Latitudinal gradient in the intensity of biotic interactions in terrestrial ecosystems: Sources of variation and differences from the diversity gradient revealed by meta-analysis

The Latitudinal Biotic Interaction Hypothesis (LBIH) states that the
intensity of biotic interactions increases from high to low latitudes.
This hypothesis, which may partly explain latitudinal gradients in
biodiversity, remains hotly debated, largely due to variable outcomes of
published studies. We used meta-analysis to identify the scope of the LBIH
in terrestrial ecosystems. For this purpose, we explored the sources of
variation in the strength of latitudinal changes in herbivory, carnivory,
and parasitism (119 publications) and compared these gradients with
gradients in the diversity of the respective groups of animals (102
publications). Overall, both herbivory and carnivory decreased towards the
poles, while parasitism increased. The latitudinal gradient in herbivory
and carnivory was threefold stronger above 50–60º than at lower latitudes
and was significant due to interactions involving ectothermic consumers,
studies using standardized prey (i.e. prey lacking local anti-predator
adaptations) and studies aimed at testing LBIH. The poleward decrease in
biodiversity did not differ between ectothermic and endothermic animals or
among climate zones and was four-fold stronger than decrease in herbivory
and carnivory. The discovered differences between the gradients in biotic
interactions and biodiversity suggest that these two global
macroecological patterns are likely shaped by different factors.