A method for the objective selection of landscape‐scale study regions and sites at the national level
2017
1. Ecological processes operating on large spatio-temporal scales are difficult to disentangle with traditional
empirical approaches. Alternatively, researchers can take advantage of ‘natural’ experiments, where experimental
control is exercised by careful site selection. Recent advances in developing protocols for designing these
‘pseudo-experiments’ commonly do not consider the selection of the focal region and predictor variables are usually
restricted to two. Here, we advance this type of site selection protocol to study the impact of multiple landscape
scale factors on pollinator abundance and diversity across multiple regions.
2. Using datasets of geographic and ecological variables with national coverage, we applied a novel hierarchical
computation approach to select study sites that contrast asmuch as possible in four key variables,while attempting
tomaintain regional comparability and national representativeness. There were three main steps to the protocol:
(i) selection of six 100 9 100 km2 regions that collectively provided land cover representative of the national
land average, (ii) mapping of potential sites into a multivariate space with axes representing four key factors
potentially influencing insect pollinator abundance, and (iii) applying a selection algorithm which maximized
differences between the four key variables, while controlling for a set of external constraints.
3. Validation data for the site selection metrics were recorded alongside the collection of data on pollinator populations
during two field campaigns. While the accuracy of the metric estimates varied, the site selection succeeded
in objectively identifying field sites that differed significantly in values for each of the four key variables.
Between-variable correlations were also reduced or eliminated, thus facilitating analysis of their separate effects.
4. This study has shown that national datasets can be used to select randomized and replicated field sites objectively
within multiple regions and alongmultiple interacting gradients. Similar protocols could be used for studying
a range of alternative research questions related to land use or other spatially explicit environmental
variables, and to identify networks of field sites for other countries, regions, drivers and response taxa in a wide range of scenarios.
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