Research

Bottom-up resource limitation: the ecosystem energy balance predicts the quality of nutrition in a herbivore prey population

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Abstract

Vegetation greenness indices from remote sensing are increasingly used in population ecology studies assuming that land surface reflectance can reflect the availability of nutritional resources for primary consumers. However, the relationship between these indices and the characteristics of the herbivore diet has been insufficiently tested. We hypothesized that in drylands, where water availability is a prime control of ecosystem functioning, remote sensing indicators of vegetation drought stress are critical to predict the nutritional quality of herbivore habitats. This hypothesis was analyzed by measuring the dynamics in diet quality for the European rabbit, a key prey in Mediterranean communities. Rabbit nutrition was measured in six habitats throughout a year using faecal nitrogen (FN) content, an indicator of the levels of ingested protein. Then we tested the accuracy for predicting diet quality of the Enhanced Vegetation Index (EVI) and two remote sensing vegetation stress indicators: the Temperature Difference Vegetation Index (TVDI) and a latent heat flux index (Hr) calculated from the dynamics of surface temperature at each site. Generalized mixed models showed that temperature indices significantly contributed to explain the dynamics of diet quality: models including either TVDI or Hr shower a better fit than those exclusively based in EVI (R2 = 0.43—0.60). Whereas FN showed a positive relationship with EVI, the effect of TVDI and Hr was negative. Extracting the temporal component further allowed us to characterize the overall quality of each habitat and to relate it with rabbit abundance. Results have far-reaching implications for assessing habitat quality and the effects of functional ecosystem changes on a keystone prey herbivore and associated communities.