Elucidating the driving factors of extinction risk of global cycad species

Abstract

Biodiversity is rapidly declining worldwide because of the anthropogenic impacts on the environment regarding goods and services it delivers to humanity. Evidence suggests that we have entered the period of sixth mass extinction of human history. Being interested in distinguishing the pre-disposition of cycads to such risk of extinction, integration of structural equation modelling (SEM) on cycads was used. This plant belongs to a gymnosperm group, which exhibit the highest rate of extinction in the plant kingdom. This present study aimed to inform conservation decision-makers to be aware of the factors that drive the extinction risk of cycad species. The specific objective was to formulate and test a meta-model that explains the patterns of the extinction risks of cycads. However, several groups of threats to cycads were identified and the most prominent were those connected to human activities. Likewise, some variables that correlate with the extinction risks of cycad species were classified. Then, a cycad phylogeny was used to calculate ED values for each species so that high–ED species were those that merit specific attention. Nevertheless, Microcycas calocoma was the species having the highest ED score (98.762 MY). By using SEM, the results demonstrated a negative but significant relationship between ED and maximum height (β= ‑0.1226; SE= 0.0439; P = 0.0076). Moreover, the findings further demonstrated significant relationships between other variables and the positive ones were maximum altitude with generation time, range with maximum height and maximum altitude with number of threats. Therefore, maximum height with generation time has a significant but negative relationship. Thus, maximum height and generation time are variables considered as best predictors for extinction risk in cycad species, with a projecting power of 99% and 48% respectively. This work is best suited to inform conservation decisions regarding the rapid loss of cycads through human activities. Therefore, we recommend decision-makers to design a bigger picture for a conservation plan on cycad species (especially those having high-ED values), to prevent their extinction; implement the legislation and regulation of human-cycad connections.