Nicol Heuermann: Tall swards and small grazers

'Why are there that many animals?' and 'How do different species coexist?' are basic questions in ecology.  Species that forage from the same resource differ in body size and morphology. But are differences in body size enough to allow species to coexist?
To answer these questions experiments were done with captive Canada geese and domestic rabbits. These species were chosen because within one species subspecies and breeds with different body size exist. 
Although the grazers used in this study were generally rather small and selected their bites at the scale of single grass leaves, there were small differences between the different subspecies. In accordance with the Jarman-Bell principle, larger geese consumed more tall grass than the smaller geese. Small geese are able to forage more efficiently on very short swards and can therefore competitively exclude larger ones from very short swards. Coexistence of grazers based on differences in body mass is therefore possible, provided the vegetation is heterogeneous.

Title thesis: Tall swards and small grazers - Competition, facilitation and coexistence of different-sized grazers