Reproductive ecology of the black rat (Rattus rattus) in Madagascar: the influence of density‐dependent and ‐independent effects

Abstract

The black rat (Rattus rattus) poses a severe threat to food security and public health in Madagascar, where it is a major cause of pre‐ and post‐harvest crop losses and an important reservoir for many zoonotic diseases, including plague. Elsewhere, ecologically based rodent management (EBRM) strategies have been developed using ecological information to inform decisions on where and when to target control. EBRM could deliver improved health and well‐being outcomes in Madagascar if adapted to the local ecological context. Using data collected from removal studies, we explored spatio‐temporal patterns in the breeding activity of the black rat (R. rattus) in domestic and agricultural habitats across Madagascar and investigated to what extent these trends are influenced by rainfall and rat density. We identified clear spatio‐temporal variation in the seasonality of R. rattus reproduction. Reproduction was highly seasonal both inside and outside of houses, but seasonal trends varied between these two habitats. Seasonal trends were explained, in part, by variation in rainfall; however, the effect of rainfall on reproductive rates did itself vary by season and habitat type. A decline in breeding intensity with increasing rat density was recorded outside of houses. This has important implications for control, as populations may compensate for removal through increased reproduction. We recommend that sustained control initiated before the main breeding season, combined with improved hygiene and adequate rodent‐proofing in homes and grain stores, could curtail population growth and reduce pre‐ and post‐harvest losses provided that these measures overcome the compensatory response of rodent populations.

Feeding and Reproductive Ecology of Rodents: A Review

“…Based on the results, it was concluded that high rainfall during the early stages of crop production provide ideal conditions for rodents in the rainy season (Scobie et al, 2023). The spatio-temporal patterns in R. rattus breeding activity also established a decline in breeding rates with an increase in population density in crop fields (Scobie et al, 2024).…”

Rodent biology and ecologically based rodent management (EBRM)—25 years of progress through promoting multidisciplinary research

“…Related to this case study, research on the breeding dynamics of R. rattus in agricultural systems in the Central Highlands of Madagascar demonstrated the importance of detailed knowledge of the biology and ecology of your pest rodent species in various habitats (from fields to households) and during different seasons before applying management (Scobie et al. 2023). Such an understanding provides insights into the best times to apply EBRM and avoids unintended consequences that may arise if there are density‐dependent and density‐independent responses in population dynamics.…”