Population modelling and genetics of a critically endangered Madagascan palm Tahina spectabilis

Abstract

Madagascar is home to 208 indigenous palm species, almost all of them endemic and >80% of which are endangered. We undertook complete population census and sampling for genetic analysis of a relatively recently discovered giant fan palm, the Critically Endangered Tahina spectablis in 2008 and 2016. Our 2016 study included newly discovered populations and added to our genetic study. We incorporated these new populations into species distribution niche model (SDM) and projected these onto maps of the region. We developed population matrix models based on observed demographic data to model population change and predict the species vulnerability to extinction by undertaking population viability analysis (PVA). We investigated the potential conservation value of reintroduced planted populations within the species potential suitable habitat. We found that the population studied in 2008 had grown in size due to seedling regeneration but had declined in the number of reproductively mature plants, and we were able to estimate that the species reproduces and dies after approximately 70 years. Our models suggest that if the habitat where it resides continues to be protected the species is unlikely to go extinct due to inherent population decline and that it will likely experience significant population growth after approximately 80 years due to the reproductive and life cycle attributes of the species. The newly discovered populations contain more genetic diversity than the first discovered southern population which is genetically depauperate. The species appears to demonstrate a pattern of dispersal leading to isolated founder plants which may eventually lead to population development depending on local establishment opportunities. The conservation efforts currently put in place including the reintroduction of plants within the species potential suitable habitat if maintained are thought likely to enable the species to sustain itself but it remains vulnerable to anthropogenic impacts.

Climate change winners and losers: The effects of climate change on five palm species in the Southeastern United States

“…However, some species may disperse in a fashion that leads to isolated founder plants that can establish new populations, if local environmental conditions are suitable (Shapcock et al, 2020). Given that four of the five species considered here are common in the nursery trade, it is possible that individuals planted in gardens outside of the native range may act facilitate naturalization for future generations, similar to the pattern observed for Trachycarpus fortunei in Switzerland (Fehr & Burga, 2016) and eight invasive palm species in Panama (Svenning, 2002).…”

Demographic modeling of the endangered subtropical rainforest shrub Graptophyllum reticulatum

“…To be consistent with field data, we based our models on a 10‐year time step. Using long‐time intervals relies on the assumption that the species is slow‐growing and has low reproductive output, so few changes would occur in populations within a year (Hayward et al., 2021; Osunkoya, 2003; Shapcott et al., 2020; Shimizu‐Kimura, Burnett, & Shapcott, 2017). Using this assumption, we approximated the gaps between two surveys to 10 years, although some were one or 2 years longer.…”

“…Since a new cluster of plants was discovered in 2011 in GR3, we only used the part of GR3 that had been consistently surveyed every year to estimate rates. Fecundity was estimated as the number of surviving seedlings produced per individual of a given class in a 10‐year time step (Hayward et al., 2021; Shapcott et al., 2020). Fecundity rates giving juveniles (F 1i for class i ) take both sexual and vegetative reproduction into account.…”

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“…& Rakotoarin. in Madagascar (Shapcott et al, 2007;Shapcott et al, 2020) have shown that the re-introduction of genetically diverse individuals from other populations will reduce the risk of inbreeding. While it is important to maintain the unique genetic diversity of each population, humanmediated disturbances have disrupted the natural processes maintaining this diversity and the risk of outbreeding depression is unwarranted (Frankham et al, 2011).…”