Bottom-up rather than top-down mechanisms determine mesocarnivore
interactions in Norway
Abstract
Interactions among coexisting mesocarnivores can be influenced by
different factors such as the presence of large carnivores, land-use,
environmental productivity, or human disturbance. Disentangling the
relative importance of bottom-up and top-down processes can be
challenging, but it is important for biodiversity conservation and
wildlife management. The aim of this study was to assess how the
interactions among mesocarnivores (red fox Vulpes vulpes, badger Meles
meles, and pine marten Martes martes) are affected by large carnivores
(Eurasian lynx Lynx lynx and wolf Canis lupus), land cover variables
(proportion of agricultural land and primary productivity), and human
disturbance, as well as how these top-down and bottom-up mechanisms are
influenced by season. We analyzed three years (2018-2020) of camera
trapping data from Norway and used structural equation models to assess
hypothesized networks of causal relationships. Our results show that
land cover variables are stronger predictors of mesocarnivore activity
than large carnivores in Norway. This might be caused by a combination
of low density of large carnivores in an unproductive ecosystem with
strong seasonality. Additionally, all mesocarnivores showed positive
interactions among each other, which were stronger in winter. The
prevalence of positive interactions among predators might indicate a
tendency to use the same areas and resources combined with weak
interference competition. Alternatively, it might indicate some kind of
facilitative relationship among species. Human disturbance had
contrasting effects for different species, benefiting the larger
mesocarnivores (red fox and badger) probably through food subsidization,
but negatively affecting apex predators (wolf and lynx) and smaller
mesocarnivores (pine marten). In a human-dominated world, this
highlights the importance of including anthropogenic influences in the
study of species interactions.