THREAT TO ECOLOGICAL BALANCES AND SURVIVAL THRESHOLDS

ANY ECOSYSTEM, NO MATTER HOW RESILIENT, CAN BE PUSHED TO A POINT OF NO RETURN OR, MORE EXACTLY, TO A THRESHOLD BEYOND WHICH LIMITING FACTORS BECOME A SEVERELY OPERATIVE THAT RECOVERY, IN PERIODS MEANINGFUL IN THE HUMAN TIME SCALE BECOME IMPOSSIBLE. FOR EXAMPLE, SOIL EROSION ON MOUNTAIN SIDES MAY REACH A POINT WHERE BED ROCK IS EXPOSED. WHEN THIS SITUATION TAKES PLACE, ONLY THE SLOW PROCESS OF PRIMARY BIOTIC SUCCESSION, WHICH HAVE BEEN OPERATING FOR CENTURIES OR MILLENNIA, CAN BUILD THE SOIL AND VEGETATION. ANOTHER THRESHOLD PROCESS, TYPICAL OF MANY AREAS, IS SOIL LATERIZATION, WHICH CAN ONLY BE ARRESTED ECONOMICALLY AT CERTAIN EARLY STAGES.ONCE A TOUGH LAYER OF LATERITE IS EXPOSED OR FORMED, RECOVERY MAY NO LONGER BE FEASIBLE. COMMUNITIES MAY REPAIR  THEMSELVES, WITH MODERATE PROTECTION, UP TO A CERTAIN POINT. BEYOND A CERTAIN LEVEL OF ABUSE OR DISTURBANCE, BIOLOGICAL REPAIR BECOMES, IN HUMAN TERMS, AN INTOLERABLY SLOW PROCESS.

CONSISTENT OVER-CROPPING OF ANY SPECIES CAN REDUCE ITS NUMBER TO LEVELS FROM WHICH RECOVERY IS NO LONGER POSSIBLE. KILLING THE LAST INDIVIDUAL ANIMAL OR CUTTING THE LAST TREE OF A SPECIES MAY NOT BE NEEDED  TO BRING ABOUT EXTINCTION. IF ANIMAL POPULATIONS ARE REDUCED TO A LEVEL AT WHICH EFFECTIVE BREEDING  DOES NOT OCCUR, OR IF THE HABITAT OF A SPECIES IS DESTROYED, RECOVERY WILL NOT TAKE PLACE, EVEN THOUGH SOME INDIVIDUALS WILL SURVIVE FOR SOME TIME. SIMILARLY FOR PLANTS, IF A MINIMUM AREA TO ENSURE REGENERATION OF CERTAIN SPECIES IS NOT MAINTAINED, THEY WILL EVENTUALLY DIE OUT. THE NUMBER OF INDIVIDUALS OR THE SIZE OF HABITAT NEEDED TO ASSURE SURVIVAL OF SPECIES HAS NOT YET BEEN GENERALLY DETERMINED. THE THRESHOLD  APPARENTLY  VARIES WITH THE GENETIC  MAKE-UP OF THE SPECIES,ITS HABITAT REQUIREMENTS AND BEHAVIOURAL CHARACTERISTICS.