Forest disturbance and vector transmitted diseases in the lowland tropical rainforest of central Panama.

OBJECTIVE: To explore possible changes in the community attributes of haematophagous insects as a function of forest disturbance. We compare the patterns of diversity and abundance, plus the behavioural responses of three epidemiologically distinct vector assemblages across sites depicting various levels of forest cover. METHODS: Over a 3-year period, we sampled mosquitoes, sandflies and biting-midges in forested habitats of central Panama. We placed CDC light traps in the forest canopy and in the understorey to gather blood-seeking females. RESULTS: We collected 168 405 adult haematophagous dipterans in total, including 26 genera and 86 species. Pristine forest settings were always more taxonomically diverse than the disturbed forest sites, confirming that disturbance has a negative impact on species richness. Species of Phlebotominae and Culicoides were mainly classified as climax (i.e. forest specialist) or disturbance-generalist, which tend to decrease in abundance along with rising levels of disturbance. In contrast, a significant portion of mosquito species, including primary and secondary disease vectors, was classified as colonists (i.e. disturbed-areas specialists), which tend to increase in numbers towards more disturbed forest habitats. At pristine forest, the most prevalent species of Phlebotominae and Culicoides partitioned the vertical niche by being active at the forest canopy or in the understorey; yet this pattern was less clear in disturbed habitats. Most mosquito species were not vertically stratified in their habitat preference. CONCLUSION: We posit that entomological risk and related pathogen exposure to humans is higher in pristine forest scenarios for Culicoides and Phlebotominae transmitted diseases, whereas forest disturbance poses a higher entomological risk for mosquito-borne infections. This suggests that the Dilution Effect Hypothesis (DEH) does not apply in tropical rainforests where highly abundant, yet unrecognised insect vectors and neglected zoonotic diseases occur. Comprehensive, community level entomological surveillance is, therefore, the key for predicting potential disease spill over in scenarios of pristine forest intermixed with anthropogenic habitats. We suggest that changes in forest quality should also be considered when assessing arthropod-borne disease transmission risk.

OBJECTIF: Explorer les changements possibles dans les attributs communautaires des insectes hématophages en fonction de la perturbation des forêts. Nous comparons les modèles de diversité et d'abondance, ainsi que les réponses comportementales de trois assemblages de vecteurs épidémiologiquement distincts sur des sites illustrant divers niveaux de couverture forestière. MÉTHODES: Au cours d'une période de trois ans, nous avons échantillonné des moustiques, des phlébotomes et des moucherons piqueurs dans les habitats forestiers du centre de Panama. Nous avons placé des pièges à lumière CDC dans la canopée de la forêt et dans le sous-étage pour recueillir les femelles en quête de sang. RÉSULTATS: Nous avons collecté un total de 168.405 diptères hématophages adultes, dont 26 genres et 86 espèces. Les environnements de forêt intacts étaient toujours plus diversifiés du point de vue taxonomique que les sites forestiers perturbés, confirmant que les perturbations avaient un impact négatif sur la richesse en espèces. Les espèces de phlébotome et Culicoïdes étaient principalement classés comme climax (spécialiste de la forêt) ou généralistes de perturbation, qui ont tendance à diminuer en abondance parallèlement aux niveaux croissants de perturbation. En revanche, une partie importante des espèces de moustiques, y compris les vecteurs primaires et secondaires de maladies, a été classée dans la catégorie des colons (c'est-à-dire spécialistes des zones perturbées), qui ont tendance à se multiplier vers des habitats forestiers plus perturbés. Dans la forêt vierge, les espèces de phlébotomes et Culicoïdes les plus répandues cloisonnaient la niche verticale en étant actives dans la canopée de la forêt ou dans le sous-étage; pourtant, cette tendance était moins nette dans les habitats perturbés. La plupart des espèces de moustiques n'étaient pas stratifiées verticalement dans leur préférence d'habitat. CONCLUSION: Nous estimons que le risque entomologique et l'exposition associée des agents pathogènes à l'homme est plus élevé dans les scénarios de forêt vierge pour les maladies transmises par les phlébotomes et Culicoïdes, alors que la perturbation des forêts pose un risque entomologique plus élevé pour les infections transmises par les moustiques. Cela suggère que l'hypothèse de l'effet de dilution ne s'applique pas dans les forêts tropicales humides où se reproduisent très abondamment les insectes vecteurs, mais non reconnus, et où des maladies zoonotiques négligées surviennent. Une surveillance entomologique approfondie au niveau de la communauté est donc la clé pour prédire le potentiel de propagation des maladies dans des scénarios de forêt vierge mélangée à des habitats anthropiques. Nous suggérons que les changements dans la qualité des forêts soient également pris en compte lors de l'évaluation du risque de propagation de maladies transmises par les arthropodes.

