DOI: 10.5061/dryad.v41ns1s3h
title: Geographic distribution change and climatic niche change of Odonates in Great Britain

description: Species are largely thought to maintain broadly static niches over time,
 an assumption underpinning much theoretical ecology including the
 implementation of ecological models to project species’ current and future
 distributions. Here, we assess niche conservatism in odonates in Great
 Britain over the past six decades by simultaneously quantifying changes in
 species geographic distribution and evaluating temporal trends in species
 realised climatic niche.
description: These results are based on an
 analysis of species occurrence records for Odonates in Great Britain that
 were downloaded from the Global Biodiversity Information
 Facility and the National Biodiversity Network Atlas for the period 1961
 and 2020. Odonates occupancy trends throughout this period were extracted
 using the Frescalo method (see Hill’s 2002 paper ‘Local frequency as a key
 to interpreting species occurrence data when recording effort is not
 known’). Occurrences were subsequently divided into two
 time periods, T1 (1961-1980) and T2 (2001-2020) and species geographic
 distribution change as well as species climatic niche change compared
 between these two periods. Species geographic shift was analysed in terms
 of the change in the geographic centre of species’ distribution between
 periods – the distance and direction between species centre at T1 and T2
 are provided. Species climatic niche change was based
 on 19 bioclimate variables and 6 climate extreme indices, following a
 Principle Component Analysis. Schoener’s D index of niche overlap was
 calculated which provides a measurement of the overlap between the
 climatic niche experienced by species at T1 and T2 ranging from 0 (no
 overlap) to 1 (compete overlap). This index is calculated by quantifying,
 for each grid cell in the climate space, the difference in smoothed kernel
 densities of species occurrence between periods. Niche expansion gives the
 proportion of species’ niche present at T2 only and niche contraction, the
 proportion of species’ niche no longer present at T2.
 Statistical tests for niche similarity between periods were used
 to determine whether observed climatic niches at T2 were statistically
 similar to observed climatic niches at T1. The hypothesis for niche
 conservatism was tested by comparing observed climatic niches at T1 with
 random simulations of species’ niches at T2 within the available climate
 space with the same kernel density distribution as T1. By repeating these
 simulations 100 times, a null distribution of species overlap values were
 generated to determine if observed species niche overlaps are more
 statistically similar (niche conservatism) or not (niche divergence) than
 random, based on a significance threshold of 0.05.
description: # Geographic distribution change and climatic niche change of Odonates in
 Great Britain ## Excel
 File: OdonataDataset This data gives the results of an analysis of Odonata
 distribution change in Great Britain during the last 6 decades of recent
 climate change. Species geographic distribution change and trend in
 occupancy is given, as well as an analysis of species climatic niche
 change. The data is structured in an excel file, with the following
 columns: **Species** - species scientific name **Suborder** - Anisoptera
 (Dragonfly) or Zygoptera (Damselfly) **Family** - species family **Annual
 Centroid Shift: Distance (km)** - the change in the geographic centre of
 species distribution between two time periods (T1: 1961-1980 and T2:
 2001-2020) given as an annual distance of shift in km (i.e. total distance
 from distribution centre at T1 and T2 divided by total 40 years)
 **Centroid Shift: Direction** - the geographic direction of change between
 species centre of distribution at T1 and T2 **Annual Occupancy Trend (%)**
 - the annual percentage change in species occupancy throughout 1961 to
 2020 **Schoener's D Overlap** - Schoener's D index of climatic
 niche overlap between T1 and T2 ranging from 0 (no overlap) to 1 (complete
 overlap) **Niche Expansion** - the proportion climatic niche at T2 not
 that was not also present at T1 **Niche Contraction** - the proportion
 climatic niche at T1 that was no longer present at T2 **p-value
 (analogue)** - the p-value results for the niche similarity test for niche
 conservatism between T1 and T2, considering only analogue climate between
 periods - i.e. the climate values consistent between periods. **Conserved
 (analogue)** - TRUE/FALSE indicating whether the niche similarity test for
 niche conservatism can be accepted, considering only analogue climate
 between periods - i.e. the climate values consistent between periods.
 **p-value (Great Britain)** - the p-value results for the niche similarity
 test for niche conservatism between T1 and T2, considering all climate
 values at T1 and T2 throughout the entire Great Britain study area.
 **Conserved (Great Britain)** - TRUE/FALSE indicating whether the niche
 similarity test for niche conservatism can be accepted, considering all
 climate values at T1 and T2 throughout the entire Great Britain study
 area. ## Raw Data: T1PresAbsTab & T2PresAbsTab This data includes
 climate information and Odonata presence/absence data for each 1km British
 National Grid. This can be processed to determine species' change in
 climate niche between periods. T1 indicates the period 1961-1980 and T2
 2001-2020. Columns 1-19 Bioclimate variables: **Bio1 - Bio19** Columns
 20-25 Extreme climate indices: **CDD** - consecutive dry days, **Rx5D** -
 maximum precipitation in five consecutive days, **FD** - number of frost
 days, **SU** - number of summer days, **TNN** - minimum of daily minimum
 temperature, **TXX** - maximum of daily maximum temperature Column 26:
 **Site** - 1km British National Grid Reference Columns 27-69: Odonata
 species data, 1 indicates presence and 0 indicates absence Column 70:
 **Easting** Column 71: **Northing** ## R Script: NicheChange Comparison of
 Odonata species' climatic niche between periods T1 and T2 from input
 species presence/absence tables: **T1PresAbsTab.csv** and
 **T2PresAbsTab.csv**. Results can be saved for each species in a directory
 under each species name. The temporal niche comparison is conducted with
 the Ecospat package, using an ordination approach whereby climate data of
 sites occupied by each species in each period is compared across the
 available environmental space - i.e. the climatological conditions
 throughout the study area across both time periods. First the climate
 variables are reduced into two components by applying a Principal
 Component Analysis calibrated from climate data of T1 and T2 combined. The
 PCA scores for the entire Great Britain study area as well as for the
 occurrence of each individual species is subsequently calculated for both
 time periods. Scores are projected onto a 1000x1000 cell grid bounded by
 the maximum and minimum PCA component scores. To determine niche change
 between periods, Schoener's D index of niche overlap is calculated as
 well as extracting niche dynamics - niche expansion (the proportion of
 species niche present at T2 only) and niche contraction (the proportion of
 species niche no longer present at T2). Statistical tests for niche
 similarity between periods are conducted, testing hypotheses for niche
 conservatism. This is tested both including the entire Great Britain study
 area as well as at the intersection of climatic variability between
 periods - i.e. analogue climates. Results are stored for each species
 under the species name. ## R Script: NicheOutput Load output of niche
 analysis and data results as an excel file. Results from **NicheChange**
 are stored as files under each species name. Running this script, the
 directory of these files is specified and data extracted - Schoner's
 D overlap, niche expansion and niche contraction, p-values for tests for
 niche conservatism (for entire study area and analogue climates) as well
 as median and variance of the PCA components for each species during each
 period. The dataframe can be saved as an excel file.