Diet comparison between sympatric European bison, red deer and fallow deer in a Mediterranean landscape

At the end of 2020, 18 European bison (Bison bonasus) were introduced to El Encinarejo estate, in the south of the Iberian Peninsula. This hunting-oriented estate has 956 hectares of dehesa, Mediterranean forest and scrubland in which about 400 red deer (Cervus elaphus) and 200 fallow deer (Dama dama) coexist with the bison. To know how trophic resources are used by these herbivore species, faecal samples were collected during the year 2021. The microhistological analysis technique was used to determine the percentage of epidermal fragments of the main functional groups (woody plants, graminoids, legumes and forbs) in each sample. The results showed significant differences between animal species and seasons of the year. Globally, woody plants are preferentially consumed in autumn and winter, graminoids in summer and legumes and forbs in spring. The woody component was the most abundant in the diet of the three species, accounting for 81% of the plant fragments present in red deer faeces, 52% in bison and 38% in fallow deer. This is the first study describing the dietary use of Pistacia lentiscus by European bison, the substantial use throughout all seasons indicates it as a very important diet source. In addition, the interspecific comparison showed that the bison significantly consumed more graminoids (21%), whereas legumes were more present in fallow deer diet (32%). Finally, red deer consumed less forbs than the other two species (8%). It is concluded that there is a certain distribution of trophic resources between the three species that may facilitate their coexistence.