Disturbance and mosquito diversity in the lowland tropical rainforest of central Panama.

The Intermediate Disturbance Hypothesis (IDH) is well-known in ecology providing an explanation for the role of disturbance in the coexistence of climax and colonist species. Here, we used the IDH as a framework to describe the role of forest disturbance in shaping the mosquito community structure, and to identify the ecological processes that increase the emergence of vector-borne disease. Mosquitoes were collected in central Panama at immature stages along linear transects in colonising, mixed and climax forest habitats, representing different levels of disturbance. Species were identified taxonomically and classified into functional categories (i.e., colonist, climax, disturbance-generalist, and rare). Using the Huisman-Olff-Fresco multi-model selection approach, IDH testing was done. We did not detect a unimodal relationship between species diversity and forest disturbance expected under the IDH; instead diversity peaked in old-growth forests. Habitat complexity and constraints are two mechanisms proposed to explain this alternative postulate. Moreover, colonist mosquito species were more likely to be involved in or capable of pathogen transmission than climax species. Vector species occurrence decreased notably in undisturbed forest settings. Old-growth forest conservation in tropical rainforests is therefore a highly-recommended solution for preventing new outbreaks of arboviral and parasitic diseases in anthropic environments.

Amblyomma tapirellum (Acari: Ixodidae) collected from tropical forest canopy.

Free-ranging ticks are widely known to be restricted to the ground level of vegetation. Here, we document the capture of the tick species Amblyomma tapirellum in light traps placed in the forest canopy of Barro Colorado Island, central Panama. A total of forty eight adults and three nymphs were removed from carbon dioxide-octenol baited CDC light traps suspended 20 meters above the ground during surveys for forest canopy mosquitoes. To our knowledge, this represents the first report of questing ticks from the canopy of tropical forests. Our finding suggests a novel ecological relationship between A. tapirellum and arboreal mammals, perhaps monkeys that come to the ground to drink or to feed on fallen fruits.

Dung beetle communities: a neotropical-north temperate comparison.

Dung beetle communities have been compared across north temperate latitudes. Tropical dung beetle communities appear to be more diverse based on studies using different methodologies. Here, we present results from a standardized sampling protocol used to compare dung beetle communities across five neotropical forests in Brazil and Ecuador and two warm, north temperate forests in Mississippi and Louisiana. Species richness in the tropical forests was three to seven times higher than the temperate forests, as would be expected by studies of other taxa across tropical and temperate latitudes. Average body size in the temperate forests was larger than the tropical forests, as predicted by Bergmann's rule. Dung beetle abundance and volume per trap-day were generally higher in Ecuador than Brazil, and higher in Mississippi than Louisiana, but there were no tropical-temperate differences. Species rank-abundance curves were similar within countries and between countries. Rank-volume distributions indicated a smaller range of beetle body sizes in Ecuador versus Brazil or the USA. Community similarity was high within countries and low between countries. Community differences between Brazil and Ecuador sites may be explained by differences in productivity based on geological age of the soils.

Dung beetle communities: a neotropical-north temperate comparison

Dung beetle communities have been compared across north temperate latitudes. Tropical dung beetle communities appear to be more diverse based on studies using different methodologies. Here, we present results from a standardized sampling protocol used to compare dung beetle communities across five neotropical forests in Brazil and Ecuador and two warm, north temperate forests in Mississippi and Louisiana. Species richness in the tropical forests was three to seven times higher than the temperate forests, as would be expected by studies of other taxa across tropical and temperate latitudes. Average body size in the temperate forests was larger than the tropical forests, as predicted by Bergmann's rule. Dung beetle abundance and volume per trap-day were generally higher in Ecuador than Brazil, and higher in Mississippi than Louisiana, but there were no tropical-temperate differences. Species rank-abundance curves were similar within countries and between countries. Rank-volume distributions indicated a smaller range of beetle body sizes in Ecuador versus Brazil or the USA. Community similarity was high within countries and low between countries. Community differences between Brazil and Ecuador sites may be explained by differences in productivity based on geological age of the soils.