title: Objective sampling design in a highly heterogeneous landscape - characterizing environmental determinants of malaria vector distribution in French Guiana, in the Amazonian region.
abstract: BACKGROUND
  Sampling design is a key issue when establishing species inventories and characterizing habitats within highly heterogeneous landscapes. Sampling efforts in such environments may be constrained and many field studies only rely on subjective and/or qualitative approaches to design collection strategy. The region of Cacao, in French Guiana, provides an excellent study site to understand the presence and abundance of Anopheles mosquitoes, their species dynamics and the transmission risk of malaria across various environments. We propose an objective methodology to define a stratified sampling design. Following thorough environmental characterization, a factorial analysis of mixed groups allows the data to be reduced and non-collinear principal components to be identified while balancing the influences of the different environmental factors. Such components defined new variables which could then be used in a robust k-means clustering procedure. Then, we identified five clusters that corresponded to our sampling strata and selected sampling sites in each stratum.
  
  
  RESULTS
  We validated our method by comparing the species overlap of entomological collections from selected sites and the environmental similarities of the same sites. The Morisita index was significantly correlated (Pearson linear correlation) with environmental similarity based on i) the balanced environmental variable groups considered jointly (p = 0.001) and ii) land cover/use (p-value << 0.001). The Jaccard index was significantly correlated with land cover/use-based environmental similarity (p-value = 0.001).
  
  
  CONCLUSIONS
  The results validate our sampling approach. Land cover/use maps (based on high spatial resolution satellite images) were shown to be particularly useful when studying the presence, density and diversity of Anopheles mosquitoes at local scales and in very heterogeneous landscapes.
authors.affiliation: ESPACE-DEV, UMR228 IRD/UM2/UR/UAG, Institut de Recherche pour le Développement, Maison de la Télédétection, 500 rue Jean-François Breton, 34093 Montpellier Cedex 5, France. emmanuel.roux@ird.fr.
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Roux
authors.forename: Pascal
authors.initials: P
authors.lastname: Gaborit
authors.forename: Christine A
authors.initials: CA
authors.lastname: Romaña
authors.forename: Romain
authors.initials: R
authors.lastname: Girod
authors.forename: Nadine
authors.initials: N
authors.lastname: Dessay
authors.forename: Isabelle
authors.initials: I
authors.lastname: Dusfour
mesh_terms: D000818:Animals; D000852:Anopheles / Q000469:parasitology; D016000:Cluster Analysis; D004463:Ecology / Q000379:methods; D017753:Ecosystem; D004784:Environmental Monitoring / Q000379:methods*; D005616:French Guiana / Q000453:epidemiology; D040362:Geographic Information Systems; D007303:Insect Vectors / Q000469:parasitology; D008288:Malaria / Q000453:epidemiology; D058998:Remote Sensing Technology