Shedding light on trophic interactions: A field experiment on the effect
of human population across latitudes on herbivory and predation patterns
Abstract
The interactions between different species in an ecosystem, such as
predation and herbivory, are crucial for maintaining the ecosystem’s
functioning, including pest control and nutrient cycling. Unfortunately,
human activities are increasingly affecting these trophic relationships,
contributing to the current decline in biodiversity, particularly due to
urbanization and climate change. The intensity of trophic interactions
is also affected by latitudinal gradients, which may be further impacted
by urbanization, such as the urban island heat effect. This study aimed
to investigate the hypothesis that the impact of human pressure on
trophic interactions varies across different latitudes. To test this
hypothesis, we selected 18 study sites at two latitudes (i.e.,
~53°N and ~50°N) with varying human
population density. We used artificial caterpillars placed on European
beech branches to assess bird predation and took standardized pictures
of the leaves to estimate insect herbivory. Remote sensing techniques
were used to estimate human pressure. We found that the intensity of
both bird predation and insect herbivory varied in response to human
pressure, with opposite trends observed depending on the latitude. At
the upper latitude, bird predation increased with human impact, while
the opposite was observed at the lower latitude. All types of herbivory
in both latitudes increased with urbanization. Moreover, at lower
latitudes, species may face a disadvantage due to the urban heat island
effect, as they tend to be relatively sensitive to temperature changes.
Conversely, at higher latitudes, some species may benefit from a softer
winter. Overall, this study highlights the complex and dynamic nature of
trophic relationships in the face of human-driven changes to ecosystems.
It also emphasizes the importance of considering both human pressure and
latitudinal gradients when assessing the ecological consequences of
future climate change scenarios, particularly in urban environments.