Meta-analysis of elevational changes in the intensity of trophic interactions: similarities and dissimilarities with latitudinal patterns

The premise that the intensity of biotic interactions decreases with
increasing latitudes and elevations is broadly accepted; however, whether
these geographical patterns can be explained within a common theoretical
framework remains unclear. Our goal was to identify the general pattern of
elevational changes in trophic interactions and to explore the sources of
variation among the outcomes of individual studies. Meta-analysis of 226
effect sizes calculated from 136 publications demonstrated a significant
but interaction-specific decrease in the intensity of herbivory, carnivory
and parasitism with increasing elevation. Nevertheless, this decrease was
not significant at high latitudes and for interactions involving
endothermic organisms, for herbivore outbreaks or for herbivores living
within plant tissues. Herbivory similarly declined with increases in
latitude and elevation, whereas carnivory showed a fivefold stronger
decrease with elevation than with latitude and parasitism increased with
latitude but decreased with elevation. Thus, although these gradients
share a general pattern and several sources of variation in trophic
interaction intensity, we discovered important dissimilarities, indicating
that elevational and latitudinal changes in these interactions are partly
driven by different factors. We conclude that the scope of the latitudinal
biotic interaction hypothesis cannot be extended to incorporate
elevational gradients.