Field sampling is biased against small-ranged species of high conservation value: a case study on the sphingid moths of East Africa

Jan Beck,Liliana Ballesteros-Mejia,Ian J Kitching,Christy M Mccain,Hitoshi Takano

doi:10.1007/s10531-018-1613-z

Abstract

The range size of species co-occurring in local assemblages is a pivotal variable in assessments of a site’s conservation value. Assemblages featuring many small-ranged species are given more priority than assemblages consisting mainly of wide-ranging species. However, the assembly of relevant information can be challenging and local range size distributions of tropical invertebrates are rarely available for conservation planning. We present such data for sphingid moths in East Africa, a highly diverse region of high conservation value. We compare geographic range size distributions based on field samples with predictions from modelled range map data. Using this system as a case study, we provide evidence for a systematic sampling bias when inferring average local range sizes from field data. Unseen species (i.e., species present but missed in local sampling) are often those with small ranges (hence, of high conservation value). Using an elevational gradient, we illustrate how this bias can lead to false, counterintuitive assessments of environmental effects on local range size distributions. Furthermore, with particular reference to sphingid moths in the study region, we show that current protected areas appear unrelated to the spatial distribution of species richness or average geographic range sizes at a local scale. We discuss the need to treat field sampled data with caution and in concert with other data sources such as probabilistic models.

Highlights

Assessing a landscape’s conservation value is a relevant step in prioritizing resources to those regions where conservation efforts are most useful (Mace et al 2007)
These estimates were based on a large compilation of specimen records, which were input for climate- and vegetation-based species distribution models (SDMs) that were subsequently expert-edited for dispersal limitation
While richness is distinctively higher in the northern part of the research area (e.g., Tanzania median richness per cell = 63; Zambia = 41), regions of small median range size stretch south along the mountain ranges into Zambia

Summary

Introduction

Assessing a landscape’s conservation value is a relevant step in prioritizing resources to those regions where conservation efforts are most useful (Mace et al 2007). Range size is a species property that is strongly and inversely linked to extinction risk (Thomas et al 2004, Harris and Pimm 2008). This may be relevant in tropical conservation, where species’ ranges are often smaller than at northern latitudes (Orme et al 2006; McCain 2009; Grünig et al 2017). With current aims of standardizing global biodiversity data availability for conservation assessments (e.g., ‘essential biodiversity variables’; Geijzendorffer et al 2016), it is timely to investigate potential problems in distilling reliable local range size distribution data for conservation from field sampling

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Conclusion