Edaphic preference determines the distribution of the island endemic Ferocactus gatesii (Cactaceae) in Bahía de los Ángeles, Mexico

Abstract

The insular endemic Gates barrel cactus, Ferocactus gatesii (Cactaceae) [syn. Ferocactus gracilis ssp. gatesii], is only found on seven islands in Bahía de Los Angeles (BLA), an International Biosphere Reserve in Baja California, Mexico. The islands have different geologic origins; some formed as a result of lava flows, and others by the cooling of magma within the crust. These rock types give rise to different soil physical properties, with F. gatesii only observed growing in granite substrates. This suggests that F. gatesii is in fact an edaphic endemic, restricted to specific soil lithologies on the small islands. Proposed edaphic properties of the preferred granite substrate include controls on soil porosity, permeability, nutrient availability and geomorphic conditions that may influence plant success. Further research is necessary to evaluate the mechanisms of soil property effects on F. gatesii presence and survival, however, recognizing this general pattern is of critical importance to conservation planning, particularly in the face of intensifying environmental stresses from increased aridity, decreasing precipitation, and illegal harvesting. This new information allows us to improve models for potential habitat in an assisted migration scenario and allows insights into the evolutionary processes that resulted in this narrowly endemic species.