In sympatric speciation, there is no geographic constraint to interbreeding. It also suggested the notion of Sapiens-Neanderthal interbreeding. Lagar Velho (Portugal) features traits that indicate Neanderthal interbreeding with modern humans dispersing into Iberia. It noted the interbreeding of Bovini species made determining relationships problematic. A ring species is a species with a counterexample to the transitivity of interbreeding. There are also reports of interbreeding difficulties between the two taxa. A population can be defined as a group of interbreeding individuals and their offspring. Disturbance by and interbreeding with livestock herds is also common. A zero value implies that the two populations are panmixis, that they are interbreeding freely. A zero value implies complete panmixis; that is, that the two populations are interbreeding freely. The "Biological Species Concept" (BSC) is a classic example of the interbreeding approach. Invaders are identified and removed by the ant colony, inhibiting competition and fungal interbreeding. There is evidence of interbreeding between female katipo and male redbacks in the wild. The interbreeding produced changes in color of the breed. The herd size, sex, interbreeding, and season did not play any role in juvenile mortality.