Demographic and genetic consequences of forest fragmentation
Our results go in line with studies addressing the impact of patch size
and isolation on the genetic diversity of cryptogamic organisms in
temporal similar historically fragmented landscapes to our study
(~30–50 years). For example, reduced genetic diversity
has been observed related to small population size, patch size
isolation, and habitat degradation (Holá et al., 2015; Patiño et al.,
2010; Wang et al., 2013; Otálora et al., 2011). As well our results in
an experimental Amazonian fragmented landscape support theoretical
predictions of island biogeography theory and metapopulation theory on
the genetic diversity (Whittaker et al., 2008; Vellend, 2003; Vellend &
Geber, 2005) observed for oceanic islands (Costanzi & Steifetten, 2019;
Hill et al., 2017; Whittaker et al., 2017; Hamabata et al., 2019), and
other insular landscape (Aycrigg & Garton, 2014; Hepenstrick et al.,
2022). However, climate and habitat fragmentation synergistic effects on
biodiversity might take a long time to be apparent (Chase et al., 2020;
Scott et al., 2021). For example, some species might become extinct
immediately after habitat disturbance, whereas others persist to
eventually become locally extinct (extinction debts) years after
deforestation isolates local populations (Tilman et al., 1994; Kuussaari
et al., 2009). During this time lag, species fitness decreases due to
low reproduction and local recruitment which will further exacerbate
under future climate extremes, such as droughts (Scott et al., 2021);
therefore, affecting species’ long-term survival probability (Figueiredo
et al., 2019). Species experiencing time-delayed extinctions (extinction
debts) are not necessarily doomed to extinction, as new colonization
events could pay for such debts (Kuussaari et al., 2009).
Under future climate scenarios, the ability of bryophyte species to
escape local extinction by tracking suitable habitats is of high concern
(Zanatta et al., 2020) despite their high dispersal capacities
(Vanderpoorten et al., 2019). Even though a diverse genetic pool of
individuals can reach a disturbed local population, effective dispersal
would be mediated by the local environmental conditions (Hedenäs et al.,
2021). Amazon lowland bryophyte communities were thought to be composed
of highly dispersive species (Schuster, 1983) with low floristic
dissimilarity mainly driven by niche process (Mota de Oliveira & ter
Steege, 2015). Yet spore traps on the 325 m height Amazon Tall Tower
Observatory (ATTO) capture few bryophyte diaspores, suggesting a low
frequency of airborne propagules in the atmosphere (Mota de Oliveira et
al., 2022). The high spatial genetic structure of Amazonian plant
species across a regional spatial scale (Nazareno et al., 2019; Ledent
et al., 2020; Campos et al., 2022), combined with non-random
deforestation events in the Amazon (Taubert et al., 2018; Matricardi et
al., 2020) will deplete important source populations for the genetic
diversity maintenance (Lowe et al., 2005). Herein, our results offer
evidence in support of our H1 for genetic drift over the 40 years that
populations have been isolated in the present fragmented landscape. This
establishes a premise that dispersal limitation in bryophyte
metapopulations (Ledent et al., 2020) will be susceptible to stochastic
demographic and genetic processes, which may accelerate even more the
pace of extinction as ecological barriers rapidly increase with
non-random deforestation in the Amazon (Taubert et al., 2018; Fischer et
al., 2021).