Exclosure experiments can give us insights into the loss of large native herbivores and also their replacement with domestic livestock. The Kenyan Long-term Exclosure Experiment (KLEE) has since 1995 allowed the examination of the separate and interactive effects of three guilds of large herbivores: wildlife, megafauna (sensu stricto), and cattle, as well as how these interact with controlled burns. This unique four-way design (overlaid on strong seasonal and interannual variation in rainfall) has begun to reveal a myriad of complex interactions (context-dependence). These allow the exploration of the many senses of ecological 'synergy': catalytic, positively and negatively non-additive, non-multiplicative, and asymptotic. We report here on several of these interactions and how they are revealed empirically and statistically.
Results/Conclusions
Some of our examples include: A) Adult acacia trees mostly survive elephants alone and fire alone, but succumb to the combination of both. B) The positive direct effects and negative indirect effects (via tree density) of herbivores on termite mound density appear to be simply additive (no net effect). C) The competitive release of rodents by the exclusion of wildlife and of cattle are also simply additive. D) The competitive effects of cattle on several wildlife species are significantly less in the presence of elephants, in a combination of a positive additive effect and negative (inverse) additive effect. E) Several woody plants are effectively suppressed by cattle alone, and by wildlife alone, but because of asymptotic limits, the combination of both herbivores is far less than additive (or multiplicative). It appears that such synergies are the norm and not the exception, and in our case reveal a rich complexity in the ecological impacts of large mammalian herbivores. These synergies also suggest that many if not all descriptive studies and experiments in ecology are strongly affected by often unseen (and uncontrolled) confounding factors.