Consistent signals of a warming climate in occupancy changes of three insect taxa over 40 years in central Europe

Abstract

Recent climate and land‐use changes are having substantial impacts on biodiversity, including population declines, range shifts, and changes in community composition. However, few studies have compared these impacts among multiple taxa, particularly because of a lack of standardized time series data over long periods. Existing data sets are typically of low resolution or poor coverage, both spatially and temporally, thereby limiting the inferences that can be drawn from such studies. Here, we compare climate and land‐use driven occupancy changes in butterflies, grasshoppers, and dragonflies using an extensive data set of highly heterogeneous observation data collected in the central European region of Bavaria (Germany) over a 40‐year period. Using occupancy models, we find occupancies (the proportion of sites occupied by a species in each year) of 37% of species have decreased, 30% have increased and 33% showed no significant trend. Butterflies and grasshoppers show strongest declines with 41% of species each. By contrast, 52% of dragonfly species increased. Temperature preference and habitat specificity appear as significant drivers of species trends. We show that cold‐adapted species across all taxa have declined, whereas warm‐adapted species have increased. In butterflies, habitat specialists have decreased, while generalists increased or remained stable. The trends of habitat generalists and specialists both in grasshoppers and semi‐aquatic dragonflies, however did not differ. Our findings indicate strong and consistent effects of climate warming across insect taxa. The decrease of butterfly specialists could hint towards a threat from land‐use change, as especially butterfly specialists' occurrence depends mostly on habitat quality and area. Our study not only illustrates how these taxa showed differing trends in the past but also provides hints on how we might mitigate the detrimental effects of human development on their diversity in the future.

Different roles of concurring climate and regional land-use changes in past 40 years’ insect trends

“…Similarly, trends of habitat specialists were more negative than those of habitat generalists (Figs. 3b and 5 ), which is in line with previous studies showing particularly strong declines in insect species specialised on certain habitats or food plants 23 , 27 , 31 , 34 . In summary, more cold-adapted species with restricted habitat ranges seem to be particularly threatened from ongoing global change, which in the case of Switzerland includes many alpine species.…”

“…Also, for dragonflies, which showed largely increasing species trends, our results are similar to findings from other regions in Europe 26 , 27 , 31 , 32 . The majority of increasing trends in grasshoppers was smaller, which adds to previous studies showing tendencies for increasing trends 33 – 35 but also for decreasing trends 27 . Because dragonflies have an aquatic life stage, the high proportion of dragonflies species showing positive trends might reflect improvements of water quality and wetland habitats made in the last decades 36 .…”

“…The important role of climate change in explaining species trends is supported by the fact that warm-adapted species tended to show positive trends, whereas cold-adapted species tended to show negative trends (Figs. 3b and 5 ), supporting the findings from previous studies 26 , 27 , 31 , 34 , 49 . Furthermore, these patterns seemed to be stronger in intervals of more rapidly increasing temperatures, although this interaction effect was weak (Fig.…”

Modeling the extinction risk of European butterflies and odonates

“…In addition, European butterfly species with smaller ranges are more vulnerable, while range size did not affect the extinction risk of European odonates. Thereby, our results underline the previous finding that improvements of the water and habitat quality have generally led to the recovery of many freshwater insects, whereas land use continues to threaten terrestrial insect diversity (Engelhardt et al, 2022). Our analyses do not support trait—extinctions risk relationships documented for well‐studied taxa such as birds and mammals, but rather suggest idiosyncratic responses of insect species to pollution, land use and climate change.…”

Codistribution as an indicator of whole metacommunity response to environmental change

“…Clearly, answers to this question will depend on the type of data available. Where trait data related to environmental preference is available, community trait shifts can give clear indications of a directional driver (Wieczynski et al 2019;Engelhardt et al 2022). However, such data is not always available, and the overall picture that emerges may be complex as species within a community may respond differently (Antão et al 2022).…”