I have read recently about the ecological phenomenon described as 'Landscapes of Fear' where the introduction of large predators can change the flora and fauna of an area quite radically. The re-introduction of wolves in Yellowstone Park is a good example. See:
A couple of years ago our granddaughter came to live with us and brought her cats into a cat-free garden and this has had quite a marked effect on biodiversity. On part of the lawn, for example, an impressive stand of cuckooflower or lady's smock (Cardamine pratensis) has developed whereas in the past the plants would have been eaten down by rabbits. In the picture above note the rabbit and mouse hunting tortoiseshell cat in the background. Ground feeding birds also avoid the lawn and there has been a marked increase in slugs and snails.
Although many species have suffered, others have done well. The cuckooflowers attracted solitary bees, bee flies, hover flies and many other insects which often find nectar and pollen providing plants scarce in early April.