Does Size Matter? Population and Patch Size Effects on Fitness Components in Pinguicula gracilis

Butterworts (Pinguicula spp.) are carnivorous plants often restricted to small, isolated populations in mountainous microclimates, making them vulnerable to inbreeding and demographic decline. In Mexico, the global hotspot for Pinguicula diversity (>50 species, 90% endemic), conservation is limited by scarce data on population biology, demography, and vulnerability. This study provides the first population size estimate for the endemic P. gracilis and evaluates how patch and population size influence biological fitness components across three localities in northeastern Mexico. Using a multi-component fitness framework and statistical models, we found that smaller populations and patches exhibit significantly reduced reproductive fitness, particularly in fruit set and seed quality. Patch size showed strong positive correlations with fruit production (r = 0.45–0.53), while isolation negatively affected seed output (r = −0.48). These results highlight the role of landscape structure in shaping fitness components, with patch size influencing reproductive effort and connectivity determining reproductive success. Our findings provide the first germplasm and population baseline for P. gracilis and a framework to identify vulnerable populations, prioritize conservation actions, and guide restoration strategies.