Predicted community consequences of spatially explicit globalchange-induced processes on plant–insect networks

Plant–insect trophic systems should be particularly sensitive to processes altering species spatial co-occurrences, as impacts on one level can cascade effectively

through the strong trophic reliance to the other level. Here, we predicted the biogeography of Lepidoptera–plant communities under global-change scenarios, exploiting

spatially resolved data on 423 Lepidoptera species and their 848 food plants across

the German state of Baden-Württemberg (ca. 36,000 km2

). We performed simulations of plant extinction and Lepidoptera expansion, and respectively assessed their

cascading consequences—namely secondary extinction of Lepidoptera and change

in functional distance of plants—on the interaction networks. Importantly, the simulations were spatially explicit, as we accounted for realistic landscape contexts of

both processes: Plant extinctions were simulated as “regional” (a species goes extinct

in the whole region at once) vs. “isolation-driven” (a species gradually goes extinct

from the peripheral or isolated localities according to its real regional distribution);

Lepidoptera expansions were simulated with random, northward, and upward directions according to real topography. The consequences were assessed based on empirical community composition and trophic relationships. When evaluated by regional

richness, the robustness of Lepidoptera assemblages against secondary extinctions

was higher under isolation-driven plant extinctions than regional plant extinction;

however, this relationship was reversed when evaluated by averaged local richness.

Also, with isolation-driven plant extinctions, Lepidoptera at the central sub-region of

Baden-Württemberg appeared to be especially vulnerable. With Lepidoptera expansions, plants' functional distances in local communities dropped, indicating a possible

increase of competition among plants, yet to a lesser extent particularly with upward

movements. Together, our results suggested that the communities' composition

context at the landscape scale (i.e., how communities, with respective species composition, are arranged within the landscape) matters when assessing global-change

influences on interaction systems; spatially explicit consideration of such context can

reveal localised consequences that are not necessarily captured via a spatially implicit,

regional perspective.

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Figure 2. Lepidoptera's secondary extinction due to simulated plant extinction across the four schemes (indicated with colours). The left panel presents regional richness and averaged local richness of remaining Lepidoptera throughout the course of simulations, respectively. The shaded areas present the 95% CI across 20 replicates. The proportion (relative to the initial state) of local Lepidoptera that has gone extinct at five selected time points (vertical dashed lines in the left panel) was visualised as five corresponding columns of maps at the right panel, all averaged across 20 replicates.

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Published in Ecology and Evolution, September 2024

Authors: Hsi‐Cheng Ho, Florian Altermatt

Full text: https://doi.org/10.1002/ece3.70272