Traits underpinning desiccation resistance explain distribution patterns of terrestrial isopods

Abstract

Predicted changes in soil water availability regimes with climate and land-use change will impact the community of functionally important soil organisms, such as macro-detritivores. Identifying and quantifying the functional traits that underlie interspecific differences in desiccation resistance will enhance our ability to predict both macro-detritivore community responses to changing water regimes and the consequences of the associated species shifts for organic matter turnover. Using path analysis, we tested (1) how interspecific differences in desiccation resistance among 22 northwestern European terrestrial isopod species could be explained by three underlying traits measured under standard laboratory conditions, namely, body ventral surface area, water loss rate and fatal water loss; (2) whether these relationships were robust to contrasting experimental conditions and to the phylogenetic relatedness effects being excluded; (3) whether desiccation resistance and hypothesized underlying traits could explain species distribution patterns in relation to site water availability. Water loss rate and (secondarily) fatal water loss together explained 90% of the interspecific variation in desiccation resistance. Our path model indicated that body surface area affects desiccation resistance only indirectly via changes in water loss rate. Our results also show that soil moisture determines isopod species distributions by filtering them according to traits underpinning desiccation resistance. These findings reveal that it is possible to use functional traits measured under standard conditions to predict soil biota responses to water availability in the field over broad spatial scales. Taken together, our results demonstrate an increasing need to generate mechanistic models to predict the effect of global changes on functionally important organisms.

Going Back to Basics: Importance of Ecophysiology when Choosing Functional Traits for Studying Communities and Ecosystems

“…However, as there is still no consensus among animal ecologists on what the most important traits are and what is the best way to measure them, establishing criteria for choosing and validating adequate traits is especially important in the scope of animal ecology. Dias et al (2013b) showed a similar rationale as the one formalized in our framework (Figure 1) for choosing traits explaining terrestrial isopod species distribution along gradients of soil moisture. They selected desiccation resistance as a potential good descriptor of species response to water availability.…”

“…Therefore, a deep ecophysiological understanding is essential to identify more responsive traits to a given environmental driver (Rosado & de Mattos 2010;Bartlett et al 2012;Dias et al 2013b). Studies on community assembly and ecosystem functioning are often using ecophysiological traits as descriptors, but hot topics (e.g.…”

“…It is essential to demonstrate that the selected traits are related to species responses to the environmental driver of interest (Rosado & de Mattos 2010;Dias et al 2013b). This validation should be done by means of experimental or observational comparative approach in the ecological context of the study system (Wardle et al…”

“…Although the functional approach has been developed mostly under the scope of plant ecology, recent studies have successfully used functional traits to explain response of animal communities to environmental factors (Blaum et al 2011;Dias et al 2013b). However, as there is still no consensus among animal ecologists on what the most important traits are and what is the best way to measure them, establishing criteria for choosing and validating adequate traits is especially important in the scope of animal ecology.…”

“…They selected desiccation resistance as a potential good descriptor of species response to water availability. Taking into account that the physiological ability of an organism to show resistance to unfavourable conditions can be determined by physiological avoidance and tolerance strategies, Dias et al (2013b) showed that water loss rate (avoidance) and fatal water loss (tolerance) explained 90% of interspecific variation in desiccation resistance, with water loss rate being the main mechanism determining species desiccation resistance. They also showed that body size could be a surrogate for desiccation resistance due to its effect on water loss rate.…”