Importance and effectiveness of correction methods for spatial sampling bias in species with sex-specific habitat preference.

AIM: Presence records from surveys with spatially heterogeneous sampling intensity are a key challenge for species distribution models (SDMs). When sex groups differ in their habitat association, the correction of the spatial bias becomes important for preventing model predictions that are biased toward one sex. The objectives of this study were to investigate the effectiveness of existing correction methods for spatial sampling bias for SDMs when male and female have different habitat preferences. LOCATION: Jura massif, France. METHODS: We used a spatially sex-segregated virtual species to understand the effect of three sampling designs (spatially biased, uniform random, and systematic), and two correction methods (targeted background points, and distance to trajectories) on estimated habitat preferences, sex ratios, and prediction accuracy. We then evaluated these effects for two empirical Capercaillie (Tetrao urogallus) presence-only datasets from a systematic and a spatially biased sampling design. RESULTS: Sampling design strongly affected parameter estimation accuracy for the virtual species: noncorrected spatially biased sampling resulted in biased estimates of habitat association and sex ratios. Both established methods of bias correction were successful in the case of virtual species, with the targeted correction methods showing stronger correction, as it more closely followed the simulated decay of detectability with distance from sampling locations. On the Capercaillie dataset, only the targeted background points method resulted in the same sex ratio estimate for the spatially biased sampling design as for the spatially unbiased sampling. MAIN CONCLUSIONS: We suggest that information on subgroups with distinct habitat associations should be included in SDMs analyses when possible. We conclude that current methods for correcting spatially biased sampling can improve estimates of both habitat association and subgroup ratios (e.g., sex and age), but that their efficiency depends on their ability to well represent the spatial observation bias.

Local prevalence and transmission of avian malaria in the Alakai Plateau of Kauai, Hawaii, U.S.A.

Avian malaria is among the most important threats to native Hawaiian forest birds. It is caused by the parasite Plasmodium relictum and is transmitted by the introduced mosquito vector Culex quinquefasciatus. Temperature increases and precipitation declines due to climate change over the last decade may be responsible for the observed recent expansion in the range and prevalence of avian malaria on the Alakai Plateau, Kauai Island. To examine the hypothesis that conditions are now favorable for transmission of malaria on the Plateau, mosquitoes were sampled with CO2 and Reiter oviposition traps at three sites (Kawaikoi, Halepa'akai, and Koke'e) on several occasions between October, 2013 and April, 2014. P. relictum infection was assessed by PCR or dissection under a microscope. We also surveyed mosquito larvae along Halepa'akai and Kawaikoi streams. We observed that Cx. quinquefasciatus is well established on the Alakai Plateau, as mosquitoes were caught on all field trips, except in April at Halepa'akai, and larvae were found throughout the year. We observed differences in adult abundance among sites and microhabitats (stream vs ridge lines).