Abstract
Temperature is the most significant environmental gradient at the global scale, impacting the distributions of species and their ecological interactions. It is now established that temperature affects several biological rates and body mass, and can, in turn, alter interaction strength. Latitudinal variation in the strength of interactions has been observed for trophic and competitive interactions and many studies support that biotic interactions are more intense at low latitudes. Nevertheless, the mechanisms underlying the temperature dependence of trophic regulation, the effect of consumers on their preys, remain unclear. The aim of our study is to get better insights on the effects of temperature on trophic regulation. We used a consumer-resource model and considered that organisms' biological rates present a unimodal thermal response and that body mass decreases with temperature. We compared three measures of interaction strength: per capita, per population and net interaction strength. Our results demonstrate that the effect of temperature on interaction strength is contingent upon which species’ biological rates are temperature dependent. When all biological rates are temperature dependent, the thermal response of interaction strength is hump-shaped following the scaling of search rate, whilst it is monotonically decreasing when only mortality rates vary with temperature. Finally, we show that temperature can indirectly impact trophic interaction strength through the temperature-size rule. A decrease in organisms' body size due to temperature induces a decrease in per capita and per population interaction strength and tend to decrease net interaction strength, depending on which trophic level follows the temperature-size rule. Our analysis gives an overview of how temperature, through various effects, may impact different measures of interaction strength.
Highlights
Temperature can strongly affect food-web structure and interaction strength (Beveridge et al, 2010; Rodríguez-Castañeda, 2013)
Discrepancies among studies about the impact of temperature on trophic regulation can arise for two reasons, among others: (1) increased temperatures induce various changes on individual metabolism and body mass that can in turn impact interaction strength in multiple ways, and (2) different measures of interaction strength are typically used from one study to another and lead to different interpretations
There is no consensus about the effect of temperature on trophic regulation, as studies are often based on different assumptions, models or measures of interaction strength (IS)
Summary
Temperature can strongly affect food-web structure and interaction strength (Beveridge et al, 2010; Rodríguez-Castañeda, 2013). Several studies have shown that changes in temperature can induce shifts in the magnitudes of top-down and bottom-up forces It can strengthen the effect of fishes on primary producers in aquatic systems (Kratina et al, 2012; Shurin et al, 2012), of spiders and vertebrate predators on plants in terrestrial systems (Barton et al, 2009) and of large mammalian herbivores on primary producers (Gibert and Delong, 2014). Some interactions are magnified with warming while others are weakened depending on the study system and the duration of the study This diversity of empirical observations suggests that the response of trophic regulation to warming could be context-dependent (Gilbert et al, 2014; Sentis et al, 2014; Amarasekare, 2015). Discrepancies among studies about the impact of temperature on trophic regulation can arise for two reasons, among others: (1) increased temperatures induce various changes on individual metabolism and body mass that can in turn impact interaction strength in multiple ways, and (2) different measures of interaction strength are typically used from one study to another and lead to different interpretations
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