New Evidence on the Linkage of Population Trends and Species Traits to Long-Term Niche Changes

Abstract

Despite the assessment of long-term niche dynamics could provide crucial information for investigating species responses to environmental changes, it is a poorly investigated topic in ecology. Here, we present a case study of multi-species niche analysis for 71 common breeding birds in Northern Italy, exploring long-term niche changes from 1992 to 2017 and their relationship with both population trends and species traits. We (i) quantified the realized Grinnellian niche in the environmental space, (ii) compared variations in niche breadth and centroid, (iii) tested niche divergence and conservatism through equivalency and similarity tests, (iv) calculated niche temporal overlap, expansion and unfilling indices, and (v) investigated their association with both population changes and species traits. Results supported niche divergence (equivalency test) for 32% of species, although two-thirds were not supported by the similarity test. We detected a general tendency to adjust the niche centroids towards warmer thermal conditions. Increasing populations were positively correlated with niche expansion, while negatively correlated with niche overlap, albeit at the limit of the significance threshold. We found moderate evidence for a non-random association between niche changes and species traits, especially for body size, clutch size, number of broods per year, inhabited landscape type, and migration strategy. We encourage studies correlating long-term population trends and niche changes with species traits’ information and a specific focus on cause-effect relationship at both the single and multiple-species level.

Investigating odonates' response to climate change in Great Britain: A tale of two strategies

“…For example, niche conservatism and niche divergence were both found among dragonfly and damselfly species, corroborating trends found in other temporal assessments of realised climatic niches (Tirozzi et al, 2022). This level of interspecific variation, and the lack of congruence in responses across phylogenetically similar groups, calls for more research across a wider set of taxa on the factors promoting niche conservatism or niche divergence in response to climate change.…”

“…Species that show greater niche flexibility (i.e., higher level of change in their climate niche over time) could be expected to expand their distribution to new geographic areas whilst maintaining occupancy in areas experiencing changes in climatic conditions. As such, we also expect a positive correlation between niche flexibility, changes in overall range size and level of range expansion (Ralston et al, 2017;Tirozzi et al, 2022;Di Cecco & Hurlbert, 2022;H2).…”

“…PCA scores for the entire study area and each species occurrence during both time periods were subsequently projected into a grid of 1000 × 1000 cells bounded by the maximum and minimum PCA component scores across both periods–that is, the gridded climate space. This methodology–calibrating the PCA with climate data from T1 and T2 combined and subsequently calculating species' PCA scores–means that the differences in position along the principal components discriminate differences between the T1 and T2 climate space, following previous temporal analyses (Ralston et al., 2017; Sillero et al., 2022; Tirozzi et al., 2022). A smooth kernel density function was applied to estimate the density of species occurrences in each cell of the climate space, correcting for the prevalence of the environments within the species range, as an additional measure to account for sampling bias and to ensure the results remain independent of the resolution of the climate grid chosen (Broennimann et al., 2011).…”

“…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. The niche comparison between periods was thereupon decomposed into three components to provide additional information about the drivers of niche change (Tirozzi et al., 2022): (i) niche expansion, the proportion of species' niche present at T2 only; (ii) niche contraction (often termed niche unfilling), the proportion of species' niche no longer present at T2 and (iii) niche stability, the proportion of niche present at both time periods. Statistical tests for niche similarity between periods were used to determine whether observed climatic niches at T2 were statistically similar to the observed climatic niches at T1 using the ecospat.niche.similarity function within ecospat.…”

“…This was to provide a complete picture of the climatic niche changes that have occurred throughout the entirety of Great Britain, including novel climatic conditions and changes between the first and the second time periods. This analysis was then repeated at the intersection of climates between the two time periods, termed the analogue climate analysis, to evaluate species niche dynamics considering only the climatic variability available during both periods thereby excluding niche shifts resulting from variation in the climatic space accessible to species (Tirozzi et al., 2022); subsequent results refer to this method unless specified otherwise.…”