What do we know about the demographic modeling of cacti? A systematic review of current knowledge

Cacti are threatened mainly by loss of habitat and illegal commerce. Because of this, it is essential to know their demographic characteristics. We systematically reviewed the publications with matrix population models (MPM) and integral projection models (IPM) in indexed journals, databases like the COMPADRE Plant Matrix Database and grey literature. In each publication, we recorded the literature characteristics, the population attributes, and the methods and metrics applied to describe them. We reviewed studies published until April 2022. We found 83 publications applied demographic modeling, 43 of which were of grey literature. Most studies were conducted in North America and on the tribe Cacteae, with a scarce representation of South American cactus. Compared to a previous review from 20 years ago, our study recorded a 488% increase in the number of publications and a 33.3% increase in the COMPADRE demographic database. We found demographic data for 65 taxa and very few studies covered a medium-to long-term period. MPMs were the most used until the 2009 when IPMs began to gain popularity. Population growth rates were commonly close to the unit (λ ≈ 1), but we identified a wide range of λ values. Species position in the demographic triangle showed that the populations in the tribes Echinocereae, Cereeae and Cylindropuntieae were located towards the end of the survival axis, while those in the tribes Cacteae, and Opuntieae had a more variable location. Applications of demographic models have focused on the analysis of life history traits (growth and turnover) and employing numerical simulations to simulate the consequences of variations in vital rates on λ. Interactions with the climate and the nurse-protected system are analyzed frequently. Nonetheless, a limited number of research explores the socioeconomic and political components of management and conservation. Finally, even though Cactaceae is the plant group with the most extensive demographic research, models are available for only 3.5% of the species.