Recently, ecologists have realised that apex predators are overwhelmingly important for the proper functioning of ecosystems. For example, the loss of whales severely reduces nutrient circulation in the oceans, leading to large declines in plankton and fish. The loss of wolves from Scotland has contributed to the highlands becoming a barren wilderness. In 1970, 40 wolves were re-introduced to Yellowstone, after being hunted to near-extinction across the USA. Put the following trophic cascade in order, from re-introduction of wolves at the top, to the present day at the bottom. 2 marks River beds stabilise, deepen and pools form Ungulates primarily graze inaccessible slopes rather than open planes and valleys Diversity of plants increases and trees grow along river banks Diversity of fish, insects, birds and mammals increases Population of ungulates (elk, deer etc) shrinks and becomes fitter Ecosystem becomes more robust to perturbations (e.g. extreme weather or invasive species).

1. Recently, ecologists have realised that apex predators are overwhelmingly important for the
proper functioning of ecosystems. For example, the loss of whales severely reduces nutrient
circulation in the oceans, leading to large declines in plankton and fish. The loss of wolves from
Scotland has contributed to the highlands becoming a barren wilderness. In 1970, 40 wolves
were re-introduced to Yellowstone, after being hunted to near-extinction across the USA. Put the
following trophic cascade in order, from re-introduction of wolves at the top, to the present day
at the bottom. 2 marks River beds stabilise, deepen and pools form Ungulates primarily graze
inaccessible slopes rather than open planes and valleys Diversity of plants increases and trees
grow along river banks Diversity of fish, insects, birds and mammals increases Population of
ungulates (elk, deer etc) shrinks and becomes fitter Ecosystem becomes more robust to
perturbations (e.g. extreme weather or invasive species)