One of the reasons, which I have mentioned before, a decline in carnivore populations can be detrimental to an ecosystem is the spread of disease. Without the proper balance of large wildlife populations (which includes your large carnivores), smaller, disease carrying species (primarily rodents) can overrun an ecosystem causing an increase in disease for local wildlife and humans alike. A study published last week looked at this phenomenon in an area in Africa called the KLEE (the Kenya Long-Term Exclosure Experiment; a well-controlled, replicated large herbivore removal experiment based in central Kenya - an area which includes species such as elephant, giraffe, zebra and lion). Through three years of sampling, this project determined that declines in large wildlife increased the occurrence of landscape-level rodent-borne disease.
The concept is pretty simple (although the analysis from the study is fairly complicated); loss of large wildlife causes a loss in the regulation of the rodent population which, in turn, causes an increase in rodents and their parasite carrying friends, the flea, which increases the amount of disease found in humans and other wildlife. The difficult part is figuring out how to counter this effect (aka prevent disease). The options – prevent the loss of large wildlife so the rodent population can naturally regulate itself or artificially regulate the rodent population. Setting out a few rodent traps out in the middle of the African savannah probably won’t do the trick so, I say, let’s try letting the megafauna do its job and keep working on large wildlife conservation to keep those large wildlife numbers where they should be.