Conservation implications for metapopulation genetics in the Amazon Forest
Anthropogenic activities are the main cause of forest conversion associated with the change in land use in Amazonia over recent decades (Curtis et al., 2018). Forest fragmentation due to commodity-driven deforestation represents the most immediate threat to the Amazonia, the synergist effects of forest loss and forest degradation (edge effects, logging, fires, and droughts) put in threaten forest ecosystems and services with nearly 38% of the forests in the region currently degraded (Chase et al., 2020; Lapola et al., 2023). Even if conservation policies with objectives of zero deforestation in the Amazon are reached by 2030, a landscape of isolated patches will remain for decades (Fischer et al., 2021).
Research efforts have been focused on determining the habitat amount, in terms of patch size and isolation, that fragmented landscape allows for biodiversity maintenance of a region (Fahrig et al., 2019, 2022; Watling et al., 2020). Conservation management debates whether efforts should be given to preserving a single large patch or several small patches (SLOSS: single large or several small) (Diamond, 1975; Tjørve, 2010). The BDFFP has focused on addressing this question, with a myriad of studies targeting different organisms, indicating an Amazonian biodiversity loss after a threshold habitat size and isolation (Laurance et al., 2011, 2018). From the organisms that have been studied at the BDFFP, few have related the demographic consequences on the evolutionary processes (drift and migration) that impact the population genetic structure in a fragmented landscape (Hamilton, 1999; Côrtes et al., 2013; Zartman et al., 2006). This has left a gap when addressing the amount of habitat for conservation genetics. In long-lived organisms, the distribution of genotypes observed in fragmented habitats is expected to reflect the historical landscape configuration, demographic patterns, and population connectivity (Carley et al., 2022). Consequently, in most long-lived organisms this association is challenging, but annual plants such as understory Heliconia(Côrtes et al., 2013) and patch-tracking epiphyllous metapopulation (Zartman et al., 2006) have been important in our understanding of the genetic consequence of habitat fragmentation.
Herein, we integrate demographic and genetic data of epiphyllous metapopulation to quantify threshold patch size for population viability and genetic maintenance for regional conservation management taking into consideration the functional connectivity. Our results support the maintenance of genetic diversity in small patches (>10-ha) when asymmetric migration allows for rescue effects of extinct genotypes among patches in a fragmented landscape (Hufbauer et al., 2015). This has large implications for conservation where growing knowledge points to biodiversity managers prioritizing demographic and genetic rescue effects of populations when designating conservation areas and targeting declining populations in degraded habitats (Hufbauer et al., 2015; Hanski et al., 2015; Auffret et al., 2017; Carley et al., 2022). Evidence-based conservation strategies in the Amazon Forest require spatial configuration of (>100–10 000-ha) large patches of non-degraded forests (Laurance et al., 2018), that will allow for the preservation of long-term evolutionary processes (Carley et al., 2022).