Cost-effective spatial sampling designs for field surveys of species distribution

Abstract

High-quality biodiversity inventories are key tools to develop effective conservation strategies, but financial resources devoted to systematic species inventories are usually limited. Different sampling strategies have been proposed to efficiently allocate such limited resources (i.e. accessibility-based, stratified random and grid samplings), but their effectiveness may depend on the aim of the survey. Our aim was to assess which approach can provide the best trade-off between sampling costs and accuracy in estimating both single species distribution and regional species set composition. We generated simulated species distribution data to compare costs and performances of the three sampling methods in assessing species distribution. When we aim at measuring species range (i.e. area of occupancy or extent of occurrence), or obtaining baseline ecological data for conservation assessments (i.e. niche breadth), grid sampling usually provided the best trade-off between performances and costs at both the species and regional levels. Otherwise, the stratified random sampling outperformed the other methods when we are interested in assessing the relative rarity (i.e. species frequency) of the species across the study area. Low quality distribution data can lead to heavily biased conclusions on biodiversity trends or impacts of environmental changes; our findings highlight that selecting the right sampling strategy is essential to obtain reliable estimates of both single species distribution and regional species set composition.

Status of the largest extant population of the critically endangered Aeolian lizard Podarcis raffonei (Capo Grosso, Vulcano island)

“…Monitoring of populations is an essential conservation task. Frequent monitoring is necessary to determine natural fluctuations, to detect declining trends, to ascertain the conservation status of populations and species and to ensure the effectiveness of eventual management measures [1][2][3][4]. This is recognised by the Habitats Directive of the European Union (Directive 92/43/EEC), which requires that member States regularly measure trends of populations of all listed species, to identify conservation priorities and to assess the efficiency of undertaken protection measures.…”

“…Monitoring programs are often limited by accessibility. Difficult access makes surveys more expensive and less feasible, thus the least accessible areas rarely are the focus of regular monitoring, and biodiversity surveys often remain concentrated in the most accessible areas [ 4 , 8 , 9 ]. Therefore, species living in inaccessible, remote areas often suffer insufficient monitoring, and declines or population changes might remain unnoticed.…”

Data sharing among protected areas shows advantages in habitat suitability modelling performance

“…Choosing the best spatial distribution of sampling effort is crucial should we want to optimize available resources. For instance, Marta et al (2019) found that when the aim is to gather information about species' ecology for conservation purposes, uniform sampling of the study area is preferable compared to stratified (habitat-specific) sampling. Similarly, in our study, we demonstrate that when the aim is to collect information about general patterns of species distributions, data-sharing is always preferable (Fig.…”

“…In this context, the choice of appropriate sampling design is crucial to make the best use of the available economic resources (Marta et al 2019). Additionally, collaboration among managers of neighbour protected areas may result in a better quality of the collected information.…”

“…Indeed, the usefulness of HSMs crucially depends on the ecological information they can capture (Sillero 2011;Araújo and Peterson 2012). The amount of captured information is strongly related to the quality of the collected data and to the sampling design adopted (Guillera-Arroita et al 2015;Marta et al 2019). When dealing with neighbouring, environmentally homogeneous sites, a key question could be if multiple, independent site-specific samplings (i.e.…”