Microhabitat conditions remedy heat stress effects on insect activity

Abstract

Anthropogenic global warming has major implications for mobile terrestrial insects, including long‐term effects from constant warming, for example, on species distribution patterns, and short‐term effects from heat extremes that induce immediate physiological responses. To cope with heat extremes, they either have to reduce their activity or move to preferable microhabitats. The availability of favorable microhabitat conditions is strongly promoted by the spatial heterogeneity of habitats, which is often reduced by anthropogenic land transformation. Thus, it is decisive to understand the combined effects of these global change drivers on insect activity. Here, we assessed the movement activity of six insect species (from three orders) in response to heat stress using a unique tracking approach via radio frequency identification. We tracked 465 individuals at the iDiv Ecotron across a temperature gradient up to 38.7°C. In addition, we varied microhabitat conditions by adding leaf litter from four different tree species to the experimental units, either spatially separated or well mixed. Our results show opposing effects of heat extremes on insect activity depending on the microhabitat conditions. The insect community significantly decreased its activity in the mixed litter scenario, while we found a strong positive effect on activity in the separated litter scenario. We hypothesize that the simultaneous availability of thermal refugia as well as resources provided by the mixed litter scenario allows animals to reduce their activity and save energy in response to heat stress. Contrary, the spatial separation of beneficial microclimatic conditions and resources forces animals to increase their activity to fulfill their energetic needs. Thus, our study highlights the importance of habitat heterogeneity on smaller scales, because it may buffer the consequences of extreme temperatures of insect performance and survival under global change.

Predicting movement speed of beetles from body size and temperature

“…The negative effects of warming on movement speed, however, can also be mitigated in nature, which cannot be captured under laboratory conditions like in our study. These coping mechanisms include either reducing movement or seeking shelter (shadow) and thereby lowering the overall energy loss [ 47 , 74 ] or shifting activity periods (seasonal and diurnal). This, however, can potentially create activity mismatches between trophic levels, hence imposing cascading effects across food webs [ 71 ], which highlights the importance of considering the combined effects of temperature and habitat structure on movement speed and behavior in more complex experimental settings or field studies.…”

“…Laboratory measurements using camera tracking can help overcome these limitations. While they cannot be used to assess natural movement patterns that depend on the environment like habitat structure or microclimates [ 74 , 76 ], they can help gain a deepened understanding about movement parameters and fundamental movement capacities. This information can then be used to inform mechanistic models, which can support predictions of potential movement patterns in natural environments [ 36 ].…”

Microclimate modulation: An overlooked mechanism influencing the impact of plant diversity on ecosystem functioning

“…This holds particular significance for species unable to regulate their body temperature, such as ectotherms. For instance, insects, being ectotherms, demonstrate an increase in activity with rising temperatures, reaching an optimal point before experiencing a drastic decline (Colinet et al., 2015; Khelifa et al., 2019; Sinclair et al., 2016; Terlau et al., 2023). Although primarily assessed at the microbial community scale, the temperature response of microbes plays a critical role in nutrient recycling and ecosystem functioning (Bradford et al., 2019; Dacal et al., 2019).…”

Insect communities under skyglow: diffuse night-time illuminance induces spatio-temporal shifts in movement and predation

“…We used a radio frequency identification (RFID) tracking system consisting of passive RFID-tags, RFID-readers (transceivers) and a host system (controller) to track the movements of our study animals (see [43] for details). We distributed 36 RFID-sensors equally across patch and matrix areas in the EcoUnits (four sensors in each patch and 20 sensors in the matrix, figure 2b).…”

“…(c) EcoUnits covered with black theatre curtains to prevent crosscontamination with light. (d )Pictures of a beetle with medium-sized RFID-tag (taken from an experiment using the same tracking approach and setting,[43]) and an artificial caterpillar prey dummy with bite marks. (Online version in colour.…”