The effects of human population density on trophic interactions are contingent upon latitude

Aim:  Studies conducted at a global scale are necessary to make
general conclusions on the effect of urbanization on trophic interactions
and explore how these effects change along latitudinal gradients. Since
biotic interactions are more intense at lower latitudes, we predict they
are less likely to be affected by human impacts than at higher latitudes.
Therefore, we test the hypothesis that the effect of urbanization
(quantified by human population density) on trophic interactions,
specifically insect herbivory and bird predation, decreases with an
increase in latitude Location:  Global (881 study sties) Time
period: 2000-2021 Major taxa studied:  Birds, arthropods and
plants. Methods:  We compiled global data on insect herbivory and
bird predation from individual studies using similar methodologies, and
fitted generalized linear mixed models to test the effect of human
population density, latitude and their interaction on these two response
variables. Results:  The intensity of herbivory and predation
decreased with the increase of human population density at lower
latitudes, remained unaffected at intermediate latitudes, and increased at
higher latitudes. Main conclusions:  The effect of urbanization
on the intensities of trophic interactions varies across latitudes, with a
reversal of the pattern at high vs. low latitudes potentially explained by
the urban heat island effect, being this pattern consistent across the two
main trophic interaction.