Root contraction does not increase long-term population growth in Pediocactus bradyi, an endangered cactus of Northern Arizona
Julieta Rojas-Pimentel, Eugenio Larios, Edgar J González

TL;DR
A study on an endangered cactus in Arizona finds that root contraction does not significantly affect long-term population growth.
Contribution
The study is the first to use long-term demographic data to model the population dynamics of Pediocactus bradyi with and without root contraction.
Findings
Root contraction had no significant effect on long-term population growth rates.
Larger cacti have higher survival and reproductive rates, while growth declines after a certain size.
Survival and growth are the most important factors influencing population growth.
Abstract
Pediocactus bradyi, a semi-globose cactus endemic to northern Arizona, displays a root-contraction mechanism to survive extreme drought: its roots contract, pulling the stem below ground during dry periods, re-emerging once rains return. To quantify how root contraction shapes population dynamics, we developed an integral projection model based on 31 years of demographic data from a P. bradyi population on the Navajo Nation Off-Reservation Trust Land. We explored two scenarios: one including root contraction and one excluding it. We found that, being ∼10% of the individuals and mostly confined to smaller individuals, root contraction did not have an effect on the long-term population growth [λ = 1.041 (1.039, 1.303) with contraction vs. λ = 1.044 (1.035, 1.289) without]. Also, we show that larger individuals have higher survival and reproductive rates, while growth declines beyond 35 mm…
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Taxonomy
TopicsBotanical Research and Applications · Plant Taxonomy and Phylogenetics · Cassava research and cyanide
