Data from: Estimating effects of species interactions on populations of endangered species

Global change causes community composition to change considerably through
time, with ever-new combinations of interacting species. To study the
consequences of newly established species interactions, one available
source of data could be observational surveys from biodiversity
monitoring. However, approaches using observational data would need to
account for niche differences between species and for imperfect detection
of individuals. To estimate population sizes of interacting species, we
extended N-mixture models that were developed to estimate true population
sizes in single species. Simulations revealed that our model is able to
disentangle direct effects of dominant on subordinate species from
indirect effects of dominant species on detection probability of
subordinate species. For illustration, we applied our model to data from a
Swiss amphibian monitoring program and showed that sizes of expanding
water frog populations were negatively related to population sizes of
endangered yellow-bellied toads and common midwife toads and partly of
natterjack toads. Unlike other studies that analyzed presence and absence
of species, our model suggests that the spread of water frogs in Central
Europe is one of the reasons for the decline of endangered toad species.
Thus, studying population impacts of dominant species on population sizes
of endangered species using data from biodiversity monitoring programs
should help to inform conservation policy and to decide whether competing
species should be subject to population management.