Geographic distribution change and climatic niche change of Odonates in Great Britain
Data files
Feb 07, 2024 version files 262.96 MB
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OdonataDataset.xlsx
14.42 KB
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README.md
5.33 KB
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T1PresAbsTab.csv
131.53 MB
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T2PresAbsTab.csv
131.41 MB
Abstract
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.
https://doi.org/10.5061/dryad.v41ns1s3h
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.
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.