line, and gecko density (individuals per 100 m2) is shown in red with a solid line. In (B), the change in species abundance is shown as an effect of change in forest cover. The probability of Aedes spp. presence is shown in yellow with a small dashed line, and the total abundance of large predators is given in blue with a large dashed line. Solid colors represent 95% confidence intervals.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/2/eaap9534/DC1

    table S1. Theoretical framework used to develop the hypothetical a priori models.

    table S2. Parameter estimates (Est.) for all direct and indirect effects in the terrestrial structural equation model.

    table S3. Parameter estimates (Est.) for all direct and indirect effects in the aquatic structural equation model.

    References (4375)

  • Supplementary Materials

    This PDF file includes:

    • table S1. Theoretical framework used to develop the hypothetical a priori models.
    • table S2. Parameter estimates (Est.) for all direct and indirect effects in the terrestrial structural equation model.
    • table S3. Parameter estimates (Est.) for all direct and indirect effects in the aquatic structural equation model.
    • References (43–75)

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