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Global and local decline of large ani­mals at the top of the food chain, so-​called “apex con­sumers”, has caused dis­rup­tion of ecosys­tems. This is shown in a study which is recently pub­lished in Sci­ence. The large ani­mals, which not nec­es­sar­ily have to be preda­tors, con­sume prey or veg­e­ta­tion at top lev­els of the food chain and are essen­tial for sta­ble ecosys­tems. The authors argue that the loss of the top con­sumers is the most per­va­sive influ­ence of Man on Mother Nature.

Some exam­ples of these dis­rup­tions which are decribed in the pub­li­ca­tion are the following:

• The extir­pa­tion of wolves in Yel­low­stone National Park led to over-​browsing of aspen and wil­lows by elk, and restora­tion of wolves has allowed the veg­e­ta­tion to recover.

• The reduc­tion of lions and leop­ards in parts of Africa has led to pop­u­la­tion out­breaks and changes in behav­ior of olive baboons, increas­ing their con­tact with peo­ple and caus­ing higher rates of intesti­nal par­a­sites in both peo­ple and baboons.

• Dra­matic changes in coastal ecosys­tems have fol­lowed the col­lapse and recov­ery of sea otter pop­u­la­tions; sea otters main­tain coastal kelp forests by con­trol­ling pop­u­la­tions of kelp-​grazing sea urchins.

Large ani­mals, once found all over the world, have been impor­tant rep­re­sen­ta­tives of fauna that shaped ecosys­tems struc­ture and dynam­ics. Hunt­ing and habi­tat frag­men­ta­tion by humans who think they must exploit nature, caused pop­u­la­tion decline not only of large preda­tors, such as wolves, lions, whales and sharks, but of large her­bi­vores, such as bison and ele­phant, too. This decline has had far-​reaching and often sur­pris­ing con­se­quences, includ­ing changes in veg­e­ta­tion, wild­fire fre­quency, infec­tious dis­eases, inva­sive species, water qual­ity, car­bon seques­tra­tion and nutri­ent cycles.

The loss of large ani­mals from an ecosys­tem trig­gers a chain of effects mov­ing down through lower lev­els of the food chain. These eco­log­i­cal phe­nom­ena, though com­pli­cated and there­fore not easy to recog­nise, are fun­da­men­tally important.

The group of inter­na­tional sci­en­tists led by James Estes from Santa Cruz Uni­ver­sity of Cal­i­for­nia, could not per­form exper­i­ments to prove their the­ory. They had to review many long-​term records and obser­va­tions of nat­ural changes over a long period to iden­tify the inter­ac­tions they describe in their pub­li­ca­tion. Or as Estes put it: “With these large ani­mals, it’s impos­si­ble to do the kinds of exper­i­ments that would be needed to show their effects.”

The study’s find­ings have pro­found impli­ca­tions for con­ser­va­tion. “To the extent that con­ser­va­tion aims toward restor­ing func­tional ecosys­tems, the re-​establishment of large ani­mals and their eco­log­i­cal effects is fun­da­men­tal,” Estes said. “This has huge impli­ca­tions for the scale at which con­ser­va­tion can be done. You can’t restore large apex con­sumers on an acre of land. These ani­mals roam over large areas, so it’s going to require large-​scale approaches.”

(Sources: web­site Santa Cruz Uni­ver­sity, 14 July 2011; Sci­ence, 15 July 2011)