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In the absence of predators to control lesser predators, people have a role

My article in the Times on 13 June 2013


‘We are as gods and have to get good at it,” the
Californian ecologist and writer Stewart Brand said recently.
Worldwide there has been a sea change in the ecological profession.
These days most ecologists recognise that there is no such thing as
a pristine wilderness and that the best biodiversity is produced by
active management to control some species and encourage others.

That means you, Mr Brock. There is little doubt that the
forthcoming badger cull will work. It will drastically reduce
tuberculosis among cattle, but only if the fanatics opposing it let
it achieve its targets. All the older objections — that badgers may
not carry TB, that killing them in sufficient numbers is
impractical, that letting them die of TB is more humane, that
vaccination alone can work — have fallen away and opponents are
left only with a circular argument: the cull won’t work because
they won’t let it.

Similar culls of wildlife dramatically reduced TB in cattle in
New Zealand, Australia, the US and other countries. Ireland has
reduced TB in cattle by badger culling over the very period when
disease incidence has been rising steeply among cattle in Northern
Ireland. Controlled experiments do not come much clearer than that.
See here and here and here for further information.

What is not often appreciated is just how much good the cull
will do to the ecosystems of rural England above and beyond its
impact on bovine TB. The badger is what ecologists call an example
of “meso-predator release”: a middle-ranking generalist predator
whose numbers are abnormally high because they no longer face
predation from larger, “apex” predators.

This is a common phenomenon. Raccoons, foxes, baboons, crows,
mink and other meso-predators have boomed where human beings have
got rid of wolves, leopards, bears, eagles and other large
carnivores. The consequence is a diminution in the numbers of
animals on which meso- predators prey: in some cases to the point
of local extinction. In moorland areas, a long study in Northumberland by the Game and
Wildlife Conservation Trust found that without fox or crow control,
the breeding success of curlews, lapwings and golden plovers is
below 20 per cent because there are too many meso-predators. With
control, breeding success was north of 60 per cent.

In most countries wildlife managers are well aware of this
“meso-predator- release” problem and discuss openly how to manage
it. In Britain, the debate is decades behind. Try using the phrase
on a middle manager from Natural England and you will get blank
looks. Although quite prepared to admit that predation plays a big
role in the population dynamics of smaller animals — Natural
England rightly opposes the introduction of fish into ponds with
newts in them, because the fish eat the young newts — such people
generally hold a theological objection to admitting that predation
affects bird and mammal populations.

I know where this theology comes from because I was taught it at
university: the dogma was that prey numbers control predator
numbers, not vice versa. There were equations and graphs to prove
it. But this is only true for specialist predators eating only one
kind of prey, such as parasitoid wasps eating aphids, or lynxes
killing snowshoe hares. Where predators generalise they can indeed
drive a prey species to the brink of extinction. Lynx cannot thrive
if hares get scarce, but a generalist predator can switch partly to
an alternative diet and keep on driving down the prey.

When I was studying zoology in Oxford, the near total absence of
hedgehogs from Wytham Woods was remarked on by a colleague. Then
somebody pointed out the abundance of badgers in the woods. Sure
enough, it transpires that badgers, undeterred by the spines, are
enthusiastic predators of hedgehogs. The boom in badger numbers is
undoubtedly one chief cause of the decline of hedgehogs. A 2006
study noted “the exclusion of hedgehogs from rural
habitats in areas where badgers are abundant”.

Likewise, badgers are eager predators of bumble bee nests,
leaving surprisingly medieval scenes of entomological devastation
when they find one. It is by no means impossible that some local
declines in bumble bees are down to too many badgers.

Moreover, if you subsidise a meso-predator with human-derived
food, somewhat paradoxically you often exacerbate the decline of
its prey. A sudden decline in desert tortoises in the Mojave Desert
in California turned out to be down to the opening of a nearby
landfill site that boosted the population of ravens, which were
killing the tortoises. In this country, meso-predators such as
crows, foxes and badgers are heavily subsidised by roadkill,
landfill and bird tables, with a big impact on their prey.

The best thing you can do for biodiversity, therefore, is to
control unnaturally large populations of meso- predators. One way
is to reintroduce apex predators. The return of the wolf has
greatly increased the population of small mammals in parts of the
American West, both because they kill foxes and coyotes, which eat
mice and squirrels, and because they kill deer, leaving more grass
for the rodents to eat. In Europe otters (in Britain) and sea
eagles (in Finland) have greatly reduced the number of mink to the
benefit of water birds and voles.

In places where the return of wolves and bears is impractical —
Gloucestershire, for example — we humans must adopt the role of
apex predator ourselves. It is no good saying we don’t want to
interfere. We already have. On the North Sea coast, for example,
catching lobsters enables their rivals, crabs, to move into
shallower water, but crabs eat more sea urchins, which would
normally graze on kelp, so kelp thrives, providing a better nursery
for young cod. Reducing lobsters boosts cod numbers — the choice is

The biologist Emma Marris, in an outstanding book, The
Rambunctious Garden
, chronicles the recent change of heart
within ecology with examples from Hawaii to the Netherlands. She
argues that ecosystem management is a dynamic and active process,
not a matter of passive protection.

To have allowed TB to increase sixfold in cattle and to explode
in badgers, as the previous Government did, is irresponsible, not
least when so many other countries are demonstrating successful
control of bovine TB through the culling of wildlife. Intervention
is a matter of ecological management of the kind we humans have to
accept. It will in the long run benefit badgers as well as many
other species, including hedgehogs and probably bumble bees.

By Matt Ridley | Tagged:  rational-optimist  the-times