Numerical response of predator to prey: Dynamic interactions and population cycles in Eurasian lynx and roe deer

The dynamic interactions between predators and their prey have two
fundamental processes; numerical and functional responses. Numerical
response is defined as predator growth rate as a function of prey density
or both prey and predator densities [dP/dt = f(N, P)]. Functional response
is defined as the kill rate by an individual predator being a function of
prey density or prey and predator densities combined. Although there are
relatively many studies on the functional response in mammalian predators,
numerical response remains poorly documented. We studied numerical
response of Eurasian lynx (Lynx lynx) to various densities of its primary
prey species, roe deer (Capreolus capreolus), and to itself (lynx). We
exploited an unusual natural situation, spanning three decades where lynx,
after a period of absence in central and southern Sweden, during which roe
deer populations had grown to high densities, subsequently recolonized
region after region, from north to south. We divided the study area into
seven regions, with increasing productivity from north to south. We found
strong effects of both roe deer density and lynx density on lynx numerical
response. Thus, both resources and intraspecific competition for these
resources are important to understand the lynx population dynamic. We
built a series of deterministic lynx–roe deer models and applied them to
the seven regions. We found a very good fit between these
Lotka-Volterra-type models and the data. The deterministic models produced
almost cyclic dynamics or dampened cycles in five of the seven regions.
Thus, we documented population cycles in this
large-predator-large-herbivore system, which is rarely done. The
amplitudes in the dampened cycles decreased towards the south. Thus, the
dynamics between lynx and roe deer became more stable with increasing
carrying capacity for roe deer, which is related to higher productivity in
the environment. This increased stability could be explained by variation
in predation risk, where human presence can act as prey refugia, and by a
more diverse prey guild that will weaken the direct interaction between
lynx and roe deer.