Current genetic diversity and connectivity
Despite fragmentation, our microsatellite analysis demonstrated that the species still retains moderate to high genetic diversity values and constitutes one genetic population. It seems that some individuals can still migrate between forest patches, allowing gene flow between forest remnants. It is also possible that our analysis did not show signs of genetic structure due to the small sample set for the northern portion of the species’ range and the absence of samples from Argentina and Paraguay, which are the farthest and most isolated areas within its distribution. Alternatively, the relatively high genetic diversity and low genetic substructure may be attributed to a time lag effect resulting from rapid landscape change—the biome has lost over 10% of its natural vegetation in the last 40 years (Proyecto MapBiomas
2022)—and population decline that has affected this species in the past several decades (Landguth et al.
2010). Therefore, we recommend future research to increase genetic sampling in these regions to better evaluate the genetic structure of
L. guttulus across its entire distribution.
Our genetic analyses suggest that
L. guttulus population size likely ranges from 8950 to 15,190 individuals (assuming approximately 10 times the estimated effective population size). Although these values are higher than the estimate produced by de Oliveira et al. (
2016), if we considered the same area of occupancy of 473,254 km
2 employed by those authors, our estimates would be within the range expected for the common population density of 1–5 individuals/100 km
2 recognized for this species (4732.54–23,662.7 individuals), demonstrating congruence between the genetic-based estimate and existing demographic projections.
Among the core areas identified, Core areas 1 and 2 were by far the strongest areas from the resistance kernel analysis and the most critical for species conservation. Core area 1 encompasses the three largest fragments of Atlantic Forest in Brazil, accounting for more than 20,000 km
2 of forest (Ribeiro et al.
2009). This area has the highest densities recorded for the species (Tortato and Oliveira
2005; Oliveira-Santos et al.
2012), but in recent years, these values seem to have dropped considerably (de Oliveira et al.
2016). This reduction in population density, however, is more likely attributed to the loss of habitat quality or insufficient protection of forest fragments, rather than habitat loss itself, as the native forest cover has remained relatively stable in this area over the last few decades (Proyecto MapBiomas
2022). Indeed, this area presents a small number of protected areas, especially in Santa Catarina state, which encompasses the largest portion of Core area 1 (ca. 95,000 km
2 or 30% of Core area 1) but has only 7 protected areas larger than 100 km
2, which protects ca. 3.5% of the core area in the state (Supplementary Information, Tables
S4,
S5 and
S6 and Fig.
S12).
Core area 2 is mostly located in the Misiones province of Argentina and has the largest remaining area of continuous Atlantic Forest (Izquierdo et al.
2011), retaining around 50% of the original native forest of the province (Izquierdo and Clark
2012; Zuleta et al.
2015). In addition to Misiones’ fragments, two Brazilian parks, Iguaçu National Park and Turvo State Park, connected to them, increase the area of the patch. Although this core area is much smaller than Core area 1, it has a higher relation of summed kernel values/km
2, showing the high predicted density of the patch. Nonetheless, despite the apparent high quality of the habitat in this area, studies with relative abundance of individuals demonstrated low detectability for
L. guttulus (Di Bitetti et al.
2010; Kasper et al.
2016; Cruz et al.
2018). It is possible that the high abundance of
L. pardalis in this area limits the numbers of
L. guttulus, increasing, even more, the importance of Core area 1.
Core area 1 and 2 are still linked to each other, with a group of corridors identified between them. Yet, these corridors were weak and located in a matrix of agricultural and urban areas, with small fragments of forest. Seventeen protected areas are found in this region, but 12 of them have less than 8 km2, and only one spans more than 25 km2 (Estação Ecológica de Mata Preta, with 82 km2), indicating the vulnerability of the connection between these two core areas.
In contrast, Core areas 3 and 4 do not present high-density values of predicted movement densities but are important for the maintenance of the species in the northern portions of its distribution. Their importance is further demonstrated by the number of corridors we identified between them and smaller patches. The states that encompass these two core areas, Minas Gerais and Espírito Santo, have also retained a relatively stable forest cover (Proyecto MapBiomas
2022), but they have few protect areas. This is specially the case of Espírito Santo state, which safeguards only about 3.5%of the core area within protected areas greater than 100 km
2 in extent (Supplementary Information, Tables
S4,
S5 and
S6 and Fig.
S12). Moreover, the few available studies demonstrate a low abundance of the species in the region (Hatakeyama
2015; Massara et al.
