Enhancing sampling design in mist-net bat surveys by accounting for sample size optimization

PLoS One. 2017 Mar 23;12(3):e0174067. doi: 10.1371/journal.pone.0174067. eCollection 2017.

Abstract

The advantages of mist-netting, the main technique used in Neotropical bat community studies to date, include logistical implementation, standardization and sampling representativeness. Nonetheless, study designs still have to deal with issues of detectability related to how different species behave and use the environment. Yet there is considerable sampling heterogeneity across available studies in the literature. Here, we approach the problem of sample size optimization. We evaluated the common sense hypothesis that the first six hours comprise the period of peak night activity for several species, thereby resulting in a representative sample for the whole night. To this end, we combined re-sampling techniques, species accumulation curves, threshold analysis, and community concordance of species compositional data, and applied them to datasets of three different Neotropical biomes (Amazonia, Atlantic Forest and Cerrado). We show that the strategy of restricting sampling to only six hours of the night frequently results in incomplete sampling representation of the entire bat community investigated. From a quantitative standpoint, results corroborated the existence of a major Sample Area effect in all datasets, although for the Amazonia dataset the six-hour strategy was significantly less species-rich after extrapolation, and for the Cerrado dataset it was more efficient. From the qualitative standpoint, however, results demonstrated that, for all three datasets, the identity of species that are effectively sampled will be inherently impacted by choices of sub-sampling schedule. We also propose an alternative six-hour sampling strategy (at the beginning and the end of a sample night) which performed better when resampling Amazonian and Atlantic Forest datasets on bat assemblages. Given the observed magnitude of our results, we propose that sample representativeness has to be carefully weighed against study objectives, and recommend that the trade-off between logistical constraints and additional sampling performance should be carefully evaluated.

MeSH terms

  • Animals
  • Brazil
  • Chiroptera*
  • Ecosystem
  • Female
  • Male
  • Population Density
  • Sample Size
  • Tropical Climate

Grants and funding

Fieldwork in Amazonia was financed by ICNT Project “Uso da Terra e Biodiversidade na Amazonia” Project (process no. 384368/2009-3). LCT was awarded a PhD studentship from the Brazilian Ministry of Education (CAPES). Fieldwork in Brazil by CAP is funded by the Darwin Initiative for the Survival of Species under project 20-001. These funders had no role in the study design, data collection and data analysis, decision to publish, or preparation of the manuscript. Casa da Floresta Ambiental SS and Fibria provided support by granting access to a portion of the data analyzed in this manuscript. Biophilium Consultoria Ambiental Ltda. provides support in the form of salaries for PFCR but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.