Population dynamics and life history of the endangered ciénega endemic Eryngium sparganophyllum in Arizona

Abstract

Eryngium sparganophyllum is a perennial endemic to ciénegas in warm North American deserts. Only four populations remain, yet little scientific knowledge exists to guide its conservation. Based on a spatially balanced sampling design, we quantified plant density, individual size, and reproductive potential of two populations in the U.S. We also assessed conditions influencing germination in the lab. The population in a warmer climate had a larger population size, higher short-term population growth rate, hosted larger individuals, and showed a negative correlation between plant size and plant density. In both populations, plant density was positively correlated with shallow soil moisture and probability of flowering was positively correlated with plant size. Seeds only germinated in the spring, and responded to interactions between temperature, light exposure and population location. We hypothesize that 1) recruitment of E. sparganophyllum may be episodic, relying on a rare niche opportunity of reliable shallow soil moisture and low competition; and 2) adult survival of the species may be limited by interspecific density dependence and climatic extremes. The conservation of this species depends on ensuring high adult survival and promoting recruitment, which can be accomplished through actively protecting extant populations and exploring restoration and introduction possibilities.