Territorial Constraints on Trap–Neuter–Return in Insular Landscapes: Demographic and Ecological Implications of a Conservation-Oriented Policy

Managing community cats on islands requires reconciling animal-welfare mandates with biodiversity protection under real operational constraints. In the Canary Islands (Spain), national Law 7/2023 endorses ethical, non-lethal colony management, while subsequent regional resolutions restrict TNR in and around protected areas, narrowing municipal room for action. We combine a multilevel governance assessment with stochastic demographic simulations parameterized from official records to compare three sterilization regimes over 20 years. The intensive regime (≈60–70%/year) reflects the coverage threshold previously identified by Spain-based modelling and field evaluations and adopted in national program guidance; the 20%/year regime represents the pre-resolution baseline widely observed across the archipelago up to December 2024; and the 4%/year regime reflects the post-resolution reality, with abrupt declines in sterilizations, operations largely confined to urban cores, and program suspensions in multiple municipalities. Minimal (4%) and low (20%) efforts produce rapid population growth, bringing numbers close to the assumed carrying capacity under our deliberately high-K configuration and sustaining high densities and associated welfare and ecological risks; only sustained high-coverage TNR prevents saturation and produces progressive declines across island contexts. Under insular constraints, outcomes are determined by achievable coverage rather than regulatory intent; aligning policy and implementation to secure continuous, high-coverage TNR—particularly in risk-sensitive areas with appropriate safeguards—offers a feasible pathway to meet animal-welfare obligations while limiting ecological pressure.