Changes in agricultural land use can explain population decline in a ladybeetle species in the Czech Republic: evidence from a process-based spatially explicit model

Changes in land use affect species interactions and population dynamics by modifying the spatial template of trophic interaction and the availability of resources in time and space. We developed a process-based spatially explicit model for evaluating the effects of land use on species viability by modelling foraging performance and energy sequestration in a stage structured, three-trophic population model. The model is parameterized with realistic parameters for a ladybeetle-aphid-host plant interaction, and is run in four realistic landscapes in the Czech Republic. We analysed whether changes in crop selection and fertilizer input could explain the dramatic and unexplained decline in abundance of the ladybeetle Coccinella septempunctata in the Czech Republic from 1978 to 2005. The results indicate that a major reduction in fertilizer input after the transition to a market economy, resulting in lower aphid population densities in cereal crops and negatively affecting energy sequestration, survival and reproduction of ladybeetles, provides a sufficient explanation for the observed population decline. Simulations further indicated that the population viability of C. septempunctata is highly dependent on availability of aphid prey in crops, in particular cereal, which serves as their major reproduction habitat. The results demonstrate how the abundance of naturally occurring predators, which are instrumental for biological pest control, depends upon the spatial resource template that are provided at the landscape scale.