2016), and our models predicted low movement density values for these core areas. However, this region is an important connectivity hub, linking the main core area to patches in the north of the species distribution and therefore has great importance for species viability in the area.
It is worth mentioning the two core areas identified as the fifth most important, depending on the evaluated scenario. One of these core areas is located in the state of Bahia and represents the northernmost known area of the species’ distribution. Despite this patch having one of the highest percentages of protected areas within the core area (Supplementary Information, Tables
S4,
S5 and
S6), it appears to be completely isolated, as no corridor was identified linking this area with any other, regardless of the scenario considered. Finally, the other core area identified as the fifth most important is in Paraguay. This country has lost approximately 30% of the biome’s forest cover within its territory in the last four decades (Proyecto MapBiomas
2022) and thus, this patch may harbor one of the last populations of
L. guttulus in the country. Furthermore, there is no protected area with more than 100 km
2 within this core area or in its surroundings (Supplementary Information, Fig.
S12). Therefore, the isolation of the Bahian patch and the lack of protection, coupled with high deforestation rates in the Paraguayan region, underscores the threat of regional extinction for this species on the edges of its distribution.
Simulations for the future
Our simulations of future population dynamics predicted a possible concerning prospect for
L. guttulus conservation, with species extinction in all core areas but Core areas 1 and, occasionally 2, 3 and 4, depending on the assessed scenario. Considering the core areas identified here, around one third of them do not contain protected areas of more than 100 km
2 (Supplementary Information, Tables
S4,
S5 and
S6; Fig.
S12). However, even in the core areas that are most well protected (with >40% of their area protected), it appears that the small size of individual protected areas, low initial population size and low density of individuals, do not enable the maintenance of long-term viable populations, leading to regional population extinction. In addition, the current connectivity between these areas seems not to be strong enough to overcome this result. This demonstrates the importance of promoting forest regeneration and creating a network of connected protected areas to keep viable populations in the long term (e.g., Cushman et al.
2018; D’Aloia et al.
2019; Kaszta et al.
2019,
2020).
Despite this concerning result, it is imperative to highlight that using a larger initial population size than the ones we used in our analysis could increase the estimations of population size and decrease extinction risk. That said, we tested two different initial population sizes based on the best existing information and they produced similar predictions of species occurrence, demonstrating that even larger plausible populations sizes will probably not avoid the extinction of the populations in the smaller core areas. Still, some simulations showed an increase in the geographic distance between Core areas 1 and 2, with the extinction of the species in some intervening patches. These two areas have the largest fragments of Atlantic Forest and the highest density of movement, and the isolation between them would probably have great impact on species genetic diversity and population numbers.
Furthermore, only ~15–20% of Core areas 1 and 2 are under protection (Supplementary Information, Tables
S4,
S5 and
S6). Although both Brazil and Argentina have kept relatively stable percentages of forest cover of the Atlantic Forest (Proyecto MapBiomas
2022), considering the importance of these core areas for the species’ survival, the small number of protected areas in them is concerning. Hence, management plans should focus on the creation and/or effectiveness of protected areas inside these core areas and the maintenance of natural fragments outside them. The Brazilian Forest Code mandates the conservation of a certain percentage of native vegetation on rural private lands (Soares-Filho et al.
2014). These fragments of habitat may work as connecting corridors but also as vital areas for the conservation of the species considering that unprotected areas seem to be important for this species’ due to the general absence or low abundance of
L. pardalis (de Oliveira et al.
2016). Therefore, measures to incentivize landowners to adhere to the Forest Code are essential for the conservation of this species. Moreover, Core area 2 and the northern portion of Core area 1 are considered important units for jaguar (
Panthera onca) conservation in the Atlantic Forest. However, jaguar populations in these areas do not seem to be connected (Paviolo et al.
2016). Thus, the creation and protection of corridors between these areas would be beneficial for other species.
Interestingly, the decrease in population size was not followed by the loss of genetic diversity in our simulation. This suggests a time lag effect in the simulated data (Kaszta et al.
2019), indicating that the surprisingly high current genetic diversity in the observed extant population is likely not reflective of an equilibrium between population size and gene flow with the landscape, and will decline with drift over time (e.g., Landguth et al.
2010). It is also possible that the size and connectivity of Core area 1 slowed the decline of global genetic diversity, even with the species going extinct in the smaller patches (Gibbs
2001).