Estimating acridid densities in grassland habitats: a comparison between presence-absence and abundance sampling designs.
Sampling methods to estimate acridid density per surface area unit in grassland habitats were compared using presence-absence data and count data. Sampling plans based on 6 yr of surveys were devised to estimate the density of Chorthippus spp., Euchorthippus spp., and Calliptamus italicus L. These acridids represented >90% of species in the study area. Sampling plans based on count data provided a reasonable tool when densities were >1/m(2) and when the level of precision was 0.20-0.30. A binomial sampling plan can be used to estimate C. italicus density with a level of precision >or=0.28. Sampling characteristics, i.e., estimated mean, actual precision, and sample size, were established on validation data sets with bootstrapping analysis. Sampling costs were also calculated according to density-dependent functions. Comparison between binomial sampling and enumerative sampling of C. italicus showed that binomial sampling required less time than enumerative sampling when densities were <or=2/m(2) and when fixed precision was >0.35. Plot area had no significant effect on sample variances of counts.
Badenhausser
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I
INRA-UGAPF, Laboratoire de Zoologie, 86600 Lusignan, France. ibadenhausser@lusignan.inra.fr
Amouroux
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P
Bretagnolle
V
V
D000818:Animals; D003198:Computer Simulation; D004463:Ecology / Q000379:methods*; D006110:Grasshoppers / Q000502:physiology*; D008954:Models, Biological; D006109:Poaceae; D011156:Population Density; D012044:Regression Analysis; D015203:Reproducibility of Results; D013997:Time Factors