LB 39-329 - Sensitivity of Predator-Prey interactions to thermal variability on the Chilean rocky shore

Research on the consequences of temperature fluctuations, from species performance to entire ecosystems, has rapidly increased over the past decade due to climate change. Beyond range shifts and organismal physiology, changes in temperature will affect the rates and final outcomes of species interactions, such as competition, predations, or facilitation, in ways that are particularly hard to predict and that have been much less studied. For instance, since temperature largely determines metabolic rates (energy demands), mobility costs and assimilation efficiency, especially in ectotherms, effective prey consumption rates may increase or decrease. At the same time, temperature affects prey vital rates, including growth, which may increase or decrease mortality due to predators. Thus, anticipating the effects of global warming requires a mechanistic understanding of how species interactions will be altered, in a manner that allows us to project organismal performance to population dynamics and to complex ecological networks. In this study, we experimentally assess the effects of the temperature variation on the interaction between two common rocky shore species in central Chile: the dominant bed-forming mussel Perumitylus purpuratus and one of its main predators, the crab Acanthocyclus hassleri. Experiments were designed to i) quantify consumption rates of the crab on different sized mussels, ii) estimate the temperature-dependent components of the functional response (attack rate and handling time), iii) measure the predator's energy demands expressed as oxygen consumption rates, and iv) estimate the ratio between the expended and consumed energy (i.e., ingestion efficiency), considering four different temperatures (11, 14 17 and 20°C). We found that the crab consumption rates and energy costs (expended energy) increased linearly with temperature, up to 0.536 ind/h and 25 J/h at 20°C, respectively. The crab ingestion efficiency followed a quadratic relationship with temperature, increasing between 11 and 14°C, peaking about 17°C, and then decreasing. The attack rate slowly increased between 11 and 17°C, and then rapidly increased afterward, while the handling time of prey diminished remarkably between 11-14°C and subsequently stabilizes. These results suggest the predator augments prey consumption by increasing prey-searching rates in response to the rise in metabolic demand associated to temperature. Consequently, the energy intake exceeds expenditure for the predator at all studied temperatures. Thus far, the effect of temperature on prey traits (i.e., byssus production, shell thickening, growth rates, etc.), and facilitative effects of mussels on predator recruitment, remain unknown and must be explored.