Cats and vegetation: a tale of two centuries

Exhibit A, from The Origin of Species, by C.R. Darwin, 1st edition, 1859, pp73-4:

I am tempted to give one more instance showing how plants and animals, most remote in the scale of nature, are bound together by a web of complex relations. ... The number of humble-bees in any district depends in a great degree on the number of field-mice, which destroy their combs and nests; and Mr. H. Newman, who has long attended to the habits of humble-bees, believes that "more than two thirds of them are thus destroyed all over England." Now the number of mice is largely dependent, as every one knows, on the number of cats; and Mr. Newman says, "Near villages and small towns I have found the nests of humble-bees more numerous than elsewhere, which I attribute to the number of cats that destroy the mice." Hence it is quite credible that the presence of a feline animal in large numbers in a district might determine, through the intervention first of mice and then of bees, the frequency of certain flowers in that district!

Exhibit B, from the Journal of Applied Ecology, 46: 73-81 (2009). Indirect effects of invasive species removal devastate World Heritage Island:

1. Owing to the detrimental impacts of invasive alien species, their control is often a priority for conservation management. Whereas the potential for unforeseen consequences of management is recognized, their associated complexity and costs are less widely appreciated.
2. We demonstrate that theoretically plausible trophic cascades associated with invasive species removal not only take place in reality, but can also result in rapid and drastic landscape-wide changes to ecosystems.
3. Using a combination of population data from of an invasive herbivore, plot-scale vegetation analyses, and satellite imagery, we show how a management intervention to eradicate a mesopredator has inadvertently and rapidly precipitated landscape-wide change on sub-Antarctic Macquarie Island. This happened despite the eradication being positioned within an integrated pest management framework. Following eradication of cats Felis catus in 2001, rabbit Oryctolagus cuniculus numbers increased substantially although a control action was in place (Myxoma virus), resulting in island-wide ecosystem effects.
4. Synthesis and applications. Our results highlight an important lesson for conservation agencies working to eradicate invasive species globally; that is, risk assessment of management interventions must explicitly consider and plan for their indirect effects, or face substantial subsequent costs. On Macquarie Island, the cost of further conservation action will exceed AU$24 million.

Ok, Darwin is a lot easier to read. He might not have needed the services of either Resilience Science or The Guardian. Maybe he wouldn’t have been published in the Journal of Applied Ecology. But he knew how many beans made five, and that’s a fact.