Relationships among parasites, physiological stress and personality in the interactions between invasive alien and native species

The thesis explored the interactions between Invasive Alien Species (IAS) and native species in the light of potential effects of parasitic infections, physiological stress and personality on individual fitness (reproductive success/investment). In particular, this study investigated the interspecific competition between the North American invasive Eastern grey squirrel (Sciurus carolinensis) and the native Eurasian red squirrel (Sciurus vulgaris), describing techniques and methods that successively have been applied to evaluate the relationships between personality, stress and parasite load. Chapter 1 reported the validation of a method to measure physiological stress in Eurasian red squirrel; Chapter 2 showed the application of this method to evaluate physiological stress in the native species in co-occurrence with Eastern grey squirrels. Chapter 3 presented estimates of personality of individual squirrels using indirect indices and their validation through correlation with direct personality measurements from arena tests. Chapter 4 examined the methods previously identified to explore the relationship between personality and parasite infections in Eastern grey squirrels. Reproductive success/investment could be influenced by the cumulative effect of factors analysed above. Chapter 5 presented the application of a staining technique of uterine scars count to estimate fecundity in invasive squirrel populations. Finally, Chapter 6 examined the relationships between parasite load, physiological stress, reproductive success and/or investment and the potential mediatory role of personality.