Integrative Foraging in Complex Landscapes: Nutrient acquisition and mixing across food patches at the primary producer-Daphnia interface
Final Report Abstract
Spatiotemporal variability in the nutritional traits of food resources (e.g. the concentrations of various mineral and biochemical nutrients or secondary metabolites) is inherent to most natural consumer-resources systems. This implies that consumers likely face intense and frequent fluctuations in nutritional quality during their lifetime. Furthermore, in many cases, consumer performance can be simultaneously co-limited by several resources nutritional traits. Hence, when feeding in nutritionally variable environments, consumers need to acquire, store and use multiple nutrients which might not co-occur temporally and spatially. Yet, most research on nutritional quality effects on consumers focuses on mean relationships thereby ignoring nutritional quality variance or covariance (in the case of co-limitation) in space or time and its potentially far-reaching consequences on the regulation of consumer populations. Within this project, we developed of a new theoretical framework (WP1) that can be applied to (1) generate mathematically-tractable predictions of the physiological effects of fluctuating co-limiting nutrients, (2) understand how each co-limiting nutrient contributes to these effects and (3) detect mechanisms such as nutritional acclimation or formation of nutrient reserve when they are at play. One of the major emerging insights is that the covariance between co-limiting nutrients (or even other environmental factors such as food density and temperature) is modulating consumer performance (covariance effect) as soon as the co-limiting nutrients act non-additively. The second major emerging insight is that the spatiotemporal grain of the nutritional landscape also modulates performance but that the way it acts is highly dependent on the capacity of the consumer to store nutrients and to acclimate its nutrient acquisition (i.e. digestion and uptake) to the dietary nutritional composition. Using eicosapentaenoic acid (EPA) and cholesterol co-limited Daphnia magna as model system (WP2) we experimentally showed that the intensity of limitation by a non-fluctuating nutrient (here the mean value of EPA) significantly modulates the variance effects (at the molecular, organismal and population level) of another fluctuating co-limiting nutrient (here Cholesterol). We also showed that Cholesterol can influence the assimilation of EPA and its conversion into ALA not only through its mean value in food but also through its temporal variance. By combining Dynamic Energy Budget (DEB) modelling and experiments with phosphorus and cholesterol co-limited Daphnia magna (WP3) we showed that for single nutrient limitation growth rate decreases with decreasing environmental frequencies (i.e. coarser grained landscape) at a rate which strongly depends on the temporal sequence (i.e. starting with low or high nutrients). For nutrient colimitation, we showed that growth rate decreases occur only at high and low frequencies (fine and coarse grained landscapes, respectively) and were strongly dependent on the covariance of the colimiting nutrients. Interestingly, we also found that covariance acts in opposite directions at the two extreme frequencies. The model qualitatively reproduced the patterns observed in the experiment indicating that dietary acclimation and reserves are major determinants of the observed patterns. In conclusion, the unique results advance our fundamental knowledge on consumer performance in nutritionally complex environments and are an essential step for understanding the role nutritional quality trait variability in consumer-resource interactions.
Publications
- (2016). Covariance modulates the effect of joint temperature and food variance on ectotherm life-history traits. Ecology Letters 19(2): 143-152
Koussoroplis AM, Wacker A
(See online at https://doi.org/10.1111/ele.12546) - (2017). Understanding and predicting individual performance in fluctuating and multifactorial environments (Concepts & Synthesis). Ecological Monographs 87(2): 178-197
Koussoroplis AM, Pincebourde S, Wacker A
(See online at https://doi.org/10.1002/ecm.1247)
