Mammals play a crucial role in maintaining ecosystems through complex plant-animal interactions. Non-native mammals can disrupt these ecological relationships, affecting both native and non-native species. We examined the diet and seed dispersal of non-native mammals: red deer (Cervus elaphus), European hare (Lepus europaeus), and wild boar (Sus scrofa), focusing on their interactions with the invasive rosehip shrub (Rosa rubiginosa). We conducted a microhistological analysis of fecal pellets to identify diet components and assess seed viability. The mammals consumed 27 food items, predominantly native plants. However, the presence of nutritious rosehip fruits resulted in a high proportion of the diet and the dispersal of a large number of seeds. Wild boar, in particular, consumed the largest proportion of the fruits and was the main disperser of viable seeds. Our results indicate that non-native mammals act as vectors for the dispersal of viable rosehip seeds. This interaction could promote a positive relationship between invasive species, facilitating the spread of R. rubiginosa in accordance with the ‘invasional meltdown’ hypothesis. Identifying such invasive interactions provides insights for management strategies aimed at preventing or delaying the spread of invasive species in the natural ecosystems of Northwest Patagonia.