Figure 8
From: Trophic overlap between expanding and contracting fish predators in a range margin undergoing change
Conceptual model outlining the ecological interactions between prey, predator and predator impact. The past scenario indicates the situation when flounders were the only dominant fish predators on mussels in the outer archipelago and where predation pressure was equal along the range. The prey and the predator had a similar distribution pattern caused by salinity requirements and consequently the total predation pressure paralleled the distribution of both species. The present scenario describes the situation when a novel predator to the system or the region has a distribution pattern that contrasts the environmental requirement of its prey. In this case, it will exert increasingly higher predation pressure at the margin of distribution of its main prey, where prey is sparse and predators are highly abundant. In our case, in west, predation pressure is still low due to high biomasses of blue mussels. Predation pressure from flounders continues being weak because of a declining flounder population. If the resource base in future declines (the solid line drops), predation pressure from roach will increase and be increasingly significant towards the west. If also the population size of roach will increase, this will cause an even larger pressure on declining mussel populations.
