Biodiversity worldwide has been declining rapidly in recent decades. Acquiring land for protection has been used as a main strategy to halt this decline. Conservation organizations commonly rely on spatial planning approaches to help identify priorities for land protection. These spatial planning approaches often assume that the overall amount of conservation funding is fixed, and that funds can be freely allocated across different candidate regions for protection. We examine these assumptions by exploring the relationship between philanthropic donations to support conservation and investments in land protection. We analyzed land protection efforts made by a conservation NGO in the US, The Nature Conservancy, and philanthropic giving to the organization. We examined possible two-way effects using a regression approach with instrumental variables. Our results indicate that investments in land acquisition may have an increasing effect on philanthropic donations at state level. However, we found only limited indications of an effect of philanthropic donations on the allocation of land acquisitions for conservation. Our findings show that the allocation of land acquisitions for conservation may affect future philanthropic donations to conservation organizations.