Novel Regimes of Extreme Climatic Events Trigger Negative Population Rates in a Common Insect

Area of Science:

• Ecology
• Climate Change Biology
• Population Dynamics

Background:

• The Intergovernmental Panel on Climate Change (IPCC) forecasts an increase in extreme weather events.
• Low-likelihood, high-impact (LLHI) events pose significant risks due to nonlinear responses in populations.
• Forecasting biodiversity responses to climate change necessitates mechanistic models integrating fundamental biological processes.

Purpose of the Study:

• To develop a mechanistic model integrating climate extremes and resource scarcity to forecast demographic impacts on insect populations.
• To assess the impact of LLHI events on the entire life cycle of a Mediterranean insect species.
• To identify critical life stages and climate drivers affecting population dynamics under current and future climate scenarios.

Main Methods:

• Constructed a matrix population model (MPM) using long-term monitoring data from an insect population in a Mediterranean region.
• Integrated the effects of extreme microclimatic heat and drought-induced host-plant scarcity on susceptible early life stages.
• Simulated population dynamics under current climatic conditions and future climate scenarios, including those not meeting the Paris Agreement targets.

Main Results:

• Juvenile life stages exhibited the largest relative contribution to population dynamics.
• Drought impacts significantly influenced simulated population rates, leading to a mosaic of declining and non-declining populations.
• Simulations indicated that LLHI heat extremes under future climate scenarios could cause widespread and severe population declines in the studied insect species.

Conclusions:

• LLHI events, particularly heat extremes, may emerge as a critical, overlooked driver of insect population declines.
• The decline of abundant insect species due to LLHI events could threaten essential ecosystem functions.
• Process-based, whole-cycle modeling approaches are crucial for accurately assessing the demographic impacts of climate change on biodiversity.