Highly Conserved Ecosystems Facing Climate Change: Rapid Shifts in Odonata Assemblages of Central European Bogs

Abstract

Freshwater diversity is declining at an alarming rate worldwide, and climate change is a key driver. However, attributing biological shifts solely to climate warming remains challenging because of confounding anthropogenic stressors. Peatbogs, being highly conserved, strictly protected, and minimally disturbed, offer a unique study system to isolate climate effects. We compared odonate assemblages in 27 Central European raised and transitional bogs between two sets of standardized surveys approximately 20 years apart (1998-2006 and 2020-2024). During this period, the mean annual air temperature has increased by 1.23°C. We tracked species richness, composition, taxonomic diversity, and functional traits (thermal tolerance, conservation value indicators, and selected morphological and life-history traits) and also examined phylogenetic patterns of species turnover. Although species richness remained stable, assemblage composition shifted markedly from cold-adapted, vulnerable bog specialists toward warm-adapted habitat generalists with lower conservation value. Notably, Ponto-Mediterranean species and those with a lower upper elevational limit increased their occupancy. Although the phylogenetic signal across the evolutionary tree of odonates was low, implying that the responses of the species to climate change were independent of their phylogenetic position, we revealed frequent genus-level replacements. These findings reinforce the position of odonates as a model group for detecting climate-driven changes in freshwater communities. Our study has revealed that climate warming alone can trigger profound reorganization of insect communities in inherently stable peatbog habitats. Specific traits linked to vulnerability (e.g., thermal index, red list status) and specialization proved to be promising predictors of future shifts in odonatofauna of temperate peatlands. The pronounced changes documented here may precede irreversible transformations of these unique ecosystems, highlighting the urgency of monitoring bog habitats and maintaining their stability under ongoing global change.

Keywords: Dragonfly Biotic Index; European Red List; Odonata; Species Temperature Index; climate change; raised and transitional bogs; temperate peatlands; trait‐based approach.

FIGURE 1

Predicted values (mean ± 95% CI) for species richness and community‐weighted means (CWM) of key species traits across bog types (raised vs. transitional) and time periods (past vs. present) based on generalized estimating equations (GEE) models. Points represent individual bogs, with richness, taxonomic diversity, or CWM values visualized by point size, scaled to species richness. Lines connect the same bogs across time periods. The ten subplots (a–j) correspond to: Species richness (a), Taxonomic diversity (b), or CWM of traits: Species Temperature Index (STI) (c), Dragonfly Biotic Index (DBI) (d), European Red List status (ERL) (e), Habitat specialization (f), Faunistic type: Ponto‐Mediterranean (g), Overwintering stage: Eggs (h), Upper limit (i), and Male body coloration: Gray‐blue (j). Significant temporal changes are indicated with an asterisk.

FIGURE 2

Correlation matrix visualizes relationships among selected dragonfly traits, with correlation coefficients ranging from −1 to +1, indicating the strength and direction of associations. Positive correlations are shown in red, while negative in blue, with darker shades indicating stronger associations for both. Significant correlations (FDR‐adjusted p < 0.050) are labeled with numerical values, while nonsignificant correlations are marked with crosses. The analyzed traits include Species Temperature Index (STI), Faunistic type: Ponto‐Mediterranean (FT:PM), Male body coloration: Gray‐blue (ColM:G‐B), Overwintering stage: Eggs (OW:E), Upper limit (Up.Lim), Dragonfly Biotic Index (DBI), European Red List (ERL), and Habitat specialization (Hab.spec).

FIGURE 3

Circular phylogenetic tree (modified from Viza et al. 2023) illustrates the evolutionary relationships among odonate species, based on genetic analysis. The tips of the tree are color‐coded according to each species' balance index, reflecting its net increase or decrease in bogs over time. Species with a strong decline (balance index < −0.40) are marked in red, moderate decline (≥ −0.40 > 0) in orange, stable presence (balance index = 0) in gray, moderate increase (balance index > 0 to ≤ 0.40) in light green, and strong increase (balance index > +0.40) in dark green.

FIGURE 4

Biplot of the partial Canonical Correspondence Analysis (partial CCA) exploring odonate species' responses to temporal changes between “past” and “present” time periods. Each triangle represents a species' position. Species that were significantly associated with either time period in the Indicator Value (IndVal) analysis are shown in bold and are depicted as black‐filled triangles, whereas the remaining species are displayed with gray‐outlined triangles. Species closer to the “present” centroid indicate stronger associations with contemporary conditions, whereas those nearer to the “past” centroid are more indicative of historical conditions. The axes represent the first two constrained ordination axes, capturing the major gradients of species‐environment interactions.