Abstract
Abundant citizen science data on species occurrences are becoming increasingly available and enable identifying composition of communities occurring at multiple sites with high temporal resolution. However, for species displaying temporary patterns of local occurrences that are transient to some sites, biodiversity measures are clearly dependent on the criteria used to include species into local species lists. Using abundant opportunistic citizen science data from frequently visited wetlands, we investigated the sensitivity of α‐ and β‐diversity estimates to the use raw versus detection‐corrected data and to the use of inclusion criteria for species presence reflecting alternative site use. We tested seven inclusion criteria (with varying number of days required to be present) on time series of daily occurrence status during a breeding season of 90 days for 77 wetland bird species. We show that even when opportunistic presence‐only observation data are abundant, raw data may not produce reliable local species richness estimates and rank sites very differently in terms of species richness. Furthermore, occupancy model based α‐ and β‐diversity estimates were sensitive to the inclusion criteria used. Total species lists (all species observed at least once during a season) may therefore mask diversity differences among sites in local communities of species, by including vagrant species on potentially breeding communities and change the relative rank order of sites in terms of species richness. Very high sampling effort does not necessarily free opportunistic data from its inherent bias and can produce a pattern in which many species are observed at least once almost everywhere, thus leading to a possible paradox: The large amount of biological information may hinder its usefulness. Therefore, when prioritizing among sites to manage or preserve species diversity estimates need to be carefully related to relevant inclusion criteria depending on the diversity estimate in focus.
Highlights
Measures of biodiversity are of central interest to many subdisciplines in ecology, from community and macroecology to functional ecology and conservation (Chapin et al, 2000; Hubbell, 2001; Isbell et al, 2017; Leibold et al, 2004; Sala et al, 2000)
For species displaying temporary patterns of local occurrences that are transient and locally occurring only during short time periods, biodiversity measures are clearly dependent on the criteria used to include species into local species lists
The difference between raw and modeled data increased with increased number of days required to be included in the richness estimate such that estimates of species richness generated from the raw observations were 50% less than species richness estimates based on occupancy models
Summary
Measures of biodiversity are of central interest to many subdisciplines in ecology, from community and macroecology to functional ecology and conservation (Chapin et al, 2000; Hubbell, 2001; Isbell et al, 2017; Leibold et al, 2004; Sala et al, 2000). Traditional standardized surveys based on, for example, 10 visits may require presence in at least three visits in order to include a species as part of the local community (e.g., defining a potential breeder in territory mapping of breeding bird surveys; Bibby, Burgess, Hill, & Mustoe, 2000) No such rule of thumb is available for situations when there are hundreds of local visits to a site, as is frequently the case for opportunistic citizen science data. Using high-density opportunistic observations at popular birding wetlands in Sweden, we applied occupancy models to estimate daily presences at all wetlands for each species during the breeding season of 3 months (see Ruete, Pärt, Berg, & Knape, 2017) From these estimates, we compiled seasonal species lists using seven different inclusion criteria of local species presence with increasing restrictiveness from 1 day to 30 days of presence, either in consecutive or nonconsecutive days during the breeding season of 3 months. We discuss how to generalize this approach to investigate other questions, such as evaluating biodiversity values at stopover and wintering sites
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